help customize "slow turn-on" duration in this circuit (link to schematics inside) - diyAudio
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Old 15th August 2006, 03:54 PM   #1
jarthel is offline jarthel  Australia
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Default help customize "slow turn-on" duration in this circuit (link to schematics inside)

http://img112.imageshack.us/my.php?i...titled3bf7.gif

that circuit was found in the datasheet of National's LM150. it doesn't say anything about customizing the duration of the slow turn-on.


also can I also place a 10uF (after the 2nd 1N4002) from Vout to ground?


thanks for the help.

ps. I have just read a similar thread and there were a lot of off-topic replies. please do it somewhere else.
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Old 15th August 2006, 04:28 PM   #2
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Changing C1 or R3 would change the turn on time.

You could probably put a 10 uF at the output.
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Old 15th August 2006, 05:12 PM   #3
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Yup, C1 and R3 look like the time delay to me as well. What will you be using this for?
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Old 15th August 2006, 11:36 PM   #4
jarthel is offline jarthel  Australia
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it's for tube heaters.

2 questions:

1. increasing r3 also increases the delay?

2. how about c1?

thank you for the help
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Old 16th August 2006, 01:08 AM   #5
infinia is offline infinia  United States
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Hi
R3 and C1 is tau or the time constant. The pnp is clamped on at turn-on so Vout is initially equal to Vref. The output slowly rises to the set output voltage after 3-4 time constants.

50K*100u= 5sec
so output goes from Vref to Vout in about 15-20sec

<edit>
This circuit is a good idea for heater warm up time and to prevent the Vreg from current limiting on start up.
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Old 16th August 2006, 01:11 AM   #6
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I'd breadboard this up, and have a play with different values for R3 and C1. The maths is good to know, as Infinia points out, but the hands on approach is more fun, (for me, anyway).
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Old 16th August 2006, 01:26 AM   #7
infinia is offline infinia  United States
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changed c1 to 10uF
Attached Images
File Type: jpg slowstart.jpg (84.6 KB, 149 views)
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Old 16th August 2006, 01:47 AM   #8
jarthel is offline jarthel  Australia
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can I use this: http://www.ortodoxism.ro/datasheets/toshiba/905.pdf


as the transistor in the circuit? just asking cause I already have it.

ps. to infinia: just sent you an email in regards to spice simulations. thanks again
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Old 16th August 2006, 03:47 AM   #9
jarthel is offline jarthel  Australia
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how about this one? http://www.jaycar.com.au/products_uploaded/PN200.pdf

Thank you for the help
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Old 16th August 2006, 04:45 AM   #10
infinia is offline infinia  United States
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Either or will do, not critical only as a switch during turn on/off.
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