Reset Circuit to Pull Down Line

Thread Starter

brightnight1

Joined Jan 13, 2018
87
I'd like to make a circuit for a programmer so that when you plug the programmer into a board, the circuit pulls the other devices on the board low (into reset). The 5V line from the programmer can only supply 20mA. I made a circuit in LT spice that amplifies the current from the 5V line and then turns another FET on to pull the line down low. R1 is to limited the voltage to 20mA, r3 is to limit the current that could momentarily rush into the gate of M1 and R2 is a simulated load. In simulation this circuit appears to work but I have the feeling I'm missing something obvious or some piece of practical information and would appreciate any feedback. If this circuit is a good solution I'll have to find the correct components to test it. the Red line is OUT_3, blue in IN_2, and green is IN_1. The spice circuit file is also attached.
Capture.JPG
 

Attachments

Thread Starter

brightnight1

Joined Jan 13, 2018
87
I was worried that only had a max of 25mA to work with but I think you're right, I should just drive a FET directly since they are voltage controlled devices, the limited current I have will be more than enough for my needs.
 

eetech00

Joined Jun 8, 2013
3,418
I was worried that only had a max of 25mA to work with but I think you're right, I should just drive a FET directly since they are voltage controlled devices, the limited current I have will be more than enough for my needs.
You can remove R1, if you like, and operate the gate at 5v. But keep the gate pull down (R2) to ensure Q1 shuts off.
 
Top