Power indicator. LED output power indicator AC load on indicator

Schematic diagrams of simple indicators of the presence of a 220V network on LEDs, we change the old neon indicator lamps to LEDs. In electrical equipment, indicator neon lamps are widely used to indicate the inclusion of equipment.

In most cases, the circuit is as in Figure 1. That is, a neon lamp is connected to an alternating current network through a resistor with a resistance of 150-200 kilos. The breakdown threshold of a neon lamp is below 220V, so it easily breaks through and glows. And the resistor limits the current through it so that it does not explode from excess current.

There are also neon lamps with built-in current-limiting resistors, in such circuits it seems as if the neon lamp is connected to the network without a resistor. In fact, the resistor is hidden in its base or in its wire lead.

The disadvantage of neon indicator lamps is a weak glow and only a pink color of the glow, and also that it is glass. Plus, neon lamps are now commercially less common than LEDs. It is clear that there is a temptation to make a similar power indicator, but on an LED, the more LEDs come in different colors and are much brighter than neon lights, and there is no glass.

But, the LED is a low-voltage device. The forward voltage is usually no more than 3V, and the reverse voltage is also very low. Even if you replace a neon lamp with an LED, it will fail due to the excess of the reverse voltage with a negative half-wave of the mains voltage.

Rice. 1. Typical scheme for connecting a neon lamp to a 220V network.

However, there are two-color two-output LEDs. In the case of such an LED, there are two multi-colored LEDs connected in anti-parallel. Such an LED can be connected in almost the same way as a neon lamp (Fig. 2), only take a resistor with a lower resistance, because for good brightness, more current must flow through the LED than through a neon lamp.

Rice. 2. Scheme of the 220V network indicator on a two-color LED.

In this circuit, one half of the two-color HL1 LED operates on one half-wave, and the other half on the other half-wave of the mains voltage. As a result, the reverse voltage on the LED does not exceed the forward voltage. The only downside is the color. He is yellow. Because usually there are two colors - red and green, but they burn almost simultaneously, because visually it looks like yellow.

Rice. 3. Diagram of a 220V network indicator on a two-color LED and a capacitor.

Figures 4 and 5 show a diagram of a power indicator on two LEDs connected in anti-parallel. This is almost the same as in Fig. 3 and 4, but the LEDs are separate for each half-cycle of mains voltage. LEDs can be either the same color or different.

Rice. 4. Scheme of the 220V network indicator with two LEDs.

Rice. 5. 220V network indicator circuit with two LEDs and a capacitor.

But, if only one LED is needed, the second one can be replaced with a conventional diode, for example, 1N4148 (Fig. 6 and 7). And there is nothing wrong with the fact that this LED is not designed for mains voltage. Because the reverse voltage on it will not exceed the forward voltage of the LED.

Rice. 6. Scheme of the 220V network indicator with an LED and a diode.

Rice. 2. 220V network indicator circuit with one LED and a capacitor.

In the schemes, LEDs were tested, two-color type L-53SRGW and one-color type AL307. Of course, you can use any other similar indicator LEDs. Resistors and capacitors can also be of other sizes - it all depends on how much current you need to let through the LED.

Andronov V. RK-2017-02.

