We all know that many people buy laser diodes. Do you know how to connect the three pins of a laser diode?

1、 Why do laser diodes have three pins?

Usually, laser diodes (LDs) come with PD pins, which is why they have three pins:

1. LD positive electrode (Anode)

2. LD negative electrode (cathode)

3. PD pin (monitoring photodiode)

Among them, LD is a laser chip that emits light, and PD is a monitoring diode that detects the intensity of laser output.

2、 Common pin connection methods

Taking common packages such as TO-18 and TO-4 as examples, the general wiring rules are:

1. LD positive electrode (Anode)

Connect to the current output terminal of the driving circuit.

2. LD negative electrode (cathode)

In most cases, it is connected to the casing and connected to the negative terminal (GND) of the drive circuit.

Pay attention to checking the specifications, as some models of LD cathodes are not directly connected to the casing.

3. PD pin (photodiode)

Not mandatory, but usually used for power monitoring and feedback.

Usually connected to the feedback end of the laser driver, it plays a role in automatic power control (APC).

If you are only conducting a simple experiment, you can also skip connecting the PD pin, but be careful to control the current and avoid burning the laser tube due to overcurrent.

3、 Wiring precautions

1. Constant current source must be used to drive

Laser diodes are very sensitive to current, and even if they exceed a few tens of milliamps, they may immediately burn out.

It is recommended to use a dedicated laser driver power supply instead of a regular power supply.

2. Avoid electrostatic damage

The pins are very sensitive to static electricity, please wear an anti-static wristband when operating.

3. Confirm the pin arrangement

The pin positions of different manufacturers and models may vary (some arranged clockwise, some counterclockwise).

Before wiring, be sure to refer to the datasheet of the model, otherwise it is easy to reverse and burn out.

4. Purpose of PD pins

In precision applications such as optical communication, medical, and distance measurement, PD forms a feedback loop with the circuit to achieve stable output power.

In ordinary experiments or low-cost applications, only two pins of LD can be connected without using PD.

The three pins of a laser diode are usually the LD positive terminal, LD negative terminal, and PD pin. The positive and negative terminals of LD are connected to a constant current driver, while PD is used to monitor power. When wiring, strictly refer to the datasheet of the model and do not blindly follow "experience".