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Old 2nd July 2007, 10:12 AM   #1
alexcd is offline alexcd  United States
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Default Power/Outut Relay Control Circuit

I tried this thread in Group Buys but I think it needs more discussion first. Here goes, again...

I thought it would be nice to create a relatively simple power/speaker output relay circuit for amp builders such as myself. Here were my requirements.

* accept momentary push button to toggle power state
* accept 12V trigger (actually 5-24V range) from receiver but with ability to change power state with on-device button.
* must have two outputs, power breaker and speaker outputs (helps with those nasty sounds at shut down)
* uses a wide range of voltages and very little power since it will most likely run whenever plugged in
* on board AC-DC (35V max to 5VDC)..
* accepts external relay power (any voltage will do) up to ~10A so you can use monster relays
* small outline but all through-hole parts (ended up 2"x4" with mounting holes)

So here is the sequence of events when you give the circuit juice.

1) There is a 0.5 second delay where nothing with happen (clears the logic states and makes sure nothing bad happens) when you initially power the unit. This is a safely precaution and should not be a problem for anyone really.

2) Toggle power with power button OR 12V trigger

3) Power turns on instantly. Speaker outputs are delayed 1 second.

4) Toggle power with power button OR 12V trigger

5) Power and speaker outputs are turned off instantly.

The circuit has been thoroughly simulated in PSPICE.

The parts cost $9.30+SH (all Mouser) and I'm hoping to get at least 20 requests for boards to drop that price to $6 each.
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Old 2nd July 2007, 10:25 AM   #2
alexcd is offline alexcd  United States
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Default schematic

schematic
Attached Files
File Type: pdf relay 070207.pdf (58.4 KB, 205 views)
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Old 2nd July 2007, 10:30 AM   #3
alexcd is offline alexcd  United States
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Default output file

output file

Seems to work!
Attached Files
File Type: pdf relay output 070207.pdf (27.4 KB, 92 views)
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Old 2nd July 2007, 10:41 AM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
Is the power on relay delayed to allow soft start?
Or would that require a second relay and delay circuit?
Would that require major modifications?
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regards Andrew T.
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Old 2nd July 2007, 10:59 AM   #5
alexcd is offline alexcd  United States
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I think you mean something like this, right?

http://sound.westhost.com/project39.htm

I did not think to add this. This would require modification but is probably something I can do.
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Old 2nd July 2007, 11:35 AM   #6
alexcd is offline alexcd  United States
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This circuit is more of a way to use momentary switch and external trigger. The trigger and switch signals work on catching their respective rising edges. This way either a trigger or button press will toggle the power. Some people would like to have a manual override to their amps without reaching behind for the infamous massive toggle switch (10A+ switches are massive.)
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Old 2nd July 2007, 12:37 PM   #7
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Hello Alexcd,

I must say that this circuit looks very familiar! While you've changed some details of the main relay drive and added the extra speaker delay, the heart of the circuit is identical to my one here: http://www.mhennessy.f9.co.uk/gainclone/control.htm

There's a couple of points to explain to anyone looking - mainly the purpose of R3/D9 and R10/D10. In my circuit, each of those diodes is an LED - Standby and On, respectively. Also, R3 should be 560 ohms (not 560K). If you're not using the LED's, omit all of these components. Alternatively, correct the diagram to show that these are in fact LEDs, and change R3 if you want the standby LED to light

I'm not sure why you are using MOSFETs to drive the relays - perhaps a personal preference "thing" - maybe you're more comfortable with understanding how they work? Or maybe to differentiate your version from mine. I don't know. Whatever, "normal" transistors are certainly cheaper here.

Also, I note that you've passed the "inhibit" signal via an inverter - I chose to apply that directly to the base of a transistor because you cannot guarantee how CMOS logic behaves as the PSU rails are rising; obviously you can with a simple transistor circuit.

Regarding the soft-start option, it would be very easy to add in the same way you've added the speaker delay. Refer to the previous paragraph, and consider using U13B for this function instead.

BTW, while the circuit is (a) nothing special and (b) in the public domain, it would be nice to receive a mention if you plan to use extracts from it. If you publish on a webpage, let me know and I'll happily link to it. I also assume that a Group Buy is non-commercial?

FWIW, I did a lot of testing and debugging of the circuit, and it's pretty sorted. There's even a PCB layout, but as includes my dangerous mains dropper PSU, I won't be publishing it! Future enhancements, as well as soft start, include DC protect - essential in any amplifier. Just a couple of transistors and some diodes for the detector that Douglas Self promotes - see page 421 of his book (4th edition). I couldn't include this in my version because the circuit wasn't transformer-isolated from the mains...

Hope this helps,

Mark

PS: I've included a view of the schematic that isn't available on the website sorry about the quality, I had to downsize it. Here you can see that most of the diodes should be 1n4148 or equivalent rather than the 1n4007 that you've used in many places. Keep to those for the relay coils, however
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File Type: gif gainclone control.gif (23.3 KB, 475 views)
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Old 2nd July 2007, 12:53 PM   #8
alexcd is offline alexcd  United States
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Yes, I did copy a lot of your circuit. I apologize for not mentioning this. The group buy thing was strictly non-commercial as well.