Load indicator
A. LATAI CO, Dnepropetrovsk, Ukraine
Sometimes the consumer of electrical energy and its switch are installed in different rooms. In such cases, it is desirable to have a visual control of the switched on state of the consumer by equipping the switch with an additional indicator. The author of this article describes a relatively simple design of such an indicator, while demonstrating a competent approach to choosing its elements. The editors hope that this side of the article will be useful to many readers.
Widely known switches are combined in one housing with an indicator of the presence of mains voltage. However, this approach does not guarantee regular operation of the consumer, since in fact only the presence of voltage at the "output" of the switch is controlled. To make sure that the voltage reaches the consumer, additional wires are needed. They are easy to provide for when installing new wiring, but when upgrading an existing one, this can cause significant difficulties.
In a number of cases, indicators that respond to the current supplied by the load are more informative and easy to install. They are connected in series with the switch and the load. No additional wires are required. An example of such a solution is the indicator proposed in . A small number of parts used allows it to fit in a standard switch housing. By adding a few more details to this indicator, we managed to expand its functions and make the device more convenient.
On fig. 1 shows a diagram of the modified indicator. When the switch SA1 is open, a weak current (approximately 9 mA) continuously flows in the circuit of the lamp EL1, limited by the capacitance of the capacitor C1. The filament of the lamp at this current remains cold and the foam and the HL1 LED crystal glows. The power consumption in this state is very small. When the SA1 switch is closed, the indicator works as described in, the color of the LED changes to red.
The permanent backlight makes it easier to use the switch in the dark. If the circuit is broken, for example, due to a lamp burnout, the LED remains off in any position.
switch SA1. This allows you to timely, even before the need arises to turn on the lighting, replace a burned-out lamp or eliminate a broken wire.
The converter of the load current into the voltage required for the LED is the diodes VD1-VD3. Ideally, if the voltage removed from them does not depend on the load power, at least in the most common range of 15 ... 200 W. To make the right choice, the current-voltage characteristics of some diodes and small-sized diode bridges were experimentally taken (the positive and negative terminals of the bridges were connected together during the measurement).
The voltage was measured in the steady state thermal regime after the diode under test was heated by the flowing current. The fact is that with an increase in the temperature of the crystal, the voltage drop across the pn junction of the diode decreases, which to some extent compensates for the increase in the voltage drop proportional to the current across the ohmic resistance of the semiconductor material. Due to this effect, the flattest dependence of voltage on current is observed for small-sized high-power diodes heated to a higher temperature (1N4007, 1N5817). This is confirmed by the experimentally taken graphs shown in Fig. 2.
It is necessary to install as many series-connected diodes into the indicator so that in total a voltage drops on them that exceeds the direct voltage drop on the "red" LED crystal (1.6 ... 1.9 V). Three 1N4007 diodes (total voltage about 2.4 V) satisfy this condition. The excess extinguishes the resistor R2. If by design
For effective reasons, instead of individual diodes, it is preferable to use a small-sized rectifier bridge, the VD2-VD5 diodes can be replaced by the circuit shown in fig. 3. This will not change the properties of the indicator.
Thermistor RK1 with a negative temperature coefficient limits the initial inrush current through the cold filament of the incandescent lamp EL1 and the diodes VD2-VD5, which helps to increase the lamp life and increase the reliability of the indicator. At the moment of switching on, almost all the mains voltage is applied to a cold thermistor with significant resistance, the current in the lamp circuit is less than the nominal one. With heating, the resistance of the thermistor decreases tenfold, and the resistance
The voltage of the EL1 lamp increases. In steady state, only 2 ... 2.5 V drops on the thermistor, which has almost no effect on the brightness of the lamp. Its "slow" inclusion is almost imperceptible, since the transient process lasts no more than 1 s.
Naturally, the use of a thermistor is effective only if the interval between turning off and then turning on the lighting exceeds 5 ... 7 minutes, necessary for its cooling. For loads that do not have a pronounced "starting" current, the thermistor is not needed and can be excluded
On fig. 4 shows photographs of a conventional flush-wiring switch with an indicator installed inside. Its board is made of foil fiberglass using a cutter. Due to its simplicity and the variety of designs of switches, the drawing of the board is not given.
Capacitor C1 - K73-17. The outputs of the HL1 LED are extended with a rigid insulated wire, and an oval-shaped hole is made for it in the switch key. The L-59SRSGW LED can be replaced with another three-pin two-color high or normal brightness, for example, the ALS331 series. When choosing an LED, it should be taken into account that a pulsed current flows through it, the peak value of KOioporo for the "red" crystal is two, and for the "green" - 3.14 times the average.
Noticeably heated diodes VD2-VD5 and thermistor RK1 are raised above the board for the entire length of the leads. Thermistor type - KMT-12. These were previously used in systems for demagnetizing the kinescope of ULPCT TVs. Since the operating temperature of the thermistor reaches 90 ° C, it should not touch other parts and the plastic case of the switch.

