MOSFET Drain to Source issue

Thread Starter

Russell15

Joined Jul 2, 2021
1
Im trying to pulse an LED on for 200 nanoseconds. Im using the DS1040z One shot pulse generator to send a pulse width of 200 nanoseconds to the gate of a MOSFET. Using an Oscilloscope, I was able to get that 200 nanosecond pulse width. But when I probe from drain to source, I get this dampening or dissipative oscillating signal at the Drain to source. Im not too sure why or whats causing this to happen. Also, my 200 nanosecond pulse is not a pretty square wave. What can I add to the circuit to improve the shape of the square wave?
 

Papabravo

Joined Feb 24, 2006
17,310
Since the gate of a MOSFET looks like a non-linear capacitor, it seems unlikely that you can achieve the square shape you are looking for. A voltage source driving a MOSFET gate will have the usual RC time constant behavior, but with the capacitance changing as a function of the voltage. An alternative strategy is to use a push-pull current source.
 

Irving

Joined Jan 30, 2016
2,320
Have you got a resistor between gate and pulse source? What voltage pulse are you giving it? Please post a schematic and part numbers
 

ronsimpson

Joined Oct 7, 2019
1,673
The DS1040z was never designed to drive a MOSFET. Depending on the turn on voltage for the MOSFET, the DS1040z is probably only supplying 2mA to the Gate. Also most MOSFETs do not like 0-5V logic levels.
I don't know what MOSFET and what current & voltage and what LED. There is not much I do know.
 
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