Re: Power Switching with mosfet
- From: Winfield <winfieldhill@xxxxxxxxx>
- Date: Mon, 22 Oct 2007 19:26:41 -0700
Jon Slaughter wrote:
I only have an n-channel enhancement mosfet(2N7002) and I'm trying
to use it to switch power to an IC.
I can only bring the gate voltage about 1.7V above the V_DS.
I'm not switching the entire voltage to the IC.
Some question I have, What is the difference between a high side
mosfet driver and a low side? A low side brings the drain within a
few mV above ground but the high side brings the source within only
several hundred mV below the drain. Shouldn't it be symmetric?
It is completely symmetric, or shall we say identical.
But this means you have to take the high-side gate as
far above its source, e.g. 3.5 volts over the drain,
as you took the low-side gate above its source=drain.
This can mean taking the high-side gate higher than
the supply voltage, which requires a special kind of
driver circuit, called a high-side driver. These have
a charged capacitor to act as the flying gate-driver
power supply. That works for periodic switching, but
for DC switching you need an isolated gate supply. I
just finished a fast DC-capable 600V high-side pulser
and powered the driver with its own 60Hz transformer.
.
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- Power Switching with mosfet
- From: Jon Slaughter
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