CN110380619B - Direct current conversion circuit, control method thereof and direct current conversion device - Google Patents

Abstract

The application discloses a direct current conversion circuit, a control method thereof and a direct current conversion device, wherein in the direct current conversion circuit, the output voltage condition of a DC-DC conversion unit is obtained through a voltage feedback circuit to obtain a voltage feedback signal, a main control circuit outputs a conversion control signal for controlling the DC-DC conversion unit according to the voltage feedback signal, and the direct current conversion circuit is in a closed-loop control state; in addition, a current feedback circuit is arranged to detect the output current condition of the DC-DC conversion unit so as to acquire a current feedback signal, a main control circuit controls whether to output an open loop control signal according to the current feedback signal, and under the condition of outputting the open loop control signal, the open loop control circuit interrupts voltage feedback of the voltage feedback circuit according to the open loop control signal, the direct current conversion circuit is in an open loop control state at the moment, and the direct current conversion circuit works with the maximum conversion efficiency, so that the conversion efficiency of the circuit is effectively improved. The direct current conversion device has high conversion efficiency due to the direct current conversion circuit with high conversion efficiency.

Description

A DC conversion circuit and its control method, and a DC conversion device

Technical field

The invention relates to the field of DC conversion, in particular to a DC conversion circuit and its control method, and a DC conversion device.

Background technique

A DC-DC converter is a device that converts electrical energy of one voltage value into electrical energy of another voltage value in a DC circuit. DC/DC converters are divided into three categories: step-up DC/DC converters, step-down converters DC/DC converters and buck-boost DC/DC converters, DC-DC converters have been widely used in mobile phones, MP3s, digital cameras, portable media players and other products.

In known technology, with the development of science and technology, higher requirements have been put forward for DC/DC converters, and performance requirements are developing in the direction of high efficiency and miniaturization. However, existing DC/DC conversion circuits cannot meet the high conversion efficiency. requirements, therefore, there is an urgent need to improve this technology.

Contents of the invention

The present invention aims to solve one of the technical problems described in the relevant description at least to a certain extent. To this end, one object of the present invention is to provide a DC conversion circuit, a control method thereof, and a DC conversion device, which can improve the DC conversion efficiency.

The technical solution adopted by the present invention is:

In a first aspect, the present invention provides a DC conversion circuit with high conversion efficiency, including a DC input terminal, a DC-DC conversion unit, a DC output terminal, and a voltage for obtaining a voltage feedback signal at the output terminal of the DC-DC conversion unit. A feedback circuit, a current feedback circuit for obtaining a current feedback signal at the output end of the DC-DC conversion unit, an open-loop control circuit and a main control circuit; the main control circuit is used to output and control the voltage feedback signal according to the The conversion control signal for the operation of the DC-DC conversion unit, the main control circuit is used to control whether to output an open-loop control signal according to the current feedback signal, and the open-loop control circuit is used to interrupt the open-loop control signal according to the open-loop control signal. The voltage feedback of the voltage feedback circuit;

The DC input terminal is connected to the input terminal of the DC-DC conversion unit, and the output terminal of the DC-DC conversion unit is respectively connected to the DC output terminal, the input terminal of the voltage feedback circuit, and the current feedback circuit. The input terminal is connected, the output terminal of the voltage feedback circuit and the output terminal of the current feedback circuit are connected to the input terminal of the main control circuit, and the output terminal of the main control circuit is connected to the DC-DC conversion unit The control terminal is connected to input the conversion control signal, the output terminal of the main control circuit is connected to the input terminal of the open-loop control circuit, and the output terminal of the open-loop control circuit is connected to the input terminal of the voltage feedback circuit. connect.

Further, the DC-DC conversion unit includes a DC-DC conversion circuit and a rectifier and filter circuit, the DC input end is connected to the input end of the DC-DC conversion circuit, and the output end of the DC-DC conversion circuit is connected to The input end of the rectifier and filter circuit is connected, and the output end of the rectifier and filter circuit is respectively connected to the DC output end, the input end of the voltage feedback circuit, and the input end of the current feedback circuit, and the main control circuit The output end is connected to the control end of the DC-DC conversion circuit.

Further, the DC conversion circuit further includes an LC resonant circuit, and the output end of the DC-DC conversion circuit is connected to the input end of the rectifier and filter circuit through the LC resonant circuit.

