Switching power supply science knowledge
Through the circuit control switching tube for high-speed road pass and cut-off. DC into high-frequency alternating current provided to the transformer to transform, thus generating the required one or more groups of voltage!
Switching power supply can be roughly divided into isolated and non-isolated two kinds of isolated must have a switching transformer, and non-isolated may not necessarily have.
The working principle of switching power supply is.
1. AC power input rectified and filtered into DC; 2.
2. Through the high-frequency PWM (Pulse Width Modulation) signal control switching tube, the DC added to the primary switching transformer.
3. Switching transformer secondary induction of high-frequency voltage, rectified and filtered to supply the load.
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. AC power input is generally to go through a current loop of something like, filter out the interference on the grid, but also filter out the power supply on the grid interference; in the same power, switching the power of the same, the switching of the power of the same.
In the same power, the higher the switching frequency, the smaller the size of the switching transformer, but the higher the requirements of the switching tube.
The secondary of the switching transformer can have more than one winding or one winding with more than one tap, in order to get the required output.
Generally should also add some protection circuits, such as no-load, short-circuit and other protection, otherwise it may burn the switching power supply
The main components of the ATX power supply
EMI filter circuit: the main role of the EMI filter circuit is to filter out the external power grid of high-frequency pulse interference on the power supply, but also play a role in reducing the switching power supply itself to the outside world of electromagnetic interference, in ** power supply generally have a two-pole EMI filter circuit. With thousands of high-tech content (AC-DC, DC-DC, DC-AC) high-frequency switching power supply, module power supply.
A level of EMI circuit: AC power socket welded on the first level of EMI power filter circuit, which is an independent circuit board, is the first set of circuits after the input of AC power, this low-pass network consisting of chokes and capacitors can filter out high-frequency clutter on the power line and in-phase interference signals, and at the same time will also be shielded by the power supply of internal interference signals, constituting the power supply anti-electromagnetic interference road line of defence.
Secondary EMI circuit: utility power into the power supply board first through the power supply fuse, and then again through the inductance and capacitance composed of channel EMI circuit to fully filter out high-frequency clutter, and then through the current limiting resistor into the high-voltage rectifier filter circuit. Fuses can blow when the power supply is too powerful or the components are short-circuited to protect the internal components of the power supply, while the current limiting resistor contains metal oxide components, which can limit the instantaneous high current and reduce the power supply to the internal components of the current impact.
Bridge Rectifier and High Voltage Filtering: The utility power after EMI filtering, and then through the full-bridge rectifier and capacitor filtering becomes a high-voltage DC. The input AC power into a pulsed DC power, there are two forms, one is the full bridge is the four diodes packaged together, one is a bridge rectifier circuit with four discrete diodes, the role of the same, the effect is the same.
Generally speaking, there should be two or more tall barrel-shaped components near the full bridge, that is, high-voltage electrolytic capacitors, whose role is to filter out the pulsating DC alternating current components and output a relatively smooth DC. The use of high-voltage electrolytic capacitors and switching circuit design has a close relationship with its capacity is often the focus of past power supply reviews, but in fact its capacity and power supply power has nothing to do, but increase its capacity will reduce the power supply ripple interference, improve the quality of the current output of the power supply.
