# How to convert 220V AC @50 Hz to 400V @ 20KHz?

Sorry, I may be asking simple question but I'm not specialized in electronics.

What I want to do is to increase the voltage from 220V AC to 400V AC. Also I want to increase the frequency from 50Hz to 20KHz. If I can adjust the voltage and frequency, that would be a privilege (I mean the output voltage could vary from 300V to 400V and the frequency from 15KHz to 20 KHz).

I know I'm supposed to use transformer to increase the voltage and rectifier/inverter to increase the frequency, but I was wondering if there are any other simple solutions? And how to design and built the circuits?

The current here is not important since I'll be using this voltage to generate electric field.

• This is an extremely dangerous project for someone "not specialized in electronics" to undertake. Both the input and output of this power supply are potentially lethal. Commented Aug 12, 2015 at 11:05

## 3 Answers

You ought to consider converting to DC then converting back to AC because directly trying to change frequency A into frequency B is too hard to do.

That's what I would do. Consider rectification of the incoming AC and smoothing with a capacitor. This will give a DC value of 311 volts. Next, using a MOSFET H bridge driver and a 2:1 step-up transformer you should be able to re-create 400V RMS at 20kHz.

For your own safety I would also consider isolating the incoming mains AC via a 1:1 isolating transformer.

Another method is to start from a lowish DC voltage (as supplied safely from a power supply) and use a MOSFET H bridge driving a step-up transformer to give you 400V AC. If your power supply is 24V then you'll need a 24:1 step-up transformer.

You should be able to use a signal generator to produce the 20kHz, amplify it with an audio amplifier, and step it up with a tube (valve) output transformer (in reverse) to 400VAC.

For example, these Hammond transformers. A 10K primary impedance to 4 ohms implies a turns ratio of sqrt(10^4/4) = 50:1, so you'd need to drive the 4 ohm winding with 8VAC (or the 8 ohm winding with 16VAC). They're capable of 30W which is about 16V at 8 ohms, so they should work.

• Think those laminations will have acceptable eddy current losses at 20KHz? Been a long while since I've taken one apart. Recently seen a ship-rated oscilloscope (60-400Hz mains power) and it's power transformer laminations were very thin. Commented Aug 12, 2015 at 16:34
• @rdtsc It's an audio transformer, not a power transformer, and the data sheet says "Frequency response at least 20 Hz. to 20 Khz. at full rated power (+/- 1 db max., ref. 1 Khz.)". Good luck on anything but a sine wave at 20kHz, however. Commented Aug 12, 2015 at 16:38
• I hope @Alsaeed tries this. I'm curious to see how much signal comes out (and what it looks like on a 'scope.) Commented Aug 12, 2015 at 16:44

with transformers you can manipulate the current/voltage but you can't change the frequency. the way it is done is by using an electronic circuit to convert to a dc voltage, then another electronic circuit using a MOSFET/Transistor H bridge to emulate AC using Pulse width modulation, you can then use an inductor capacitor filter to make it into a proper sine wave.

james