LED transistor flasher

One of the simplest schemes in amateur radio electronics is the LED flasher on one transistor. Its production can be done by any newcomer who has a minimum set for soldering and half an hour of time. The considered scheme, although it is simple, however, It allows you to visually see the avalanche breakdown of the transistor, as well as the operation of the electrolytic capacitor. Including, by selection of capacity it is possible to easily change the frequency of flashing of the LED. You can also experiment with input voltage (in small ranges), which also affects the operation of the product.

Design and operation

The flasher consists of the following elements:
  • power supply;
  • resistance;
  • capacitor;
  • transistor;
  • LED.
The scheme works according to a very simple principle. In the first phase of the cycle, the transistor is “closed”, that is, it does not transmit current from the power source.Accordingly, the LED does not glow. The capacitor is located in the circuit to the closed transistor, therefore it accumulates electrical energy. This happens until the voltage at its terminals reaches a value sufficient to ensure the so-called avalanche breakdown. In the second phase of the cycle, the energy accumulated in the capacitor “breaks through” the transistor and the current passes through the LED. It flashes for a short time, and then goes out again, as the transistor closes again. Then the flasher operates in a cyclic mode and all processes are repeated.
LED flasher on the transistor

Required materials and radio components

To assemble an LED flasher with your own hands, working from a power source with a voltage of 12 V, you will need the following:
  • soldering iron;
  • rosin;
  • solder;
  • 1 kΩ resistor;
  • capacitor with a capacity of 470-1000 μF at 16 V;
  • KT315 transistor or its more modern analog;
  • classic LED;
  • simple wire;
  • 12 V power supply;
  • matchbox (optional).
  • The last component acts as a body, although you can assemble the circuit without it. Alternatively, a circuit board can be used. The hinged installation described below is recommended for beginner hams. This method of assembly allows you to quickly navigate the scheme and do it right the first time.

    Flasher assembly sequence

    Manufacturing a 12 V LED flasher is carried out in the following sequence. First of all, all the above components, materials and tools are prepared. For convenience, it is better to immediately fix the LED and power wires to the case. Next to the conclusion "+" you should solder the resistor.
    LED flasher on the transistor
    LED flasher on the transistor
    LED flasher on the transistor
    The free “resistance leg connects to the emitter of the transistor. If KT315 is placed marking down, then this conclusion will be at its extreme right. Further, the emitter of the transistor is connected to the positive terminal of the capacitor.You can determine it by marking on the body - “minus” is indicated by a light band. The next step is to connect the collector of the transistor with a positive LED output. At KT315 - this is the leg in the middle. The "plus" LED can be determined visually. Inside the element there are two electrodes, differing in size. The smaller one will be positive.
    LED flasher on the transistor
    LED flasher on the transistor
    Now it remains only to solder the negative output of the LED to the corresponding conductor of the power source. The “minus” of the capacitor is connected to the same line. The LED flasher on one transistor is ready. By applying power to it, you can see its work on the principle described above. If you want to reduce or increase the flashing frequency of the LED, you can experiment with capacitors with different capacitances. The principle is very simple - the greater the capacity of the element, the less often the LED will flash.
    LED transistor flasher
    LED flasher on the transistor
    Quite often, even correctly assembled circuit does not work correctly. If the LED just lights up (does not blink), or does not go out completely, it's enough to change the input voltage. On an adjustable power supply, this is done simply by turning the knob in the right direction. If the power supply is unregulated, then the corresponding additional resistance can be selected in the circuit.