Further, the DC conversion circuit further includes a current detection circuit for obtaining a current feedback signal from an input end of the DC-DC conversion circuit. The DC input end communicates with the DC-DC conversion circuit through the current detection circuit. The input terminal is connected, and the output terminal of the current detection circuit is connected with the input terminal of the main control circuit.

Further, the DC-DC conversion circuit includes a first power tube, a second power tube and a transformer, and the negative terminal of the DC input terminal is connected with the negative output terminal of the first power tube and the negative terminal of the second power tube. The output terminals are all connected, and the control terminal of the first power tube and the control terminal of the second power tube serve as the control terminals of the DC-DC conversion circuit respectively; the positive output terminal of the first power tube and the The first input end of the transformer is connected, the positive output end of the second power tube is connected to the second input end of the transformer, the positive end of the DC input end is connected to the intermediate input end of the transformer, and the The output terminal is connected to the input terminal of the rectifier and filter circuit.

Further, the first power tube and/or the second power tube are MOS tubes, the gate of the MOS tube is the control end of the power tube, and the source of the MOS tube is the negative output end of the power tube, so The drain of the MOS tube is the positive output terminal of the power tube.

Further, the rectifier and filter circuit includes a rectifier bridge and a filter capacitor, the output end of the DC-DC conversion circuit is connected to the input end of the rectifier bridge, and the output end of the rectifier bridge is connected to the input end of the filter capacitor. connection, the output end of the filter capacitor is respectively connected to the DC output end, the input end of the voltage feedback circuit, and the input end of the current feedback circuit.

Further, the voltage feedback circuit includes an operational amplifier and a reference voltage circuit. The output terminal of the DC-DC conversion unit is connected to the non-inverting input terminal of the operational amplifier. The output terminal of the reference voltage circuit is connected to the operational amplifier. The inverting input terminal of the operational amplifier is connected to the input terminal of the main control circuit.

Further, the open-loop control circuit includes a switch tube and a signal input terminal for receiving the open-loop control signal. The signal input terminal is connected to the control terminal of the switch tube. The positive output terminal of the switch tube It is connected to the non-inverting input terminal of the operational amplifier, and the negative output terminal of the switch tube is connected to the ground.

Further, the main control circuit is also used to control whether to output the open-loop control signal according to the current feedback signal and the voltage feedback signal.

In a second aspect, the present invention provides a DC conversion device, including the high conversion efficiency DC conversion circuit.

In a third aspect, the present invention provides a control method for a DC conversion circuit, applied to the high conversion efficiency DC conversion circuit, including:

Determine whether the DC conversion circuit is overloaded according to the current feedback signal;

If it is determined to be overloaded, the main control circuit outputs an open-loop control signal to the open-loop control circuit;

The open-loop control circuit interrupts the voltage feedback of the voltage feedback circuit according to the open-loop control signal;

The main control circuit performs open-loop control on the DC-DC conversion unit.

The beneficial effects of the present invention are:

In the DC conversion circuit of the present invention, the output voltage of the DC-DC conversion unit is obtained through the voltage feedback circuit to obtain the voltage feedback signal. The main control circuit outputs the conversion control signal that controls the DC-DC conversion unit according to the voltage feedback signal. At this time, The DC conversion circuit is in a closed-loop control state; in addition, a current feedback circuit is set up to detect the output current of the DC-DC conversion unit to obtain a current feedback signal. The main control circuit controls whether to output an open-loop control signal based on the current feedback signal. In the case of signal, the open-loop control circuit interrupts the voltage feedback of the voltage feedback circuit according to the open-loop control signal. At this time, the DC conversion circuit is in the open-loop control state. The DC conversion circuit works at the maximum conversion efficiency, improving circuit utilization and effectively improving It improves the conversion efficiency of the circuit and overcomes the technical problem in the known technology that the DC/DC conversion circuit cannot meet the requirement of high conversion efficiency. On the other hand, the DC conversion device has a high conversion efficiency due to a DC conversion circuit with high conversion efficiency.

Description of the drawings

Figure 1 is a structural block diagram of an embodiment of a high conversion efficiency DC conversion circuit in the present invention;

Figure 2 is a circuit diagram of an embodiment of the DC input terminal, current detection circuit and DC-DC conversion unit in the present invention;

Figure 3 is a circuit diagram of an embodiment of an open-loop control circuit and a voltage feedback circuit in the present invention.

