Powerful DC-DC converter. Boost DC-DC converter
To convert voltage of one level to voltage of another level, it is often used pulse voltage converters using inductive energy storage devices. Such converters are characterized by high efficiency, sometimes reaching 95%, and have the ability to produce increased, decreased or inverted output voltage.
In accordance with this, three types of converter circuits are known: buck (Fig. 1), boost (Fig. 2) and inverting (Fig. 3).
Common to all these types of converters are five elements:
- power supply,
- key switching element,
- inductive energy storage (inductor, inductor),
- blocking diode,
- a filter capacitor connected in parallel with the load resistance.
The inclusion of these five elements in various combinations allows you to implement any of the three types of pulse converters.
The converter output voltage level is regulated by changing the width of the pulses that control the operation of the key switching element and, accordingly, the energy stored in the inductive energy storage device.
Stabilization of the output voltage is realized by using feedback: when the output voltage changes, the pulse width automatically changes.
Buck switching converter
The step-down converter (Fig. 1) contains a series-connected chain of switching element S1, inductive energy storage L1, load resistance RH and filter capacitor C1 connected in parallel with it. Blocking diode VD1 is connected between the connection point of the key S1 with the energy storage device L1 and the common wire.
Rice. 1. Operating principle of a step-down voltage converter.
When the switch is open, the diode is closed, energy from the power source is accumulated in an inductive energy storage device. After the switch S1 is closed (open), the energy stored by the inductive storage L1 is transferred through the diode VD1 to the load resistance RH. Capacitor C1 smoothes out voltage ripples.
Boost switching converter
The step-up pulse voltage converter (Fig. 2) is made on the same basic elements, but has a different combination: a series chain of inductive energy storage L1, diode VD1 and load resistance RH with a filter capacitor C1 connected in parallel is connected to the power source. The switching element S1 is connected between the connection point of the energy storage device L1 with the diode VD1 and the common bus.
Rice. 2. Operating principle of a boost voltage converter.
When the switch is open, current from the power source flows through the inductor, which stores energy. Diode VD1 is closed, the load circuit is disconnected from the power source, key and energy storage device.
The voltage across the load resistance is maintained thanks to the energy stored on the filter capacitor. When the switch is opened, the self-induction EMF is summed with the supply voltage, the stored energy is transferred to the load through the open diode VD1. The output voltage obtained in this way exceeds the supply voltage.
Pulse type inverting converter
A pulse-type inverting converter contains the same combination of basic elements, but again in a different connection (Fig. 3): a series circuit of switching element S1, diode VD1 and load resistance RH with filter capacitor C1 is connected to the power source.
Inductive energy storage L1 is connected between the connection point of the switching element S1 with the diode VD1 and the common bus.
Rice. 3. Pulse voltage conversion with inversion.
The converter works like this: when the key is closed, energy is stored in an inductive storage device. Diode VD1 is closed and does not pass current from the power source to the load. When the switch is turned off, the self-inductive emf of the energy storage device is applied to a rectifier containing diode VD1, load resistance Rн and filter capacitor C1.
Since the rectifier diode passes only negative voltage pulses into the load, a voltage of a negative sign is formed at the output of the device (inverse, opposite in sign to the supply voltage).
Pulse converters and stabilizers
To stabilize the output voltage of pulse stabilizers of any type, conventional “linear” stabilizers can be used, but they have low efficiency. In this regard, it is much more logical to use pulse voltage stabilizers to stabilize the output voltage of pulse converters, especially since such stabilization is not at all difficult.
Switching voltage stabilizers, in turn, are divided into stabilizers with pulse-width modulation and stabilizers with pulse-frequency modulation. In the first of them, the duration of control pulses changes while their repetition rate remains unchanged. Secondly, on the contrary, the frequency of control pulses changes while their duration remains unchanged. There are also pulse stabilizers with mixed regulation.
Below we will consider amateur radio examples of the evolutionary development of pulse converters and voltage stabilizers.
Units and circuits of pulse converters
The master oscillator (Fig. 4) of pulse converters with an unstabilized output voltage (Fig. 5, 6) on the KR1006VI1 microcircuit operates at a frequency of 65 kHz. The output rectangular pulses of the generator are fed through RC circuits to transistor key elements connected in parallel.
Inductor L1 is made on a ferrite ring with an outer diameter of 10 mm and a magnetic permeability of 2000. Its inductance is 0.6 mH. The efficiency of the converter reaches 82%.
Rice. 4. Master oscillator circuit for pulse voltage converters.
Rice. 5. Diagram of the power part of a step-up pulse voltage converter +5/12 V.
Rice. 6. Circuit of an inverting pulse voltage converter +5/-12 V.
The output ripple amplitude does not exceed 42 mV and depends on the capacitance value of the capacitors at the device output. The maximum load current of devices (Fig. 5, 6) is 140 mA.
The converter rectifier (Fig. 5, 6) uses a parallel connection of low-current high-frequency diodes connected in series with equalizing resistors R1 - R3.
This entire assembly can be replaced by one modern diode, designed for a current of more than 200 mA at a frequency of up to 100 kHz and a reverse voltage of at least 30 V (for example, KD204, KD226).
As VT1 and VT2, it is possible to use transistors of the KT81x type with a p-p-p structure - KT815, KT817 (Fig. 4.5) and p-p-p - KT814, KT816 (Fig. 6) and others.
To increase the reliability of the converter, it is recommended to connect a diode of type KD204, KD226 in parallel with the emitter-collector junction of the transistor so that it is closed to direct current.
