Inventory of components used in switching power supply design

At present, switching power supply is widely used in almost all electronic equipment with the characteristics of small, light weight and high efficiency. It is an indispensable power supply mode for the rapid development of the electronic information industry. The design of switching power supply is not as simple as imagined, especially for the children who just contact the research and development of switching power supply, his peripheral circuit is very responsible, which uses a wide variety of components, different performance. In order to design the switching power supply with high performance, we must understand the types and main functions of the components in the switching power supply.

This article will summarize this part of knowledge. There are many kinds of components used in the peripheral circuit of switching power supply with different performance, which can be roughly divided into general components and special components. The types and main functions of universal components in switching power supply are as follows:

First, resistor

1. Sampling resistance - constitutes the output voltage of the sampling circuit, the sampling voltage to the feedback circuit.

2. Voltage balancing resistance - plays a voltage balancing role in the symmetrical DC input circuit of the switching power supply, also known as balance resistance.

3. Voltage divider - constitute resistance voltage divider.

4. Drain resistance - when the power can be electromagnetic interference (EMI) filter capacitor stored charge discharge.

5. Current limiting resistance - A current limiting resistor used as a current limiting resistor for voltage regulators, optocouplers, and input filter capacitors.

6. Current detection resistor - Used with overcurrent protection circuit to limit the output current limit of switching power supply.

7. Shunt resistor - provides a bypass for current.

8. Load resistance: Load resistance (including equivalent load resistance) of the switching power supply.

9. Minimum load resistance - Minimum load resistance required to maintain the normal operation of the switching power supply to prevent the output voltage from being too high due to the open load.

10. False load - temporary load (such as resistance wire, cement resistance) when testing the performance indicators of the switching power supply.

11. Filter resistance - Used as filter resistance in LC filter, RC filter, π filter.

12. Bias resistance - provides bias to the control end of the switching power supply, or used to stabilize the operating point of the transistor.

13. Protection resistance - often used in RC type absorption circuit or VD, R, C clamp protection circuit.

14. Frequency compensation resistors - such as RC-type frequency compensation networks that make up error amplifiers.

15. Damping resistance -- prevents resonance in the circuit.

Two, capacitor

1. Filter capacitor - constitutes the input filter, output filter, etc.

2. Coupling capacitance-also known as straight capacitance, its action to block DC signal, only let AC signal through.

3. De-coupling capacitor - For example, de-coupling capacitor of power supply can prevent self-excited oscillation.

4. Soft start capacitor - Constitute a soft start circuit, in the process of soft start so that the output voltage and output current slowly build up.

5. Compensation capacitor-form RC frequency compensation network.

6. Acceleration capacitance - Used to increase the switching speed of the transistor.

7. Oscillating capacitor - can form RC type, LC type oscillator.

8. Differential capacitance - Constitutes a differential circuit to obtain a sharp pulse.

9. Bootstrap capacitor - Used to raise the power supply voltage of the input stage, can also form a voltage feedforward circuit.

10. Delay capacitor - and resistance constitute RC type delay circuit.

11. Energy storage capacitance-e.g. pump capacitances in polarity reversal DC/DC converters.

12. Phase-shifting capacitor - constitutes a phase-shifting circuit.

13. Double voltage capacitor - and diode constitute double voltage rectifier circuit.

14. Noise cancellation capacitor - used to filter out the noise interference in the circuit.

15. Neutralizing capacitance -- Eliminates self-excited oscillation of the amplifier.

16. Capacitor to suppress interference - in EMI filter, can filter out series mode and common mode interference respectively.

17. Safety capacitor -- including X capacitor and Y capacitor.

18. X capacitor -- can filter out common-mode interference generated by coupling capacitors of primary winding and secondary winding, and can provide a return path for interference current from primary side coupling to secondary side, preventing the current from coupling to the earth through the secondary side.

19. Y capacitor - can filter out string mode interference between power grids, often used in EMI filters.

Three, inductor

1. Filter inductance - constitute LC filter.

2. Energy storage inductor - often used in step-down or boost DC/DC converter circuit.

3. Oscillation inductance - constitute LC type oscillator.

4. Common-mode inductance, also known as common-mode choke, is often used in EMI filters to inhibit common-mode interference.

5. Series mode inductor - also known as series mode choke, it adopts single winding structure, generally in series in the input circuit of the switching power supply.

6. Frequency compensation inductance - constitute LC type, LCR type frequency compensation network.

Iv. Transformer

1. Power frequency transformer - the AC power supply for transformer and isolation, and then through the rectifier filter to DC/DC converter (switch regulator) power supply.

2. High-frequency transformer - for high-frequency power supply energy storage, voltage change and isolation, suitable for switching power supply without power frequency transformer.

Five, diode

1. Rectifier diode - low frequency rectifier, high frequency rectifier.

2. Continuous current diode - often used in step-down DC/DC converter; If the relaying diode is connected in parallel at both ends of the winding of relay and motor, it can provide a release circuit for the back electromotive force to avoid damage to the drive tube.

3. Clamp diode - Constitute VD, R, C clamp circuit, absorption peak voltage, MOSFET power field effect tube plays a protective role.

4. Blocking diode - The diode in the clamp protection circuit, also known as damping diode.

5. Protection diode - Used in the half wave rectifier circuit, in the negative half cycle to provide AC circuit.

6. Isolation diode - can realize signal isolation.

7. Anti-saturation diode - the diode is connected in series on the base of the power switch tube, which can reduce the saturation depth of the power switch tube and improve the turn-off speed.

Vi. Rectification bridge

Change the AC voltage into a pulsating DC voltage and send it to the filter. The rectifier bridge can be composed of four rectifier diodes or a finished rectifier bridge can be used.

Seven, pressure regulator pipe

Constitute a simple voltage regulator circuit; Connected to the output end of the switching power supply, used to stabilize the output voltage when no load; A side clamp protection circuit is composed of a voltage regulator, a quick recovery diode and a resistance and tolerance element. Constitute overvoltage protection circuit.

Eight, transistor

Power switch tube for PWM modulator; The voltage control and current control loops of constant voltage/constant current output switching power supply are formed. The cut-off control ring of the cut-off output switching power supply is constituted. Constitute switch regulator on/off control, under voltage, over voltage protection, over current protection circuit.

9. Field effect transistor

A MOSFET is used as a power switching tube for a PWM modulator or a switching regulator.

X. Operational amplifier

An external error amplifier, voltage control ring and current control ring are constituted.