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Smooth turning on of the LEDs with your own hands. Brightness control for LED backlighting of auto instrumentation. Scheme for smooth ignition of LEDs Smooth ignition of the LED strip with your own hands

In some cases, it is required to implement a circuit for smoothly turning on or off the light-emitting diode (LED). This solution is especially in demand in the organization of design solutions. To implement the plan, there are two ways to solve it. The first is the purchase of a ready-made ignition unit in a store. The second is making a block with your own hands. As part of the article, we will find out why it is worth resorting to the second option, and also analyze the most popular schemes.

Buy or do it yourself?

If you urgently need or don’t have the desire and time to assemble a soft turn on LED block with your own hands, then you can buy a finished device in the store. The only downside is the price. The cost of some products, depending on the parameters and the manufacturer, may be several times higher than the cost of a do-it-yourself device.

If you have time and especially desire, then you should pay attention to the long-developed and time-tested schemes for smoothly turning LEDs on and off.

What do you need

In order to assemble a smooth ignition circuit for LEDs, you first need a small set of radio amateurs, both skills and tools:

  • soldering iron and solder;
  • textolite for the board;
  • body of the future device;
  • a set of semiconductor devices (resistors, transistors, capacitors, LEDs, diodes, etc.);
  • desire and time;

As you can see from the list, nothing special and complicated is required.

The basis of soft start basics

Let's start with elementary things and remember what an RC circuit is and how it is related to the smooth ignition and decay of the LED. Look at the diagram.

It consists of only three components:

  • R is a resistor;
  • C - capacitor;
  • HL1 - backlight (LED).

The first two components make up the RC - circuit (the product of resistance and capacitance). By increasing the resistance R and the capacitance of the capacitor C, the ignition time of the LED increases. When decreasing, the opposite is true.

We will not delve into the basics of electronics and consider how physical processes (more precisely, current) proceed in this circuit. It is enough to know that it underlies the operation of all smooth ignition and damping devices.

The considered principle of RC - delay underlies all solutions for smoothly turning on and off LEDs.

Schemes of smooth switching on and off of LEDs

It makes no sense to disassemble bulky circuits, because to solve most problems, simple devices operating on elementary circuits cope. Consider one of these schemes for smoothly turning on and off LEDs. Despite its simplicity, it has a number of advantages, high reliability and low cost.

Consists of the following parts:

  • VT1 - field effect transistor IRF540;
  • C1 - capacitor with a capacity of 220 mF and a voltage of 16V;
  • R1, R2, R3 - resistors with a nominal value of 10, 22, 40 kOm, respectively;
  • LED - LED.

Operates from a voltage of 12 volts according to the following algorithm:

  1. When the circuit is turned on in the power circuit, current flows through R2.
  2. At this time, C1 is gaining capacity (charging), which ensures the gradual opening of the VT field
  3. Increasing gate current (pin 1) flows through R1, and causes the drain of the field device VT to gradually open.
  4. The current goes to the source of the same VT1 field device and then to the LED.
  5. The LED gradually increases the emission of light.

The attenuation of the LED occurs when the power is removed. The principle is reversed. After the power is turned off, the capacitor C1 begins to gradually give up its capacitance to the resistances R1 and R2.

The discharge rate, and thus the rate of smooth fading of the LED, can be controlled by the value of the resistance R3. Experiment to understand how the value affects how quickly the LED lights up and fades out. The principle is the following - higher resistance, slower attenuation, and vice versa.

The main element is the field n-channel MOSFET transistor IRF540, all other semiconductor devices play an auxiliary role (piping). It is worth noting its important characteristics:

  • drain current: up to 23 Amperes;
  • polarity: n;
  • drain-source voltage: 100 volts.

More detailed information, including CVC, can be found on the manufacturer's website in the datasheet.

Improved version with the ability to set the time

The option considered above assumes the use of a device without the possibility of adjusting the time of ignition and attenuation of the LED. And sometimes it's necessary. For implementation, you just need to supplement the circuit with several elements, namely R4, R5 - adjustable resistances. They are designed to implement the function of adjusting the time of full switching on and off of the load.

The considered schemes for smooth ignition and attenuation are perfect for implementing designer lighting in a car (trunk, doors, front passenger footwell).

