Switching power supply
Which 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 supplies are generally composed of pulse width modulation (PWM) control ICs and MOSFETs. With the development and innovation of power electronics technology, switching power supply technology is constantly innovating. At present, the switching power supply is widely used in almost all electronic equipment due to its small size, light weight and high efficiency. It is an essential power supply method for the rapid development of today’s electronic information industry.
The main purpose
Its products are widely used in industrial automation control, military equipment, scientific research equipment, LED lighting and other fields.
Main type
There are two modern switching power supplies: one is DC switching power supply; the other is AC switching power supply.
The main introduction here is only the DC switching power supply. Its function is to convert the original ecological power supply (coarse power) with poor power quality, such as city power supply or battery power supply, into a high-quality DC voltage (fine power) that meets the requirements of the equipment.
The core of the DC switching power supply is the DC/DC converter. Therefore, the classification of it depends on the classification of DC/DC converters. In other words, their classification are basically the same, and also the classification of them.
DC/DC converters
It can be divided into two categories according to whether there is electrical isolation between input and output: one is called isolated DC/DC converters with isolation; the other is called non-isolated converters without isolation DC/DC converter.
Isolated DC/DC converters
It can also be classified according to the number of active power devices. There are two types of single-tube DC/DC converters: Forward and Flyback. Two-tube DC/DC converters include Double Transistor Forward Converter, Double Transistr Flyback Converter, Push-Pull Converter and Half-Bridge Converter Four kinds. The four-tube DC/DC converter is a Full-Bridge Converter.
According to the number of active power devices, non-isolated DC/DC converters can be divided into three types: single-tube, double-tube and four-tube.
Six types of single-tube DC/DC converters
Buck DC/DC converters, Boost DC/DC converters, and Buck Boost DC/DC converters. , Cuk DC/DC converter, Zeta DC/DC converter and SEPIC DC/DC converter. Among the six single-tube DC/DC converters, Buck and Boost DC/DC converters are basic, and Buck-Boost, Cuk, Zeta, and SEPIC DC/DC converters are derived from them. The double-tube DC/DC converter has a double-tube series-connected boost (Buck-Boost) DC/DC converter. Four-tube DC/DC converters are commonly used as Full-Bridge Converters.
When the isolated DC/DC converter realizes electrical isolation between output and input, it is usually realized by a transformer. Because the transformer has the function of voltage transformation, it is beneficial to expand the output application range of the converter and also facilitate the realization of multiple outputs of different voltages. , Or multiple outputs of the same voltage.
When the voltage and current ratings of the power switch tubes are the same, the output power of the converter is usually proportional to the number of switch tubes used. Therefore, the more the number of switching tubes, the greater the output power of the DC/DC converter. The output power of the four-tube type is twice that of the two-tube type, and the output power of the single-tube type is only 1/4 of that of the four-tube type.
The combination of a non-isolated converter and an isolated converter can obtain some characteristics that a single converter does not have.
Two types of DC/DC converters
According to the transmission of energy, there are two types of DC/DC converters: one-way transmission and two-way transmission. The DC/DC converter with bidirectional transmission function can transmit power from the power supply side to the load side, and can also transmit power from the load side to the power supply side.
Self-excited and other controlled types constitute DC/DC converters.self-excited converter is a converter that uses the positive feedback signal of the converter itself to realize the self-sustained periodic switching of the switching tube. For example, the Royer converter is a typical push-pull self-excited converter. an external special control circuit produce the control signal of the switching device in the other-controlled DC/DC converter.
DC/DC converter classification
According to the switching conditions of the switching tube, Hard Switching and Soft Switching constitute the DC/DC converter.
hard-switching DC/DC converters
The switching devices of hard-switching DC/DC converters turn on or turn off the circuit under the condition of voltage or current flowing, so there will be a large overlap loss during the turn-on or turn-off process, the so-called Switching loss. When the working state of the converter is constant, the switching loss is also constant, and the higher the switching frequency, the greater the switching loss.
At the same time, the oscillation of the distributed inductance and parasitic capacitance of the circuit during the switching process will also cause additional loss. Therefore, The switching frequency of hard-switching DC/DC converters cannot be too high.
Soft-switching DC/DC converter
The switch tube of the soft-switching DC/DC converter, during the turn-on or turn-off process, or the voltage applied to it is zero, that is, zero-voltage switching, or through the switch tube The current is zero, that is, zero current switching. This soft-switching method can significantly reduce the switching loss and the oscillation. So that greatly increase the switching frequency, creating conditions for the miniaturization and modularization.
Power field effect tube (MOSFET) is a switching device with more applications. It has a higher switching speed, but at the same time it also has a larger parasitic capacitance. When turned off it, we fully charge its parasitic capacitance under the action of external voltage.
