want slowly raise the DC on a standard PSU design. cosmetic reason :)

[andre tchmil]

hey guys , I need to slowly raise the DC to light up some LED's
PSU is a basic design with LM317 and the standard components. 1000/100/1uf caps, 240R etc
any ideas on how to mod  ?
It's pure for cosmetic reasons

thanks in advance

 

[bruce0]

Use an LM339 (4 comparators) or a single comparator, and build a voltage divider with a threshold.  When the voltage goes up, the comparator stops sinking current and the led takes it instead. 

There is a battery charger at ESP west sound or whatever, and there is a vu meter / circuit in one of my posts that does a similar thing.

You can use an opamp but the transistor is better

I don't really know what you are trying to do, but this will turn an led on at higher voltage.

 

[JohnRoberts]

google  a "cap multiplier"...

JR

 

[bruce0]

Oh, I get it. You want to actually slowly raise the voltage on the PSU.  The PSU is for actual LED illumination.

Sorry my response was to create an indicator.

So where does this big virtual cap go?  On the adjust pin of the 317?  Or as the output reservoir?  I suppose either would work.

 

[andre tchmil]

yes I was a bit unclear.
I want make the led slowly light up , instead of banging in.

 

[kooma]

make a somekind of soft start psu
but do you want it for the leds only or whole circuit?


found example as attachement

 

[andre tchmil]

make a somekind of soft start psu
but do you want it for the leds only or whole circuit?

good question, only for the Led supply

 

[Andy Peters]

hey guys , I need to slowly raise the DC to light up some LED's
PSU is a basic design with LM317 and the standard components. 1000/100/1uf caps, 240R etc
any ideas on how to mod  ?
It's pure for cosmetic reasons

thanks in advance

I don't know, let's see ... digital pot on the bottom resistor in the feedback divider? Control the output voltage with a tiny micro?
-a

 

[audiomixer]

now thats seems to me like overkill....

I quite like kooma's post. the cap is slowly charged. putting the transistor 'out of the equation' when the cap is fully charged. you can set the time constant with R3 / C2. bigger R means slower startup time. this could be added easily into existing standard LM317 board... only additional components to the textbook config. easy enough to put onto som veroboard and done!

- Michael

 

[JohnRoberts]

Ok I googled capacitance multiplier for you...

No I won't build it for you.

JR

 

[andre tchmil]

I googled this  8)

http://pcbheaven.com/circuitpages/LED_Fade_In_Fade_Out_Dimmer/

looks similar.

thanks for the guidance

 

[andre tchmil]

hm, while we're at it, can I take it a step further?

would it be possible to add a kind of bad contact/ stuttering effect before the led fully glows ?

'm serious guys

 

[Andy Peters]

hm, while we're at it, can I take it a step further?

would it be possible to add a kind of bad contact/ stuttering effect before the led fully glows ?

'm serious guys

And now my microcontroller idea doesn't seem so ridiculous ...

-a

 

[andre tchmil]

hm, while we're at it, can I take it a step further?

would it be possible to add a kind of bad contact/ stuttering effect before the led fully glows ?

'm serious guys

And now my microcontroller idea doesn't seem so ridiculous ...

-a

less vague , more details please  8)

 

[audiomixer]

hm, while we're at it, can I take it a step further?

would it be possible to add a kind of bad contact/ stuttering effect before the led fully glows ?

'm serious guys

And now my microcontroller idea doesn't seem so ridiculous ...

-a

Jup, agreed

-michael

 

[JohnRoberts]

Funny I have been accused of suggesting microprocessors as the answers for every problem (like the worker with only a hammer in his tool kit), but even I think this is over kill for the OP's initial request.

With a cheap micro you can make LEDs do pretty much anything you want.  You can vary the brightness to plan by using PWM to vary the duty cycle of on to off...

Alternately you could use the micro to vary the voltage of a PS .

I am not enthusiastic enough to provide more details, and do not encourage this pursuit.

KISS.

JR

 

[mjrippe]

Use microcontroller pin to turn LED on and off at random periods at first.  Then change to PWM to control brightness.  Low duty cycle ramping up to high.

 

[mjrippe]

Hi John, simultaneous post I guess!  I think that with the added requirement of flickering/"stuttering" effect the simplest way to do it is with a micro.  I can picture throwing the switch and watching the LED blink dimly a few times as though trying to stabilize, then fading up to full intensity.  Very cool effect, but total overkill for a rack mount piece of audio gear.  Perhaps the OP has something else in mind like an art project or special custom build.

 

[Andy Peters]

Use microcontroller pin to turn LED on and off at random periods at first.  Then change to PWM to control brightness.  Low duty cycle ramping up to high.

Exactly, and don't bother with the regulator at all, if its only purpose is to drive the LED.

-a

 

[JohnRoberts]

At the risk of stating the obvious, why drive an LED inside an audio product with a square wave??

A slow fade can be accomplished (quietly) with a big ass cap, or small cap and impedance multiplier (this the third and last time I will suggest this).

Amuse yourselves.

JR