Soft start LED strip. Scheme of smooth ignition and attenuation of LEDs
Greetings to all beginner electronics engineers and lovers of radio engineering and those who like to do something with their own hands. In this article I will try to kill two birds with one stone: I will try to tell you how to make a printed circuit board of excellent quality yourself, which will not differ in any way from the factory counterpart, thus we will do it. This device can be used in a car to connect LEDs. For example, as in .
For work we need:
- Transistors - IRF9540N and KT503;
- Capacitor for 25 V 100 pF;
- Diode rectifier 1N4148;
- Resistors:
- R1 - 4.7 kOhm 0.25 W;
- R2 - 68 kOhm 0.25 W;
- R3 - 51 kOhm 0.25 W;
- R4 - 10 kOhm 0.25 W.
- Screw terminals, 2- and 3-pin, 5 mm
- One-sided textolite and FeCl3 - ferric chloride
Working process.
First of all, we need to prepare the board. To do this, we mark the conditional boundaries of the board on the textolite. We make the edges of the board a little more than a track pattern. Once the edges of the borders have been marked, you can start cutting. You can cut with scissors for metal, and if they are not at hand, you can try to cut with a clerical knife.
After the board has been cut out, it needs to be sanded. To do this, sand the board under water with sandpaper with a grain size of P800-1000. Next, dry and degrease the surface with the 646th solvent. After that, touching the board is not recommended.
Next, download the program, which is at the end of the article, SprintLayout and use it to open the board layout and print it on a laser printer on glossy paper. It is important that the printer settings are set to high definition and high image quality when printing.
Then it will be necessary to heat the prepared board with an iron and attach our printout to it and iron the board thoroughly for several minutes.
Next, let the board cool down a bit, after which we lower it for a few minutes in a cup of cold water. The water will make it easy to peel the glossy paper off the board. If the gloss is not completely torn off, then you can simply roll the rest of the paper slowly with your fingers.
Then it will be necessary to check the quality of the tracks, if there is minor damage, then you can tint the bad places with a simple marker.
So, the preparatory stage is completed. Left . To do this, we put our board on double-sided tape and glue it on a small piece of foam and lower it into a solution of ferric chloride. To speed up the etching process, you can shake the cup with the solution.
After the excess copper is etched, it will be necessary to wash the board in water and use a solvent to clean the toner from the tracks.
It remains to drill holes. For our device, drills with a diameter of 0.6 and 0.8 mm were used.
It is important not to overheat the tracks otherwise you can damage them.
It remains to assemble our device. Previously, it is recommended to print the circuit with symbols on plain paper and, guided by it, place all the elements on the board.
After everything is soldered, it is necessary to completely clean the board from the flux. To do this, carefully wipe the board with the same 646 solvent and thoroughly wash with a brush and soap and dry.
After drying, we connect and check with the help of the performance of the assembly. To do this, we connect the "constant plus" and "minus" to the power supply, and instead of the LEDs, we connect a multimeter and check if there is voltage. If there is tension, it means that the flux is not completely confused.
As you can see, the board manufacturing process is not a very complicated process. This method of making a board is called LUT (laser-ironing technology). As mentioned above, this assembly can be used for ( , , , ), or in any other places where LEDs and 12 volt power are used -
Thank you all for your attention! I will be happy to answer all your questions!
Good luck on the road!!!
NECESSARILY!!!
Devices whose actions and properties are little known to you, especially homemade ones, connect through fuses.
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:
- When the circuit is turned on in the power circuit, current flows through R2.
- At this time, C1 is gaining capacity (charging), which ensures the gradual opening of the VT field
- Increasing gate current (pin 1) flows through R1, and causes the drain of the field device VT to gradually open.
- The current goes to the source of the same VT1 field device and then to the LED.
- 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.
Output
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.
This article will consider several options for implementing the idea of smooth turning on and off the LEDs for the backlight of the instrument panel, cabin light, and in some cases more powerful consumers - dimensions, dipped 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 double switch for the dimensions 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 large 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!
