flyback

Description: The first unit was purchased for US$ 3. It features an internal rectifier, but even after removing it from the epoxy, its performance remained subpar. The next two units were kindly provided by Francis Rutherford at the Regional Occupations Program and Electronics Lab at Mendocino High School. One of these had a built-in multiplier and produced minimal output. An identical unit received for free but new exhibited the same issue. The other unit included a built-in diode, which was not tested after removal, although it functioned adequately. The last unit, however, proved to be a success; three were acquired for $12. This unit does not contain a diode and performs strongly. The core of the flyback system is the driver, and two different circuits have been tested. One is a classic design commonly found on various websites, utilizing a single 3055 transistor. The schematic is straightforward, with the theory of operation being equally simple. When voltage is applied, the transistor allows current flow, energizing the primary coil and creating a magnetic field that induces voltage in the secondary coil. Simultaneously, voltage is generated in the feedback coil, which turns the transistor off. Once the transistor is off, the feedback coils are de-energized, allowing the transistor to conduct again, thus repeating the cycle. This and the subsequent circuit automatically drive the flyback at its resonant frequency. Resistor values are not critical; any close approximation will suffice. The driver circuit employs two 50-ohm resistors in parallel to achieve 25 ohms and two 100-ohm resistors in series with a 50-ohm resistor to reach 250 ohms. These resistors are rated at 10 watts, ensuring they remain cool during operation and are available from Radio Shack. While this circuit operates satisfactorily, an alternate circuit design yields better performance and is nearly as easy to construct. This design incorporates an additional transistor, making it preferable for those who wish to experiment with the differences. This schematic is known as a "push-pull" oscillator. The number of windings on the primary coil serves as a good starting point, but reducing the number of turns on the primary increases the turns ratio between the primary and secondary, resulting in higher output voltage. Testing has demonstrated that as few as one turn on the primary can generate output voltages between 36-54 kV at a current draw of 10 amps. However, this configuration resulted in transformer failure due to arcing between the primary and secondary. Although the final system is not complete, a "rat's nest" style setup has been documented. The columns of data include input voltage in VDC, primary turns, feedback turns, output voltage (measured via a standard 100:1 HV probe to a DMM, necessitating multiplication by 100), DC supply current, output frequency in kHz, and primary resistor value in ohms. Some discrepancies were noted in the results; for instance, increasing resistor values generally led to higher output voltage. Challenges with reliable voltage readings were encountered, as holding the probe yielded lower readings compared to placing it on a glass table. Additionally, minor factors, such as crossing test leads, significantly affected measurements. Despite these issues, the data provides a general indication of expected performance. Based on experience, it is believed that output voltages exceeded 40 kV, with impressive plasma generation observed. The secondary produced plasma within a nickel-sized area at a distance of one inch from the glass table, necessitating a two-inch separation to cease plasma activity. The circuits utilize 3055 transistors, which exhibit variability in performance; some units sourced from Radio Shack are erratic, with some being robust while others fail.

The flyback driver circuit operates on the principle of magnetic induction, utilizing a transformer to step up voltage. The primary coil, when energized by the transistor, generates a magnetic field that induces a high voltage in the secondary coil. The feedback mechanism is crucial for sustaining oscillation; it ensures that the transistor switches off at the appropriate time, preventing saturation and allowing for continuous operation. The push-pull configuration enhances efficiency by utilizing two transistors to alternate the current flow, effectively doubling the frequency of the output, which can be advantageous for applications requiring high-voltage pulses.

In designing the circuit, attention must be paid to the winding ratios of the transformer. The primary coil's inductance and the number of turns directly influence the voltage output. Experimentation with different configurations, such as varying the turns ratio, can yield different performance characteristics. The use of high-power resistors ensures that the circuit can handle the energy levels without overheating, while the choice of transistors impacts the overall reliability and efficiency of the circuit. Careful consideration of component ratings, layout, and connections is essential to prevent failures and achieve optimal performance in high-voltage applications.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 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 and can be gotten from Radio Shack.

This circuit works pretty well, but the next circuit works much better, and is almost as easy to build. As you can see, all this schematic adds is an extra transistor, so unless you want to experiment with the differences between the two circuits as I did, build this one.

This schematic is referred to as a "push pull" oscillator. The number of windings shown on the primary is a good place to start, but remember that less wraps on the primary increases the turns ratio between the primary and the secondary. This give you more volts! I have used as little as one turn on the primaries, and measured somewhere between 36-54 kV, pulling 10 amps!

Naturally, I blew that transformer in a poof of smoke and flame, it arced over between the primary and the secondary. I haven`t finished my final system, but here is a picture of a "rat`s nest" style setup. The columns are, in order: Input voltage in VDC, number of primary turns, number of feedback turns, output voltage measured through a standard 100:1 HV probe to a DMM so multiply by 100, DC supply current, output frequency in kHz, and resistor value for the primary resistor in ohms.

There are some discrepancies in the result. For example, in all cases but one increasing the resistor value increased the output voltage. I have been having difficulty getting reliable voltage readings. For example, when I hold the probe I get much lower readings than if I put it on the glass table. Even little things like if the test leads cross each other make a large difference, so all measurements here must be taken with a grain of salt. Nonetheless, they serve to give an indication of what to expect. I must say that from experience, I am sure I was pushing at least 40kV or more. The plasma spewing from this beast was impressive! An inch away from a glass table, the secondary was blasting plasma in an area at least the size of a nickel.

I had to get it at least 2 inches from the table to make it stop. Transistors: Both of these circuits use 3055 transistors. The ones from Radio Shack are erratic, some of them are quite strong, and others blow inst