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5ms-100ms duration pulse at 300V DC

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ark5230

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I am constructing a square pulse generator capable of giving 5ms-100ms duration pulse at 300V DC. Current requirements are low (around few mA). Pulse duration is selected by a thumbwheel switch.
I used AT89S51 to generate 5ms-100ms duration pulses.
I have a 300 V DC power supply.
As the pulses are short duration relays can not be used. What is a suitable way of switching this 300 volts using control signal from microcontroller 89s51.
Any suggestion or link will be appreciated.
Thanks in advance.
 

If you don't need isolation from HV you may consider combination of P-channel MOSFET as "main" switch driven by N-channel Mosfet - see attached configuration ..
Both MOSFETs have to be rated for more than HV ..

IanP
:D
 

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    ark5230

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IanP
Thnaks a lot for the info.
I will try to search the right mosfet for Q1 and Q2, hopefully the data sheet will help deciding R. The other series resistor marked "**" and the zener like diode ESD are the issues. May be any 6-9V zener will serve the purpose, please advise.
Thanks again.
 

The data sheet of the P-channel MOSFET should provide you with enough information to calculate both resistors ..
First, find out what -U[GS]value is sufficient to switch this MOSFET on, it will be somewhere around minus 10V, so the rest from the 300V will be dropped on (**) ..

The other component named “ESD” can be substituted by a Zener diode, slightly higher than the switching voltage that will be used to drive the N-channel MOSFET ..

IanP
:D
 

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    ark5230

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Can you suggest suitable MOSFET for both if the current requirement is not more than 20 mA at 300V and the duration of pulse is in the range of 5ms to 100 ms.
 

As N-channel MOSFET you may use the BUZ92 and as P-channel MOSFET the IRFR9310 seems to be a good candidate for the job ..
In the attached simulation the IRFR was not available and it was substituted by similar device (rated only for 240V) .. see attached picture ..

http://www.irf.com/product-info/datasheets/data/irfr9310.pdf

IanP
:D
 

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