What is a high-speed optocoupler

Like a photocoupler, it assembles light-emitting diodes and phototransistors together and uses light signals to transmit information, realizing electrical->optical->electrical transmission of circuit signals (photocouplers). This is for the purpose of circuit The input and the electricity are in a completely isolated state to realize the electrical isolation of the input and output parts, and improve its anti-interference ability, reliability and stability. This kind of information transmission method is better than all ordinary transformers and relays for signal transmission. The solution, but its advantage lies in high speed, that is, the signal transmission speed is fast, which is very commonly used in the design of the signal transmission speed.

We use 6N137 to explain in detail. Other products can be deduced by analogy. Please refer to the product manual for details. There is an 850 nm wavelength AlGaAs LED and an integrated detector. The detector consists of a photodiode and a high-gain linear operational amplifier. It is composed of a Schottky clamped open-collector triode.

Its working principle is that the signal is input from pin 2 and pin 3, the light-emitting diode emits light, and it is transmitted to the photodiode through the on-chip optical channel. The reverse-biased phototube is turned on after the light is illuminated, and is sent to the AND gate after the current-voltage conversion. One input terminal, and the other input of the AND gate is the enable terminal. When the enable terminal is high, the AND gate outputs a high level. After the output transistor is reversed, the photoelectric isolator outputs a low level. When the input signal current is less than the trigger threshold or the enable terminal is low, the output is high, but this logic high is an open collector, and a pull-up resistor or voltage adjustment circuit can be added to the receiving circuit.

(1) Features and advantages

It has the characteristics of unidirectional transmission of information, bandwidth, low parasitic feedback, strong noise cancellation ability, and good anti-electromagnetic interference performance. Therefore, it has been more and more widely used in both digital and analog circuits. It also has the advantages of small size, close coupling, low driving power, fast action speed, and wide operating temperature range. With the development of semiconductor devices, various performance parameters will be improved.

These products have strong and stable anti-noise ability, highly flexible supply voltage operating range and a variety of compact package options, and have high common mode rejection and short propagation delay, provide strong and efficient operation, can reduce PCB board Space, used in AC and DC brushless motor drives, industrial inverters, air conditioners, renewable energy converters, sewing machines and switching power supply IPM interfaces, as well as gate drive applications and general digital isolation; short propagation delay, providing fast switching speed , Thereby reducing the dead time and improving the efficiency and precision of movement. Its response speed reaches the order of ns, which greatly expands the application of photocouplers in digital signal processing.

(2) Need to pay attention to parameters (common photocoupler parameters)

A, INPUT DATA

B, Operating Voltage Range

C, Input DC Voltage

D, Type Input Current

E, Transmission Frequency

F, OUTPUT DATA

G, Operating Voltage Range

H, Continuous Load Current

It also includes parameters such as conversion rate, slew rate, fan-out coefficient, maximum input and output circuit, and operating temperature.

(3) Application fields of high-speed optocouplers

A. It can be used for PLC high-speed counter, servo motor control, rotary encoder control, grating ruler output and PLC and single-chip pulse signal conversion; PLC, servo motor control system anti-interference processing; various standard and non-standard pulse signals interchange; Arbitrary waveform (sine wave, triangle wave, irregular waveform) to square wave pulse signal, etc.

B. In the switch circuit, it is often required to have a good electrical isolation between the control circuit and the switch, which is difficult to achieve for general electronic switches, but it is very easy to achieve with it.

C. It is used for bistable output circuit. Since light-emitting diodes can be connected in series with two emitter circuits respectively, it can effectively solve the problem of output and load isolation.

D. Compose various logic circuits. Because its anti-interference performance and isolation performance are better than transistors, the logic circuit formed by it is more reliable.

E. Applied to digital circuits, it can amplify pulse signals.

F. Used in high-voltage control, replacing transformers, replacing contact relays, and used in A/D circuits and other occasions.

G. It is used in bistable output circuit. Since light-emitting diodes can be connected in series into two emitter circuits respectively, it can effectively solve the problem of output and load isolation.

H. Used in linear circuits, with high ground linearity and excellent electrical isolation performance.