I changed the outputs to MOSFET because the current drive transistor circuit would not be adaptable for different relay coils. It may be adjusted for each user but I thought that would be too much of a hassle.

560k is a typo but I did in fact simulate it that way.

D9/10 are LED but I didn't find them quickly in PSPICE so I didn't use them. Also I used 1N4007 for the same reason. I was going to publish an accurate BOM at some point.

The additional inverter required for a soft-start is not available on the DIP14. If there is simply a larger package of inverters available I would get that and add an extra delayed output. NOTE: U13 does not exist. I used a single 6-inverter chip but PSPICE did not like me cut/pasting it around. Basically i have a lot of house keeping to do on the schematic but the idea is there.
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Old 2nd July 2007, 02:21 PM   #9
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Quote:
Originally posted by alexcd
Yes, I did copy a lot of your circuit. I apologize for not mentioning this. The group buy thing was strictly non-commercial as well.
No worries - glad to have provided some inspiration

Quote:
I changed the outputs to MOSFET because the current drive transistor circuit would not be adaptable for different relay coils. It may be adjusted for each user but I thought that would be too much of a hassle.
I used a current source because of the wildly varying supply voltage, but here things are easier for you. I would stick with the original current source, as it will protect the circuit from mistakes caused by the relay being mounted off-board. Just choose a value of current that is higher than the largest anticipated relay current, then it will saturate (like a switch), but have built-in (short-term) short-circuit protection.


Quote:
D9/10 are LED but I didn't find them quickly in PSPICE so I didn't use them. Also I used 1N4007 for the same reason.
Yes, I wondered if that might be the case

Quote:
The additional inverter required for a soft-start is not available on the DIP14. If there is simply a larger package of inverters available I would get that and add an extra delayed output.
Yes, I know that you're using a hex inverter, but I was suggesting doing away with the inverter for the power-on inhibit (labelled U13B on your schematic) and using it for for the soft-start delay instead. But if you prefer not to change that, then there are myriad ways of implementing it using discrete transistors.

As an aside, have you considered a solid-state relay for the soft-start? That worked well for my A4 amp, where space was a problem. But perhaps you're trying to keep mains off the PCB?

Another thing - you're powering this circuit from the amp rails? Have you considered mains-fail detect? With my original mains-dropper PSU, the circuit drops out instantly, but if you power it from the main smoothing caps in an amp, the circuit won't drop out when the mains fails. Maybe not a proplem - maybe the amp deals with it gracefully, but if you're aiming for a general-purpose module that any amp can use, it's worth considering... It would only need 2 transistors...

Best regards,

Mark
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Old 2nd July 2007, 02:39 PM   #10
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Quote:
Originally posted by mhennessy

I used a current source because of the wildly varying supply voltage, but here things are easier for you. I would stick with the original current source, as it will protect the circuit from mistakes caused by the relay being mounted off-board. Just choose a value of current that is higher than the largest anticipated relay current, then it will saturate (like a switch), but have built-in (short-term) short-circuit protection.
That does sound good and all but I have a wildly varying need for current. I am definitely more comfortable using them but I agree that I am throwing out the built-in short-circuit protection. A slightly more complicated 2-stage current source may be adequate (first 200% to mechanically switch the relay, then say 50% current to maintain it.) I would still need to guess on the current.

Quote:
Originally posted by mhennessy

Yes, I know that you're using a hex inverter, but I was suggesting doing away with the inverter for the power-on inhibit (labelled U13B on your schematic) and using it for for the soft-start delay instead. But if you prefer not to change that, then there are myriad ways of implementing it using discrete transistors.

As an aside, have you considered a solid-state relay for the soft-start? That worked well for my A4 amp, where space was a problem. But perhaps you're trying to keep mains off the PCB?
No I had not thought of a soft-start at all until this point. I think I can come up with something though.

Quote:
Originally posted by mhennessy

Another thing - you're powering this circuit from the amp rails?
That is possible but I would have liked to power-down the amplifier rails during non-operation hence the speaker output delay. I have a auxiliary 12Vac transformer that I was going to rectify and double as my relay coil power supply and reduce to 5VDC with a LDO reg since the current is minimal.

Quote:
Originally posted by mhennessy

Have you considered mains-fail detect? With my original mains-dropper PSU, the circuit drops out instantly, but if you power it from the main smoothing caps in an amp, the circuit won't drop out when the mains fails. Maybe not a proplem - maybe the amp deals with it gracefully, but if you're aiming for a general-purpose module that any amp can use, it's worth considering... It would only need 2 transistors...
That is definitely something else to consider.

I have some work to do but I would like to make this as fully functional as possible without going nuts on parts. As of right now the parts cost $9.30 which is a bit high for something this basic. My selections may have been a bit over-kill.
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