With a lamp power of more than 150 W, it is useful to drill several ventilation holes in the front cover of the switch. And if the lamp power is 60 W or less, it is necessary to cut off half of it from the thermistor disk by filing with a file. This will double the initial resistance of the thermistor and reduce its cooling surface by the same factor. Required operating temperature and low
voltage losses will be achieved at lower current.
Establishing the signaling device is reduced to setting the selection of resistor R2 current through the "red" crystal of the LED 8 ... 10 mA. The current through the "green" crystal, which depends on the capacitance of the capacitor C1, is not affected by the value of the resistor R2. The current value is determined by the voltage drop across the resistor R2, measured by a pointer voltmeter
trom of the magnetoelectric system (for example, with an avometer Ts4315).
LITERATURE
1. Yushin A. Key switches with light indication. - Radio, 2005, No. 5, p. 52.
2. Gorenko S. Indicator of the included load. - Radio, 2005, No. 1, p. 25.

Looking for a light switch or an outlet in the dark is an unpleasant task. Household lighting switches appeared on sale, equipped with indicators that highlight their location. By slightly improving the circuit, such an indicator can be turned into a load connection indicator.
The load connection indicator (PPN) is a device built into the socket and indicating the presence of contact between the inserted mains plug from any household appliance and the socket. The indicator is especially convenient if the connected devices do not have their own network indicator. The PSI is also useful for electronic products that have on indicators located in the secondary power circuit, as it allows you to check their input circuits.
The IPN consists of:
- load current sensor on diodes VD2...VD6;
- L-shaped filter R1-C1;
- key field effect transistor VT1;
- indication block on elements VD9, VD10, R2, HL1.
If no load is connected to the socket XS1, then no current flows through the diodes VD1 ... VD6, the storage capacitor C1 is discharged and the field effect transistor VT1 is closed. The drain current VT1 is zero, the HL1 indicator is off.

When the load is connected to the socket XS1, the load current flows through the opposite-parallel connected diode VD1 and the chain of diodes VD2...VD6. Negative half-waves of the mains voltage pass through VD1. and positive - through VD2.. .VD6. The voltage drop across the diodes VD2 ... VD6 through the resistor R1 is fed to the storage capacitor C1 and charges it to a value exceeding the cutoff voltage of the field-effect transistor VT1. Transistor VT1 opens, and current flows through its source-drain channel, resistor R2, LED HL1 and diode VD9. LED HL1 glows brightly, signaling the connection of the load. Resistor R2 is current-limiting, diode VD9 prohibits the flow of current through the load during reverse half-cycles of the mains voltage. Diode VD10 protects HL1 from reverse voltage.
It should be noted that the direct voltage drop across the diodes VD2 .. VD6 depends on the power of the load connected to the XS1 socket and also decreases with a decrease in load power. Therefore, in order for the indicator to "react" even to low-power (less than 1 W) loads, a KP504A field-effect transistor is used in the PSI circuit. It has a maximum source-drain voltage of 240 V and allows switching current in the drain circuit up to 0.25 A. The control voltage (0 ... 10 V) is applied to the gate relative to
source. The KP504A transistor has a cutoff voltage of +0.6 V. The maximum power of the connected load is determined by the maximum forward current of the VD1 ... VD6 diodes (1.7 A) and should not exceed 500 ... 700 W.
The circuit uses resistors of the OMLT type. Capacitor C1 - oxide, type K50-35 or foreign production with an operating voltage of at least 16 V. Diodes VD1 ... VD6 - type KD226V. KD226G. KD226D. Diodes VD9, VD10 can be replaced by KD105B, KD102A or other miniature ones with a permissible reverse voltage of at least 200 V. Fuse FU1 - ceramic, miniature. It is installed in the head of the fuse holder of the DPB type and, together with the HL1 LED, is placed on the front (top) panel of the socket. With fuses soldered into the PCB, a fuse holder can be dispensed with. LED HL1 - almost any low voltage with a working current of up to 20 mA. To increase the brightness of the glow as HL1, it is recommended to use high-brightness LEDs, for example, ARL-5213PGC (green). ARL-3214UWC (white). ARL-n3214UBC (blue). If with some types of LEDs, when VT1 is closed, a slight illumination of the LED will be observed, the LED should be shunted with a resistor with a resistance of 3 ... 8.2 kOhm.
When the PSU is installed in a socket, the aluminum mains wires suitable for the socket clamps are disconnected from them and connected to the PPI input through mounting adapters. All components of the PSU, except for HL1 and FU1, are located on the board, the dimensions of which are determined by the internal dimensions of the socket.

