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Unread 28-09-2006, 11:23
Richard Wallace's Avatar
Richard Wallace Richard Wallace is offline
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Re: victor 885 parts

Quote:
Originally Posted by Cirrussport
So basically I need to look at whatever voltage is usually needed on the low side to turn on the mosfet. then take the supply voltage and increase it by this number to run the gate.

For example.
If it takes 8v to turn on the mosfet on the low side.
And my source voltage is 18v

Then i need to run the upper gates with the sum of those voltages.

Required gate voltage(top side) = supply voltage + Required gate voltage(bottom side).

And that ic that was mention is im guessing used to help create this extra voltage?

I think i got it but i may be totally wrong.

Thanks

Craig
You've misunderstood my use of the word "source". I meant it to indicate one of the terminals of a FET, not a voltage supply. I recall being similarly confused when I first encountered that term, as a sophomore EE student about thirty years ago.

A FET has three terminals called source, gate, and drain. To turn it on [i.e., to get it to conduct with a low resistance called R_DS(on)] you apply about 10V between the gate and source terminals. Please refer to the IRL3103 datasheet, conveniently hosted by FRC 358.

So each of the gate drive circuits for high-side devices in an N-channel FET bridge must be referenced to the respective source terminal. This is accomplished by establishing charge on a capacitor by means of the special purpose IC mentioned in my earlier post.
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