Converter with master oscillator-multivibrator
To obtain an output voltage of 30...80 V P. Belyatsky used a converter with a master oscillator based on an asymmetrical multivibrator with an output stage loaded on an inductive energy storage device - inductor (choke) L1 (Fig. 7).
Rice. 7. Circuit of a voltage converter with a master oscillator based on an asymmetrical multivibrator.
The device is operational in the supply voltage range of 1.0. ..1.5 V and has an efficiency of up to 75%. In the circuit, you can use a standard inductor DM-0.4-125 or another with an inductance of 120...200 μH.
An embodiment of the output stage of the voltage converter is shown in Fig. 8. When a rectangular control signal cascade of 7777-level (5 V) is applied to the input of the converter output when it is powered from a voltage source 12 V voltage received 250 V at load current 3...5 mA(load resistance is about 100 kOhm). Inductance of inductor L1 is 1 mH.
As VT1, you can use a domestic transistor, for example, KT604, KT605, KT704B, KT940A(B), KT969A, etc.
Rice. 8. Option for the output stage of the voltage converter.
Rice. 9. Diagram of the output stage of the voltage converter.
A similar output stage circuit (Fig. 9) made it possible, when powered from a voltage source 28V and current consumption 60 mA get output voltage 250 V at load current 5 mA, The inductance of the choke is 600 µH. The frequency of control pulses is 1 kHz.
Depending on the quality of the inductor, the output voltage can be 150...450 V with a power of about 1 W and an efficiency of up to 75%.
A voltage converter based on a pulse generator based on a DA1 KR1006VI1 microcircuit, an amplifier based on a field-effect transistor VT1 and an inductive energy storage device with a rectifier and filter is shown in Fig. 10.
At the converter output at supply voltage 9V and current consumption 80...90 mA tension is generated 400...425 V. It should be noted that the value of the output voltage is not guaranteed - it significantly depends on the design of the inductor (choke) L1.
Rice. 10. Circuit of a voltage converter with a pulse generator on the KR1006VI1 microcircuit.
To obtain the desired voltage, the easiest way is to experimentally select an inductor to achieve the required voltage or use a voltage multiplier.
Bipolar pulse converter circuit
To power many electronic devices, a bipolar voltage source is required, providing both positive and negative supply voltages. The diagram shown in Fig. 11 contains much fewer components than similar devices due to the fact that it simultaneously functions as a boost and inverter inductive converter.
Rice. 11. Converter circuit with one inductive element.
The converter circuit (Fig. 11) uses a new combination of main components and includes a four-phase pulse generator, an inductor and two transistor switches.
Control pulses are generated by a D-trigger (DD1.1). During the first phase of the pulses, inductor L1 stores energy through transistor switches VT1 and VT2. During the second phase, switch VT2 opens and energy is transferred to the positive output voltage bus.
During the third phase, both switches are closed, as a result of which the inductor again accumulates energy. When the VT1 key is opened during the final phase of the pulses, this energy is transferred to the negative power bus. When pulses with a frequency of 8 kHz are received at the input, the circuit provides output voltages ±12 V. The timing diagram (Fig. 11, right) shows the formation of control pulses.
Transistors KT315, KT361 can be used in the circuit.
The voltage converter (Fig. 12) allows you to obtain a stabilized voltage of 30 V at the output. A voltage of this magnitude is used to power varicaps, as well as vacuum fluorescent indicators.
Rice. 12. Circuit of a voltage converter with a stabilized output voltage of 30 V.
On a DA1 chip of type KR1006VI1, a master oscillator is assembled according to the usual circuit, producing rectangular pulses with a frequency of about 40 kHz.
A transistor switch VT1 is connected to the output of the generator, which switches the inductor L1. The amplitude of the pulses when switching the coil depends on the quality of its manufacture.
In any case, the voltage on it reaches tens of volts. The output voltage is rectified by diode VD1. A U-shaped RC filter and a zener diode VD2 are connected to the output of the rectifier. The voltage at the output of the stabilizer is entirely determined by the type of zener diode used. As a “high-voltage” zener diode, you can use a chain of zener diodes having a lower stabilization voltage.
A voltage converter with an inductive energy storage, which allows maintaining a stable regulated voltage at the output, is shown in Fig. 13.
Rice. 13. Voltage converter circuit with stabilization.
The circuit contains a pulse generator, a two-stage power amplifier, an inductive energy storage device, a rectifier, a filter, and an output voltage stabilization circuit. Resistor R6 sets the required output voltage in the range from 30 to 200 V.
Transistor analogues: VS237V - KT342A, KT3102; VS307V - KT3107I, BF459 - KT940A.
Buck and invert voltage converters
Two options - step-down and inverting voltage converters are shown in Fig. 14. The first one provides the output voltage 8.4 V at load current up to 300 mA, the second allows you to obtain a voltage of negative polarity ( -19.4 V) at the same load current. The output transistor VTZ must be installed on the radiator.
Rice. 14. Circuits of stabilized voltage converters.
Transistor analogues: 2N2222 - KTZ117A 2N4903 - KT814.
Step-down stabilized voltage converter
A step-down stabilized voltage converter that uses the KR1006VI1 (DA1) microcircuit as a master oscillator and has load flow protection is shown in Fig. 15. The output voltage is 10V when the load current is up to 100mA.
Rice. 15. Step-down voltage converter circuit.
When the load resistance changes by 1%, the output voltage of the converter changes by no more than 0.5%. Transistor analogues: 2N1613 - KT630G, 2N2905 - KT3107E, KT814.
Bipolar voltage inverter
To power electronic circuits containing operational amplifiers, bipolar power supplies are often required. This problem can be solved by using a voltage inverter, the circuit of which is shown in Fig. 16.
