Introduction to the types and functions of components in switching power supplies

The design of switching power supply is very familiar to power supply engineers, but it is not as simple as imagined, especially for novices. Its peripheral circuit is very complex, and the types of components used are also relatively numerous, with different performances. In order to design a high-performance switching power supply, it is necessary to understand and comprehend the types and main functions of each component in the switching power supply. The components used in the peripheral circuit of the switching power supply can be roughly divided into two categories: general components and special components. This article analyzes the types and main functions of each component in the switching power supply.

 

 

1. Sampling resistors-constitute the sampling circuit of the output voltage and send the sampled voltage to the feedback circuit;
2. Voltage equalizing resistors-play the role of voltage equalization in the symmetrical DC input circuit of the switching power supply, also known as balancing resistors;
3. Voltage divider resistors-constitute resistor dividers;
4. Discharge resistors-can discharge the charge stored in the capacitor in the electromagnetic interference (EMI) filter when the power is off;
5. Current limiting resistors-play the role of current limiting protection, such as used as current limiting resistors for voltage regulators, optocouplers and input filter capacitors;
6. Current detection resistors-used in conjunction with overcurrent protection circuits to limit the output current limit of the switching power supply;
7. Shunt resistors-provide bypass for the current;
8. Load resistors-load resistors of the switching power supply (including equivalent load resistors);
9. Minimum load resistors-the minimum load resistors required to maintain the normal operation of the switching power supply, which can avoid excessive output voltage due to open loads;
10. Dummy load - a temporary load when testing the performance indicators of a switching power supply (such as a resistor wire or cement resistor);
11. Filter resistor - used as a filter resistor in LC filters, RC filters, and π filters;
12. Bias resistor - provides bias voltage to the control end of the switching power supply, or is used to stabilize the operating point of the transistor;
13. Protection resistor - commonly used in RC absorption circuits or VD, R, and C clamp protection circuits;
14. Frequency compensation resistor - such as the RC frequency compensation network that constitutes the error amplifier;
15. Damping resistor - prevents resonance in the circuit.

 

 

1. Filter capacitors - form input filters, output filters, etc.;
2. Coupling capacitors - also known as DC blocking capacitors, which block DC signals and only allow AC signals to pass;
3. Decoupling capacitors - such as power supply decoupling capacitors, which can prevent self-oscillation;
4. Soft start capacitors - form soft start circuits, which slowly build up the output voltage and output current during the soft start process;
5. Compensation capacitors - form RC type frequency compensation networks;
6. Acceleration capacitors - used to increase the switching speed of transistors;
7. Oscillation capacitors - can form RC type and LC type oscillators;
8. Differential capacitors - form differential circuits to obtain sharp pulses;
9. Bootstrap capacitors - used to increase the power supply voltage of the input stage, and can also form voltage feedforward circuits;
10. Delay capacitors - form RC type delay circuits with resistors;
11. Energy storage capacitors-for example, pump capacitors in polarity reversal DC/DC converters;
12. Phase shifting capacitors-form phase shifting circuits;
13. Voltage doubling capacitors-form voltage doubling rectifier circuits with diodes;
14. Noise elimination capacitors-used to filter out noise interference in circuits;
15. Neutralizing capacitors-eliminate the self-oscillation of amplifiers;
16. Interference suppression capacitors-in EMI filters, they can filter out series-mode and common-mode interference respectively;
17. Safety capacitors-including X capacitors and Y capacitors;
18. X capacitors-can filter out common-mode interference generated by coupling capacitors between primary and secondary windings, and can provide a return path for interference currents coupled from the primary side to the secondary side, preventing the currents from coupling to the ground through the secondary side;
19. Y capacitors-can filter out series-mode interference between power grids, and are often used in EMI filters.

 

 

1. Filter inductor - constitutes LC filter;
2. Energy storage inductor - often used in buck or boost DC/DC converter circuits;
3. Oscillation inductor - constitutes LC oscillator;
4. Common mode inductor - also known as common mode choke, often used in EMI filter, plays a role in suppressing common mode interference;
5. Series mode inductor - also known as series mode choke, it adopts a single winding structure and is generally connected in series in the input circuit of the switching power supply;
6. Frequency compensation inductor - constitutes LC type and LCR type frequency compensation network.

 

 

1.  Power frequency transformer - transforms and isolates the AC power supply, and then supplies power to the DC/DC converter (i.e. switching regulator) after rectification and filtering;
2. High-frequency transformer-stores energy, transforms and isolates high-frequency power, suitable for switching power supplies without industrial frequency transformers;

 

 

1.  Rectifier diode-low-frequency rectification, high-frequency rectification;
2. Freewheeling diode-commonly used in step-down DC/DC converters; if a freewheeling diode is connected in parallel at both ends of the winding of a relay, motor, etc., a discharge circuit can be provided for the back electromotive force to avoid damage to the driver tube;
3. Clamping diode-constitutes a VD, R, C type clamping circuit to absorb peak voltage and protect MOSFET power field effect tubes;
4. Blocking diode-a diode in a clamping protection circuit, also known as a damping diode;
5. Protection diode-used in half-wave rectification circuits to provide a circuit for AC power in the negative half cycle;
6. Isolation diode-can achieve signal isolation;
7. Anti-saturation diode-connecting a diode in series to the base of a power switch tube can reduce the saturation depth of the power switch tube and increase the turn-off speed.

 

Rectifier bridge - converts AC voltage into pulsating DC voltage and sends it to the filter. The rectifier bridge can be composed of four rectifier diodes, or a finished rectifier bridge can be used.

Zener diode - forms a simple voltage stabilizing circuit; connected to the output end of the switching power supply to stabilize the output voltage when no load; the primary side clamping protection circuit is composed of the Zener diode, fast recovery diode and resistor and capacitor components; it constitutes an overvoltage protection circuit.