CN202019303U - Switching power supply - Google Patents

Abstract

A switching power supply, including an input electromagnetic interference filter, a rectification filter circuit, a power conversion circuit, a PWM control circuit and an output rectification filter circuit, the power conversion circuit is connected to the output rectification filter circuit through a coupling transformer, and the power conversion circuit is connected to the coupling transformer The primary coil, the output rectification and filtering circuit is connected to the secondary coil of the coupling transformer, the power conversion circuit includes power tubes S1-S4, capacitors C1-C3, inductor Lk and diodes D1-D2; the power tube S1 in the power tubes S1-S4 , power tube S3 is connected in series as a super forearm, and antiparallel diodes D1-D2, capacitors C1-C3 for external absorption; power tube S2, power tube S4 form a lagging arm; output rectification filter circuit includes field effect tube Sc, Diode Da, diode Db, diode Dc and capacitor Cc; field effect transistor Sc is connected in parallel with diode Dc, and then connected in series with capacitor Cc to form a frequency doubling circuit. The dual-channel full-bridge conversion mode has two mutually dynamically adjusted control systems, which can achieve system stability and output voltage regulation characteristics during wide-range output.

Description

switching power supply

technical field

The utility model relates to a switching power supply of an electric power system, in particular to the improvement of a power conversion circuit and an output rectifying and filtering circuit in the switching power supply.

Background technique

The switching power supply uses a circuit to control the switching tube to perform high-speed on and off. A device that converts direct current into high-frequency alternating current and supplies it to a transformer for transformation, thereby generating one or more sets of voltages required. Its main circuit includes input electromagnetic interference filter (EMI), rectification and filtering circuit, power conversion circuit, PWM (pulse width modulation) controller circuit, output rectification and filtering circuit, etc. The auxiliary circuit includes input overvoltage and undervoltage protection circuit, output overvoltage and undervoltage protection circuit, output overcurrent protection circuit, output short circuit protection circuit, etc.

At present, DC/DC (power conversion circuit) is widely used in hard switching mode (including direct diode rectification, synchronous rectification, etc.) and soft switching mode. Among them, due to hard switching, when the power tube is turned on and off, the voltage/current is not zero, and the stress of high voltage and high current greatly increases the switching loss, resulting in low converter efficiency. Therefore, the application of simple hard switching in high-efficiency power converters Very limited.

The application of soft switching greatly reduces the switching loss because the electronic stress of the switching tube is zero, which is very helpful for designers to apply higher conversion frequency and obtain higher conversion efficiency. There are also many soft switching technologies, the most widely used is the resonant soft switching technology, which is to achieve the purpose of zero voltage/zero current when turning on/off through resonance. And this kind of resonant soft switch is divided into resonant soft switch with auxiliary switch control and resonant soft switch without auxiliary switch. The resonant soft switch with auxiliary switch has certain limitations in application due to its complicated control and complicated circuit.

"Power Supply Technology Application" 2008 No. 12 (International Standard Serial Number: ISSN 0219-2713), "Development of ZVZCS PWM Soft-switching DC Power Supply Based on UC3875" (Mu Xiangyong, Chen Qingchuan, Zhu Ming), introduced the phase-shifting resonance in detail Control the electrical characteristics and basic functions of the chip UC3875, and use it as the control core to design a 1.2kW, 70kHz phase-shifting ZVZCS PWM soft-switching DC power supply. The simulation experiment was carried out, and the experiment showed that the structure of the control part with UC3875 as the core is simple and reliable, and the switching tubes of the main circuit of the power supply have realized soft switching, and overcome the shortcomings of the simple ZVS or ZCS soft switching mode, which can effectively reduce the switching tube The loss caused during the switching process is conducive to increasing the switching frequency of the power supply and reducing the volume and weight of the power supply. However, analyzing the specific technical solution provided by this document (Figure 1 of this document), it is not difficult to find that the frequency on both sides of the transformer is the same. In this way, in the case of a wide input range and a large load change, the zero-voltage turn-on of the hysteresis power tube is not ideal.

