Simple Universal Speaker Delay Using A Triac - Page 3 - diyAudio
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Old 6th December 2012, 12:11 PM   #21
Mooly is online now Mooly  United Kingdom
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Quote:
Originally Posted by AndrewT View Post
Why are you not considering the conventional back emf solution: the diode across the coil?

I prefer the diode + zener after D.Self and others told us that it allows faster opening.
Good question... my thinking was this,

To save on parts, was suppression needed in the first place as the triac doesn't even come close to any danger area.

The actual transient spike on the triac did exceed the 1N914 P.I.V. rating with some values of relay coil inductance hence the suggestion of the 1N4007. Add the small cap mentioned and even this problem disappears.

I haven't measured it using Dougs Selfs method but suspect it wouldn't achieve much here because the actual switch off time depends on the collapse of the rail and then the triac dropping out of conduction.
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Old 6th December 2012, 02:38 PM   #22
Bonsai is offline Bonsai  Taiwan
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Nice circuit Mooly!
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Old 6th December 2012, 02:40 PM   #23
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Thanks Bonsai
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Old 9th December 2012, 12:33 PM   #24
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These two short 10 second video clips show how effective this triac circuit is. The format is .wmv (Windows Media Video) and so should play on any Windows PC. To make the video files small (short run time) the timing delay cap is reduced in value to give a short switch on delay.

Both clips show the relay and two led's.
The YELLOW one shows when the supply is present.
The GREEN one is supplied through the relay contacts and so show when the speakers would be connected.

Also turn the sound up and LISTEN to how smartly the contacts close.

In the first clip you will see the YELLOW led goes on and off. That is the supply being deliberately interupted to show how reliable the reset feature is. You always get the proper delay when power is re-applied.

In the second clip the resistor supplying the relay has been increased to 47K. This enables you to see the rapid switch on feature in isolation. The high value resistor does not allow sufficient holding current and so the relay keeps dropping out.

In the first clip the resistor was 6K8 with a 24 volt relay coil. That shows the energy saving feature in operation. The boost cap was 33uf in both cases.
Attached Files
File Type: zip Relay Operation.zip (934.9 KB, 74 views)
File Type: zip Efficiency Circuit.zip (928.7 KB, 60 views)
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Old 9th December 2012, 01:36 PM   #25
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once again, nice work.
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Old 9th December 2012, 01:59 PM   #26
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once again, nice work.
Thanks Andrew.
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Old 9th December 2012, 03:00 PM   #27
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Why use triacs that add distortion over a relay that provides a solid connection ?

Why are ppl so afraid of using relays in the signal path ?
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Old 9th December 2012, 05:11 PM   #28
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Originally Posted by Tekko View Post
Why use triacs that add distortion over a relay that provides a solid connection ?

Why are ppl so afraid of using relays in the signal path ?
Hi Tekko,

I think you've misunderstood the circuit It is a relay driver.
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Old 9th December 2012, 05:32 PM   #29
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You might want to look at the moc3011 http://www.fairchildsemi.com/ds/MO/MOC3010M.pdf Just for fun. It is a zero crossing turn on optoisolated triac.

This will drive a relay directly from the AC line. (Yes it is not the low voltage circuit you designed.)

The downside of your circuit is the single rectifier makes the power transformer unhappy.

It also introduces noise back into the AC line.

The upside is the use of a zener to slow charge and fast discharge the timing network.
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Old 9th December 2012, 05:48 PM   #30
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Hi Simon,

The current drawn by my triac circuit is absolutely minimal and and won't impact on the PSU of any power amplifier.

The opto isolated triacs are interesting devices, I've used them for AC power control.
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