Build a Fly back Transformer Driver Circuit Diagram

This is an efficient flyback driver for modern cylindrical rectified television flybacks. Many sites doesnt provide circuits driving these transformers, they simply say that they are bad.

I dont agree. In fact I built this circuit. I spent a lot of time for finding resonant frequency (around 15Khz) and duty cycle. These transformers best work at around 90% duty cycle. You may notice corona breakdown at terminals and pfffff sound (as well as the ozone smell) when adjusting the off time trimmer to near 500-300 ohms. Of course it will work for other tipes of flyback as frequency and duty cycle have a large range.

 Flyback Transformer Driver Circuit Diagram

Frequency range can be increased using multiposition switch for other values of C3 capacitor ,for example 2 nF for 80KHz-200000KHz, but didnt found flybacks with so high resonant frequencies, in addition with higher values of c3 , eg 200nF, 2uF the
frequency will drop making possible the use of ignition coils, and rectified power transformers @50Hz to charge high voltage electrolitic caps at 300-400V). Unfortunately my ignition coil died because insulation breakdown (too long drawn arcs)...
I was able to power a small (20cm) Spark Gap tesla coil Using these dc rectified flybacks to charge primary tank capacitor.

The operation is simple
The 555 is wired as an astable and the capacitor is charged only through the 4,7Kohm trimmer (notice the diode) and discharged only through the 2.2 Kohm trimmer, making the duty cycle full adjustable. The square wave is then feed in a totem pole made up of a 2N3904 and a 2N3906, which are cheap, and easy to find. The totem pole ensures the gate being charged and discharged very fast (approx 50nS i think). The IRF840 is a cheap (i found it for 4euros) reliable and powerful power mosfet, it has current capability of 8 A continuous and 32A pulse, 800V drain source voltage, protecting internal zener diode. There is a snubbing network to ensure that voltage spikes are kept low (unless the insulation of the transformer start to leak) protecting both transistors and 555 IC. 100 ohm is a compromise between decay time and voltage spike.

Comments and specifications:
The 100 ohm snubber must me a 5W resistor, or it will burn at long operations
The led is only for safety purposes
Use a dead man switch (pushbutton) for safety
The power supply must supply at least 2-3 A if you want decent arcs (20000 KV)

Dangers:
The flyback driven in this way can supply a significant current, aldough the heart fibrillation starts at 30mA
I recommend caution to avoid painful arc-burns.
The arc is a hot plasma, never operate the circuit in presence of flammable substances.
Charging high voltage capacitors is a serious life threat, so if you arent unexperienced just draw arcs and no more

This device when rectified generates static voltage that can be a little annoying.... (or fun, i sprayed with corona a plastic pen from positive terminal and then i was able to attract little pieces of paper)

Disclaimer:
I dont assume any responsibility of the damages or discruptions dove by this device, to persons or things. Any irresponsable action would be a serios danger. This is high voltage threat it with respect.

author: Jonathan Filippi

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Economical Switching LED Driver Circuit

The usual method of operating an LED from a voltage which is higher than its forward voltage is well known. A limiting resistor is used to limit the LED current to its rated value. Learn how to make an economical LED driver circuit.
Calculating the value of the  resistor is simple enough: supply  voltage minus LED forward voltage divided by the maximum current rating of the LED. The formula is: Thus the voltage difference between supply voltage and forward voltage  is dropped by the limiting resistor. However, the disadvantage is that the power dissipated by the limiting resistor is fairly high if the supply  voltage is relatively high. Thus, for  example, with a supply voltage of 24 V and a current of 25 mA the power dissipated is greater than 0.5 W. There is an alternative: the circuit shown here only requires 0.1 W. lt is effectively a switched current source. The current source is based on transistor T1 and the oscillator uses a 3140 operational amplifier.

When transistor T1 conducts, a current flows via coil L1, LED D1 and resistor R3 to earth. The current curve is shown in figure 2. As soon as T1 turns on and a current flows, the current rises together with the volt- age at R3 from zero volts. This voltage is now applied to the non- inverting input of the operational amplifier. A reference voltage of approximately 0.25 V is applied via voltage divider Rl/R2 to the inverting input. lf the rising voltage at the non-inverting input reaches the level of the reference voltage, the output of the operational amplifier switches to a high voltage potential. Transistor T1 turns off and the current through the LED flows via diode D2. As shown in figure 2, the current drops; the voltage at R3 therefore drops also. Once the current and voltage are sufficiently low, the operational amplifier switches over again and the transistor turns on.

This operation is repeated periodically. The switching point is adjusted with preset potentiometer P1. This governs the changeover voltage at pin 3 of the operational amplifier which, in turn, governs the maximum LED current. lt should not exceed 50 mA. The frequency of the oscillator (which is also the switching frequency for the transistor) is deter- mined by coil L1 and by the switching hysteresis adjusted with P 1. With the specified value of 4.7mH the switching frequency is about 15 kHz with a period of approximately 65 ps. Two other switching frequencies using different coil inductances can be found in the following table: Coil T F 2.2 mH 35 ,us 30 kHz 10 mH 150,is 6kHz P1 should be adjusted to obtain the lowest frequency at which the circuit still starts to oscillate.

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