In addition to a purely decorative function, for example, car interior lighting, the use of soft start, or ignition, is of fundamental practical importance for LEDs - a significant extension of the service life. Therefore, we will consider how to make a device for solving such a problem with your own hands, is it worth it to make it yourself or is it better to buy a ready-made one, what is required for this, and also what circuit options are available for amateur manufacturing.
The first question that arises when it is necessary to include a module for the smooth ignition of LEDs in the circuit is whether to make it yourself or buy it. Naturally, it is easier to purchase a ready-made block with the given parameters. However, this method of solving the problem has one serious disadvantage - the price. When making it yourself, the cost of such a device will decrease several times. In addition, the assembly process will not take much time. In addition, there are proven options for the device - it remains only to acquire the necessary components and equipment and connect them correctly, in accordance with the instructions.
Note! LED lighting is widely used in automobiles. For example, it can be daytime running lights and interior lighting. The inclusion of a soft ignition unit for LED lamps allows, in the first case, to significantly extend the life of the optics, and in the second case, to prevent the driver and passengers from being blinded by the abrupt switching on of a light bulb in the cabin, which makes the lighting system more visually comfortable.
What do you need
To correctly assemble a soft ignition module for LEDs, you will need a set of the following tools and materials:
- Soldering station and a set of consumables (solder, flux, etc.).
- Fragment of a textolite sheet for creating a board.
- Case for housing components.
- Necessary semiconductor elements - transistors, resistors, capacitors, diodes, ice crystals.
However, before proceeding with the independent manufacture of a soft start / attenuation unit for LEDs, you need to familiarize yourself with the principle of its operation.
The image shows a diagram of the simplest device model:
It has three work items:
- Resistor (R).
- Capacitor module (C).
- LED (HL).
A resistor-capacitor circuit based on the principle of RC-delay, in fact, controls the ignition parameters. So, the greater the value of resistance and capacitance, the longer the period or the more smoothly the ice element turns on, and vice versa.
Recommendation! At the moment, a huge number of soft ignition block circuits for 12V LEDs have been developed. All of them differ in a characteristic set of pluses, minuses, level of complexity and quality. There is no reason to manufacture devices with extensive boards on expensive components on your own. The easiest way is to make a module on a single transistor with a small strapping, sufficient for slow turning on and off the ice bulb.
Schemes of smooth switching on and off of LEDs
There are two popular and self-made options for soft ignition schemes for LEDs:
- The simplest.
- With the function of setting the start period.
Read also Dynamic monitor backlight: characteristics, scheme, settings
Consider what elements they consist of, what is the algorithm of their work and the main features.
A simple scheme for smoothly turning off LEDs
Only at first glance, the smooth ignition scheme presented below may seem simplified. In fact, it is very reliable, inexpensive and has many advantages.
It is based on the following components:
- IRF540 is a field type transistor (VT1).
- Capacitive capacitor 220 mF, rated at 16 volts (C1).
- A chain of resistors for 12, 22 and 40 kilo-ohms (R1, R2, R3).
- Led-crystal.
The device operates on a 12 V DC power supply according to the following principle:
- When the circuit is energized, current begins to flow through block R2.
- Due to this, the C1 element is gradually charged (the capacitance rating increases), which in turn contributes to the slow opening of the VT module.
- The increasing potential at pin 1 (field gate) provokes the flow of current through R1, which contributes to the gradual opening of pin 2 (VT drain).
- As a result, the current passes to the source of the field unit and to the load and provides a smooth ignition of the LED.
The process of extinction of the ice element proceeds according to the opposite principle - after the power is removed (opening the "control plus"). In this case, the capacitor module, gradually discharging, transfers the capacitance potential to the blocks R1 and R2. The speed of the process is regulated by the value of the element R3.
The main element in the soft ignition system for LEDs is the MOSFET IRF540 transistor of the field n-channel type (as an option, you can use the Russian model KP540).
The remaining components are related to the strapping and are of secondary importance. Therefore, it would be useful to give here its main parameters:
- The drain current is within 23A.
