CN103516202B - The pulse ON/OFF control technology of Switching Power Supply and device thereof - Google Patents

Abstract

The invention discloses a pulse switch control method and device for a switch power supply. According to the output state of the switching converter, the controller generates equal-period on or off pulses to realize the control of the switching converter: at the beginning of the clock signal, the output voltage value of the switching power supply is sampled and fed back to the voltage comparator, and compared with the reference Voltage value comparison: when the sampled output voltage is lower than the reference voltage, the switch tube is turned on within the clock cycle to increase the output voltage; on the contrary, when the sampled output voltage is higher than the reference voltage, the The switching tube is turned off in the clock cycle, so that the output voltage drops, so as to realize the pulse on/off control of the switching power supply. The invention can be used to control switching converters of various topological structures, and has the advantages that the control loop is simple and reliable, no compensation network is needed, the transient response speed is fast, and the light-load efficiency is high.

Description

Pulse ON/OFF Control Technology of Switching Power Supply and Its Device

technical field

The invention relates to an electronic power switching device, especially a pulse on/off control method and device for a switching power supply.

Background technique

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. Compared with the traditional linear regulated power supply, the switching power supply has the advantages of high efficiency and small size, which makes the switching power supply technology gradually become a hot spot in people's application and research. The rapid development of power electronic devices provides a large development space for switching power supplies, making them develop in the direction of small size, light weight, high efficiency, and high power density, which has attracted widespread attention from the industry and has broad application prospects. . In the 1980s, the computer power supply fully realized the switching power supply, and took the lead in completing the replacement of the computer power supply. In the 1990s, various electronic and electrical equipment fields, program-controlled switches, communications, electronic testing equipment, control equipment, etc. have widely used switching power supplies as their power supply, which has promoted the rapid development of switching power supply technology. The switching power supply is mainly composed of two parts: a power converter and a controller. The power converter, also known as the power circuit, mainly includes a switching device, a transformer device and a rectification and filtering circuit. Common power converter topologies include Buck converter (step-down converter), Boost converter (boost converter), Buck-Boost converter (boost-boost converter), forward converter, flyback converter Wait. The controller can detect the change of the input or output voltage of the power conversion circuit, and accordingly generate a corresponding switching signal to control the working state of the switching device of the power conversion circuit, so as to adjust the energy delivered to the load to stabilize the output of the switching power supply. The structure and working principle of the controller are determined by the control method adopted by the switching power supply. For the same power circuit topology, the adoption of different control methods will affect the steady-state accuracy and dynamic performance of the system, so the research on control methods is becoming increasingly important.

At present, many applications require switching power supplies to have a good transient response speed, but it is difficult to meet this requirement with traditional pulse width modulation (PWM) technology; in addition, portable electrical equipment and other equipment with standby functions, standby In the state, the load is light. At this time, if the effective switching frequency of the converter is reduced, the conversion loss of the converter can be reduced and the overall efficiency of the power supply can be improved.

The traditional voltage-type pulse width modulation technology is the most common modulation method of switching power supply. Its control idea is: use the error amplifier to compare the output voltage of the switching power supply with the reference voltage to obtain the error signal, and then use the comparator to compare the error signal with the fixed frequency sawtooth wave signal to obtain the pulse width signal to control the conduction of the switching device. On and off to make the output voltage reach the desired value. When the load fluctuates, due to the existence of the compensation network, the error signal changes relatively slowly, so the pulse width also changes slowly, which makes the dynamic response speed of the switching power supply slow. On the other hand, improper design of the compensation network will cause system instability, and its design process is very cumbersome, thus limiting the integration and promotion of the control circuit to a large extent.

Pulse frequency modulation (PFM) technology is another common form of switching power supply modulation method. Unlike pulse width modulation technology, it adjusts the duty cycle by changing the pulse frequency instead of the pulse width, thereby adjusting the output voltage value. However, when the input voltage or load changes in this modulation method, the operating frequency will fluctuate greatly, making it difficult to design an EMI filter.

Contents of the invention

The object of the present invention is to provide a control method of a switching power supply so as to overcome the above disadvantages of the prior art.

The technical solution of the present invention is: according to the output state of the switching converter, the controller generates equal-period on or off pulses to realize the control of the switching converter. The specific technical solution adopted is: at the beginning of the clock signal, the output voltage value of the switching power supply is sampled and fed back to the voltage comparator, and compared with the reference voltage value: when the sampled output voltage is lower than the reference voltage, then at the clock signal The switching tube is turned on during the clock cycle to increase the output voltage; on the contrary, when the sampled output voltage is higher than the reference voltage, the switching tube is turned off during the clock cycle to reduce the output voltage, thereby realizing the pulse on/off of the switching power supply. off control.

