We all know that laser diodes occupy a large share in the market. Many customers reported that when using laser diodes, one or two lights suddenly turned off. What happened? How to judge whether the laser diode is broken? Today, Xiaobian gives you a brief talk.

1. Drive circuit problem

The laser diode must be driven by a constant current source, rather than a DC power supply.

If there is something wrong with the driving circuit, such as the burning of the constant current chip, excessive output current or complete disconnection, the laser diode will definitely not light up.

2. Reverse polarity

Don't underestimate this problem, many engineers who have just started have been recruited.

Generally, laser diode has three pins: LD+, LD- and PD (photosensitive diode), but different brands have different pin orders.

Korean QSI, Japanese, and domestic definitions are slightly different. Once connected, the chip is directly burned through.

Before wiring, be sure to read the original factory specification and confirm the pin definition, especially LD and PD.

3. Too high temperature and poor heat dissipation

High-power laser diode is extremely sensitive to temperature. As long as the junction temperature exceeds 80℃, its lifetime will drop sharply.

Sometimes it is not completely burned, but the internal quantum efficiency decreases-the performance is that the light becomes dark or even not bright.

Touch the radiator after electrifying (be careful to burn your hands). If it burns badly, it is probably overheating.

Or measure the chip shell temperature to see if it exceeds the rated value;

In this case, cool for a while before measuring, and sometimes "resurrect" a little brightness.

Second, how to determine whether the laser diode is broken?

If you want to judge more accurately whether the laser diode is completely broken, you can use the following steps:

1. Measure the forward and reverse resistance with a multimeter.

Remove the diode from the circuit and measure it with a multimeter diode:

Forward conduction voltage: generally between 1.6V and 2.2V;

There should be no conduction in the reverse direction.

If both the forward and reverse directions are on or off, it is probably burnt out.

2, with a current-limiting power supply test.

Prepare an adjustable constant current source (the maximum current should not exceed 1/10 of the rated value of the chip), and slowly increase the current to see if there is weak red light (for visible light laser).

If there is no reaction at all, 80% of the internal PN junction is broken down.

3. Observe the output of monitoring diode PD.

Many laser diodes have a PD (Photosensitive Diode) for detecting output power feedback.

If the PD has no response signal after power-on, it means that the chip itself does not emit light.

Some time ago, I had a client who worked as a laser ranging module. When they were debugging, they suddenly found that a QSI 635nm laser diode did not emit light, thinking that it was burned and scrapped directly. Later, we asked them to send it back for testing, and it was found that it was not the chip that was broken, but the feedback loop driving the constant current module was broken, resulting in zero output current.

After changing the driver, the "broken" diode returned to normal light emission, and the output power did not decay at all.

So sometimes, the diode doesn't light up, which doesn't mean it's really bad, but "the external circuit doesn't give it a chance."

Although the laser diode is small, it is a "high-precision" device.

Suddenly it doesn't light up, which is not necessarily broken. It may be a current problem, a temperature problem, or even a wiring problem.

If it is determined to be broken after investigation, it can only be replaced, because the internal structure of the laser chip is extremely fine and it is impossible to repair it.