BASIC ELECTRONICS FOR EVERYONE

Visual Capacitor Charge Discharge Circuit

Capacitor Charge Discharge Circuit

Simple Capacitor Charge Discharge Circuit
If you have built the first two circuits in this series, Light Emitting Diode Circuit and the Transistor Controlled LED Circuit this one should be a piece of cake. This circuit combines the LED and the series resistor from circuit two with another series resistor and a capacitor. A capacitor and resistor form what is known as an 'RC Time Constant'. This means it takes a certain amount of time depending on the value of the resistor and capacitor (RC) to reach a given level of charge.
With this circuit we can "see" the capacitor charge up and discharge by watching the brightness of the LED.

Capacitor Charge Discharge Circuit Construction

Lay out all the parts in front of you. You should have a 9 volt battery, a 9 volt battery connector, a 1000 ohm resistor 1/2 watt or smaller, a 2200 uF 16 volt or greater capacitor, a 470 ohm 1/2 watt or less resistor and an light emitting diode.

As before start by finding the cathode lead of the LED. One lead can be longer or a small flat on the side of the LED can also mark the which lead is the cathode. It is also shown on the package it came in. Connect the cathode lead to the black wire of the battery connector. (ground) Next connect the anode of the LED to one end of the 470 ohm resistor and the other end to the positive terminal of the capacitor. Now connect one lead of the 1K ohm resistor also to the positive lead of the capacitor and the other end to the red positive wire of the battery connector.

Now this is a little bit different. Instead of connecting the connector to the battery, we want to just hold it against the battery terminals. This is so we can apply and remove the voltage quickly.

Circuit Operation

Hold the connector to the battery. Notice the time it takes for the LED to come up to full brightness. Now pull the connector away from the battery. Again notice that the LED now remains on even with the battery disconnected. This is because the capacitor is supplying the energy to run the LED. The time it took to come up to full brightness was the capacitor storing energy from the battery. Changing the value of the 1K resistor will change how long it takes to charge the capacitor.