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[DPRG] 555 PWM Circuit

Subject: [DPRG] 555 PWM Circuit
From: Kipton Moravec kip at kdream.com
Date: Tue Sep 5 06:20:25 CDT 2006

A typical MOSFET needs the gate to turn on at about 10 volts. At 5 Volts
the MOSFET does not turn on all of the way, and the resistance of the
MOSFET is high so it gets hot.

There are logic level MOSFETS that turn on at 4.5V the IRF540 is not one
of them (if I remember correctly).

Look at the datasheet for the 555 timer. The schematic indicates it will
run to 18 volts.  Try to run the whole circuit at 12V with your IRF540
and see if it works.

I am doing this all from memory, without looking up the datasheets, but
since you are a student, you should verify what I am saying by reading
the datasheets.

Kip

On Tue, 2006-09-05 at 16:25 +0800, Amigo Chen wrote:
> Hi, I'm an EEE student from Singapore. Regarding the schematic shown on 
> http://www.dprg.org/tutorials/2005-11a/ , what should i do if i would like 
> to change the mosfet to a IRF540? I'm having problems with another circuit 
> of the same type but the motor just wont turn after all the connections are 
> done.
> 
> Thank You.
> 
> 
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-- 
Kipton Moravec <kip at kdream.com>


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