The device contains a square pulse generator loaded onto inductor L1. The voltage from the inductor is rectified by diode VD2 and supplied to the output of the device (filter capacitors C3 and C4 and load resistance). Zener diode VD1 ensures a constant output voltage - it regulates the duration of the pulse of positive polarity on the inductor.
Rice. 16. Voltage inverter circuit +15/-15 V.
The operating frequency of generation is about 200 kHz under load and up to 500 kHz without load. Maximum load current is up to 50 mA, device efficiency is 80%. The disadvantage of the design is the relatively high level of electromagnetic interference, which, however, is also typical for other similar circuits. A DM-0.2-200 throttle was used as L1.
Inverters on specialized chips
It is most convenient to collect highly efficient modern voltage converters, using microcircuits specially created for these purposes.
Chip KR1156EU5(MC33063A, MC34063A from Motorola) is designed to work in stabilized step-up, step-down, inverting converters with a power of several watts.
In Fig. Figure 17 shows a diagram of a step-up voltage converter based on the KR1156EU5 microcircuit. The converter contains input and output filter capacitors C1, SZ, C4, storage choke L1, rectifier diode VD1, capacitor C2, which sets the operating frequency of the converter, filter choke L2 for smoothing ripples. Resistor R1 serves as a current sensor. The voltage divider R2, R3 determines the output voltage.
Rice. 17. Circuit of a step-up voltage converter on the KR1156EU5 microcircuit.
The operating frequency of the converter is close to 15 kHz at an input voltage of 12 V and rated load. The range of voltage ripples on capacitors SZ and C4 was 70 and 15 mV, respectively.
Inductor L1 with an inductance of 170 μH is wound on three glued rings K12x8x3 M4000NM with PESHO 0.5 wire. The winding consists of 59 turns. Each ring should be broken into two parts before winding.
A common spacer made of PCB with a thickness of 0.5 mm is inserted into one of the gaps and the package is glued together. You can also use ferrite rings with a magnetic permeability of over 1000.
Execution example buck converter on the KR1156EU5 chip shown in Fig. 18. A voltage of more than 40 V cannot be supplied to the input of such a converter. The operating frequency of the converter is 30 kHz at UBX = 15 V. The voltage ripple range on capacitors SZ and C4 is 50 mV.
Rice. 18. Scheme of a step-down voltage converter on the KR1156EU5 microcircuit.
Rice. 19. Scheme of an inverting voltage converter based on the KR1156EU5 microcircuit.
Choke L1 with an inductance of 220 μH is wound in a similar way (see above) on three rings, but the gluing gap was set to 0.25 mm, the winding contained 55 turns of the same wire.
The following figure (Fig. 19) shows a typical circuit of an inverting voltage converter based on the KR1156EU5 microcircuit. The DA1 microcircuit is powered by the sum of the input and output voltages, which should not exceed 40 V.
Converter operating frequency - 30 kHz at UBX=5 S; the range of voltage ripples on capacitors SZ and C4 is 100 and 40 mV.
For inductor L1 of the inverting converter with an inductance of 88 μH, two K12x8x3 M4000NM rings with a gap of 0.25 mm were used. The winding consists of 35 turns of PEV-2 0.7 wire. Inductor L2 in all converters is standard - DM-2.4 with an inductance of 3 μGh. Diode VD1 in all circuits (Fig. 17 - 19) must be a Schottky diode.
For getting bipolar voltage from unipolar MAXIM has developed specialized microcircuits. In Fig. Figure 20 shows the possibility of converting a low level voltage (4.5...5 6) into a bipolar output voltage 12 (or 15 6) with a load current of up to 130 (or 100 mA).
Rice. 20. Voltage converter circuit based on the MAX743 chip.
In terms of its internal structure, the microcircuit does not differ from the typical design of similar converters made on discrete elements, however, the integrated design makes it possible to create highly efficient voltage converters with a minimum number of external elements.
Yes, for a microcircuit MAX743(Fig. 20) the conversion frequency can reach 200 kHz (which is much higher than the conversion frequency of the vast majority of converters made on discrete elements). With a supply voltage of 5 V, the efficiency is 80...82% with output voltage instability of no more than 3%.
The microcircuit is equipped with protection against emergency situations: when the supply voltage drops 10% below normal, as well as when the case overheats (above 195°C).
To reduce ripple at the output of the converter with a conversion frequency (200 kHz), U-shaped LC filters are installed at the device outputs. Jumper J1 on pins 11 and 13 of the microcircuit is designed to change the value of the output voltages.
For low level voltage conversion(2.0...4.5 6) in stabilized 3.3 or 5.0 V there is a special microcircuit developed by MAXIM - MAX765. Domestic analogues are KR1446PN1A and KR1446PN1B. A microcircuit for a similar purpose - MAX757 - allows you to obtain a continuously adjustable output voltage within the range of 2.7...5.5 V.
Rice. 21. Circuit of a low-voltage step-up voltage converter to a level of 3.3 or 5.0 V.
The converter circuit shown in Fig. 21, contains a small number of external (hinged) parts.
This device works according to the traditional principle described earlier. The operating frequency of the generator depends on the input voltage and load current and varies over a wide range - from tens of Hz to 100 kHz.
The magnitude of the output voltage is determined by where pin 2 of the DA1 microcircuit is connected: if it is connected to a common bus (see Fig. 21), the output voltage of the microcircuit KR1446PN1A equals 5.0±0.25 V, but if this pin is connected to pin 6, then the output voltage will drop to 3.3±0.15 V. For the microcircuit KR1446PN1B the values will be 5.2±0.45 V and 3.44±0.29 V, respectively.
