# Polarity switching and amplification of square wave?

Discussion in 'General Electronics Chat' started by electronice123, Feb 19, 2009.

1. ### electronice123 Thread Starter Senior Member

Oct 10, 2008
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I need to build a circuit which does the following:

20kHz square wave amplified to high voltage with a transformer which has both a positive and negative output. I need the outputs to switch polarity every pulse.

How can this be done?

2. ### KL7AJ AAC Fanatic!

Nov 4, 2008
2,182
415
A step up transformer with a center tap can do that, if it's carefully terminated.

eric

3. ### electronice123 Thread Starter Senior Member

Oct 10, 2008
309
0
Can you explain in detail how that works?

4. ### KL7AJ AAC Fanatic!

Nov 4, 2008
2,182
415

You can generally pass a square wave through a transformer if you avoid any self-resonant frequencies, and it's got enough bandwidth to pass at least the fifth harmonic. For example, at 20 KHz, you want a transformer that's flat up to around 100KHz. Most of your high quality switching power supply transformers can do that. You need to put a matched load resistance on it, however, or it may "ring" which may or may not be a problem. How critical is it to have a very sharp square wave on the output?

eric

5. ### electronice123 Thread Starter Senior Member

Oct 10, 2008
309
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From what I can tell it's not critical.

6. ### bertus Administrator

Apr 5, 2008
19,159
3,833
Hello,

For what do you need the high voltage ?
How high is your high voltage ?

Greetings,
Bertus

7. ### electronice123 Thread Starter Senior Member

Oct 10, 2008
309
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The high voltage will be used to charge a capacitor with a polar liquid dielectric. It has been said that the liquid dielectric can be heated, I'm doing it for a science experiment but I don't think it will work.
500V-1000V will be plenty

8. ### bertus Administrator

Apr 5, 2008
19,159
3,833
Hello,

How many current will flow in the dielectric ?

You could use a inverter like schematic with a CT transformer like eric siad.
Here are some schematics used for fluorescent lamps.
http://ludens.cl/Electron/Fluolamp/fluolamp.html
The last one is designed for ca. 25 khz.
(You can drive the transistors with a controlled oscillator in stead of selfoscillating).

Greetings,
Bertus

9. ### electronice123 Thread Starter Senior Member

Oct 10, 2008
309
0
I think the secondary will be less than 100mA.

10. ### bertus Administrator

Apr 5, 2008
19,159
3,833
Hello,

So you end up with 50 to 100 Watts.
Then the proposed schematics I shown you are to small.

Perhaps you can scale it up.

Greetings,
Bertus

11. ### electronice123 Thread Starter Senior Member

Oct 10, 2008
309
0
I'll keep working and researching and see what I can figure out!