Another popular pattern

The second most popular scheme for smoothly turning LEDs on and off is very similar to the two considered, but they differ greatly in how they work. Switching on is controlled by minus.

The scheme was widely used in those places where one part of the contacts closes on the minus, and the other on the plus.

Differences of the scheme from those considered earlier. The main difference is a different transistor. The field worker must be replaced with a p-channel one (marking is indicated in the diagram below). It is necessary to “flip” the capacitor, now the plus of the conder will go to the source of the transistor. Do not forget, the modified version has a power supply with reverse polarity.

Video

For an in-depth understanding of everything that happens in the considered options, we suggest watching an interesting video, the author of which, using the electronic circuit design program, gradually shows the principle of operation of the smooth turning on and off of the LED in different options. After carefully watching the video, you will understand why it is necessary to use a transistor.

Conclusion

The considered solutions are the most popular and in demand. On the Internet, on forms, there are big discussions about the simplicity and low functionality of these schemes, but practice has shown that in everyday life their functionality is enough in full. A big plus of the considered solutions for turning LEDs on and off is ease of manufacture and low cost. It will take no more than 3-7 hours to develop a ready-made solution.

Recently I decided to assemble a circuit that would allow me to light up any LED strip (whether in a car or at home) smoothly. I did not reinvent the wheel, and decided to google a little. When searching on almost every site, I found circuits where the LED load is severely limited by the capabilities of the circuit.

I wanted the circuit to just smoothly raise the output voltage, so that the diodes flare up smoothly and the circuit was necessarily passive (it did not require additional power and would not consume current in standby mode) and would definitely be protected by a voltage regulator to increase the life of my backlight .

And since I haven’t learned how to etch the boards yet, I decided that first I need to master the simplest circuits and use ready-made circuit boards during installation, which, like the rest of the circuit components, can be purchased at any radio parts store.

In order to assemble a smooth ignition circuit for LEDs with stabilization, I needed to purchase the following components:

In general, a ready-made circuit board is a fairly convenient alternative to the so-called “LUT” method, where almost any circuit can be assembled using the Sprint-Layout program, a printer, and the same textolite. So, beginners should still first master a simpler option, which is much simpler and, most importantly, “forgives mistakes” and also does not require a soldering station.

Having slightly simplified the original scheme, I decided to redraw it:


I know that the transistor and the stabilizer are indicated differently in the diagrams, but it’s easier for me, and it will be clearer for you. And if, like me, you managed to take care of stabilization, then you need an even simpler scheme:


The same, but without the use of the KREN8B stabilizer.

R3 - 10K Ohm
R2 - 51K Ohm
R1 - from 50K to 100K ohm (the resistance of this resistor can control the speed of ignition of the LEDs).
C1 - from 200 to 400 microns F (you can choose other capacities, but you should not exceed 1000 microns F).
At that time, I needed two smooth ignition boards:
- for the already made highlighting of the legs.
- for smooth ignition of the dashboard.

Since I took care of the stabilization of the LEDs that illuminate my legs for a long time, I no longer needed Krenka in the ignition circuit.


Scheme of smooth ignition without a stabilizer.


For such a circuit, I used only 1.5 sq cm of the circuit board, which costs only 60 rubles.


Scheme of smooth ignition with a voltage stabilizer.


Dimensions 25 x 10 mm.

The advantages of this circuit is that the connected load depends only on the capabilities of the power supply (car battery), and on the IRF9540N field-effect transistor, which is very reliable (it makes it possible to connect 140W of load through itself at a current of up to 23A (information from the Internet). The circuit can withstand 10 meters of LED strip, but then the transistor will have to be cooled, since in this design it is possible to attach a radiator to the field radiator (which, of course, will lead to an increase in the area of ​​\u200b\u200bthe circuit).

During the first testing of the circuit, a short video was shot:



Initially, R1 was 60K Ohm and I didn’t like the fact that it took about 5-6 seconds to ignite to full brightness, later another 60K Ohm resistor was added to R1 and the ignition time decreased to 3 seconds, which was the most .

And since the ignition circuit for lighting the legs had to be connected to the break of the main power circuit, without thinking for a long time how to isolate it, I simply stuffed it into a piece of a bicycle chamber.

