# Series RC circuit for LED

Discussion in 'LEDs and Optoelectronics' started by rajat, Sep 12, 2013.

1. ### rajat

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0
Jun 3, 2012
Hello All,

Just an easy question probably, I have got Series RC circuit, i.e.

9v --(connected to) --Reistor (330 Ohm)--- Capacitor (220 microfarads)

This charged capicitor to approx 6 v.

NOW

Resistor (330 Ohm)---Capicitor(220 microfarads)--LED

But LED will not light??
Can anyone explain please explain why as for my understanding,I have got enough volt of 6 v where as LED needs only 1.7 v.

I am not sure on current. I am assuming as I am using 9 v @1.5 amp battery to charge the capicitor, the current should also be approx to 1.5 amp.

Sorry if it is very simple questions...i have spent hours trying to understand but could not come to any conclusion.

2. ### BobK

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1,686
Jan 5, 2010
Have you tried lighting the LED directly from the battery to make sure it is working?

Are you sure you have the correct polarity?

I tried this and I get quite a flash, diminishing over about 2 seconds.

Bob

3. ### GonzoEngineer

321
2
Dec 2, 2011
You dumped 220 mF into an LED without a series resistor in between?
I am afraid you might have blown the LED!

4. ### BobK

7,682
1,686
Jan 5, 2010
Gonzo,

He has a resistor.

Bob

5. ### GonzoEngineer

321
2
Dec 2, 2011
But, his pseudo-diagram doesn't show it in series with the LED.

6. ### davennModerator

13,654
1,888
Sep 5, 2009
yeah that's what I was thinking ... he's dumping the cap directly into the LED

Dave

Last edited: Sep 14, 2013
7. ### BobK

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1,686
Jan 5, 2010
Since the diagram does not show a circuit, I guess it is ambiguous. He should have seen a flash though, at least once!.

Bob

8. ### rajat

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Jun 3, 2012
Sorry guys for late reply.

As they say picture says thousand words...so I have clicked pictures to make it easier

I am a beginner in electronics.To answer your queries..LED is working fine. I tried to load pic but they exceeded size limitation of the site. Hence i have to use picassa

Pic 1: Shows all led are working

Pic 2: Size of Capicitor 22 uf @ 25 V sufficient for 9v battery used.

Pic 3: Capcitor charged to approx 6 V using 9V battery

Pic 4: Battery removed but charged capicitor will not light the LED.

I used Series RC circuit to charge capicitor as shown in Pic 3 but still no light to LED in Pic 4.

9. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,412
2,780
Jan 21, 2010
The reason is that your last circuit isn't a circuit.

Here's what you can try.

1) connect the resistor and the capacitor on the breadboard so that the capacitor charges. I think you are doing this correctly.

2) remove the battery

3) connect a LED in the place of the battery

What you are doing at present has a non circuit going X---RESISTOR---CAPACITOR----LED---X. Nothing will happen until you join the X's together. Note that the LED must be oriented correctly or it won't work.

10. ### BobK

7,682
1,686
Jan 5, 2010
So the diagram was not ambiguous after all -- there was no circuit.

Bob

11. ### rajat

16
0
Jun 3, 2012
Thanks you guys for all your replies. It worked like a charm and I got LED lighted for 2 sec.

12. ### Jibby

15
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Sep 12, 2013
Because of the capacitor the voltage across the LED is much more than its tolerance level so it is actually failing and it is giving an impression that it is not working.

13. ### BobK

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1,686
Jan 5, 2010
Jibby,

You should read the entire thread before responding. The issue was already resolved.

Bob