The principle of RCC power adapter transformer

　　At present, most power adapter transformers (regardless of self-excited or other-excited circuits) are voltage stabilizing circuits controlled by the PWM system. In this type of power adapter transformer, the switching power tube is always on/off periodically, and the PWM controller only changes the pulse width of each cycle. Because the PWM controller works in the linear region, it will not saturate or cut off, will not make the pulse width of a certain cycle zero, nor will it run out of control and approach the maximum pulse width naturally set by the intermittent oscillator. Therefore, it can be said that this control is continuous, only changing the "quantity" without changing the "quality".

　　The non-periodic air purifier power adapter transformer is different. The pulse control process is not linear and continuous, but only has two states of "0" and "1": when the output voltage of the power adapter transformer exceeds the rated value, the pulse controller enters In the saturated conduction state, the switching power tube stops oscillating; when the output voltage of the power adapter transformer is lower than the rated value, the pulse controller is turned off and the switching power tube starts to oscillate. Therefore, the pulse controller has only two states of "0" and "1", and its oscillation is discontinuous and non-periodic. The time ratio of the switching power tube between the two states of "0" and "1" depends on the size of the load. When the current consumed by the load equipment decreases, the output voltage of the power adapter transformer will not decrease rapidly due to the prolonged discharge time of the filter capacitor, and the switching power tube will be in the cut-off state. The switching power will not turn on again until the output voltage drops below the rated value. through. The cut-off time of the switching power tube depends on the size of the load current. For this type of power adapter transformer, the on/off of the switching power tube is not controlled by the PWM system, but is controlled by the level switch after sampling and comparing the output voltage.

　　Therefore, this kind of periodic power adapter transformer is very suitable for power supply to equipment with intermittent load or large load change. The development cycle of the non-periodic power adapter adopts the externally excited circuit conversion structure. The voltage comparator composed of operational amplifier samples the output voltage and turns it into a control signal level to feedback and control the output pulse of the externally excited oscillator. . When the output voltage of the power adapter maintains the rated voltage, the comparator outputs a high level, the oscillator turns off the output pulse signal, and the switching power tube is turned off. When the output voltage is lower than the rated value, the comparator outputs a low-level signal after sampling and calculation, and the oscillator pulse turns on the switching power tube to make the output voltage of the power adapter return to the rated value. After the non-periodic power adapter is widely used in household appliances, in order to simplify the circuit structure, most of the circuit structure adopts the self-oscillation mode, and directly uses the voltage regulator tube as the level switch. Because its control process is the combination of the time ratio of the oscillation state and the blocking state (also known as the suppression state), it is called the oscillation suppression converter (RINGING CHOKE CONVERTER in English), or RCC type power adapter for short. The big difference in the circuit is: the PWM power adapter is composed of an independent sampling error amplifier and a DC amplifier to form a pulse width modulation circuit, while the RCC power adapter is only composed of a voltage regulator tube to control the conduction and conduction of the power tube. Shut down.

　　The basic working principle of RCC type suffix power adapter is shown in the figure below. The switching power tube Q1 and the pulse transformer T1 form a common intermittent oscillating circuit, R2 is the starting resistance, and C4 and C5 are positive feedback capacitive elements. After the circuit starts to oscillate, the secondary induction pulse of the transformer T1 is rectified by the rectifier diodes D4 and D5, and then filtered by the filter capacitors C2 and C6 to provide working voltage to the load equipment.

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