Shenzhen LEDs: How to Identify the Positive and Negative Leads of an LED

Release Date:

2021-04-12

　　Use the multimeter on the R×1K range, and alternately connect the red and black test leads. Light-emitting diode With the two leads connected, during one of the measurements you will observe that the meter needle first swings to the right by a certain distance, and then begins to vibrate slightly (oscillate) while remaining in that position, with an amplitude of about one scale division. This phenomenon indicates that the integrated circuit inside the LED is oscillating under the influence of the 1.5 V battery voltage within the multimeter; the resulting pulsed current causes the pointer to jitter. However, because the voltage is too low, the LED does not yet emit light. Nevertheless, this observation confirms that the red and black test leads are connected correctly—that is, the multimeter’s black lead is connected to the LED’s positive terminal.

 

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　　Note: When determining the anode and cathode of a light-emitting diode, never assume—as you would with a regular diode—that the measurement with the lower resistance indicates the black test lead is connected to the LED’s anode.

 

　　What about the anode and cathode of a light-emitting diode? Actually, it’s very simple, Light-emitting diode The longer lead is the positive terminal, and the shorter lead is the negative terminal. If the leads are of equal length, the larger pad inside the LED is the negative terminal, while the smaller pad is the positive terminal. On a multimeter: connect the red test lead to the “+” terminal and the black test lead to the “–” terminal; when measuring an LED, the low-resistance range will not provide a readable reading, so use the RX10K range instead. Touch the two test leads to the two terminals of the LED. If the resistance is low, the black test lead is connected to the positive terminal; if the resistance is high, the black test lead is connected to the negative terminal. When an LED is used in conjunction with TTL components, it is generally necessary to connect a 470 Ω current-limiting resistor in series to prevent damage to the device.

 

　　How can you quickly identify the anode and cathode of a light-emitting diode? It’s actually quite simple: the longer lead is the anode, and the shorter lead is the cathode. If the leads are the same length, the larger internal contact inside the LED is the cathode, while the smaller one is the anode. When using a multimeter, connect the red test lead to the “+” terminal and the black test lead to the “–” terminal; however, the low-resistance range on the multimeter won’t work for measuring LEDs—use the RX10K range instead. Touch the two test leads to the two terminals of the LED. If the measured resistance is low, the black lead is connected to the anode; if the resistance is high, the black lead is connected to the cathode. When an LED is used in conjunction with TTL components, it is generally necessary to connect a 470 Ω current-limiting resistor in series to prevent damage to the device.

 

　　Use a multimeter to make the determination. Light-emitting diode Method for determining the positive and negative electrodes:

 

　　Use the multimeter on the R×1K range, and alternately connect the red and black test leads. Light-emitting diode With the two leads connected, during one of the measurements you will observe that the meter needle first swings to the right by a certain distance and then begins to vibrate slightly at that position, with an amplitude of about one scale division. This phenomenon indicates that the integrated circuit inside the LED is oscillating under the 1.5 V battery voltage supplied by the multimeter; the resulting pulsed current causes the pointer to jitter. However, because the voltage is too low, the LED does not yet emit light. Nevertheless, this observation confirms that the red and black test leads are connected correctly: the black lead is connected to the LED’s positive terminal.

 

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