How to make a flashing LED

You are deprived of the opportunity to buy a ready-made flashing LED, where the necessary elements are embedded in the flask to perform the necessary function( it remains to connect the battery) - try to collect the author's scheme. It will take a little: calculate the resistor of the LED, which sets together with the capacitor the oscillation period in the circuit, limit the current, choose the type of key. For some reason, the country's economy is working in the mining industry, electronics buried deep in the earth. With the element base strained.

The principle of operation of the

LED Connecting the LED, find out the minimum of theory - the portal Your Technician is ready to help. The area of ​​the p – n junction, due to the existence of hole and electronic conductivity, forms a zone of energy levels unusual for the thickness of the main crystal. When recombining, charge carriers release energy, if the value is equal to the quantum of light, the junction of the two materials begins to radiate. Hue is defined by some values, the ratio is as follows:

E = h c / λ;h = 6.6 x 10-34 is Planck's constant, c = 3 x 108 is the speed of light, the Greek letter lambda denotes the wavelength( m).

It follows from the statement: a diode can be created where the difference in energy levels is present. This is how LEDs are made. Depending on the level difference, the color is blue, red, green. Rare LEDs have the same efficiency. Weak consider the blue, which historically appeared last. The efficiency of LEDs is relatively small( for semiconductor technology), rarely reaches 45%.The specific conversion of electrical energy into useful light is simply amazing. Each watt of energy produces photons 6–7 times larger than the filament helix in equivalent consumption conditions. Explains why LEDs today have a solid position in lighting technology.

Creating flashers based on semiconductor elements is incomparably easier. Enough of relatively low voltages, the circuit will start working. The rest is reduced to the correct selection of key and passive elements to create a sawtooth or pulse voltage of the desired configuration:

1. Amplitude.
2. Duty Rate.
3. Repetition Rate.

Obviously, connecting a 230 volt LED to a network looks like a bad idea. There are similar schemes, but it is difficult to make blinking, the element base is absent. LEDs operate at much lower supply voltages. The most accessible are:

• A voltage of +5 V is present in the charge devices of telephone batteries, iPad and other gadgets. True, the output current is small and not necessary. In addition, +5 V is not hard to find on the bus of the power supply unit of a personal computer. With the limitation of the current problems are eliminated. The wire is red; look for earth on black.
• Voltage + 7. .. + 9 It occurs on the chargers of hand-held radio stations, commonly referred to as walkie-talkies. A great many firms, each has standards. Here are powerless to give specific recommendations. Walkie-talkies are more likely to fail due to the characteristics of use, extra chargers can usually be obtained relatively cheaply.
• LED connection scheme will work better from +12 volts. Standard voltage microelectronics, we will meet in many places. The computer unit contains a voltage of -12 volts. The conductor insulation is blue, the wire itself is left for compatibility with old drives. In our case, it may be necessary, do not be at hand elemental base power +12 volts. Complementary transistors are hard to find, turn on instead of the original ones. The ratings of the passive elements remain. The LED turns on the reverse side.
• A nominal of -3.3 volts at first glance seems unclaimed. I’m lucky enough to get on SMD RGB LEDs SMD0603 4 rubles a piece. But! The voltage drop in the forward direction does not exceed 3 volts( reverse connection is not needed, but in case of incorrect polarity, the maximum voltage is 5).

The LED device is clear, the burning conditions are known, let's get down to implementing the idea. Make the element blink.

Testing

Flashing RGB LEDs

Computer power supply is an ideal option for testing SMD0603 LEDs. You just need to put a resistive divider. According to the scheme of technical documentation, the resistance of the pn junctions in the forward direction is estimated by enlisting the help of a tester. Direct measurement is not possible here. We will assemble the circuit shown below:

1. The microcircuit is given together with the numbers of the feet according to the technical characteristics.
2. Power is applied to the cathode, the voltage polarity is negative.3.3 volts is enough to open pn junctions.
3. Variable resistor need a small nominal. The figure is set with a maximum limit of 680 ohms. In this position must be initially.
4. The resistance of the open p – n junction is small, a considerable margin is needed so that the diodes do not get stray( remember that the maximum forward voltage is 3 V).The fact is taken into account: at low voltage, the resistance of each LED will be 700 Ohms. In parallel, the total resistance is calculated by the formula shown in the figure. Substituting 700 as three input parameters, we get 233 ohms. The resistance of the LEDs when they are just starting to open( at least, so we suppose).
   

