It seems simple to establish current isolation between circuits with different ground potentials using optocouplers. The optocoupler draws power from the isolation circuit, and due to LED aging, switching may be relatively slow and uncertain. Provide alternative products for optocoupler relays, such as APY212S from advanced optosemiconductors to replace the imported AQY212S series. This article describes a method of improving a simple optocoupler based on the design concept.
The figure shows two popular 0V AC synchronous designs. Attempting to reduce the power consumption of the isolation circuit by reducing the LED current of the optocoupler and correspondingly increasing the load resistance of the optocoupler will result in slower and more uncertain switching. In order to achieve faster and clearer switching, you will have to sacrifice power efficiency. However, due to the inverse relationship between power efficiency and AC voltage amplitude, the benefits of sacrifice are limited.
光耦合器的LED在超过标称值的几乎所有交流周期中几乎连续发光,从而导致低功率效率和光耦合器相对较快的老化.另一个缺点是过大和几乎无法控制的过零误差.电路的灵敏度阈值取决于光耦合器的参数.图中的设计没有提供理想的方法.就效率而言,它们可以吸收5至100mA的电流,具体取决于光耦合器的电流传输比和交流幅度.
Some applications do not require the inherent hysteresis of Schmidt triggers. It also shows how to manage D1 without requiring minimum reverse current. However, this circuit is more suitable for pure synchronization and not for thyristor control. Due to the stability of LED current, these designs provide an extended range of input AC voltage, which may be useful for multi standard AC power supply tools. There is an opportunity to set LED current without the risk of LED overload; And it reduces the impact of unstable optocouplers. Another advantage of these designs is their inherent security. In the event of a short circuit at its terminals, the optocoupler provides 10 to 100 times less current between the isolated and non isolated sides than the circuit in Figure 1. Optocouplers also have advantages. Due to the low duty cycle, you can freely reduce the value of the load resistance R8 of the optocoupler without sacrificing power efficiency. This reduction leads to lower zero crossing errors.