This article will consider several options for implementing the idea of ​​​​smooth turning on and off the LEDs for backlighting the instrument panel, cabin light, and in some cases more powerful consumers - dimensions, low beam, and the like. If your instrument panel is illuminated with LEDs, when you turn on the dimensions, the illumination of the instruments and buttons on the panel will light up smoothly, which looks quite impressive. The same can be said about the interior lighting, which will light up smoothly, and fade out smoothly after closing the car doors. In general, a good option for tuning the backlight :).

The control circuit for smooth switching on and off the load, controlled by the plus.

This circuit can be used to smoothly turn on the LED backlight of the car dashboard.

This scheme can also be used for smooth ignition of standard incandescent lamps with low power spirals. In this case, the transistor must be placed on a radiator with a dissipation area of ​​about 50 square meters. cm.

The scheme works as follows.
The control signal comes through the 1N4148 diodes when voltage is applied to the "plus" when the parking lights and ignition are turned on.
When any of them is turned on, current is supplied through a 4.7 kΩ resistor to the base of the KT503 transistor. In this case, the transistor opens, and through it and the 120 kΩ resistor, the capacitor begins to charge.
The voltage on the capacitor gradually increases, and then through a 10 kΩ resistor it enters the input of the IRF9540 field effect transistor.
The transistor gradually opens, gradually increasing the voltage at the output of the circuit.
When the control voltage is removed, the KT503 transistor closes.
The capacitor is discharged to the input of the IRF9540 field effect transistor through a 51 kΩ resistor.
After the end of the process of discharging the capacitor, the circuit stops consuming current and goes into standby mode. The current consumption in this mode is negligible. If necessary, you can change the ignition and decay time of the controlled element (LEDs or lamps) by selecting the resistance values ​​​​and the capacitance of the 220 microfarad capacitor.

With proper assembly and serviceable parts, this circuit does not need additional settings.

Here is a printed circuit board option for placing the details of this circuit:

This circuit allows you to smoothly turn on / off the LEDs, as well as reduce the brightness of the backlight when you turn on the dimensions. The latter function can be useful in case of excessively bright illumination, when in the dark the instrument illumination begins to blind and distract the driver.

The circuit uses a KT827 transistor. The variable resistance R2 is used to set the brightness of the backlight in the mode of included dimensions.
By selecting the capacitance of the capacitor, you can adjust the time of tanning and fading of the LEDs.

In order to implement the function of dimming the backlight when the dimensions are turned on, you need to install a dual dimensions switch or use a relay that would work when the dimensions are turned on and close the switch contacts.

Soft turn off LEDs.

The simplest circuit for smooth fading of the VD1 LED. Well suited for the implementation of the function of a smooth fading of interior light after closing the doors.

Almost any diode VD2 is suitable, the current through it is small. The polarity of the diode is determined in accordance with the figure.

Capacitor C1 is an electrolytic, large capacity, we select the capacity individually. The larger the capacitance, the longer the LED burns after the power is turned off, but you should not install a capacitor with too large a capacity, as the contacts of the limit switches will burn due to the high charging current of the capacitor. In addition, the larger the capacitance, the more massive the capacitor itself, there may be problems with its placement. Recommended capacitance 2200uF. With such a capacity, the backlight fades within 3-6 seconds. The capacitor must be designed for a voltage of at least 25V. IMPORTANT! When installing the capacitor, observe the polarity! An electrolytic capacitor may explode if the polarity is reversed!

Surely a lot of people would like to bring something new to their car. Today we will consider how to make small design changes to the backlight of a car .... or maybe not a car, you can also control the LED strip, for example, in interior lighting

Our device will smoothly turn on and off the load, produce smooth ignition.

How it works

We connect a +12 volt power supply to VCC +. We connect the control plus to REM, specifically in the car it will be the plus of the ignition. With LED contacts, everything should be clear, "+" and "-" LEDs.

In the T1 circuit, the BC817 transistor is a domestic analogue of the KT503. Transistor T2 - IRF9540.

If you want to increase the ignition time, you need to increase the value of R2, to reduce accordingly, lower it. To control the damping time, a similar operation must be done with the resistor R3.

To minimize the board, I used SMD resistors, and for convenience I used terminal blocks.

The boards are made by LUT technology. And after the done manipulations, we get a compact and useful device: