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Old 7th November 2012, 05:53 PM   #1
tuhkam is offline tuhkam  Estonia
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Default NE555 turn on delay problem

Hi!

I have built a timed turn on for B+ on my EL84 SE amplifier. The regulator puts out voltage to the timer, but the timer refuses to switch the relay.

Could anybody confirm, that the below schematic should function at least in theory?

The relay, as well as the diode parallel to the coil is not shown on the schematic.
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File Type: png 12V_timer.png (9.0 KB, 139 views)

Last edited by tuhkam; 7th November 2012 at 05:55 PM. Reason: Addition
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Old 7th November 2012, 06:02 PM   #2
Mooly is online now Mooly  United Kingdom
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Look at the monostable circuit here,

555 timer IC - Wikipedia, the free encyclopedia
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Old 7th November 2012, 06:18 PM   #3
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Hi,
Check this site they have a lots of LM555 circuit. There are some that look like what are you looking. Check the one power on delay circuit.
Link to the side:LM555 Timer Circuits
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Old 8th November 2012, 11:59 PM   #4
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Your design contains a mistake. Your timer IC's pins 2 and 6 are connected to the positive supply; that is not correct.

You may not be aware that the free circuit simulator program LTSPICE includes a circuit model of the NE555. So you can simulate your 555 circuit in software and observe its behavior. An entire "cycle of learning" (re-design, re-simulate, re-analyze) can be performed in less than an hour.

If you want a delay longer than approx 1 second, I recommend using the CMOS version of the 555. Part number LMC-555 and its equivalents, has got much lower input leakage / input bias current, so it will not disrupt the very high impedances found in long-timeconstant circuits.

If you are comfortable with digital circuitry, you may want to investigate the CD4541 http://www.ti.com/lit/ds/symlink/cd4541b.pdf , also sold as the MC14541 http://www.onsemi.com/pub_link/Colla...MC14541B-D.PDF . It will let you set the delay to seconds, minutes, or hours, without requiring high value, low leakage capacitors. Digital counters are simply excellent at providing accurate delays using inexpensive parts.

Last edited by Mark Johnson; 9th November 2012 at 12:27 AM. Reason: add link to digital timer chip
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Old 9th November 2012, 07:31 AM   #5
tuhkam is offline tuhkam  Estonia
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Thank you all! I will go back to simulation and the breadboard before making a new pcb.
I'll also check the digital solution, thanks!
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Old 9th November 2012, 07:36 AM   #6
Mooly is online now Mooly  United Kingdom
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Also remember that the original 555 (not the CMOS or low power ones) can drive a relay directly as it has 200ma source/sink ability.
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