# Driver Circuit for FET - RF Cafe Forums

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np101010
Post subject: driver circuit for FET
Unread postPosted: Mon Dec 27, 2004 9:43 am
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Joined: Thu Nov 04, 2004 9:02 pm
Posts: 7
Hello,

I am looking for some info on the design of a driver circuit to convert TTL input to control voltages to the FET gate to switch it on and off.

Thanks,

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Guest
Post subject: FET Driver Circuit
Unread postPosted: Mon Dec 27, 2004 1:56 pm

If you go onto the Hittite website (www.hittite.com) and look at the data sheet for the HMC232C8 you will see a suggested driver circuit. Hittite switches are fets which are controlled by their gates.

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garylsmith2k
Post subject: TTL FET driver
Unread postPosted: Sun Jan 02, 2005 4:02 pm
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Joined: Sun Oct 31, 2004 3:01 pm
Posts: 5
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Hi,

I use a TTL source to drive a FET connected to VCC to power on/off cell phone circuits. The FET source is tied to Vcc through 100K resistor to the Gate. The TTL source pulls the gate high or low depending.

If you are concerned abourt continuous power you could drop the gate input voltage with a series diode or a voltage. I have not had to use either and they waste battery life, although that may not matter to your application.

_________________
Cheers,
Gary Smith

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np101010
Post subject:
Unread postPosted: Mon Jan 03, 2005 4:19 am
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Joined: Thu Nov 04, 2004 9:02 pm
Posts: 7
Hello Garry,

Can you explain further. I cannot follow the connections to source and gaet that you have explained.

thanks

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Guest
Post subject: FET Driver Circuit
Unread postPosted: Mon Jan 03, 2005 9:44 am

What Gary is suggesting is to place a 100K ohm resistor between the gate of the FET and the source. VCC of 5V mus be applied at the source. When 0V is applied to the gate, then VGS=0-5=-5V, therefore turning FET off. If 5V is applied to the gate, then VGS=5-5=0V and FET will be on. This is a common technique, you just have to make sure to use blocking caps at the outputs/inputs and if you use shunt FETS to float them with a capacitor to ground. I would attach a schematic but do not think this forum has that capability?

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np101010
Post subject: Thanks
Unread postPosted: Wed Jan 05, 2005 1:50 pm
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Joined: Thu Nov 04, 2004 9:02 pm
Posts: 7
Thanks for the info. I actually had to convert 0v and 5v to -2v and 0.5v; I figured how to do it now.

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Guest
Post subject: Re: driver circuit for FET
Unread postPosted: Thu Jan 20, 2005 9:40 am

np101010 wrote:
Hello,

I am looking for some info on the design of a driver circuit to convert TTL input to control voltages to the FET gate to switch it on and off.

Thanks,

Posted  11/12/2012

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