This Simple Voltage and Current tester can be used to measure the forward Voltage drop and current through Semiconductor Diodes like LED, Infrared diode, Photo diodes, Silicon diodes etc. This is ideal to assess the voltage and current drops through these devices during circuit design and calculating the power consumption in a particular section of the circuit.
Different types of LEDs including power LEDs are now used in various applications. The voltage rating of these devices range between 1.8 to 5 volts. Current rating also varies from 20 mA to 50 mA. So by assessing the actual voltage and current consumption, it is easy to get full brightness without damaging the device. This will also prevents the unnecessary heating of these delicate devices and their breakdown
The circuit is a current regulator using the Darlington PNP transistor BD 140. It provides 9 volts and around 50 mA current to the device under test. Switch S1 is used to select the Voltage and current measurement. If S1 is placed in position 1, the circuit measures the current drop across the device under test. A 100 mA meter is placed in series with the current path. So that when the device is connected to point A and B, meter shows the current flowing through the device
When S1 is placed in position 2 and the device is connected to points A and B, voltage drop in the device can be measured. The 0-30 Volt meter is connected parallel to the device under test. So that it can give the voltage drop across the device.
Since diodes are One-way conductors, observe polarity while connecting to points A and B. Anode should be in A and Cathode in B. Connect small Alligator Clips to points A and B to hold the device under test.