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.
__________________
Richard Wallace
Mentor since 2011 for FRC 3620 Average Joes (St. Joseph, Michigan)
Mentor 2002-10 for FRC 931 Perpetual Chaos (St. Louis, Missouri)
since 2003
I believe in intuition and inspiration. Imagination is more important than knowledge. For knowledge is limited, whereas imagination embraces the entire world, stimulating progress, giving birth to evolution. It is, strictly speaking, a real factor in scientific research.
(Cosmic Religion : With Other Opinions and Aphorisms (1931) by Albert Einstein, p. 97)