1. What is a switching power supply
2. The difference between a switching power supply and an ordinary power supply
3. The types and diagrams of common switching power supplies 4.
Series switching power supply and parallel switching power supply application
1. What is a switching power supply
Switching Mode Power Supply (English: Switching Mode Power Supply), also known as switching power supply, switching converter, is a high-frequency power conversion device. Its function is to convert a standard voltage into the voltage or current required by the user through different forms of architecture.
2. Brief description
Switching power supply is a kind of power supply that uses modern power electronic technology to control the time ratio of switching on and off to maintain a stable output voltage. Switching power supply is generally composed of pulse width modulation (PWM) control IC and MOSFET. With the development and innovation of power electronics technology, switching power supply technology is constantly innovating. At present, switching power supply is widely used in almost all electronic devices due to its small size, light weight and high efficiency. It is an indispensable power supply method for the rapid development of today's electronic information industry.
With the rapid development of power electronics technology, the relationship between power electronic equipment and people's work and life is becoming increasingly close, and electronic equipment is inseparable from a reliable power supply. In the 1980s, the computer power supply fully realized the switching power supply, and took the lead in completing the computer. In the 1990s, switching power supplies entered various electronic and electrical equipment fields one after another. Program-controlled switches, communications, electronic testing equipment power supplies, control equipment power supplies, etc. have widely used switching power supplies, which has promoted the rapid development of switching power supply technology. .
Second, the difference between switching power supply and ordinary power supply
1. Switching power supply converts direct current into high-frequency pulse current, stores electric energy in inductance and capacitance components, and uses the characteristics of inductance and capacitance to release electric energy according to predetermined requirements to change output voltage or current; linear power supply first The alternating current is reduced in voltage amplitude by a transformer, and then rectified by a rectifier circuit to obtain pulsed direct current, and then filtered to obtain a direct current voltage with tiny ripple voltage. In order to achieve high-precision DC voltage, it must be stabilized by a voltage stabilizing circuit.
2. The switching power supply can step down or boost the voltage; the linear power supply can only step down.
3. The switching power supply has high efficiency; the linear power supply has low efficiency.
4. The control speed of the linear power supply is fast and the ripple is small; the ripple of the switching power supply is large.
Three: common switching power supply types and diagrams
1. According to the technology, the connection mode of the switching tube, and the power supply technology, the switching power supply can be divided into a series switching power supply and a parallel switching power supply. The switching tube of the series switching power supply is connected in series between the input voltage and the output load, which belongs to the step-down voltage regulator circuit; while the switching tube of the parallel switching power supply is connected in parallel between the input voltage and the output load, which belongs to the step-up type Regulator circuit.
2. According to the switching type, common switching power supplies include, (PWM) flyback switching power supply, (PWM) forward switching power supply, (QR) quasi-resonant switching power supply, half-bridge switching power supply, LLC (resonant type) switch power supply.
Switching switching power supply diagram:
Four: series switching power supply and parallel switching power supply
1. Series switching power supply, DC-DC step-down power supply
1. Common to all topological duty ratio equations
2. Step-down power supply duty ratio DC transfer function
3. Calculation cycle rate T = 1/f
4. Turn-off time Toff = (1-D)*T
5. Volt-second product Et = VO*Toff
6. If r=0.4 L*I= Et/r
7. Input current IL = IO=
8. Inductance L= L*I/IO
9. Inductor rated current = (1+r/2) * IL
1. Parallel switching power supply, DC-DC boost power supply
1. Common to all topological duty ratio equations
2. Step-down power supply duty cycle DC transfer function
3. Calculation cycle rate T = 1/ f
4. On-time Ton = D*T
5. Volt-second product Et = VO* Toff
6. If r=0.4 L*I= Et / r
7. Input current IL = IO / (1-D)
8. Inductance L= L*I / IO
9. Inductor rated current = (1+r/2 )* IL
Five: Diagram of switching power supply
1. AC input (90-265V/50-60Hz)
2. Thermistor (anti-surge)
3. High-frequency common-mode inductor (suppresses electromagnetic interference in the power supply)
4. X capacitor (EMI filtering, differential mode consideration Interference signal)
5. Low-frequency common-mode inductance (suppresses electromagnetic interference in power supply)
6. Bridge stack, high-voltage electrolysis (bridge rectification)
7. High-voltage MOS
8. Power management chip
9 High-frequency transformer
10. Y capacitor (eliminates common-mode interference signal)
11. Secondary rectifier tube (Schottky diode)
12. Low frequency filter (π) 13. Secondary output power common mode
6. Example calculation and application of switching power supply
Schematic diagram of flyback power supply
Flyback power supply design essentials:
1. First determine the AC input voltage range,
To calculate the input DC high voltage VMAX;
2. Estimate VZ inverse peak voltage according to VMAX;
3. Calculate the rated inverse peak value according to the highest inverse peak value;
4. Calculate the primary and secondary winding turns ratio;
Working principle of switching power supply
5. Calculate the rectified voltage of the minimum AC input power supply;
6. The duty cycle of the minimum voltage input;
7. Calculate the load current according to the output power, current and voltage;
8. Calculate power consumption and current according to output power and efficiency;
9. Calculate the actual duty cycle according to the input current;
10. Calculate the duty cycle of the minimum voltage input;
12. Calculate volt-seconds;
13. Estimate the inductance of the primary side of the high-frequency transformer;
