source:Industry News Popular:adapter release time:2021-07-02 10:40:20 Article author:sznbone
For original beginners who have never touched the design of power adapters, it is a good choice to repeat the design provided by the IC manufacturer, which can resolve the entire circuit caused by many design errors caused by the first time. The design failed.
Therefore, the author recommends that beginners practice the design plan provided by the IC manufacturer first, and figure out the working status of the UC3842 through the design plan provided by the IC manufacturer, and how the components and circuits that need to be designed by themselves should be designed. Begin to gradually understand the design of the flyback power adapter using UC3842, and then upgrade it to be able to independently apply other control ICs and other design requirements to be able to design the circuit more successfully.
The most primitive application of UC3842 is the primary-side feedback method to "stabilize" the output voltage. First of all, the feedback form of this circuit is the simplest and does not require an "abhorrent" optocoupler, avoiding the failure of the optocoupler. The output voltage is too high and the switch tube voltage is too high, which causes the switch tube to be burnt down. Relatively speaking, it is a feedback form with higher reliability than the optocoupler.
Why do you say that optocouplers are "deeply disgusting"? The reason is that the reliability of optocouplers is even worse than that of electrolytic capacitors. The tolerance of power supply engineers to electrolytic capacitors is approaching the limit. Then, 30 years ago, optical couplings Reliability will be intolerable. If you can't use it, you won't use it. This is the reason why the primary feedback was used in the past.
Due to the unsatisfactory load regulation rate of the output voltage fed back from the primary side of the transformer, today after the greatly improved performance of the photocoupler and the updated circuit design concept, the feedback isolation method of the photocoupler is used to enter the power adapter circuit. , If the photocoupler and circuit design patterns of the year are still used, the reliability of the power adapter must still be low.
In this way, the voltage of the auxiliary winding on the primary side and the voltage of the secondary winding are proportional to their turns ratio. Therefore, detecting the voltage of the auxiliary winding on the secondary side also indirectly detects the voltage on the secondary winding of the transformer, and also detects Output voltage. Once the primary side auxiliary winding voltage is stabilized, the output voltage will be "stabilized". This is the principle of using transformer primary side feedback to stabilize the output voltage. This method is still widely used in LED drive circuits even today, which shows that Reliability and simplicity.
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