Maximum converter output current - 100 mA. Chip MAX765 provides output current 200 mA at voltage 5-6 and 300 mA under tension 3.3 V. Converter efficiency is up to 80%.
The purpose of pin 1 (SHDN) is to temporarily disable the converter by connecting this pin to common. The output voltage in this case will drop to a value slightly less than the input voltage.
The HL1 LED is designed to indicate an emergency reduction in the supply voltage (below 2 V), although the converter itself is capable of operating at lower input voltage values (up to 1.25 6 and below).
The L1 inductor is made on a K10x6x4.5 ring made of M2000NM1 ferrite. It contains 28 turns of 0.5 mm PESHO wire and has an inductance of 22 µH. Before winding, the ferrite ring is broken in half, after being filed with a diamond file. Then the ring is glued with epoxy glue, installing a 0.5 mm thick textolite gasket in one of the resulting gaps.
The inductance of the inductor obtained in this way depends to a greater extent on the thickness of the gap and to a lesser extent on the magnetic permeability of the core and the number of turns of the coil. If you accept the increase in the level of electromagnetic interference, then you can use a DM-2.4 type inductor with an inductance of 20 μGh.
Capacitors C2 and C5 are type K53 (K53-18), C1 and C4 are ceramic (to reduce the level of high-frequency interference), VD1 is a Schottky diode (1 N5818, 1 N5819, SR106, SR160, etc.).
Philips AC power supply
The converter (Philips power supply unit, Fig. 22) with an input voltage of 220 V provides a stabilized output voltage of 12 V with a load power of 2 W.
Rice. 22. Diagram of the Philips network power supply.
The transformerless power supply (Fig. 23) is designed to power portable and pocket receivers from an AC mains voltage of 220 V. It should be taken into account that this source is not electrically isolated from the supply network. With an output voltage of 9V and a load current of 50 mA, the power supply consumes about 8 mA from the network.
Rice. 23. Scheme of a transformerless power source based on a pulse voltage converter.
The mains voltage, rectified by the diode bridge VD1 - VD4 (Fig. 23), charges capacitors C1 and C2. The charging time of capacitor C2 is determined by the circuit constant R1, C2. At the first moment after turning on the device, thyristor VS1 is closed, but at a certain voltage on capacitor C2 it will open and connect circuit L1, NW, to this capacitor.
In this case, capacitor S3 of large capacity will be charged from capacitor C2. The voltage on capacitor C2 will decrease, and on SZ it will increase.
The current through inductor L1, equal to zero at the first moment after opening the thyristor, gradually increases until the voltages on capacitors C2 and SZ are equalized. As soon as this happens, the thyristor VS1 will close, but the energy stored in the inductor L1 will for some time maintain the charge current of the capacitor SZ through the opened diode VD5. Next, the diode VD5 closes, and the relatively slow discharge of the capacitor SZ through the load begins. Zener diode VD6 limits the voltage across the load.
As soon as the thyristor VS1 closes, the voltage on capacitor C2 begins to increase again. At some point, the thyristor opens again, and a new cycle of operation of the device begins. The opening frequency of the thyristor is several times higher than the voltage pulsation frequency on capacitor C1 and depends on the ratings of the circuit elements R1, C2 and the parameters of the thyristor VS1.
Capacitors C1 and C2 are MBM type for a voltage of at least 250 V. Inductor L1 has an inductance of 1...2 mH and a resistance of no more than 0.5 Ohm. It is wound on a cylindrical frame with a diameter of 7 mm.
The winding width is 10 mm, it consists of five layers of PEV-2 0.25 mm wire, wound tightly, turn to turn. An SS2.8x12 tuning core made of M200NN-3 ferrite is inserted into the frame hole. The inductance of the inductor can be varied within wide limits, and sometimes even eliminated completely.
Schemes of devices for energy conversion
Diagrams of devices for energy conversion are shown in Fig. 24 and 25. They are step-down energy converters powered by rectifiers with a quenching capacitor. The voltage at the output of the devices is stabilized.
Rice. 24. Scheme of a step-down voltage converter with transformerless mains power supply.
Rice. 25. Option of a step-down voltage converter circuit with transformerless mains power supply.
As VD4 dinistors, you can use domestic low-voltage analogues - KN102A, B. Like the previous device (Fig. 23), power supplies (Fig. 24 and 25) have a galvanic connection with the supply network.
Voltage converter with pulse energy storage
In the S. F. Sikolenko voltage converter with “pulse energy storage” (Fig. 26), switches K1 and K2 are made on KT630 transistors, the control system (CS) is on a K564 series microcircuit.
Rice. 26. Circuit of a voltage converter with pulse accumulation.
Storage capacitor C1 - 47 µF. A 9 V battery is used as a power source. The output voltage at a load resistance of 1 kOhm reaches 50 V. The efficiency is 80% and increases to 95% when using CMOS structures such as RFLIN20L as key elements K1 and K2.
Pulse-resonant converter
Pulse-resonant converters designed by the so-called. N. M. Muzychenko, one of which is shown in Fig. 4.27, depending on the shape of the current in the VT1 switch, they are divided into three types, in which the switching elements close at zero current and open at zero voltage. At the switching stage, the converters operate as resonant converters, and the rest, most of the period, as pulse converters.
Rice. 27. Scheme of a pulse-resonance converter N. M. Muzychenko.
A distinctive feature of such converters is that their power part is made in the form of an inductive-capacitive bridge with a switch in one diagonal and with a switch and power supply in the other. Such schemes (Fig. 27) are highly efficient.
