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From: Ken Smith
Subject: Re: Mosfet and rectifiers
Date: 10 Sep 2002 16:03:42 GMT
Organization: a2i network
In article <firstname.lastname@example.org>,
>I'm building a 0-90vdc motor speed controller. I have a seperate power supply
>for my motors and for my logic circuit. I have a pair of PIC processors
>outputting PWM into a pair of MOSFets rated at 5amp 400volt. The signal is
>going thru a 7407 with a 10k resistor pulling hi to 12vdc.
Using a 7407 is ok if you only want to turn the mos-fets on and off at
about 100/120Hz. The 10K pull up will make the turn on quite slow. If
the PIC is programmed to make the mos-fets switch at some phase with
respect to the mains, it should be ok. If not use a stronger driver.
Remember that mos-fets have a body diode in them. Sketch it into your
circuit and ask your self "will a current going through here cause
trouble?" The back-EMF of the motor may try to drive current that way.
Check the highest current that could flow with the motors stopped and the
power up to max. This may be high enough that you will want to add
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