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PSU for tube amp - 555 timer delay turn on
PSU for tube amp - 555 timer delay turn on
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Old 10th October 2018, 01:32 PM   #11
KatieandDad is offline KatieandDad  United Kingdom
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Quote:
Originally Posted by Ketje View Post
Keep it simple
Mona
You'd have to experiment with that circuit. You might find that the 470R and the LED might pull enough current through the relay to activate it.
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Old 10th October 2018, 02:57 PM   #12
Mooly is offline Mooly  United Kingdom
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PSU for tube amp - 555 timer delay turn on
Here you go. The 555 output goes low after 25 seconds which also turns on the relay (not sure where your pin outs came from ).

If the 555 output doesn't quite make it to 5 volts (it should) then you will need a resistor across base and emitter to hold the transistor off.

Third image shows the LED currents. They are unequal because of the differing turn on volts between red and green and so you will need to alter the two resistors to give desired brightness of each.

Final image shows the relay current.
Attached Images
File Type: png 555_1.png (55.3 KB, 115 views)
File Type: png 555_2.png (39.3 KB, 104 views)
File Type: png 555_3.png (44.9 KB, 94 views)
File Type: png 555_4.png (43.7 KB, 91 views)
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Old 10th October 2018, 03:32 PM   #13
Ketje is offline Ketje  Belgium
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Originally Posted by KatieandDad View Post
You'd have to experiment with that circuit. You might find that the 470R and the LED might pull enough current through the relay to activate it.
Relais for 5V has a resistance 50...100Ω, that leaves no more then 1volt for the relais, and even less with the LED in the circuit.So no problem.
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Old 10th October 2018, 04:48 PM   #14
kodabmx is online now kodabmx  Canada
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Too easy? NE555 DC 12V Delay Relay shield Timer Switch Adjustable Module 0 To 10 Second | eBay
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Old 10th October 2018, 10:15 PM   #15
aros71 is offline aros71  New Zealand
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Quote:
Originally Posted by Ketje View Post
Keep it simple
Mona
That 470R needs to be 100R to get 1.7volt @ 20mA thru the LED

And in this design, I fear the flyback diode across the relay coil might interfere when the IC is in the OFF state.
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Old 11th October 2018, 06:45 PM   #16
Ketje is offline Ketje  Belgium
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Originally Posted by aros71 View Post
That 470R needs to be 100R to get 1.7volt @ 20mA thru the LED

And in this design, I fear the flyback diode across the relay coil might interfere when the IC is in the OFF state.
100R is much to small, big chance the relais will go on immediately.But why 20mA ? modern LED's need only 2mA and 470R gives ~7mA.
The flyback diode only prevents the voltage on the drain to go any higher then 5,6volt at turn-off.
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Old 11th October 2018, 08:56 PM   #17
Elvee is offline Elvee  Belgium
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I agree with Mona, but in the unlikely case of a too low LED current/too high relay current, the solution is simple: add a suitably low resistor in parallel with the relay (but it shouldn't be needed, except perhaps for prehistoric components)
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Old 15th October 2018, 06:35 AM   #18
Dr Croubie is offline Dr Croubie
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Sounds like something I designed last year for a tube amp, using a 556 to control two separate supplies to pre-amp and power-amp tubes.


I wasn't sure (at that point) how I would be controlling the HT power supplies so I built in two outputs per channel: one goes high (2V less than Vcc) and the other is an open-drain that clamps to ground when the timing period is up.
Vcc on mine is just the 12V heater supply but depending on the chip can be anywhere 5-15V.
Either of these can drive an LED, either high-output with resistor to ground, or Vcc through resistor to open-drain, which could work with either common-anode or common-cathode designs.



I understand that you've already bought the LEDs as the bidirectional type, but my circuit could still be wangled for that way. Just construct a resistor voltage-divider such that the current goes through the 'heat' LED on startup, then the FET shorts out a resistor to make the current go the other way through the 'run' LED. And seeing as I got bored, I simulated it on spice just to check that it would work.


Or ditch the LEDs you've already bought, I think mine looks just as nice with both LEDs shining after the heatup phase instead of turning one off (they were some IP67 jobbies from Jaycar, I think you can get them in NZ). The photo is my turntable preamp, so only using 1-channel for the timer as it's all a single HT voltage.



And it's all on a PCB measuring 24x24mm with 2mm connectors, and still got two M3 holes for standoffs. I've got a few dozen left, want one?


(edit, grabbed the coil data for a random 5V relay here: https://docs-apac.rs-online.com/webd...6b814b2cde.pdf and chucked it into the simulation. It only picks up at 80% of 5V = 4V, so it definitely won't turn on until the mosfet does. Also, only ~7mA of current through the LEDs, adjust resistor values to taste...)
Attached Images
File Type: png 556.PNG (75.6 KB, 35 views)
File Type: png 556top.PNG (88.4 KB, 23 views)
File Type: png 556bot.PNG (37.9 KB, 11 views)
File Type: jpg IMG_20171222_0902390s.jpg (493.8 KB, 12 views)
File Type: png 556spice.PNG (103.3 KB, 17 views)

Last edited by Dr Croubie; 15th October 2018 at 06:56 AM.
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