Today we will look at several circuits of simple, one might even say simple, pulsed DC-DC voltage converters (converters of direct voltage of one value to direct voltage of another value)
What are the benefits of pulse converters? Firstly, they have high efficiency, and secondly, they can operate at an input voltage lower than the output voltage. Pulse converters are divided into groups:
- - bucking, boosting, inverting;
- - stabilized, unstabilized;
- - galvanically isolated, non-insulated;
- - with a narrow and wide range of input voltages.
To make homemade pulse converters, it is best to use specialized integrated circuits - they are easier to assemble and not capricious when setting up. So, here are 14 schemes for every taste:
This converter operates at a frequency of 50 kHz, galvanic isolation is provided by transformer T1, which is wound on a K10x6x4.5 ring made of 2000NM ferrite and contains: primary winding - 2x10 turns, secondary winding - 2x70 turns of PEV-0.2 wire. Transistors can be replaced with KT501B. Almost no current is consumed from the battery when there is no load.
Transformer T1 is wound on a ferrite ring with a diameter of 7 mm, and contains two windings of 25 turns of wire PEV = 0.3.
Push-pull unstabilized converter based on a multivibrator (VT1 and VT2) and a power amplifier (VT3 and VT4). The output voltage is selected by the number of turns of the secondary winding of the pulse transformer T1.
Stabilizing type converter based on the MAX631 microcircuit from MAXIM. Generation frequency 40…50 kHz, storage element - inductor L1.
You can use one of the two chips separately, for example the second one, to multiply the voltage from two batteries.
Typical circuit for connecting a pulse boost stabilizer on the MAX1674 microcircuit from MAXIM. Operation is maintained at an input voltage of 1.1 volts. Efficiency - 94%, load current - up to 200 mA.
Allows you to obtain two different stabilized voltages with an efficiency of 50...60% and a load current of up to 150 mA in each channel. Capacitors C2 and C3 are energy storage devices.
8. Pulse boost stabilizer on the MAX1724EZK33 chip from MAXIM
Typical circuit diagram for connecting a specialized microcircuit from MAXIM. It remains operational at an input voltage of 0.91 volts, has a small-sized SMD housing and provides a load current of up to 150 mA with an efficiency of 90%.
A typical circuit for connecting a pulsed step-down stabilizer on a widely available TEXAS microcircuit. Resistor R3 regulates the output voltage within +2.8…+5 volts. Resistor R1 sets the short circuit current, which is calculated by the formula: Is(A)= 0.5/R1(Ohm)
Integrated voltage inverter, efficiency - 98%.
Two isolated voltage converters DA1 and DA2, connected in a “non-isolated” circuit with a common ground.
The inductance of the primary winding of transformer T1 is 22 μH, the ratio of turns of the primary winding to each secondary is 1: 2.5.
Typical circuit of a stabilized boost converter on a MAXIM microcircuit.
A powerful and fairly good step-up voltage converter can be built based on a simple multivibrator.
In my case, this inverter was built simply to review the work; a short video was also made with the operation of this inverter.
About the circuit as a whole - a simple push-pull inverter, it’s hard to imagine simpler. The master oscillator and at the same time the power part are powerful field-effect transistors (it is advisable to use switches like IRFP260, IRFP460 and similar) connected using a multivibrator circuit. As a transformer, you can use a ready-made trans from a computer power supply (the largest transformer).
For our purposes, we need to use 12 Volt windings and the middle point (braid, tap). At the output of the transformer, the voltage can reach up to 260 Volts. Since the output voltage is variable, it needs to be rectified with a diode bridge. It is advisable to assemble the bridge from 4 separate diodes; ready-made diode bridges are designed for network frequencies of 50 Hz, and in our circuit the output frequency is around 50 kHz.
Be sure to use pulsed, fast or ultra-fast diodes with a reverse voltage of at least 400 Volts and a permissible current of 1 Ampere or higher. You can use diodes MUR460, UF5408, HER307, HER207, UF4007, and others.
I recommend using the same diodes in the master circuit circuit.
The inverter circuit operates on the basis of parallel resonance, therefore, the operating frequency will depend on our oscillatory circuit - represented by the primary winding of the transformer and the capacitor parallel to this winding.
Regarding power and performance in general. A correctly assembled circuit does not require additional adjustment and works immediately. During operation, the keys should not heat up at all if the transformer output is not loaded. The idle current of the inverter can reach up to 300mA - this is the norm, higher is already a problem.
With good switches and a transformer, you can remove power in the region of 300 watts, in some cases even 500 watts, from this circuit without any problems. The input voltage rating is quite high, the circuit will work from a source of 6 Volts to 32 Volts, I didn’t dare to supply more.
Chokes - wound with a 1.2mm wire on yellow-white rings from the group stabilization choke in the computer power supply. The number of turns of each inductor is 7, both inductors are exactly the same.
Capacitors parallel to the primary winding may heat up slightly during operation, so I advise you to use high-voltage capacitors with an operating voltage of 400 Volts or higher.
The circuit is simple and fully operational, but despite the simplicity and accessibility of the design, this is not an ideal option. The reason is not the best field key management. The circuit lacks a specialized generator and control circuit, which makes it not entirely reliable if the circuit is intended for long-term operation under load. The circuit can power LDS and devices that have built-in SMPS.
An important link - the transformer - must be well wound and correctly phased, because it plays a major role in the reliable operation of the inverter.
The primary winding is 2x5 turns with a bus of 5 wires 0.8 mm. The secondary winding is wound with a 0.8 mm wire and contains 50 turns - this is in the case of self-winding of the transformer.
LM2596 is a step-down DC-DC converter, it is often produced in the form of ready-made modules, costing about $1 (search for LM2596S DC-DC 1.25-30 V 3A). By paying $1.5, you can buy a similar module on Ali with LED indication of input and output voltage, turning off the output voltage and fine-tuning buttons with displaying values on digital indicators. Agree - the offer is more than tempting!