A. OZNOBIKHIN, Irkutsk.

Looking for a light switch or an outlet in the dark is an unpleasant task. It is much more pleasant when you see a glowing indicator in the dark and focus on it. It is especially useful to equip with such an indicator those sockets that power devices that do not have on indicators and fuses. I offer an improved version of the device, equipped with a fuse blown indicator.

When there is no contact between the plug of the connected load and the socket, the indicator does not light up, indicating that there is no “power take-off” by the load. If the load is taking power, the blue indicator is lit, and when the load is drawing excessive power, the fuse blows and the red flashing LED turns on.

The load connection indicator (PSI) consists of (Fig. 1):

• fuse FU1 with blown indicator on elements VD1, VD2, R1, HL1, C1;
• power bypass circuit on the VD6 diode;
• load current sensor on diodes VD4, VD5 and detector VD7, R2, C2;
• key field effect transistor VT1;
• display unit on the elements VD8, HL2, R4, R3, VD3.

When the FU1 fuse blows, if the load is connected to the XS1 socket, the current flows through the elements of the blown indicator that were previously shunted by the zero resistance of the fuse. Rectifier diode VD1 passes only negative

half-waves of the mains voltage that come through the current-limiting resistor R1 to the storage capacitor C1 and the load connected in parallel to it - a blinking HL1 LED. VD1 protects HL1 from reverse voltage, and the Zener diode VD2 protects HL1 from direct current overload.

When the load is not connected to the socket XS1, no current flows through the diodes VD4.VD6, the storage capacitor C2 is discharged and the field effect transistor VT1 is closed.

The channel resistance (source-drain) is very high, and the HL2 indicator is off.

When the load is connected to the socket XS1, the load current flows through the back-to-back diode VD6 and the chain of diodes VD4, VD5. The negative half-waves of the mains voltage from the bottom of the mains wire circuit pass through VD6, and the positive ones through VD4 and VD5.

The direct voltage drop across the diodes VD4 and VD5 through the resistor R2 and the diode VD7 enters C2 and charges it to a value exceeding the cut-off voltage (+0.6 V) of the field-effect transistor VT1. Transistor VT1 opens and through its channel, VD8, HL2, R4 connected in parallel, and then current flows through R3 and VD3. LED HL2 glows brightly, signaling the connection of the load. Resistor R3 is current-limiting, diode VD3 prohibits the flow of current during reverse half-cycles of the mains voltage. Resistor R4 eliminates the backlight HL2 when VT1 is closed and, if necessary, is selected in the range from 3 to 8.2 kOhm.

The direct voltage drop across the current sensor (VD4, VD5) depends on the power of the connected load. In order for the indicator to "react" even to low-power (less than 1 W) devices, a relatively scarce field-effect transistor is used in the circuit. KP504A. It has a maximum source-drain voltage of 240 V and allows you to switch the current in the drain circuit up to 0.25 A. The control voltage at the gate relative to the source is from 0 to 10 V. Cut-off voltage. KP504A is +0.6 V. The maximum load power connected to the XS1 socket is determined by the limiting forward current of the VD4.VD6 diodes (1.7 A) and should not exceed 500.700 W.

