1. Main circuit
Inrush current limiter: Limit the inrush current on the input side when the power is turned on.
Input filter: Its function is to filter the clutter existing in the grid and prevent the clutter generated by the machine from feeding back to the grid.
Rectification and filtering: Directly rectify the AC power of the grid into a smoother DC.
Inverter: Convert the rectified direct current into high-frequency alternating current, which is the core part of the high-frequency switching power supply.
Output rectification and filtering: Provide stable and reliable DC power according to the needs of the load.
2. Control circuit
On the one hand, take samples from the output end, compare with the set value, and then control the inverter to change its pulse width or frequency to stabilize the output; The control circuit performs various protection measures for the power supply.
3. Detection circuit
Provide various parameters and various instrument data in operation in the protection circuit.
4. Auxiliary power supply
Realize the software (remote) startup of the power supply, and supply power for the protection circuit and the control circuit (chips such as PWM).
1. The working principle of pulse oscillator
1) Start of the pulse oscillator
The power supply provides forward bias voltage to the b pole (base) and e pole (emitter) of Q3 (transistor) through R10, R10A and R15, forcing Q3 to enter the conducting state.
2. Oscillation process of pulse oscillator
When Q3 enters the conduction state, +Vc will pass through the primary coil of the pulse transformer, the c pole, e pole of Q3, and R15 to the -Vc of the power supply. At this time, the secondary coil of the pulse transformer will generate an induced potential, and the secondary One end of the coil is connected to -Vc, and the other end is connected to the b pole of Q3 through R12 and C8, and the polarity of the induced potential and the self-inductive potential of the primary coil are of the same polarity (the upper ends of the primary coil in the figure have the same name. terminal), so that the b pole of Q3 gets a larger base current, which accelerates the conduction of Q3 until Q3 enters the saturation state. The circuit is shown in Figure 3.
When Q3 is saturated, Ic no longer changes, and the waveform is from t0 to t3 in Figure 4. After the saturation process from t3 to t4, the polarity of the self-inductive potential and the induced potential will be reversed, that is, the upper is negative and the lower is positive. The reversed potential in the secondary coil, the positive pole is added to the e pole of Q1 through R15, and the negative pole is added to the b pole of Q3 through R12 and C8, so that Q3 is in a reverse bias, prompting Q3 to quickly transition from saturation to Off state, t4 to t6 in the figure. After Q3 is turned off, the reverse potential and reverse current generated in the primary coil are quickly absorbed by the absorption circuit composed of D8, R17, and C7, from t6 to t7 in the figure. One oscillation cycle is completed. After that, the oscillator circuit will repeat the above process over and over again.
The frequency of the pulse oscillator is determined by the inductance of C8 and the connected secondary coil.