Below is a schematic diagram of this converter board (key components are marked in the picture at the end). At the input there is protection against polarity reversal - diode D2. This will prevent the regulator from being damaged by incorrectly connected input voltage. Despite the fact that the lm2596 chip can process input voltages up to 45 V according to the datasheet, in practice the input voltage should not exceed 35 V for long-term use.
For lm2596, the output voltage is determined by the equation below. With resistor R2, the output voltage can be adjusted from 1.23 to 25 V.
Although the lm2596 chip is designed for a maximum current of 3 A of continuous operation, the small surface of the foil mass is not sufficient to dissipate the generated heat over the entire operating range of the circuit. Also note that the efficiency of this converter varies greatly depending on the input voltage, output voltage and load current. Efficiency can range from 60% to 90% depending on operating conditions. Therefore, heat removal is mandatory if continuous operation occurs at currents of more than 1 A.
According to the datasheet, the feedforward capacitor must be installed in parallel with resistor R2, especially when the output voltage exceeds 10 V - this is necessary to ensure stability. But this capacitor is often not present on Chinese inexpensive inverter boards. During the experiments, several copies of DC converters were tested under various operating conditions. As a result, we came to the conclusion that the LM2596 stabilizer is well suited for low and medium supply currents of digital circuits, but for higher output power values a heat sink is required.
Company STMicroelectronics produces microcircuits for creating non-isolated DC/DC converters with high quality indicators, requiring a small number of external components.
The continuous development of ICs for DC/DC converters is characterized by the following factors:
- increasing the operating conversion frequencies (the maximum conversion frequency for STMicroelectronics microcircuits is 1.7 MHz), which allows you to dramatically reduce the size of external components and minimize the area of the printed circuit board;
- reduction in the size of microcircuit packages due to high conversion frequencies (the DFN6D package has dimensions of only 3x3 mm);
- increased specific output current density (DFN6D package provides output current up to 2.0A; DFN8 and PowerSO-8 packages can operate at currents up to 3.0A);
- increased efficiency and reduced power consumption when switched off, which is especially important for self-powered devices.
STM divides its non-isolated DC/DC converter ICs into two groups. The first group has an operating frequency of up to 1 MHz (parameters are summarized in Table 1), the second group has a conversion frequency of 1.5 and 1.7 MHz (parameters, see Table 2). Microcircuits of the series have also been added to the second group ST1S10 with a nominal conversion frequency of 0.9 MHz (the maximum conversion frequency for these chips can reach 1.2 MHz). ST1S10 series microcircuits can operate when synchronized from an external oscillator in the frequency range from 400 kHz to 1.2 MHz.
Table 1. STMicroelectronics microcircuits for DC/DC converters with conversion frequencies up to 1 MHz
| Name | Topology | Vin., V | Vout., V | Iout., A | Frequency conversion, MHz |
Entrance shutdowns |
Frame |
|---|---|---|---|---|---|---|---|
| L296 | Step-down | 9…46 | 5,1…40 | 4 | up to 200 | Eat | MULTIWATT-15 |
| L4960 | Step-down | 9…46 | 5,1…40 | 2,5 | up to 200 | No | HEPTAWATT-7 |
| L4962 | Step-down | 9…46 | 5,1…40 | 1,5 | up to 200 | Eat | HEPTAWATT-8, DIP-16 |
| L4963 | Step-down | 9…46 | 5,1…40 | 1,5 | 42…83 | No | DIP-18, SO-20 |
| L4970A | Step-down | 12…50 | 5,1…50 | 10 | up to 500 | No | MULTIWATT-15 |
| L4971 | Step-down | 8…55 | 3,3…50 | 1,5 | up to 300 | Eat | DIP-8,SO-16W |
| L4972A | Step-down | 12…50 | 5,1…40 | 2 | up to 200 | No | DIP-20, SO-20 |
| L4973D3.3 | Step-down | 8…55 | 0,5…50 | 3,5 | up to 300 | Eat | DIP-8,SO-16W |
| L4973D5.1 | Step-down | 8…55 | 5,1…50 | 3,5 | up to 300 | Eat | DIP-8,SO-16W |
| L4974A | Step-down | 12…50 | 5,1…40 | 3,5 | up to 200 | No | MULTIWATT-15 |
| L4975A | Step-down | 12…50 | 5,1…40 | 5 | up to 500 | No | MULTIWATT-15 |
| L4976 | Step-down | 8…55 | 0,5…50 | 1 | up to 300 | Eat | DIP-8,SO-16W |
| L4977A | Step-down | 12…50 | 5,1…40 | 7 | up to 500 | No | MULTIWATT-15 |
| L4978 | Step-down | 8…55 | 3,3…50 | 2 | up to 300 | Eat | DIP-8,SO-16W |
| L5970AD | Step-down | 4,4…36 | 0,5…35 | 1 | 500 | Eat | SO-8 |
| L5970D | Step-down | 4,4…36 | 0,5…35 | 1 | 250 | Eat | SO-8 |
| L5972D | Step-down | 4,4…36 | 1,23…35 | 1,5 | 250 | No | SO-8 |
| L5973AD | Step-down | 4,4…36 | 0,5…35 | 1,5 | 500 | Eat | HSOP-8 |
| L5973D | Step-down | 4,4…36 | 0,5…35 | 2 | 250 | Eat | HSOP-8 |
| L5987A | Step-down | 2,9…18 | 0.6…Vin. | 3 | 250…1000 | Eat | HSOP-8 |
| L6902D | Step-down | 8…36 | 0,5…34 | 1 | 250 | No | SO-8 |
| L6920D | Step-up | 0,6…5,5 | 2…5,2 | 1 | up to 1000 | Eat | TSSOP-8 |
| L6920DB | Step-up | 0,6…5,5 | 1,8…5,2 | 0,8 | up to 1000 | Eat | miniSO-8 |
