Relays with delay

Thx for adding the clarification. You are securing the input voltage for the relay coils by means of Q1/Q2 and Q3/Q4 as I'm getting a very low voltage in the current setup.

Do I understand correctly that changing R3 is changing the time?
 
That's more or less it. The extra circuitry is there to isolate the delay from the drive. In terms of final drive you would consider the tail current and the beta of Q3 and Q4.

In terms of the delay it depends on R1, R3, R8, R11 and C1. Sorry about that one. I'm lazy so I would mess in LTSpice.

LTspice | Design Center | Analog Devices


Switching occurs when Va rises above Vb. It should be more or less independent of the supply voltage.


Play with R8 and C1 but keep R8 > R11
 

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