Capasitor discharge resistor & pull down

Thread Starter

Jesu84

Joined Aug 29, 2021
1
Hello!
I'm designing circuit where I control IC with negative trigger by grounding TRIG. SW will be ON few seconds but TRIG must be ON only fraction of second. So thats why capasitor C3. It works fine first time, but when SW is ON second time C3 is fully charged and TRIG will stay positive. Thats why I added R3 to discharge C3. Is there better way to do trigger control or is this desing fine?


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Ian0

Joined Aug 7, 2020
3,489
Hello!
I'm designing circuit where I control IC with negative trigger by grounding TRIG. SW will be ON few seconds but TRIG must be ON only fraction of second. So thats why capasitor C3. It works fine first time, but when SW is ON second time C3 is fully charged and TRIG will stay positive. Thats why I added R3 to discharge C3. Is there better way to do trigger control or is this desing fine?


View attachment 246822
Just make C3 a lot smaller. 100nF, for example
You can also make R3 smaller. As long as it is greater than half R4 it will work, although you will lose noise immunity. 22k would work.
If I were being pedantic, I would suggest that R4 be renamed "pull UP resistor"!
 
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