my friend mentionned i could use a transistor for a project i was working on.

originally i was going to use 30,000uF capacitor to fade some leds to nill...

now i was told that i can use a transistor and a really tiny capacitor to fade the same couple leds.

can anyone confirm this? If true, then what type of transistor should i be using?

Also, how can i determine the fade time using a trans and a cap?

Thanks

 

What exactly are you trying to do? When you state leds do you mean Light Emitting Diodes? If so, a 30,000uF cap seems to be very large. How did your friend suggest wiring this? If you want fade control, you probably needs some type of potentiometer or at least a switch that directs current through various resistors. LED's don't usually require very much power to light up anyway. Give some more detail and there may yet be an answer!

 

a typical LED's operating current is 10 mA to 20 mA as I remember. The advantage of using a transistor could be the independent timing control, especially with a MOS transistor which has an isolated gate to set up whatever timing needed. To a very large degree no matter what load is in the drain-source path, the set timing won't change. Yes for the small current it's not necessary to use a transistor.

 

oh basically i would be using the 30k uF to fade uhm.. not sure yet... maybe around 4 LEDS. I will be applying 3 volts to all 4 leds
this will be 12 volts resisted to 3V. Parallel to this circuit is a few caps. 10k each... this way the power goes into the caps and also flows to the LED's.
once power source is cut, the caps dissipate whatever power they have left, to the leds. 30k gave me around a 4 second fade time. Looks pretty cool too.

Instead of using such big caps, i was told that i can use a transistor and a small cap of... i dunno... 4.7uF (not sure yet) and the transistor would regulate the power coming out of the cap going to the led. meaning i wouldn't need to user such huge caps...

the only problem is that today is the first day i've learned about transistors... hehe

i've seen them before, i've blown alot of them before with 27+ volts, just for the hell of it... BUT i've never used one.

I know the have a collector an emmitor and a straight through wire.
correct?

I see bipolar transistors, mosfet transistors, and a ton of other kinds.

what kind would i need for a 3volts source. My goal is jiaxima96 might know ;-) hehe is basically to make some leds fade down to dark... in a range of 4 seconds... if i can even regulate the delay time... then even better


it's pretty cool learning this stuff hehe

 

How would one setup this timing?

my friend had to go and mention i could use transistors... ugh gots me asking questions... hehe

 

I think I'll probably do it sometime tomorrow afternoon, to draw one or two typical circuits using bipolar and MOS transistors for LED fading, for your reference. BTW yesterday someone asked where the file attachment feature is. I don't see it either. turned off, or there is a screen bug?

 

Looks like we can't attach files any more. The lower left screen says "Forum Rules: You may not post attachments".
Hi multiplexor, if you don't mind posting your email address I can email you the circuits with explanations. They are done now.

 

damn your fast! wow... hehe

hmm email to multiplexor@hotmail.com



thanks a lot. it'll be great to learn up on transistors and see working diagram.

if i can user this method instead of a bunch of huge caps... well it'll save space, and i could probably add it to the dome light. Since the dome light doesn't have enough space to fit 10k*3 caps.



again, thanks a million,

Frank

ps: i'm guessing they turned off file
attachments cause of the server problems? Or
it has become a paying member feature type thing...

 

you have male

arg, i mean mail...