Compared with prior art, the beneficial effect of the present invention is:

1. Compared with the existing pulse width modulation technology, the present invention uses fixed-period on-pulse and off-pulse signals as the drive of the switching device. When the load of the switching power supply changes suddenly, the controller can realize continuous reading on or off If multiple clock cycles are interrupted, the switching power supply can quickly recover to a steady state;

2. Compared with the existing pulse width modulation technology, when the switching power supply of the present invention is in a light-load state, the controller will generate more off pulses, reduce the number of switching operations, reduce the effective switching frequency of the converter, and improve the conversion rate. efficiency;

3. Compared with the existing pulse frequency modulation technology, when the input voltage or load of the switching power supply of the present invention changes, the on and off pulses of the switching device are always generated in units of clock cycles, that is, the frequency spectrum of the switching signal Does not move on the frequency axis with changes in input voltage or load, thereby reducing the difficulty of designing EMI noise filters;

4. The controller directly compares the output voltage with the reference voltage without compensation network, which simplifies the control loop design, enhances the system stability, and improves the transient response speed.

Another object of the present invention is to provide a device for realizing the pulse on/off control method of the switching power supply. Under the same inventive conception, corresponding to realizing the pulse on/off control method of switching power supply, two specific implementation devices are proposed. The realization device is composed of a voltage detection device, a comparator, a D flip-flop, a clock circuit and a driving circuit; wherein: the voltage detection device, the comparator, the D flip-flop and the driving circuit are sequentially connected, and the clock circuit is connected to the D flip-flop.

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Description of drawings

Fig. 1 is a structural block diagram of a device for realizing the technical solution adopted by the control system of the present invention.

FIG. 2 is a schematic diagram of the circuit structure of Embodiment 1 of the present invention.

FIG. 3 is a schematic diagram of the corresponding relationship between the output voltage and the driving signal in Embodiment 1 of the present invention.

FIG. 4 is a time-domain simulation waveform diagram of a switching power supply in Embodiment 1 of the present invention.

FIG. 5 is a light-load time-domain simulation waveform diagram of a switching power supply in Embodiment 1 of the present invention.

FIG. 6 is a time-domain simulation waveform diagram of the output voltage of the switching power supply of Embodiment 1 of the present invention and the traditional voltage-type PWM modulation when the load changes suddenly.

FIG. 7 is a frequency-domain simulation waveform diagram of the voltage signal between the drain and the source of the power switching tube of the switching power supply according to Embodiment 1 of the present invention and the conventional voltage-type PWM modulation.

FIG. 8 is a schematic diagram of the circuit structure of Embodiment 2 of the present invention.

In Figure 4: (a) is the drive signal waveform output by the controller; (b) is the converter output voltage waveform; (c) is the clock signal waveform.

In Figure 5: (a) is the drive signal waveform output by the controller; (b) is the converter output voltage waveform; (c) is the clock signal waveform.

In Fig. 6: (a) is the output voltage waveform of the switching power supply with traditional voltage PWM modulation when the load changes suddenly; (b) is the output voltage waveform of the switching power supply according to Embodiment 1 of the present invention when the load changes suddenly.

In Fig. 7: (a) is the spectrum diagram of the voltage signal between the drain and the source of the power switch of the switching power supply modulated by traditional voltage PWM; (b) is the voltage between the drain and the source of the power switch of the switching power supply according to Embodiment 1 of the present invention Signal Spectrum Diagram.

detailed description

Embodiment one

Adoption of technical solutions:

Fig. 1 shows that the specific embodiment of the present invention is: the pulse on/off control method and device thereof of switching power supply, and its controller is mainly made up of comparator, D flip-flop, clock circuit and driving circuit. The output voltage is compared with the reference voltage after the detection device, and the output of the comparator is synchronously triggered by the D flip-flop to generate on/off pulses; the on/off pulses are used to control the switching device of the converter after passing through the drive circuit, thereby obtaining the desired stable output voltage.

Figure 2 and Figure 3 show the application of pulse on/off control technology in Buck converter.