Utility model content

Aiming at the above problems, the utility model provides a switching power supply capable of controlling the accurate resonance of a lagging power tube when a phase-controlled soft switch changes in load.

The technical scheme of the utility model is: comprising an input electromagnetic interference filter, a rectification filter circuit, a power conversion circuit, a PWM control circuit and an output rectification filter circuit, the power conversion circuit is connected to the output rectification filter circuit through a coupling transformer, and the power conversion circuit connecting the primary coil of the coupling transformer, the output rectification filter circuit is connected to the secondary coil of the coupling transformer,

The power conversion circuit includes power transistors S1-S4, capacitors C1-C3, inductors Lk, and diodes D1-D2; the power transistors S1 and power transistors S3 in the power transistors S1-S4 are connected in series to form a super forearm, and reverse Connect the diodes D1-D2 in parallel and capacitors C1-C3 for external absorption; the power tube S2 and power tube S4 form a lagging arm;

The output rectifying and filtering circuit includes a field effect transistor Sc, a diode Da, a diode Db, a diode Dc and a capacitor Cc; the field effect transistor Sc is connected in parallel with the diode Dc, and then connected in series with the capacitor Cc to form a frequency multiplication circuit.

An auxiliary winding is also provided on the secondary coil, and the auxiliary winding is connected to the PWM controller circuit.

The PWM control circuit is provided with a UC3875 chip, and the power transistors S1-S4 are respectively connected to the UC3875 chip.

The utility model first adopts the DC/DC conversion of the phase control soft switch technology. The purpose of using the phase control soft switch technology is to avoid the complex application control of the resonant soft switch, and at the same time, the switch tube can be turned on under the zero voltage/zero current state. And cut-off, thus greatly reducing the switching loss of power devices, effectively improving the efficiency. Reduced weight and volume of the module.

The dual-channel full-bridge conversion mode is used to improve the efficiency of the conversion transformer, and the dual-channel full-bridge conversion can be mutually balanced and dynamically adjusted during low-voltage output and high-voltage output, which effectively improves the loss of duty cycle caused by the single full-bridge mode. The instability of the output voltage and the insufficient phase margin of the control system cause problems such as unstable operation of the system.

Through the frequency multiplication phase control unit, the phase change of the DC conversion is controlled, and the load balance of the two phase control circuits is dynamically adjusted to achieve the characteristics of the DC frequency multiplication conversion and the fundamental frequency of each phase control circuit. That is to say, the PWM switching frequency of the whole machine is doubled, and corresponding to each phase-controlled full-bridge conversion circuit, their working frequency is the basic frequency.

The utility model adopts the resonant soft switch technology without auxiliary switch, that is, the phase control soft switch technology, which has the advantages of simple basic circuit, simple control, few fault points, and high controllable stability. And it innovatively uses frequency multiplication technology, adopts double main circuit frequency multiplication phase control conversion mode, and dynamically and automatically adjusts the load changes of dual main circuits through the dual circuit phase shift control unit, effectively making up for the phase control circuit in a wide range of input. And in the case of large load changes, the zero-voltage turn-on of the hysteresis tube is not ideal.

This phase-shifting frequency multiplication technology, because it solves the accurate resonance control of the lagging power tube by the phase-controlled soft switch when the load changes, has a great advantage in terms of the conversion efficiency of the whole machine compared to other types of soft-switching technologies. The relatively simpler and more stable control main loop brings wide application adaptability, and it has a leading level in the field of high-efficiency and energy-saving applications. Compared with the existing technology, the current DC/DC applications basically use single-bridge conversion circuits. This topology is suitable for systems whose output voltage needs to be stabilized. For the application of wide-range output adjustment, it will cause excessive transformation ratio. Large, the duty cycle is lost, causing the output voltage to oscillate and be unstable, and even the voltage cannot be stabilized at low voltage. And it is easy to cause the phase margin of the control system to be insufficient and the system to work unstable. The dual-channel full-bridge conversion mode has two mutually dynamically adjusted control systems, which can achieve system stability and output voltage regulation characteristics during wide-range output.

