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Relay driver circuit with timer
- Thread starter Ejaz
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- #3
Whoops! Yes, you are right - I had not actually done the sums until now. Even with a 5.6 megohm resistor it would need a 100uF capacitor, and device input current and capacitor leakage current would be a real problem.
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.
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.
Hi Ejaz,
Take a look at Motorola's MC1455P. In fig 26 in the datasheet ( ) 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:
It should give you some ideas. also, look at:
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
Take a look at Motorola's MC1455P. In fig 26 in the datasheet ( ) 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:
It should give you some ideas. also, look at:
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
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