With all the new LED's available with forward voltages of 3 volts or more the diode tester on a multi meter is no longer suitable for testing these components.

Can someone suggest a suitable circuit for testing these or a method.

Many thanks Rodney

 

A 9V battery and a 1kΩ series resistor or
two 1.5V batteries and a 220Ω series resistor.

 

A lab power supply with adjustable voltage and current, digitally metered outputs of same, RS232 input for computer control of V & I with data logging capability.

 

Best to use the higher V, 9 V or 12 V, with 470 to 1 k ohms in series with LED; add 2 red LED in series across test terminals. With no LED in test or a reversed LED, red LED's will be on. With correct polarity , test LED will light, reds off. With reversed test LED V will be limited to about 5 V which is usually safe for LED.

 

The simplest circuit for a functional test would be as Mr. Chips suggested except I would use three 1.5V batteries in series with a 220Ω instead of two, to insure there is sufficient voltage for the higher voltage LEDs.

 

As the ranges of VF's and current ratings between LEDs are vastly different than they were a few years ago stating a supply voltage level and resistance is mostly pointless here..
3 x 1.5V or 1 x 9V or 1 x 12V batteries ain't gonna do squat if the LED's Vf is greater than that.
Ideally the "tester" would have a voltage exceeding the Vf of the LED (could be 9V..could be 12V... could be 30V,etc...) and sufficient current to allow a visual level of illumination.

 

I believe we did this a few days ago. Same TS, same question.

 

Déjà vu all over again?

 

Hello,

Did you ever see this thread?
A really simple led tester

Bertus

 

With all the new LED's available with forward voltages of 3 volts or more the diode tester on a multi meter is no longer suitable for testing these components.

Can someone suggest a suitable circuit for testing these or a method.

Many thanks Rodney

Some people favour the "joule thief" blocking oscillator/inverter - if you don't like winding coils, you can cross-connect the parallel inductors in a common mode choke from a small SMPSU such as in a scrap set top box.

Another favourite is the well known astable oscillator with a 470uH choke as one of the collector loads.

Both options run on a single 1.5V cell and rely entirely on inductor back emf to make the LED Vf.

 

With all the new LED's available with forward voltages of 3 volts or more the diode tester on a multi meter is no longer suitable for testing these components.

Get a different multimeter. My free Harbor Freight meters work fine for LED testing. They glow dimly - probably 1mA or so.