- The polarity value is n.
- The drain-source voltage rating is 100V.
Important! Due to the fact that the speed of ignition and attenuation of the LED depends entirely on the value of the resistance R3, you can choose the required value to set a certain time for soft start and turn off the ice bulb. In this case, the selection rule is simple - the higher the resistance, the longer the ignition, and vice versa.
Improved version with the ability to set the time
Often there is a need to change the period of smooth ignition of the LEDs. The scheme discussed above does not provide such an opportunity. Therefore, two more semiconductor components need to be introduced into it - R4 and R5. With their help, you can set the resistance parameters and thereby control the ignition speed of the diodes.
There are cases when it is necessary to smoothly turn on the LEDs used for lighting or backlighting, and in some cases turn off. Soft ignition may be required for various reasons.
Firstly, when turned on instantly, the light hits the eyes hard and makes us squint and squint, waiting for our eyes to get used to the new level of brightness. This effect is associated with the inertia of the eye accommodation process and, of course, takes place not only when LEDs are turned on, but also when any other light sources are turned on.
It's just that in the case of LEDs, it is aggravated by the fact that the radiating surface is very small. In scientific terms, the light source has a very large overall brightness.
Secondly, purely aesthetic goals can be pursued: you must admit that a light that smoothly lights up or goes out is beautiful. The LED power circuit needs to be improved properly. Consider two different ways to smoothly turn LEDs on and off.
Delay by RC circuit
The first thing that should come to mind to a person familiar with electrical engineering is the introduction of a delay by including an RC chain in the power circuit of the LEDs: a resistor and a capacitor. The scheme is shown in Fig.1. When voltage is applied to the input, the voltage on the capacitor, as it charges, will increase in a time approximately equal to 5τ, where τ=RC is the time constant. That is, in simple terms, the time the light is turned on will be determined by the product of the capacitance of the capacitor and the resistance of the resistor. Accordingly, the greater the capacitance and resistance, the longer the ignition of the LEDs will take. When the power is turned off, the capacitor will discharge to the LEDs. The time during which a smooth decay will occur will also be determined by τ, but in this case, instead of R, the product will include the dynamic resistance of the LEDs. For example, a 2200 uF capacitor and a 1 kΩ resistor would theoretically "stretch" the turn-on time by 2.2 seconds. Naturally, in practice, this value will differ from the calculated one both due to the spread of parameters (for electrolytic capacitors, the tolerances for the nominal value are usually very large) of the RC circuit, and due to the parameters of the LEDs themselves. We must not forget that the p-n junction will begin to open and emit light at a certain threshold value. The simplest scheme presented makes it possible to understand the principle of operation of this method well, but it is of little use for practical implementation. To obtain a working solution, we will improve it by introducing several additional elements (Fig. 2). 
The circuit works as follows: when the power is turned on, the capacitor C1 is charged through the resistor R2, the transistor VT1, as the gate voltage changes, reduces the resistance of its channel, thereby increasing the current through the LED. Turning off the power will cause the capacitor to discharge through the LEDs and resistor R1.
Let's turn on the "brains" ...
If the circuit must provide greater flexibility and functionality, for example, without changing the hardware, we want to get several operating modes and set the ignition and decay times more accurately, then it's time to include a microcontroller and an integrated LED driver with a control input in the circuit. The microcontroller is capable of counting the necessary time intervals with high accuracy and issuing commands to the control input of the driver in the form of PWM. Switching operating modes can be foreseen in advance and display the appropriate button for this. It is only necessary to formulate what we want to get and write the corresponding program. An example is the high power LED driver LDD-H, which is available with current ratings from 300 to 1000 mA and has a PWM input. The scheme for including specific drivers is usually given in those. manufacturer's description (data sheet). Unlike the previous method, the time to turn on and off will not depend on the spread of the parameters of the circuit elements, the ambient temperature, or the voltage drop across the LEDs. But you will have to pay for accuracy - this solution is more expensive.