Relay driver circuit with timer
Relay driver circuit with timer
(OP)
I need to drive a miniature relay with maximum coil voltage of 5 V and minimum coil current of 200 mA by a timer circuit. The circuit need to turn it ON & OFF every 8-10 minutes. Please help! Thanks in advance!





RE: Relay driver circuit with timer
RE: Relay driver circuit with timer
RE: Relay driver circuit with timer
You could try the TLC555 version from Texas Instruments (and others). This is a CMOS version so has minute input currents to the chip allowing much higher resistors and smaller capacitors to be used for the timing components.
Alternatively how about a digital approach? The CMOS 4000 series CD4060B is a 14-stage binary ripple counter with built-in RC oscillator. You should be able to get a long enough delay from that with the oscdillator running at a few Hz, but it would of course need an additional driver transistor to power the relay.
RE: Relay driver circuit with timer
Take a look at Motorola's MC1455P. In fig 26 in the datasheet ( http://www.onsemi.com/pub/Collateral/MC1455-D.PDF ) it has a schematic for a sequential chain of timers. This still may not address your Iout requirement though, as the MC1455 has an abs max sink/source capability of 200mA. You may consider a small form factor SSR with a logic level input. Omega used to have SFF SSR's (about 1in x .75in x .75 in) and probably still do.
An NE558N quad-timer IC may help conserve board real estate and is well suited to sequential timing with long delays. look at the app note here:
http://www.semiconductors.philips.com/acrobat/applicationnotes/AN171.pdf
It should give you some ideas. also, look at:
http://www1.jaycar.com.au/images_uploaded/relaydrv.pdf
It has some schematics and good design practices for driving relays with transistors as well as from timers(BONUS!).
The Philips App Note has a nifty voltage controlled timer with a 50:1 ratio that I am going to have to build for an upcoming project. I'm glad you posted your question as I would not have stumbled across the Philips sheet without your question.
Good luck, you'll do just fine :)!
Foxfur
RE: Relay driver circuit with timer