Description of drawings

Fig. 1 is a schematic diagram of the structure of the power conversion circuit and the output rectification filter circuit in the utility model.

Detailed ways

The utility model comprises an input electromagnetic interference filter, a rectification filter circuit, a power conversion circuit, a PWM control circuit and an output rectification filter circuit, the power conversion circuit is connected to the output rectification filter circuit through a coupling transformer, and the power conversion circuit is connected to the coupling transformer The primary coil, the output rectification filter circuit is connected to the secondary coil of the coupling transformer, as shown in Figure 1:

The power conversion circuit includes power transistors S1-S4, capacitors C1-C3, inductors Lk, and diodes D1-D2; the power transistors S1 and power transistors S3 in the power transistors S1-S4 are connected in series to form a super forearm, and reverse Connect the diodes D1-D2 in parallel and capacitors C1-C3 for external absorption; the power tube S2 and power tube S4 form a lagging arm;

The output rectifying and filtering circuit includes a field effect transistor Sc, a diode Da, a diode Db, a diode Dc and a capacitor Cc; the field effect transistor Sc is connected in parallel with the diode Dc, and then connected in series with the capacitor Cc to form a frequency multiplication circuit.

An auxiliary winding is also provided on the secondary coil, and the auxiliary winding is connected to the PWM controller circuit.

The PWM control circuit is provided with a UC3875 chip, and the power transistors S1-S4 are respectively connected to the UC3875 chip.

According to Figure 1, from the topological form of the main circuit, it can be seen that it is asymmetrical. The basic control method of the four main power transistors is phase-shift control. The super forearm is S1, S3, anti-parallel diode and external absorption capacitor; the lagging arm is S2, S4, without anti-parallel diode and absorption capacitor. The control sequence of the auxiliary tube (FET) Sc is to trigger a monostable high-level signal on the rising edge of the control pulses of the super-forearms S1 and S3 to control the opening time of the auxiliary tube. Therefore, the switching frequency of the auxiliary tube is twice that of the primary tube, and it works in a double frequency state. The purpose of this circuit is to realize the zero-voltage switch of the super-forearm S1 and S3, and the zero-current switch of the lagging arm S2 and S4, so as to reduce the switching loss of the supervisor, and to improve the working frequency of the whole machine while realizing high conversion efficiency in the full load range. .

The working principle of the utility model is briefly described as follows:

When S1 and S4 are turned on, the energy of the primary side is transmitted to the secondary side. After S1 is turned off, the primary current turns to C1 and C2, C1 is charged, and C2 is discharged. At this time, the turn-off voltage on S1 rises slowly, which is a zero-voltage turn-off. Until the anti-parallel diode of the lower tube S3 is turned on. At this time, the lower tube S3 is opened, which belongs to zero pressure opening. The rising edge of the S3 turn-on pulse triggers a high level to turn on the auxiliary tube SC at the same time. At this time, the voltage of the clamp capacitor on the secondary side is added to the secondary side to become an excitation, and a higher voltage will be induced on the primary side. The function of this voltage is Make the primary side current reset quickly, and prepare conditions for the lagging arm S2, S4 zero current switch. After the primary current returns to zero, the auxiliary tube SC is turned off. Once the auxiliary tube is turned off, the secondary side is equivalent to a short circuit, and the voltage on the primary side is correspondingly zero. At this time, the voltage on the DC blocking capacitor C3 will be reversely added to the lagging arm S4 tube. During design, as long as the pulsating voltage on the DC blocking capacitor is limited The principle of amplitude and the reasonable use of the inversion characteristics of the IGBT can successfully prevent the reverse flow of the primary current of the transformer and ensure that the IGBT does not undergo reverse avalanche breakdown. Thereafter, the lagging arm S4 is turned off with zero current. Due to the existence of the leakage inductance of the primary side, the opening of the lagging arm S2 is also zero current opening. The current on the primary side is reversed and enters the cycle of the second half cycle. At this time, the rectifier tube on the secondary side is also completing the commutation. Due to the existence of the clamp capacitor Cc, the reverse peak voltage of the rectifier tube can be well suppressed.