Table 2. Microcircuits for step-down DC/DC converters with conversion frequencies from 0.9 to 1.7 MHz
| Series | Name | Iout., A | Vin.,V | Vout., V | Frequency conversion, MHz |
Entrance shutdowns |
Frame |
|---|---|---|---|---|---|---|---|
| ST1S03 | ST1S03PUR | 1,5 | 3…16 | 0,8…12 | 1,5 | No | DFN6D (3x3 mm) |
| ST1S03A | ST1S03AIPUR | 3…5.5 | 0,8…5.5 | 1,5 | Eat | DFN6D (3x3 mm) | |
| ST1S03APUR | 1,5 | No | |||||
| ST1S06 | ST1S06PUR | 2,7…6 | 0,8…5.5 | 1,5 | Eat | DFN6D (3x3 mm) | |
| ST1S06A | ST1S06APUR | 1,5 | No | ||||
| ST1S06xx12 | ST1S06PU12R | 2,7…6 | 1,2 | 1,5 | Eat | DFN6D (3×3 mm) | |
| ST1S06xx33 | ST1S06PU33R | 3,3 | 1,5 | Eat | |||
| ST1S09 | ST1S09IPUR | 2,0 | 2,7…5,5 | 0,8…5 | 1,5 | Eat | DFN6D (3x3 mm) |
| ST1S09PUR | 1,5 | No | |||||
| ST1S10 | ST1S10PHR | 3,0 | 2,5…18 | 0.8…0.85Vin. | 0,9 (0,4…1,2)* | Eat | PowerSO-8 |
| ST1S10PUR | DFN8 (4x4 mm) | ||||||
| ST1S12xx | ST1S12GR | 0,7 | 2,5…5,5 | 1,2…5 | 1,7 | Eat | TSOT23-5L |
| ST1S12xx12 | ST1S12G12R | 1,2 | |||||
| ST1S12xx18 | ST1S12G18R | 1,8 | |||||
| * - the range of conversion frequencies when synchronizing from an external generator is indicated in parentheses. | |||||||
The main part of the microcircuits for DC/DC converters from Table 1 has a conversion frequency of up to 300 kHz. At such frequencies, the choice of inductances at the DC/DC output is easier, since for the operating frequencies of the microcircuits from Table 2 (1.5 and 1.7 MHz), special attention must be paid to the frequency characteristics of the inductors. Figures 1 and 2 show, as examples, the circuit diagrams recommended by the manufacturer for connecting microcircuits. L5973D(output current up to 2.0 A at conversion frequency 250 kHz) and ST1S06(output current up to 1.5 A at conversion frequency 1.5 MHz).
Rice. 1.
Rice. 2.
From Figures 1 and 2 it can be seen that microcircuits with relatively low conversion frequencies, by modern standards, require a larger number of external electronic components that are larger in size compared to components of converters operating at frequencies above 1 MHz. The DC/DC ICs in Table 2 provide much smaller PCB sizes, but require greater care in wiring to reduce radiated EMI.
Some microcircuits allow you to control the switching on and off of converters due to the presence of the INHIBIT input. An example of the inclusion of such microcircuits is shown in Fig. 3. ST1S09(without INHIBIT input) and ST1S09I(with INHIBIT input). The lower part of this figure shows the recommended values of resistors R1 and R2 for generating output voltages of 1.2 and 3.3 V.
Rice. 3.
If there is a high voltage level (more than 1.3 V) at the control input VINH, the ST1S09I chip is in the active state; when the voltage at this input is less than 1.4 V, the DC/DC converter is turned off (its own consumption is less than 1 μA). The version of the microcircuit without a control input at pin 6 instead of the VINH input has a “PG = Power Good” output (power is normal). The formation of the “Power Good” signal is illustrated in Fig. 4. When the value of 0.92xVFB is reached at the FB input (FeedBack or feedback input), the comparator switches and a high voltage level is generated at the PG output, informing that the output voltage is within acceptable limits.
Rice. 4.
Conversion efficiency
using the example of ST1S09 and ST1S09I chips
The efficiency of a DC/DC buck converter is highly dependent on the on-chip insulated gate transistors (MOSFETs) that act as the switch. One of the problems with high-frequency converters is related to the transistor's gate charging current when controlled by a PWM controller. Losses in this case are practically independent of the load current. The second problem that reduces efficiency is the power dissipated in the transistor during switching from one state to another (during these periods of time the transistor operates in linear mode). Losses can be reduced by providing steeper switching edges, but this increases electromagnetic noise and interference in the power supply circuits. Another reason for the decrease in converter efficiency is the presence of active drain-source resistance (Rdson). In a properly designed circuit, efficiency reaches its maximum value when static (ohmic) and dynamic losses are equal. It should be noted that the output rectifier diode also contributes its share of dynamic and static losses. An incorrectly selected inductance at the output of a DC/DC converter can further significantly reduce the conversion efficiency, which makes it necessary to remember its high-frequency properties. In the worst case, at high conversion frequencies, the output choke may lose its inductive properties, and the converter simply will not work.
STMicroelectronics has been producing high-power field-effect transistors and diodes with very high dynamic and static characteristics for many years. Possession of well-established technology for the production of MOSFET transistors allows the company to integrate its field-effect transistors into microcircuits for DC/DC converters and achieve high conversion efficiency values.
