Relay drive for -12V and GND controlled with the positive voltage 2

[homoly]

Hello,

Currently I am adapting some additional modul to the existing design with dual +12V and -12V supply were the +12V is no more sufficient enough to drive the 160 mA power relay I need, so I would like to use -12V and GND to energize the coil. For driving the switching component I have 12V and 0V for my disposal from CMOS logic. For this reason I would like to ask you if you have some real word proven circuit able to solve this problem. My first ideas are to use P channel JFET driving MOSFET or using inverting OPAMP with -1 gain driving NPN bipolar transistor ( -12V on C and 0V on E ) but before eventual reinventing the wheel I would like to know the opinion of someone with more experience in electronic design than I have.

 

[itsmoked]

Not clear.

Are you saying you want to run the relay on your -12V supply?



What signal are you going to control this relay with?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[homoly]

Exactly, I would like to energize the coil from -12 and GND rail and the switch controling the coil energizing should be controlled by CMOS 4001 NOR gate output supplying 0V or +12V.

 

[benta]

Easiest and cheapest is probably an optocoupler driving a transistor driving the relay.

Benta.

 

[OperaHouse]

Using an opto isolator is always a safe bet. Another choice is to use a 15-20V zener with a series resistor driving the base of PNP transistor with the emitter connected to -12V rail. A FET would also work with the zener being 12-15V.

 

[homoly]

Thank you all for the response. The optocoupler seems to be the most "painless" solution so I will start on the prototype with this one.

 

[itsmoked]

Wait! What is the relay for? What are you switching with it?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

There could be an even less painful way...

Keith Cress
kcress -

http://www.flaminsystems.com

 

[homoly]

I am disconnecting the 230VAC / 40A power supply with 2 NC contacts of the relay and the coil is driven by 12VDC.

 

[itsmoked]

OK. I was going to suggest going straight to PhotoMOS solid state relays but for the service you've just stated it would not work well.

Sorry.
Carry on.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[homoly]

Keith, thank you anyway for the suggestion. At least in different application I will have one more idea .