# My capacitor does not do what I expect it to do

Fixed: The capacitor was defective. It works well with a different one.

I’m new to electronics and need your help.

I built a circuit similar to this one (see comment for the exact components):

I expect the LED to remain on for a short time when I release the button, my capacitor discharging and providing current to the base, keeping the transistor open.

It does not. What am I doing wrong?

Adding some pictures of my actual circuit:

• I am expecting it to be on for a long time too. With the information you give, something is wrong, but without further info, impossible to say where the problem is. Maybe you built the circuit wrong? Commented Jan 7, 2021 at 16:17
• Consider uploading a photo of your circuit letting us clearly see the connections and components - we might see something obvious:) Commented Jan 7, 2021 at 16:32
• yep. Nr. 1 reason for beginner transistor circuits not working: mixing up the leads on the transistor, or thinking that all transistors have the same pinout and using a different one without adjusting the connections. Commented Jan 7, 2021 at 16:34
• Also note that it's not a good idea to short a capacitor directly to a voltage source. The resulting current could for example brown out your supply or damage your switch contacts. Use a small resistor in series to limit the current to something reasonable. Remember I=C*dv/dt. Commented Jan 7, 2021 at 16:45
• Your expectation seems to be correct. 100uF * 100k = 10,000 ms or 10 seconds time constant. That should be long enough to see something. So there must be something wrong with the circuit. Double-check the wiring and the component values. Commented Jan 7, 2021 at 16:54

My guess is that your capacitor has the wrong (too small) value, or you connected a polarized capacitor with reversed polarity.

It is also possible that the base resistor (33k) actually has a much smaller value. You need to verify that both of those components have the correct value and are connected properly.

I replaced the capacitor with another one (smaller cause that’s all I had) and it’s working so I guess my previous cap was defect..

Thanks a lot to all of you who took some time to help me

• I would suspect there wasn't a good connection with the original capacitor on the breadboard. Commented Jan 8, 2021 at 17:16

There are many troubleshooting techniques. Here I would recommend simplifying the circuit until the LED illuminates.

Try the left circuit, if it doesn't work, short the E-C of the transistor (right circuit).

simulate this circuit – Schematic created using CircuitLab

• Thank you Mattman, the LED was turning on but as soon as the button was released, it was turning off while I was expecting it to remain on for a short time Commented Jan 7, 2021 at 17:09

This image shows two NPN transistors. Which one do you have connected correctly?

• It’s working now (it was the capacitor) Commented Jan 7, 2021 at 19:53