Electronics > Electronics

Square wave pulse (0-2.5kV)&(0.2-100msec)

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ellendort:
I intend to use my power supply (3000V - 130mA).

I need some guidance and reference on how to design a pulse generator to produce square wave pulses where the pulse width (0.2-100msec) and the pusle height(0-2500V) is adjustable.
Perhaps maybe by using a microcontroller or by charging a capacitor or high voltage amplifier.

My aim is to apply a manually triggered square wave pulse on my sample load resistance in between 2 electrodes with electrode distance 0.1cm or 0.2cm or 0.4cm. The voltage and my load samples are generally divided into two category as below,

1) Voltage: 0-2500V
Load sample resistance: 2000ohm - 5000ohm

2) Voltage: 0-500V

Ok then what you want is a MOSFET:
http://www.societyofrobots.com/electronics_tutorial.shtml#mosfet
Ok I admit that tutorial kinda sucks, been too lazy to rewrite it though . . . here is another tutorial that uses MOSFETS:
http://www.societyofrobots.com/schematics_h-bridgedes.shtml

Basically you apply your signal to the gate of the mosfet, and put the other two leads (drain and source) in serious with your 3000V power supply. Basically the gate acts as an electronic on/off switch for your 3000V power supply.

So all you do then is apply your square wave pulse to the gate. You can do this with a simple function generator if you have it, or with a 555 timer IC, or with a microcontroller with very simple programming. Simple as in it is the same as the code to make an LED blink fast.

You probably should amplify the voltage (with an op-amp) from your signal to the mosfet gate to like ~20V just to make the mosfet more efficient. Higher gate voltages means higher efficiency and less overheating.

quick schematic:

3000V Source
|
signal generator ---- op-amp ----- mosfet
|                                     |
|                                     |
Ground                            Ground

Just one side comment, you do realize that your circuit will be drawing an insane 1250 watts?!? (power=2500V*.130A=1250W)

Anyway let me know if you have questions, I kind of breezed by on this and didnt explain it that well.

ellendort:
I will charge a capacitor and discharge through cascaded MOSFET to generate square wave pulse.
Any reference assume i wants to cascade the MOSFET(600V) in series for switching?

As i mention before i need to manually triger the pulse. 1 or 2 pulse or perhaps more than that. How do i control this?
Can i use this circuit for the manual triggering and to drive the MOSFET to generate square wave?
http://www.edn.com/article/CA236418.html

But i'm not sure the frequency adjust here as to my application because different square wave design has different controllable fequency and as for the pulse width will it be possible 0.2-100msec?

--- Quote from: ellendort on March 26, 2006, 10:01:20 PM ---I will charge a capacitor and discharge through cascaded MOSFET to generate square wave pulse.
Any reference assume i wants to cascade the MOSFET(600V) in series for switching?

--- End quote ---

Hmmm I dont understand your first question.

If you want that much variable control, I still recommend using a microcontroller. You can have a single manual button attached to trigger a pre-programmed event, such as your square wave.

ellendort:
Pls refer to the attached figure.
100Kohm*1uF=Approx. 100msec

How can i control the time so as the triggered pulse will stop at the preset value which is controllable from 0.2-100msec.