flyback


Posted on Feb 5, 2014

The first one I bought for US$ 3. It has an internal rectifier, and even after I dug it out of the epoxy, performance was still poor. The next two were given to me by the ever kind and helpful Francis Rutherford at the Regional Occupations Program and Electronics Lab at Mendocino High School. One had a built in multiplier or something, and put out


flyback
Click here to download the full size of the above Circuit.

almost nothing. An identical one I got free but new did the same thing. The other had a built in diode, and I never tried digging it out, although it performed OK. The last one is a winner though, I got 3 of these for 12 bucks. No diode, and a strong performer. The heart of the flyback system is the driver. So far I have tried two different circuits. One is the classic circuit found on many web sites using one 3055 transistor. I copied this schematic from. As you can see, it`s a very simple circuit. It`s theory of operation is simple too. When voltage is applied the transistor allows current to flow. The primary coil is energized and creates a magnetic field, which in turn induces voltage on the secondary coil. At the same time, it creates voltage in the feedback coil, and this current switches the transistor off. With the transistor off, the feedback coils are de-enegized, allowing the transistor to conduct again, repeating the cycle. The nifty thing about this (and the next) circuit is it automatically drives the flyback at it`s resonant frequency. The values of the resistors aren`t critical, anything close will work. Here is a picture of my single transistor driver circuit. Resistor-wise, if you look closely, you can see I am using 2*50 ohm resistors in parallel to achieve 25 ohms, and 2*100 ohms and a 50 ohm resistors in series to achieve 250 ohms. These resistors are way overrated at 10 watts, but they barely get warm...




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