PC817 optocoupler in Darlington configuration with 2N4401 OR ANY NPN

[asking]

Can i use this configuration to drive 12 VDC SSR Relay or 12 VDC Coil Relay ? Please suggest do i need to keep 220R Resistor in between 2 Transistor ? If i use as darlington pair directly will it damage PC817 ?

Please suggest.

 

[crutschow]

That will drive the relays but you need a diode across terminals 1 and 2 (anode to 1) to suppress the inductive spike of a mechanical relay coil.

The value of R20 is too low, as the opto coupler cannot provide that much current (worst-case, the output current is 50% of the input current).
Thus R20 needs to be at least 1.3kΩ
A Darlington pair will work fine to output more current as long as it's connected the same as you show Q5.

 

[asking]

That will drive the relays but you need a diode across terminals 1 and 2 (anode to 1) to suppress the inductive spike of a mechanical relay coil.

The value of R20 is too low, as the opto coupler cannot provide that much current (worst-case, the output current is 50% of the input current).
Thus R20 needs to be at least 1.3kΩ
A Darlington pair will work fine to output more current as long as it's connected the same as you show Q5.

Thanks for verification, yes i will put diode across relay if i use mechanical relay. I think for SSR i don't need any such protection.

 

[KlausST]

Hi,

for an SSR you don´t need an optocoupler at all.
And many SSRs work with 5V input voltage.

Klaus

 

[vishwasvogga]

hi , opto coupler cant drive highcurrent , so 220R resistance is very low , check the datasheet for max current can be driven , and use golden V=IR rule to calculate Resistance