Driving 12 Volts relay by 5 Volts Microcontroller

microcontroller relay

Dear Members,
Can I drive a 12 Volts 400 Ohms relay (like LEONE SC5-S-DC12V OR GOODSKY RW-SH-112D)by a '51 microcontroller working at 5 Volts?
I normally use 5 Volts 100 Ohms relays (GOODSKY GS-SH-205T-DS) with a BC557/8B and a 10 KOhms resistance connected between the port pin and the base. The collector goes to ground and the emitter to the relay coil,
the other end of which is connected to the Vcc +5Volts,the usual IN4148 is across the coil.This unisolated arrangement works faultless even with inductive loads like fridge.
When the same arrangement is used with 12Volts relay connected to 12v,the
relay is put on only once by the microcontroller as desired, by clearing the
port pin;but the relay cannot be put off by setting high the port pin.It appears that the transistor is leaking.Since the whole arrangement is on a transformerless platform,I would not like to fiddle and adjust bias.What is the proper design or shall I forget 12 Volts relays in this context?
With best regards
A.S.Rudra

bs170 relay

Simply use a transistor to drive the relay. You then drive the transistror from the micro's output pin.
Of course, the logic is inverted, since now the pin has to be high to turn on the relay, but that is easy to fix.

bs170 microcontroller

Use a BS170 MOSFET to drive the relay, no base resistor needed and can be driven by high impedance. if you need SMD version select BSS138, regards, Paul.

bs170 12v relay

If you still need this relay to be driven by "L"-ow signal on the micro's pin - below is an example on how to do this ..

Regards,
IanP

12v relay microcontroller

I agree that 2N7000 or BS170 (TO-92) or 2N7002 (SOT-23) make good low current low side switches.

Also consider ULN2803 8-bit parallel sinking driver or MIC5841A serial-to-parallel 8-bit sinking drivers.

Good luck. Regards, Mike

driving relay with microcontroller

connect the relay collector to the relay one point and the other side to 12V. emitter to ground. and a 1K resister to the base from controller. for SC5 Sugar Cube relay BC547 will do fine. it is the cheap and best way. and you can put a In4148 accross the relay in reverse Bised

bs170 and relay

hi
this may help