The circuit uses resistors of the OMLT type. Capacitor C1 - type K50-35 or foreign production with an operating voltage of at least 16 V, C2 - KM. Diodes VD1, VD3, VD8 - KD105B, KD102A or other miniature ones with a permissible reverse voltage of at least 200 V, VD4.VD6 - KD226V, KD226G, KD226D, VD7 - germanium. D2 or. D9 with any letter. Zener diode VD2 - low-power, with a stabilization voltage of 3.9 ... 5.6 V, for example, KS139, KS147A, KS447A, KS156A. The HL1 LED can be replaced with a 5mm red MSD ARL-5013URC-B or a high brightness non-flashing MSD such as yellow ARL-5213UYC. In the latter case, the capacitor C1 can be excluded. The HL2 LED can be replaced with any low-voltage green (ARL-5213PGC), white (ARL-3214UWC) or blue (ARL-3214UBC) color, preferably high brightness.

Almost all elements of the device are placed on a printed circuit board, the drawing of which is shown in Fig.2. The board is built into a power outlet or into an adapter-splitter ("tee"), which is plugged directly into the outlet. It is possible to place it in the body of the socket block at the end of the extension cord - "carrying". Fuse FU1 for current. FOR - ceramic, miniature. It is installed in the head type fuse holder. DPB and is placed on the front panel of the socket so that it does not interfere with the inclusion of plugs. When the indicator is installed in the socket, the network wires that fit the socket contacts are carefully disconnected and connected to the board through the terminal clamp blocks.

About a year ago, I got the idea to assemble a 12-220 volt voltage converter. For implementation, a transformer was needed. The search led to the garage, where the Solntsev amplifier was found, which I assembled about 20 years ago. Simply removing the transformer and thus destroying the amplifier did not raise a hand. The idea was born to revive it. In the process of reviving the amplifier, a lot has changed. Including output power indicator. The scheme of the former indicator was cumbersome, assembled on K155LA3, etc. Even the Internet did not help to find it. But another very simple, but no less effective output power indicator circuit was found.

LED indicator scheme

This scheme is well described on the Internet. Here I will only briefly describe (retell) about her work. The output power indicator is assembled on the LM3915 chip. Ten LEDs are connected to the powerful outputs of the comparators of the microcircuit. The output current of the comparators is stabilized, so there is no need for quenching resistors. The supply voltage of the microcircuit can be in the range of 6 ... 20 V. The indicator reacts to the instantaneous values ​​of the sound voltage. The divider of the microcircuit is designed so that each subsequent LED turns on when the input signal voltage increases by v2 times (by 3 dB), which is convenient for controlling the power of the UMZCH.

The signal is taken directly from the load - the UMZCH acoustic system - through the divider R * / 10k. The range of powers indicated on the diagram 0.2-0.4-0.8-1.6-3-6-12-25-50-100 W is true if the resistance of the resistor R * = 5.6 kOhm for Rn = 2 Ohm, R*= 10 kOhm for Rn=4 Ohm, R*= 18 kOhm for Rn=8 Ohm and R*=30 kOhm for Rn=16 Ohm. LM3915 makes it easy to change display modes. It is enough just to apply voltage to pin 9 of the LM3915 IC, and it will switch from one display mode to another. Contacts 1 and 2 are used for this. If they are connected, then the IC will switch to the "Luminous column" indication mode, if left free - "Running dot". If the indicator will be operated with UMZCH with a different maximum output power, then you only need to select the resistance of the resistor R * so that the LED connected to pin 10 of the IC glows at the maximum power of the UMZCH.

As you can see, the circuit is simple and does not require complex configuration. Due to the wide range of supply voltages for its operation, I used one shoulder of a pulsed bipolar power supply UMZCH +15 volts. At the signal input, instead of selecting individual resistors, R* set a variable resistance of 20 kOhm, which made the indicator universal for acoustics of different impedance.

To change the display modes, I provided for the installation of a jumper or a button with fixation. In the final, he closed with a jumper.