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Registered Member #5323
Joined: Fri Jun 15 2012, 02:14PM
Location:
Posts: 104
I have a 1700v sic N-ch Mosfet (C2M10001700D) that I want to use to switch a 1000 volt power source on/off at between 3 hz-100 khz. I'd like to control the Mosfet with my table top function signal generator, but am concerned about destroying my signal gen due to high voltage. Any suggestions how the signal gen can be interfaced to the Mosfet while protecting the signal gen from high voltage damage?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
An opto isolator of suitable voltage rating.
A pulse trans former of suitable rating.
Secondary protection provided by spark arrestors, pea neons, TVS diodes etc.
If you are switching an inductive load, very high transients - spikes - could appear. It wouldn't take very long before these spikes figure out how to couple themselves into your signal generator by some route you hadn't expected, so don't make the mistake of relying on one method alone! It may work very well until it stops working, and the funeral directors come knocking to measure up your signal generator for a place in the scrap yard.
Electrons under high tension have a very giving nature: they like to share their charge with anyone or anything they can. They are also famously lazy, so if they can see a quick shortcut to Earth via a TVS diode, they'll usually prefer that to all the bother of wandering around the maze of a PC board inside a signal generator, puncturing any CMOS they come across as they find their way to the ground.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
If you are using the square wave function to gate the device if follows that the transmission line from the function generator will be set up to have a very low SWR. Otherwise the rise time would be lost. These lines work both ways.
If the connecting lead is properly screened, you could put your generator inside a Faraday cage, and, power it from batteries, also inside the cage.
you said " but am concerned about destroying my signal gen due to high voltage. "
The best answer perhaps is to use someone else's generator.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
I would not use a signal generator for more than quick tests, but it's improbable that the 1000 V supply can damage the generator. The mosfet would have to fail with a short-circuit from drain to gate (easy) and an open circuit between drain and source (difficult), supposing that the source is grounded and the generator connected between gate and source. If the impedance of the 1000 V source is high, a neon lamp across the output of the generator may be enough protection. Make a solid assembly, and use a simple 555 oscillator.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Perhaps my suggestions have been much too conservative - as Antonio's comments seem to suggest - but so long as I have been a member of this forum, there have always been reports of instruments ruined by high voltages appearing in places where they were not expected.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
Most accidents are caused by lack of care in the assembly and of attention while connecting and disconnecting things. I recently destroyed an oscilloscope probe when a 100 pf capacitor charged at 20 kV, mounted precariously balanced over other parts in a temporary assembly, fell over it.
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Help to protect a Signal Gen from HV damage
