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Subject: Re: HI FI amplifier question: help needed
Date: Sat, 07 Sep 2002 21:40:33 +0100
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Guillaume sjm wrote:
> Second question: a Mosfet can accept how much V on its Gate ? is it about
> the power supply or much less ? i noticed on some schematics that there is a
> zener diode of about 15 Volts on the gate to protect it. In this case, is
> the Voutput limited to +-15Volts ?
As Kevin says, most MOSFETs have a maximum gate to source voltage (Vgs)
of 20V. Look at the data sheet for the MOSFET you are using.
Vgs is the potential difference between the gate and the source, not the
gate voltage with respect to ground (unless the source shorted to
ground). For example, if the source of the MOSFET was at 1000V with
respect to ground most MOSFETs would survive a gate voltage of 1019V
with respect to ground since the difference is only 19V. DO NOT TRY THIS.
If your amplifier is working correctly the source voltage of the MOSFET
will go up when the gate voltage goes up, Vgs should therefore be much
less than 20V. Your output voltage will therefore not be limited to the
maximum gate to source voltage.
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