stabilizing power for VU-meter lights ???

[matthias]

hello,

I have 2 light bulbs each has 12V and suffers 80ma


I use a 7812 to get the 12 v for the lamps...
the lamps are connected in parallel, so that each lamp gets its 12V

the problem is, that the light is flickering sometimes...
(every minute for a few seconds...)

I've connected a 1000µ electrolytic cap to ground to stabilize the power..
is that enough or should I try a higher value ??

or are there any other tricks to prevent the lights from flickering ??


thanks,
mat

 

[gyraf]

you don't need stabilizing for that. There's clearly something else wrong.. Maybe regulator overheating and going into protection?

 

[matthias]

thanks for the fast response...


the regulator gets only a little bit warm... but not hot...


here's a short schematic...

I'm a little bit unsure about the 330n cap, because I have more positiv regulators in that circuit...

 

[gyraf]

The capacitor between the output pin and gnd shouldn't be bigger than 10uF..

 

[BYacey]

The output cap should be smaller, 0.1mfd or so, a 1000mfd cap will not allow the regulator to track accurately. Put the 1000 mfd on the input line of the regulator instead. Have you considered just using a power dropping resistor?

 

[matthias]

thanks !!

I thought the big cap would "buffer" the voltage ...


should I also add a 100n cap to ground
I've seen this in many other ps schematics...??


thanks
mat

 

[BYacey]

You really only need the 100nF if the 1000 mfd isn't close to the regulator; for pilot lights I'm not even sure this would matter.

 

[matthias]

I would replace the 1000mfd cap by a 10mfd cap and add a 100n??

is this correct so, or should I lave the 10mfd completely out...??

 

[BYacey]

I think you only really need the 100nF on the output, and the 1000mfd on the input of the regulator. It wouldn't hurt to also place a 100nF in parallel with the 1000 mfd on the input side of the regulator.