protection diode for mosfet

Thread Starter

0001T

Joined Feb 28, 2007
15
Hi, I am making use of a power mosfet (RFD16N05) as a switch to heat up a DUT (12-15V, 2.5A max). Would it be necessary to connect a protection diode across the DUT to prevent damages to the mosfet?

If the diode is required; how do i size it?

Thanks
 

SgtWookie

Joined Jul 17, 2007
22,230
Then it's inductive, and you should use a protective diode.

Also consider using a small capacitor in the neighborhood of 100pF-500pF to give the diode time to conduct. Switching is pretty quick, but it's not instantaneous. The capacitor will slow the rise time of the voltage spike.
 

Thread Starter

0001T

Joined Feb 28, 2007
15
Then it's inductive, and you should use a protective diode.

Also consider using a small capacitor in the neighborhood of 100pF-500pF to give the diode time to conduct. Switching is pretty quick, but it's not instantaneous. The capacitor will slow the rise time of the voltage spike.
thanks once again
 

Thread Starter

0001T

Joined Feb 28, 2007
15
i have wired the diode to across my DUT (wire) and circuit is running okay.
however, my operation is cyclic in nature...i realised that after a certain cycles (observed to be about 15 cycles), there seems to be some residual current coming from the supposingly 'open' mosfets. i have LEDs connected parallel to the DUT as well...so i observed that the LEDs are still dimly lighted even though the mosfet gate voltage is cut. what could be the cause of this? it seems like the mosfets are behaving somewhat like a capacitor. what should i do?

the mosfets are controlled by a basic stamp microcontroller, and a 10k ohm resistor is wired in series from the I/O of the basic stamp to the gate of the mosfet.
 
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