FETs unwanted turn on

Thread Starter

Freezyoff

Joined Jan 17, 2020
1
Good day everyone, may god save us from this pandemic.

I have schematics and pcb layout below, all share the same Source and Ground.
- Optocoupler triggered by ESP and will trigger the relay.
- BT1, BT2, BT3 & BT4 work as buttons, when applied with +5V (pressed) FETs (MS1, MS2, MS3 & MS4) capacitor charged and relay triggered.
- FETs will keep turn on until capacitor supply, no longer able to drive the FETs.
- SW-DELAY act as switch to choose which capacitor should use the delays.

The problem arise as follow:
1. Choose any Button (e.g. BT1) and press it for a few seconds. Naturally FETs (MS1) will turn on, relay triggered and capacitor charged. FETs will keep turn on until capacitor no longer able to drive it (but still have some charge in it).
2. Once FETs MS1 turn off, choose any button (e.g. BT2) and press it for a few seconds. Following things happen:
  1. Naturally FETs (MS2) will turn on, relay triggered and capacitor charged. FETs will keep turn on until capacitor no longer able to drive it (but still have some charge in it).
  2. Previous FETs (MS1) turn on too, and turn off after a few second (probably because capacitor C5/C6 fully empty).
3. Once FETs MS2 turn off, choose any button (e.g. BT3) and press it for a few seconds. The problem keep repeating, The previous FETs turn on too. Often i found 2 previous FETs (MS1 & MS2) turn on at the same time and turn off after a few second.
4. The problem stop repeating if i wait all FETs turn off and add more minutes waiting all capacitor fully empty.

My question are:
1. What happen with my FETs? do i need replace the FETs?
2. How to prevent unwanted FETs turn on?

thank you.


Attachments:

1. PCB Layoutpcb-layout.jpg




2. Schematics
schematics.jpg






3. Schamtics Simplified
schematics-inline.jpg
 

KeithWalker

Joined Jul 10, 2017
1,221
Each capacitor connected to the delay button has no discharge path when it's contacts are open to ground. It will charge up once when the contacts close and then stay charged.
Regards,
Keith
 
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