If we did not discharge this part of the charge before turning on it, we will consume it inside the device, which is the capacitive turn-on loss. In order to reduce or eliminate this loss, the power FET should adopt the zero voltage turn-on method (ZVS). Insulated Gate Bipolar Transistor (IGBT) is a composite switching device. The tailing of the current during turn-off will lead to a large turn-off loss. If the current flowing through it is reduced to Zero, the switching loss can be significantly reduced, so the IGBT should adopt a zero current (ZCS) turn-off method.
Under the zero voltage condition we turned off IGBT and reduced the turn-off loss. But when we turned on the MOSFET under the zero current condition, we can’t reduce the capacitive turn-on loss. ResonantConverter, RC, Qunsi-Tesonant Converter, QRC, Multi-ResonantConverter, MRC, ZVS PWM Converter, ZCS PWM Converter, ZVT PWM converters, and ZVT PWM converters are all soft-switching DC converters. The development of power electronic switching devices and zero-switching converter technology has promoted the development of high-frequency switching power supplies.
Basic component
The switching power supply is roughly composed of the main circuit,
It consists of four parts: control circuit, detection circuit, and auxiliary power supply.
Main circuit
Impulse current limit: limit the impulse current on the input side at the moment the power is turned on.
Input filter: Its function is to filter the clutter that exists in the power grid and prevent the clutter generated by the machine from being fed back to the power grid.
Rectification and filtering: Directly rectify the AC power of the grid into a smoother DC.
Inverter: Convert the rectified DC power into high-frequency AC power, which is the core part of the high-frequency switching power supply.
Output rectification and filtering: Provide a stable and reliable DC power supply according to the needs of the load.
Control circuit
On the one hand, we take samples from the output terminal and compared with the set value. And we control the inverter to change its pulse width or pulse frequency to stabilize the output. On the other hand, according to the data the test circuit provided, the protection circuit identified it. In order to provide The control circuit carries out various protection measures for the power supply.
Detection circuit
Provide various parameters and various instrument data in operation in the protection circuit.
Auxiliary power supply
Realize the software (remote) start of the power supply, and supply power for the protection circuit and the control circuit (chips such as PWM).
Main classification
People in the field of switching power supply technology are developing related power electronic devices,
320W single group switching power supply
320W single group switching power supply
While developing switching frequency conversion technology, the two promote each other. Promoting the development of switching power supply in the direction of light, small, thin and so on. And anti-interference with a growth rate of more than two digits every year. AC/DC and DC/DC constitute the switching power supplies.
Miniature low power switching power supply
Switching power supplies are becoming popular and miniaturized. Switching power supplies will gradually replace all applications of transformers in life. In digital display meters, smart meters, mobile phone chargers, and so on, we use low-power micro-switching power supplies firstly. At this stage, the country is promoting the construction of smart grids, and the increasing requirements for electric energy meters. Switching power supplies will gradually replace the application of transformers in electric energy meters.
Reversing series switching power supply
The reversing series switching power supply and the general series switching power supply differs in the output voltage.
What is the difference between PFC power supply and switching power supply?
Among the PFC switching power supplies, the switching regulated power supply is a very important part. The switching power supply function in the PFC and the ordinary switching power supply differs in power supply.
After rectification, the power supply of the chopper we use unfiltered pulsating positive half-cycle voltage. Due to the series of “switching” work of the chopper, we chopp the pulsating positive voltage into a current waveform. The characteristics are:
- The current waveform is discontinuous, and its envelope and the phaseis the same as the voltage waveform.
- Due to the effect of chopping, the half-wave pulsating DC power becomes high-frequency “AC” power. we should rectifie high-frequency “AC” power again before stabilized it.
- The power system achieves that the AC voltage and current are in phase and the voltage and current waveforms are in line with the sinusoidal waveform. Which not only solves the problem of power factor compensation, but also solves EMC and EMI problem. After rectifiering, this high-frequency “AC” power, filtered into a DC voltage (power supply). In some materials, B+PFC is this DC voltage.The B+PFC voltage output by the chopper is generally higher than the original. The reason to choose high voltage is: its line voltage drop and the filter capacitor capacity is small.
At present, in the PFC switching power supply part, the chopper tube (K) has two working modes:
- Continuous conduction mode (CCM): The operating frequency of the switching tube is constant, and the conduction duty cycle (coefficient) changes with the amplitude of the chopping voltage.
- Discontinuous conduction mode (DCM): The operating frequency of the chopper switch tube changes with the size of the voltage(the “on” and “off” times in each switching cycle are equal).
an IC completes The PFC and the excitation part.
