Product introduction: 1. The AC power input is rectified and filtered into DC; 2. The switching tube is controlled by a high-frequency PWM (pulse width modulation) signal, and that DC is added to the primary of the switching transformer; 3. The secondary of the switching transformer induces high frequency
1. The AC power input is converted to DC power after rectification and filtering;
2. The switching tube is controlled by a high-frequency PWM (pulse width modulation) signal, and direct current is added to the primary side of the switching transformer;
3. High frequency voltage is generated on the secondary side of the switching transformer, which is supplied to the load after rectification and filtering;
4. The output part is fed back to the control circuit through a certain circuit to control the PWM duty cycle to achieve the purpose of stable output.
There is a door on the power switch. The power is on when the door is opened, and the power is stopped when the door is closed. So what is the door? Some switching power supplies use thyristors, and some use switching tubes. The performance of these two components is similar. They conduct and cut off by adding pulse signals to the base (switch tube) control pole (thyristor). When the voltage on the control rod rises, the pulse signal is sent out in half a cycle, the switching tube or thyristor is turned on, the 300V output voltage after 220V rectification and filtering is turned on, and it is sent to the secondary side through the switching transformer, and then according to each The ratio of the circuit to increase or decrease the voltage.
When the oscillation pulse occurs in the negative half cycle, the voltage of the base electrode of the power regulator tube or the control electrode of the thyristor is lower than the original set voltage, the power regulator tube is cut off, the 300V power supply is cut off, and the secondary voltage of the switching transformer is not available. At this time, the working voltage required by each loop is maintained by the discharge of the filter capacitor after the secondary rectification. When the positive half-cycle signal of the next pulse arrives, the previous process is repeated. This kind of switching transformer is called a high frequency transformer because its operating frequency is higher than 50 Hz and low frequency. So how to get the pulse to drive the switch tube or thyristor? This requires an oscillating circuit to produce. We know that the transistor has a characteristic, that is, the voltage from the base to the emitter is 0.65-0.7v, that is, the amplified state, higher than 0.7v is the saturated conduction state, -0.1V--if 0.3V works in the oscillation state, adjust the work After the point, deep negative feedback will generate negative pressure. The frequency of the oscillation tube is determined by the charging and discharging time of the capacitor on the base. The higher the oscillation frequency, the larger the output pulse amplitude, and vice versa, the smaller, which determines the output voltage of the power regulator.
So, how to stabilize the working voltage of the secondary output of the transformer? Generally speaking, a set of coils is wound on a switching transformer. The voltage obtained at the upper end of the coil is used as the reference voltage after rectification and filtering. Then, through the optocoupler, the reference voltage returns to the bottom of the oscillation tube to adjust the oscillation frequency. If the secondary voltage of the transformer increases, the output voltage of the sampling coil will also increase, and the positive feedback voltage obtained by the optocoupler will also increase. When this voltage is applied to the bottom of the oscillation tube, the oscillation frequency will decrease and the secondary output voltage will tend to stabilize