help customize "slow turn-on" duration in this circuit (link to schematics inside)

[jarthel]

help customize "slow turn-on" duration in this circuit (link to schematics inside)

http://img112.imageshack.us/my.php?image=untitled3bf7.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.

 

[davidallancole]

Changing C1 or R3 would change the turn on time.

You could probably put a 10 uF at the output.

 

[pinkmouse]

Yup, C1 and R3 look like the time delay to me as well. What will you be using this for?

 

[jarthel]

it's for tube heaters.

2 questions:

1. increasing r3 also increases the delay?

2. how about c1?

thank you for the help

 

[infinia]

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.

 

[pinkmouse]

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).

 

[infinia]

changed c1 to 10uF

 

[jarthel]

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

 

[jarthel]

how about this one? http://www.jaycar.com.au/products_uploaded/PN200.pdf

Thank you for the help

 

[infinia]

Either or will do, not critical only as a switch during turn on/off.

 

[cerrem]

It would be simpler to avoid the transistor all together and use just a C across the lower divider resistor...The problem with that is the size of the C would be huge and expensive ...So the transistor and 10uF cap, 50K are acting as a Capacitive multiplier, looking in to the emmiter.... This way a smaller cap can be used..

Chris