   The formula for calculating the total resistance of

5. It will be necessary to control the mode with a tester( see the figure).We constantly measure the voltage on the LED chip, at the same time reducing the resistance value, while the potential difference rises to 2.5 V. It is simply dangerous to increase the voltage, perhaps, many will stop at 2.2 V.3.3 - 2.5) / 2.5 = R lane / R total, R lane - resistance of the variable resistor, when the voltage on the tester display reaches 2.5 V. R total = 3.125 R lane.

Wire +3.3 V of the computer power supply unit of orange isolation, we take the ground circuit from black. Please note: it is dangerous to turn on the module without load. Ideal to connect a DVD drive or other device. It is allowed in the presence of the ability to handle devices under current to remove the side cover, remove the necessary contacts from there, do not remove the power supply. Connecting LEDs illustrates the scheme. Measured resistance on parallel connection of LEDs and stopped?

We explain: in the operational state of the LEDs, it will be necessary to turn on several, we will do the same setup. The supply voltage on the chip is 2.5 volts. Note that the LEDs are flashing, the readings are inaccurate. The maximum does not exceed 2.5 volts. Indication of successful operation of the circuit is expressed by the flashing of the LEDs. To part of flickered, remove power from unnecessary. It is allowed to assemble a debugging circuit with three variable resistors - one per branch of each color.

Now we know how to make a flashing LED backlight with your own hands. Is it possible to vary the response time. We believe that containers should be used inside. Perhaps their own parasitic elements pn transitions of LEDs. By connecting a variable capacitor parallel to the input circuit, you can try to change something. The value is very small, measured in pF.The small chip is devoid of large capacities. We assume that a resistor connected in parallel to the microcircuit( see the dotted line in the figure), seated on the ground, will form an exact divider. Stability will increase.

Ratings need to take significant, do not forget: significantly limit the current flowing through the LEDs. In fact, you need to think about the issue according to the situation

Normal LED blinking

flashing LED circuit The figure shown in the figure uses avalanche transistor for operation. KT315B, used as a key, has a maximum reverse voltage between the collector and the base of 20 volts. Dangerous in this inclusion is not enough. The modification of KT315ZH parameter is 15 volts, much closer to the selected supply voltage of +12 volts. The transistor should not be used.

Avalanche breakdown abnormal pn junction mode. Due to the excess of the reverse voltage between the collector and the base, the atoms are ionized by strikes of accelerated charge carriers. Formed mass of free charged particles entrained by the field. Eyewitnesses claim: for the breakdown of the transistor KT315, a reverse voltage is required, applied between the collector and the emitter, amplitude 8-9 V.

A few words about the operation of the circuit. At the initial moment of time, the capacitor starts charging. Connected to +12 volts, the rest of the circuit is broken - the transistor switch is closed. Gradually, the potential difference increases, reaches the voltage of the avalanche breakdown of the transistor. The capacitor voltage drops sharply, two open pn junctions are connected in parallel:

1. Transistor is in breakdown mode.
2. LED is open due to direct connection.

In total, the voltage will be about 1 volt, the capacitor begins to discharge through open p – n junctions, only the voltage drops below 7–8 volts, and the luck ends. The transistor key closes, the process repeats again. The circuit has inherent hysteresis. The transistor opens at a higher voltage than it closes. Due to the inertia of the processes. See how the LED works.

Resistor ratings, capacitances determine the oscillation period. The capacitor can be taken much less by turning on a small resistance between the collector of the transistor and the LED.For example, 50 ohms. The discharge constant will increase dramatically, it will be easier to visually check the LED( the burning time will increase).Clearly, the current should not be too large, the maximum values ​​are taken from reference books. It is not recommended to connect LED lamps due to the low thermal stability of the system and the presence of abnormal transistors. We hope the review turned out to be interesting, the pictures are intelligible, the explanations are clear.