General component types and main functions in switching power supplies

At present, switching power supplies are widely used in almost all electronic devices due to their small size, light weight and high efficiency. It is an indispensable power supply method for the rapid development of the electronic information industry.

Designing the switching power supply is not as simple as imagined. Especially for the children's shoes developed with the contact switching power supply, his peripheral circuit is very responsible. The components used are various and the performance is different. In order to design a high-performance switching power supply, it is necessary to understand the types and main functions of the components in the switching power supply.

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

First, the resistor:

1. Sampling resistor—A sampling circuit that forms the output voltage and sends the sampled voltage to the feedback circuit.

2. Voltage equalization resistor—The voltage equalization function is also used in the symmetrical DC input circuit of the switching power supply, also known as the balance resistor.

3. Voltage divider resistors - form a resistor divider.

4. Bleed Resistor—Discharges the charge stored in the capacitor in the electromagnetic interference (EMI) filter when the power is turned off.

5. Current limiting resistor - acts as a current limiting resistor, such as a current limiting resistor for a Zener, optocoupler, and input filter capacitor.

6. Current Sense Resistor—Used with an overcurrent protection circuit to limit the output current limit of the switching power supply.

7. Shunt Resistor—Bypass the current.

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

9. Minimum Load Resistance—The minimum load resistance required to maintain proper operation of the switching power supply avoids excessive output voltage due to open load.

10. False load—A load (such as a resistance wire or a cement resistor) that is temporarily connected when testing the performance specifications of the switching power supply.

11. Filter resistor—Used as a filter resistor in LC-type filters, RC-type filters, and π-type filters.

12. Bias Resistor—Provides a bias to the control terminal of the switching power supply or stabilizes the operating point of the transistor.

13. Protection resistors - commonly used in RC type absorption circuits or VD, R, C type clamp protection circuits.

14. Frequency compensation resistor—for example, an RC type frequency compensation network that forms an error amplifier.

15. Damping resistor—Prevents resonance in the circuit.

Second, the capacitor:

1. Filter capacitors—constituting input filters, output filters, and so on.

2. Coupling Capacitor - Also known as a DC-blocking capacitor, it acts to block the DC signal and only allows the AC signal to pass. 3. Undo capacitors—such as power supply decoupling capacitors—can prevent self-oscillation. 4. Soft-Start Capacitor—This constitutes a soft-start circuit that slowly establishes the output voltage and output current during soft-start.

5. Compensation Capacitor - Forms an RC type frequency compensation network. 6. Acceleration Capacitor - used to increase the switching speed of the transistor. 7. Oscillation Capacitor - It can form an RC type or LC type oscillator. 8. Differential Capacitor—Constructs a differential circuit to obtain a sharp pulse. 9. Bootstrap capacitor—used to boost the supply voltage of the input stage and also form a voltage feedforward circuit. 10. Delay Capacitor—The resistor forms an RC delay circuit.

11. Energy storage capacitors—such as pump capacitors in polarity-reversed DC/DC converters. 12. Phase Shift Capacitor - Forms a phase shifting circuit. 13. Doubled Capacitor—The diode forms a voltage doubler rectifier circuit. 14. Noise Cancellation Capacitor—Used to filter out noise interference in the circuit.

15. Neutralize Capacitor—Remove the self-oscillation of the amplifier. 16. Capacitor to suppress interference - In EMI filters, serial mode and common mode interference can be filtered out separately. 17. Safety Capacitor—Includes X and Y capacitors.

18. X Capacitor—Filters the common mode interference generated by the primary winding and secondary winding coupling capacitors, providing a return path for the interference current coupled from the primary side to the secondary side, preventing the current from coupling to the earth through the secondary side. . 19. Y Capacitor - Filters the string-mode interference between the grids and is commonly used in EMI filters.

Third, the inductor:

1. Filter inductor - constitutes an LC filter.

2. Energy storage inductors - commonly used in buck or boost DC/DC converter circuits. 3. Oscillation Inductor - constitutes an LC type oscillator. 4. Common mode inductors—also known as common mode chokes—are commonly used in EMI filters to suppress common mode interference. 5. Series mode inductor - also known as series mode choke, it uses a single winding structure, generally connected in series in the input circuit of the switching power supply. 6. Frequency compensation inductance - constitutes LC type, LCR type frequency compensation network.

Fourth, the transformer:

1. Power frequency transformer—transforms and isolates the AC power supply, and then supplies power to the DC/DC converter (ie, switching regulator) after rectification and filtering.

2. High-frequency transformer—Storage, voltage transformation and isolation of high-frequency power supply, suitable for switching power supply without power frequency transformer.

Five, diode:

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

2. Freewheeling diodes - commonly used in buck DC/DC converters; if a freewheeling diode is connected across the windings of relays, motors, etc., a bleeder circuit can be provided for the back EMF to avoid damage to the drive tube. 3. Clamping diodes - form a VD, R, C clamp circuit that absorbs the spike voltage and protects the MOSFET power field effect transistor. 4. Blocking Diode - A diode in a clamp protection circuit, also known as a damper diode. 5. Protection Diode—Used in a half-wave rectification circuit to provide a loop to the AC during the negative half cycle. 6. Isolation Diode - Signal isolation. 7. Anti-saturation diode—Connecting the diode in series with the base of the power switch tube reduces the saturation depth of the power switch tube and increases the turn-off speed.

Sixth, rectifier bridge

The AC voltage is changed to a pulsating DC voltage and sent to the filter. The rectifier bridge can be composed of four rectifier diodes, and a finished rectifier bridge can also be used.

Seven, the regulator tube

It constitutes a simple voltage regulator circuit; it is connected to the output end of the switching power supply to stabilize the output voltage at no load; the Zener clamp, the fast recovery diode and the RC component form a primary side clamp protection circuit; constitute an overvoltage protection circuit.

Eight, transistor

A power switch tube used as a PWM modulator; a voltage control and current control loop constituting a constant voltage/constant current output type switching power supply; a cut-off control loop constituting a cut-off output type switching power supply; and an on/off forming a switching regulator Control, undervoltage, overvoltage protection, overcurrent protection and other circuits.

Nine, field effect transistor

The MOSFET is used as a power switch for a PWM modulator or a switching regulator controller.

X. Operational Amplifier

It constitutes an external error amplifier, voltage control loop, and current control loop.