The D trigger is synchronously triggered by the clock signal V _clk , the trigger period is T, and the result of comparing the output voltage with the comparator is sent to the D flip-flop. When the clock signal comes, if the output voltage V _o is lower than the reference voltage V _ref and the comparator outputs a high level, then the switch is turned on in this clock cycle and the output voltage rises; otherwise, if the output voltage V _o is lower than the reference voltage V _ref High, the comparator outputs a low level, then the switch tube is turned off in this clock cycle, and the output voltage drops. After the system works stably, in the stable working state, the output voltage will fluctuate in a small range near the reference voltage, and the driving pulse is a combination of on-pulse and off-pulse in a large cycle period. The switching tube needs at least one turn-on pulse and one turn-off pulse to complete a switching action, so the minimum switching period of the converter is twice the clock period. In the discontinuous inductor current mode, the proportion of the conduction pulse will increase with the increase of the load power; in the continuous conduction mode of the inductor current, the proportion of the conduction pulse is only related to the input and output voltage gain, and has nothing to do with the load.

Simulation result analysis:

Figure 4 is the result of time-domain simulation of the control method of the present invention using PIM software, the horizontal axis of Figure 4 (a) and (b) is time (ms), and the vertical axis of (a) is the driving signal amplitude (V), the vertical axis of (b) is the output voltage (V). Simulation conditions: input voltage V _in =14V, output voltage V _o =V _ref =6V, inductor L=5.6uH, capacitor C=470uF, load R=3Ω, clock frequency f _C =200kHz.

Figure 5 load R = 7.5Ω, other simulation conditions are the same as Figure 4. Comparing Figure 4 and Figure 5, it can be seen that after the load is reduced, the number of turn-off pulses increases and the effective switching frequency decreases. It can be seen that the present invention can improve the light-load efficiency of the converter by reducing the effective switching frequency.

Figure 6 is a time-domain simulation waveform diagram of the output voltage dynamic response of the switching power supply using traditional voltage-type PWM modulation and the switching power supply of the present invention in the case of sudden changes in the load, and sub-graphs (a) and (b) correspond to the traditional voltage-type PWM modulation and the present invention respectively. Invention, the horizontal axis is time (ms), and the vertical and horizontal axes are output voltage (V). In Fig. 6, the load changes step by step from 1.0A to 2.5A at 5ms, and the system response time needs 0.4ms when using traditional voltage-type PWM modulation (switching frequency f _s = 100KHz); while the transient response speed of the present invention is very fast , with almost no response time, the system goes into steady state immediately. It can be seen that the switching power supply adopting the present invention has very good load dynamic characteristics.

Fig. 7 is a simulation spectrum diagram of the voltage signal between the drain and source of the power switch tube of the switching power supply using the traditional voltage PWM modulation and the present invention, sub-graphs (a) and (b) respectively correspond to the traditional voltage type control and the present invention, horizontal The axis is the frequency (KHz), and the vertical axis is the amplitude (V) of the voltage signal between the drain and source of the power switch tube after Fourier transform (FFT). It can be seen from Figure 7 that after the present invention is adopted, the voltage signal between the drain and the source of the power switch tube has a smaller amplitude at the corresponding frequency, so the system will generate smaller electromagnetic interference (EMI) noise, which is beneficial to EMI filtering device design.

Embodiment two

Fig. 8 shows that, compared with the first embodiment, the power converter of this embodiment is a flyback converter, and the control device is the same as that of the first embodiment, except that the conduction pulse Pon has a maximum duty cycle limitation. It is also proved by simulation that the output voltage of the flyback converter adopted in the present invention is stable, the dynamic response speed is fast, and the noise of electromagnetic interference (EMI) is small.

In addition to being used to control the two power converters in the above embodiments, the present invention can also be used in Boost converters, Buck-boost converters, Cuk converters, forward converters, half-bridge converters, full-bridge converters, etc. A switching power supply composed of power circuits.

Claims (2)

1. the pulse switch control method of Switching Power Supply, is characterized in that, according to the output state of switch converters, and the cycle conductings such as controller generation or shutoff pulse, to realize the control to switch converters:

Voltage comparator is fed back at the output voltage values of clock signal start time sampling switch power supply, controller under the operating mode of uncompensated network directly with output voltage compared with reference voltage: when the output voltage sampled is lower than reference voltage, then actuating switch pipe within this clock cycle, makes output voltage rise; On the contrary, when the output voltage sampled is higher than reference voltage, then on-off switching tube within this clock cycle, makes output voltage decline, thus the pulse ON/OFF realizing Switching Power Supply controls.

2. realize a device for the pulse switch control method of Switching Power Supply described in claim 1, be made up of voltage check device, comparator, d type flip flop, clock circuit and drive circuit; It is characterized in that, voltage check device, comparator, d type flip flop and drive circuit are linked in sequence, and clock circuit is connected with d type flip flop.