In Fig. 5 (a, b, c) shows typical dependences of the conversion efficiency on certain parameters under different operating conditions as an example. The graphs of the dependence of the efficiency on the output current reach maximum values of about 95% at a current of 0.5 A. Further, the decline in these characteristics is quite gentle, which characterizes only a slight increase in losses as the output current increases to the maximum value.
Rice. 5a.
In Fig. Figure 5b shows the dependence of the efficiency on the output voltage level of DC/DC converters on the ST1S09 and ST1S09I microcircuits. As the output voltage increases, the efficiency increases. This is explained by the fact that the voltage drop across the transistors of the output stage is practically independent of the output voltage at a constant output current, therefore, as the output voltage increases, the percentage of insertion losses will decrease.
Rice. 5 B.
In Fig. Figure 5c shows the dependence of the efficiency on the value of the output inductance. In the range from 2 to 10 μH, the conversion efficiency remains virtually unchanged, which allows you to select the inductance value from a wide range of ratings. Of course, you need to strive for the highest possible level of inductance to provide better filtering of the output current ripple voltage. It is clear that as the output current increases, the efficiency decreases. This is explained by an increase in losses in the output stages of DC/DC converters.
Rice. 5th century
Comparison with chips from other manufacturers
Tables 3, 4 and 5 show the parameters of microcircuits with similar functional significance from other manufacturers.
From Table 3 it can be seen that FAN2013MPX is a complete analogue for the microcircuit ST1S09IPUR, but STMicroelectronics has an additional chip in this series ST1S09PUR with the presence of the “Power Good” output, which expands the developer’s choice.
Table 3. Close replacement chips for DC/DC converters from other manufacturers
| Manufacturer | Name | Iout max., A | Frequency conversion, MHz |
Power Good | Compatibility according to the conclusions |
Frame |
|---|---|---|---|---|---|---|
| STMicroelectronics | ST1S09PUR | 2 | 1,5 | Eat | Eat | DFN3x3-6 |
| ST1S09IPUR | No | Eat | ||||
| Fairchild Semiconductor | FAN2013MPX | 2 | 1,3 | No | Eat | DFN3x3-6 |
Table 4 shows functional replacements (no pin compatibility) from other manufacturers for microcircuits ST1S10. The main advantage of the ST1S10 microcircuits is the presence of synchronous rectification in the output stages, which provides higher conversion efficiency. In addition, the DFN8 package (4x4 mm) is smaller in size compared to the packages of functionally similar microcircuits from other manufacturers. The internal compensation circuit allows you to reduce the number of external components for piping the microcircuits.
Table 4. Close replacements for ST1S10PxR chips for step-down DC/DC converters from other manufacturers
| Manufacturer | Name | Iout max., A | Synchronous rectification | Compensation | Soft launch | Compatibility according to the conclusions |
Frame |
|---|---|---|---|---|---|---|---|
| STMicroelectronics | ST1S10PHR | 3 | Eat | Internal | Interior | - | PowerSO-8 |
| ST1S10PUR | DFN8 (4x4 mm) | ||||||
| Monolithic Power Systems | MP2307/MP1583 | 3 | Yes/No | External | External | No | SO8-EP |
| Alpha & Omega Semiconductor | AOZ1013 | 3 | No | External | Interior | No | SO8 |
| Semtech | SC4521 | 3 | No | External | External | No | SO8-EP |
| AnaChip | AP1510 | 3 | No | Internal | Interior | No | SO8 |
Table 5 shows possible replacements for the chips ST1S12. The main advantage of the ST1S12 microcircuits is the higher value of the maximum permissible output current: up to 700 mA. The MP2104 microcircuit from MPS is pin-compatible with the ST1S12 microcircuit. The LM3674 and LM3671 chips can only be considered as a close functional replacement for the ST1S112 due to the lack of pin compatibility.
Table 5. Close replacements for ST1S12 chips for step-down DC/DC converters from other manufacturers
| Manufacturer | Name | Iout (max.), mA |
Frequency conversion, MHz |
Vin (max.), V | Entrance shutdowns |
Compatibility according to the conclusions |
Frame |
|---|---|---|---|---|---|---|---|
| STMicroelectronics | ST1S12 | 700 | 1,7 | 5,5 | There is | - | TSOT23-5L |
| Monolithic Power Systems | MP2104 | 600 | 1,7 | 6 | There is | There is | TSOT23-5L |
| National Semiconductor | LM3674 | 600 | 2 | 5,5 | There is | No | SOT23-5L |
| LM3671 | 600 | 2 | 5,5 | There is | No | SOT23-5L |
Choosing chips for
DC/DC converters on the website
To quickly search for electronic components using known parameters, it is most convenient to use the website . For parametric search on this site, it is strongly recommended to install and use the free website viewer (browser) “Google Chrome”. Working in this browser speeds up the search several times. Microcircuits for DC/DC converters from STMicroelectronics can be found on the website under the following path: “Power management” ® “IC for DC/DC” ® “Regulators (+ switch)”. Next, you can select the “ST” brand and activate the “Warehouse” filter to select only those components that are in stock. The result of these actions is shown in Fig. 6. You can make a more specific selection according to the required parameters using other filters.
Conclusion
The correct choice of microcircuits for DC/DC converters in devices with autonomous power supplies is especially important. In some cases, selecting the appropriate power supply can be difficult, but by taking the time to design and select your device's power design, you can gain an edge over your competitors with a smaller, lower cost solution with higher power conversion efficiency. STMicroelectronics DC/DC converter ICs make selection easier and enable you to realize the benefits inherent in them when creating competitive power supply circuits.
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