# h bridge for high voltage

Discussion in 'General Electronics Chat' started by ariemeir, Jun 27, 2013.

1. ### ariemeir Thread Starter Member

Jun 24, 2011
68
1
Hi guys,

I have a high voltage source (~400v, generated from a disposable camera)
and i would like to use it to generate roughly 100us pulses into a purely resistive load (say once a second). (Assume i have enough capacitance next to the camera so drops are not a problem).

The thing is that i want these pulses to be bipolar, somewhat alike a motor which i want to spin in alternate directions.So naturally i started looking at h-bridge topologies.

I have 4 high voltage n-channels in my disposal so i thought - wouldn't it be neat if i could come up with an h-bridge running on 4 n-channels ? (23nm60nd)
I found this circuit with 4 n-channels:
http://www.hvlabs.com/Images/hbridgefund2.jpg

But the problem (as the author indeed mentions) is that the source of A1 is floating, so if i simply crank the gate to 5v, it wouldn't set the source to 5v, indeed when measured it is roughly 3v or so. The author suggests using a hbridge driver circuit, or i guess i could use a p-channel, but then - how do i avoid using the 400v switching signals i need to keep this h-bridge turned off (or even on, i cannot take it all the way to ground - only 20v or so below the source voltage)

My question is :
What would be a quick and dirty way for me to implement this dual polarity switching capability. Please note that i am switching the voltage basically into a resistor, so the inductive considerations relevant to motors shouldn't pose constraint in my case.

Thanks for all advice !
Lenny

2. ### BobTPH Senior Member

Jun 5, 2013
1,347
293
You need a high and low side driver IC. You can find these that are designed to drive N channel MOSFETS one the high side. Make sure it allows more than 400V.

Bob

ariemeir likes this.
3. ### ariemeir Thread Starter Member

Jun 24, 2011
68
1
Dear BobTPH, thanks for your reply,

I found this module http://www.fairchildsemi.com/ds/FA/FAN7390.pdf
which seems to fit my voltage levels and the price tag.

Inside digikey this component's location is
PMIC - MOSFET, Bridge Drivers - External Switch

I tried to find an explanation for the difference external vs. internal switch, but with no success - could you share a few words on this ?

Also , in a typical application circuit of the above driver
I found this module http://www.fairchildsemi.com/ds/FA/FAN7390.pdf
(page 2)
i see some components such as Rboot, Cboot, Dboot , but the datasheet doesn't mention how these should be chosen. Since this is my first time using a mosfet driver, would you provide a few words of guidance how to go about this ?

Thanks a lot.
Lenny

4. ### shortbus AAC Fanatic!

Sep 30, 2009
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