Since the phase shifting and frequency doubling technology uses a dual main circuit phase control circuit, it is necessary to have two complete phase control full bridge main circuits, and at the same time, it is necessary to use a magnetic material with high magnetic permeability as a conversion transformer. For ordinary DC/DC There will be a certain increase in cost. The application of this technology is mainly to improve the conversion efficiency of the converter, so at present this technology is mainly used in some fields that require high conversion efficiency and work reliability.

The utility model is tested, and its technical index is as follows:

Working temperature -40 degrees to 120 degrees range;

Input voltage range 200VDC-400VDC (165VAC-265VAC);

Output voltage DC14V ~ 260V;

Rated output current 10A;

The rated output voltage is 220V/110V;

Adopt the basic conversion frequency above 100K (equivalent to the conversion frequency of the whole machine 200K);

Efficiency ≥ 95%;

When the output current of the DC/DC converter exceeds 11A, the output will be disconnected; it will return to normal when the power is turned on again; it has a short-circuit protection function.

Finally, the utility model is summarized as follows: Since the core of this technology is to control two complete phase-shifting full-bridge main conversion circuits respectively through the phase-controlled frequency multiplication circuit, and the phase-controlled technology allows the two main circuits to resonate in order, To achieve the purpose of frequency doubling. At the same time, the load current of the two loops is adjusted by dynamically adjusting the circuit, so as to achieve the purpose of synchronous and coordinated work of current sharing output. So how to rationally design these two circuits is the main difficulty of whether this project can be realized.

The design of the phase-controlled frequency multiplication circuit is based on the dedicated UC3875 chip as the main control chip of the phase-shift soft switch. The base frequency PWM signal of the conversion circuit is sent out through the UC3875. By designing a frequency multiplication circuit with a controllable and adjustable dead zone, the The PWM frequency divides to generate two PWM signals, and the phase angle between them is adjustable. Then the two-way PWM signals are used to control the two-way phase-shifting main circuit switching tubes respectively, so as to achieve the purpose of orderly conversion.

The principle of dynamic adjustment circuit design is to design an auxiliary winding of the main conversion transformer, sample the dynamic current ratio change of the main transformer, control the dynamic adjustment of the current sharing current through the feedback of the op amp, and affect the dead zone adjustment of the frequency multiplication circuit, so as to achieve dynamic The purpose of adjusting the load of double and double circuits.

Claims (3)

1. Switching Power Supply, comprise input Electromagnetic interference filter, current rectifying and wave filtering circuit, power conversion circuit, pwm control circuit and output rectifier and filter, described power conversion circuit links to each other by coupling transformer with output rectifier and filter, power conversion circuit connects described coupling transformer primary coil, output rectifier and filter connects described coupling transformer secondary coil, it is characterized in that

Described power conversion circuit comprises power tube S1-S4, capacitor C1-C3, inductor Lk and diode D1-D2; Power tube S1 among the described power tube S1-S4, power tube S3 serial connection is for leading arm, and the described diode D1-D2 of reverse parallel connection, plays the capacitor C1-C3 of external absorption; Described power tube S2, power tube S4 constitute lagging leg;

Described output rectifier and filter comprises field effect transistor Sc, diode Da, diode Db, diode Dc and capacitor C c; Described field effect transistor Sc also meets diode Dc, is connected in series with capacitor C c to constitute frequency multiplier circuit again.

2. Switching Power Supply according to claim 1 is characterized in that, also is provided with auxiliary winding on the described secondary coil, and described auxiliary winding connects described PWM controller circuitry.

3. Switching Power Supply according to claim 1 is characterized in that, is provided with the UC3875 chip in the described pwm control circuit, and described power tube S1-S4 connects the UC3875 chip respectively.