what is a laser diode?
Semiconductor laser diode emitting red light when working, the wavelength is about 600nm, used in laser pointer, bar code reader, laser printer, CD and VCD machine and other circuits.
Semiconductor laser diode is the core device of laser head, and is widely used in CD and laser disc player.
l The symbols and internal structure of common laser diodes.
There are two diodes in the interior. LD is a laser transmitter tube, PD is a light power detection tube, and the negative feedback circuit can be used to automatically control the power of the laser diode. Common cathode is the most commonly used. Laser diodes are mostly double structured gallium arsenide three compound semiconductor laser diodes. It is a near infrared laser tube with a wavelength of about 780nm and a rated power of 3~5mW. The shape has two kinds of flat head and oblique head. For different circuits, the edge notch is a positioning mark, so as not to be wrong. The laser diode has the advantages of small volume, light weight, low power consumption, simple driving circuit, convenient modulation, mechanical shock and vibration resistance. But it is extremely sensitive to overvoltage, overcurrent and electrostatic interference. If used without attention, it will cause damage to the resonant cavity and cause permanent damage.
l Detect a laser diode
(1) determine the order of the arrangement of the pins. The multimeter is placed in the R*1 thousand ohm file. According to the method of detecting the normal diode and the reverse resistance, the arrangement order of the laser diode can be determined.
The forward voltage drop of the laser diode LD is larger than that of the ordinary diode, so the forward resistance is large, and the multimeter pointer meter is deflected to the right. And the right deflection is large, and the reverse resistance should be infinite. The resistance is infinitely large. The forward voltage drop of the PD diode is small, so the forward electric pointer is directed by a small multimeter.
(2) discriminant method of laser diode
1) measuring PD reverse resistance to diode LD plus voltage PD resistance should be significantly reduced, indicating LD.PD all are good.
2) increase the voltage of diode LD and reduce the luminescence at 1.6V; when 2.8V, the luminescence is stronger and the current is measured. If in 35~ 60mA, light is strong, then it is good, weak is bad, no light is bad.
3)Observe with CD-ROM, do not install CD-ROM, dismantle the rear cover, and observe whether there are dark red spots during the visit.
4) using a dedicated laser power detector to directly detect the mirror, aging when the general power is less than 0.1mW.
A digital multimeter is used to monitor the voltage drop of the load resistance in the driving circuit and calculate the current. When the current exceeds 100mA, the dimming power control potentiometer has a very small change in current, and it will break or open if the current is too large or too small.
Remove laser diode, measure positive and reverse resistance. In normal, the reverse is infinity, and the forward is 20~ 30k2. If it is greater than 75k2, the characteristic is not good; if it is greater than 90k2, it can not be used (this method is suitable for selecting laser diodes).
If you want to know more, our website has product specifications for the laser diodes, you can go to ALLICDATA ELECTRONICS LIMITED to get more information