High Voltage Source (Flyback Transformer)

[ifryd]

Hi I want to design high voltage source. I need to obtain source with variable frequency output of high alternating voltage.

The most desired circuit is this one:

**broken link removed**

but here are the questions:

1) How to design it to obtain on secondary winding variable high voltage. I want to get spikes of +HV and -HV on the same output. (one pin ground, second pin with changing +HV, -HV)
Circuit from the link gives spikes only in one direction...


2) Would be good to use these flyback transformers on slow frequencies such as from 200Hz to 2000Hz? Most designers say these circuit should operate on 17KHz? Apart from that I found transformer manufacturer who state that his transformers should work with range of frequency : 15- 60kHz

High Voltage Transformers

Adam

 

[FvM]

Symmetrical bipolar pulses can't be achieved in flyback mode. You basically need a generator and output stage, that generates the intended waveform at lower voltage and can step it up with a transformer.

You should start with specifying the requirements more exactly:
- peak voltage
- required output current respectively intended load impedance
- waveform/timing

 

[ifryd]

Hi FvM

I think you are right, I should start from basic questions what I want to achieve:

1) peak voltage: min 10KV
2) required output current - I would like to put output voltage from second wiring to coils. I haven`t designed these coils yet...
3) waveform/ timing: bidirectional impulses of high energy, as far to timing as I said I want to operate on frequencies from 200Hz to 2000Hz. So 2000Hz would be equivalent to obtaining 4000 bipolar pulses on output.

 

[poorchava]

If you're aiming at 10 kV output, you can look around for a HV transformer from a CRT TV or computer display. This way you would't have to wind the transformer by yourself.

As for the drive: you can use some dedicated PWM driver (TL494 for example) or some small Microcontroller (some kind of ATTiny13 or a small MSP430). In addition you would have to find a driver for MOSFETs to obtain high rise and fall times in order to minimize heat dissipation in transistor(s).

As for the frequency: speaking in simple terms the higher the frequency, the smaller the fransformer of a given power throughoutput is. Good example being a 500W transformer. The ordinary toroidal 50 Hz mains transformer of that power would weigh about 4 kg and be of a size comparable to kitchen bowl. On the other hand a SMPS transformer operating at 30 kHz for the same power would be of a size comparable to a pack of cigarettes and would weigh a couple of hundreds of grams at the most.

Another thing is the magnetostriction effect. It's the effect of ferromagnetic material being strained as an effect of magnetic field. If such strain alternates with some frequency it might be audible for humans, which is highly undesired (very annoying buzzing or squeaking like sound). 17 kHz is beyond hearing threshold for humans (excluding some individuals) so the magnetostriction buzzing is not audible.