How to measure the quality of chip optocouplers? What are the methods to measure the quality of optocouplers?

SMD optocoupler is a type of optocoupler. Optocoupler is also called photoelectric isolator or photoelectric coupler, or optocoupler for short. So how to measure the quality of SMD optocoupler? It is a device that uses light as a medium to transmit electrical signals. Usually, the light emitter (infrared light emitting diode LED) and the light receiver (photosensitive semiconductor tube, photoresistor) are encapsulated in the same tube shell. When an electrical signal is added to the input end, the light emitter emits light, and the light receiver generates photocurrent after receiving the light, which flows out from the output end, thus realizing the "electric-light-electric" conversion.

How to check the quality of the optocoupler:

To judge whether the optocoupler is good or not, you can measure the forward and reverse resistance of its internal diode and transistor in the circuit. The following three more reliable detection methods are available.

1. Comparison method: Remove the suspected problematic optocoupler, use a multimeter to measure the forward and reverse resistance of its internal diode and transistor, and compare it with the measured value of the corresponding pin of a good optocoupler. If the resistance value is significantly different, it means that the optocoupler is damaged.

2. Digital multimeter detection method The following uses EL817 optocoupler detection as an example to illustrate the digital multimeter detection method. The detection circuit is shown in Figure 1. During the detection, insert the + terminal {1} ​​and - terminal {2} of the diode inside the optocoupler into the c and e jacks of the Hfe of the digital multimeter respectively. At this time, the digital multimeter should be set to the NPN gear; then connect the C pole {5} pin of the phototransistor inside the optocoupler to the black test lead of the pointer multimeter, and the e pole {4} pin to the red test lead, and set the pointer multimeter to the RX1k gear. In this way, the deflection angle of the pointer multimeter pointer, which is actually the change of photocurrent, can be used to judge the condition of the optocoupler. The greater the rightward deflection angle of the pointer, the higher the photoelectric conversion efficiency of the optocoupler, that is, the higher the transmission ratio, and vice versa; if the needle does not move, it means that the optocoupler is damaged.

3. The photoelectric effect judgment method still takes the detection of EL817 optocoupler as an example, and the detection circuit is shown in Figure 2. Set the multimeter to the RX1k resistance block, and connect the two test leads to the output terminals {4} and {5} of the optocoupler respectively; then connect a 1.5V battery in series with a 50-100Ω resistor, connect the positive terminal of the battery to the {1} pin of EL817, and the negative terminal to the {2} pin, or the positive terminal to the {1} pin and the negative terminal to the {2} pin, and then observe the deflection of the pointer of the multimeter connected to the output terminal. If the pointer swings, it means that the optocoupler is good, if it does not swing, it means that the optocoupler is damaged. The larger the swing deflection angle of the multimeter pointer, the higher the sensitivity of the photoelectric conversion.

How to measure the quality of 817 optocoupler

Method 1: Use the PN junction measurement end of the digital multimeter, connect the red test lead "battery + pole" to the "1" end of the optocoupler, and the black test lead "battery - pole" to the "2" end of the optocoupler (even if the light-emitting diode of the optocoupler is forward-conducted). Use another meter to measure the resistance of the "3" and "4" ends, disconnect or connect the input end (light-emitting diode end), and the output end resistance should change significantly, indicating that the modified optocoupler is good. In addition, the multimeter at the light-emitting diode end can be replaced by a battery string current limiting resistor.

Method 2: The judgment method of the optocoupler PC817 is to first use the diode mode of the multimeter to detect the light-emitting end of the optocoupler, and then apply a voltage of about five volts to the light-emitting end to determine whether the transistor end is good or bad.

Method 3: Set the multimeter to the R*100OΩ position, connect the black pen to terminal 1 and the red pen to terminal 2, the resistance is generally 5KΩ-8KΩ, this value is the forward resistance of the light-emitting diode, the smaller the better, the reverse resistance should be as large as possible, generally above 10MΩ. Then connect the black pen to terminal 3 and the red pen to terminal 4, the resistance should be above 100KΩ, after swapping the pen, the resistance on the reverse side should be ∞, otherwise it means the optocoupler is damaged. In the switching power supply circuit, damage to the optocoupler and its auxiliary circuits is a common cause of excessive output voltage.

This does not prove that it is good, there is still one step to do. Use 2 multimeters to measure at the same time, let the light-emitting tube light up, and the photoelectric tube conduct to prove that it is good. You can use a No. 7 or No. 5 battery for the 1-2 end, and pay attention to not testing for too long.

How to use a multimeter to measure the quality of an optocoupler

1. Use the R×10 setting to measure the input and output pins in turn. Their resistance values ​​should be infinite, that is, there should be no leakage resistance between the transmitting tube and the receiving tube. 2. Use a 3V dry battery in series with a small potentiometer, connect it to the input end, rotate the potentiometer shaft to see if the resistance of the collector and emitter at the output end changes. If there is a change, it is normal.