Detailed ways

It should be noted that, as long as there is no conflict, the embodiments and features in the embodiments of this application can be combined with each other.

Example 1

Referring to Figure 1, Figure 1 exemplarily shows a structural block diagram of a high conversion efficiency DC conversion circuit. The high conversion efficiency DC conversion circuit includes a DC input terminal 1, a DC-DC conversion unit 2, a DC output terminal 3, and is used to obtain A voltage feedback circuit 7 for a voltage feedback signal at the output end of the DC-DC conversion unit 2, a current feedback circuit 8 for obtaining a current feedback signal at the output end of the DC-DC conversion unit 2, an open-loop control circuit 6 and a main control circuit 5; The main control circuit 5 is used to output a conversion control signal that controls the operation of the DC-DC conversion unit 2 according to the voltage feedback signal. The main control circuit 5 is used to control whether to output an open-loop control signal according to the current feedback signal. The open-loop control circuit 6 is used to The voltage feedback of the voltage feedback circuit 7 is interrupted according to the open-loop control signal, so that the voltage feedback circuit 7 cannot perform voltage feedback.

Specifically, the DC input terminal 1 is connected to the input terminal of the DC-DC conversion unit 2, and the output terminal of the DC-DC conversion unit 2 is respectively connected to the DC output terminal 3, the input terminal of the voltage feedback circuit 7, and the input terminal of the current feedback circuit 8. connection, the output end of the voltage feedback circuit 7 and the output end of the current feedback circuit 8 are connected to the input end of the main control circuit 5, and the output end of the main control circuit 5 is connected to the control end of the DC-DC conversion unit 2 to input conversion control signal, the output terminal of the main control circuit 5 is connected to the input terminal of the open-loop control circuit 6, and the output terminal of the open-loop control circuit 6 is connected to the input terminal of the voltage feedback circuit 7. In actual use, the DC conversion circuit passes through the DC output terminal 3 connected to the load.

In this embodiment, the output voltage of the DC-DC conversion unit 2 is obtained through the voltage feedback circuit 7 to obtain the voltage feedback signal. The main control circuit 5 outputs a conversion control signal that controls the DC-DC conversion unit 2 according to the voltage feedback signal. At this time The DC conversion circuit is in a closed-loop control state; in addition, a current feedback circuit 8 is set to detect the output current of the DC-DC conversion unit 2 to obtain a current feedback signal. The current feedback signal can reflect the load condition of the DC conversion circuit, such as heavy load. and light load, the main control circuit 5 controls whether to output an open-loop control signal according to the current feedback signal. For example, when it is determined to be a heavy load based on the current feedback signal, an open-loop control signal is output; when it is determined to be a light load, a closed-loop control signal is output; In the case of outputting an open-loop control signal, the open-loop control circuit 6 interrupts the voltage feedback of the voltage feedback circuit 7 according to the open-loop control signal. At this time, the DC conversion circuit is in an open-loop control state, and the DC conversion circuit operates at maximum conversion efficiency, improving It improves the utilization rate of the circuit, effectively improves the conversion efficiency of the circuit, and overcomes the technical problem in the known technology that the DC/DC conversion circuit cannot meet the requirement of high conversion efficiency. When outputting the closed-loop control signal, the open-loop control circuit 6 does not interrupt the voltage feedback of the voltage feedback circuit 7, and the main control circuit 5 outputs the conversion control signal that controls the DC-DC conversion unit 2 according to the voltage feedback signal, that is, the DC-DC at this time The conversion unit 2 is in a closed-loop control state.

Specifically, a preset current value is set, and the current value of the current feedback signal is compared with the preset current value. When the current value of the current feedback signal is greater than the preset current value, the circuit is in an overload state. When the current value of the current feedback signal When the value is less than the preset current value, the circuit is in a light load state.

On the other hand, the main control circuit can also control whether to output an open-loop control signal based on the current feedback signal and voltage feedback signal, obtain the output power (P=UI) based on the current feedback signal and voltage feedback signal, and then based on the output power and the preset output The power determines the load condition of the DC conversion circuit, that is, it determines whether the circuit is lightly loaded or heavily loaded. When the circuit is overloaded, an open-loop control signal is output, and when the circuit is lightly loaded, a closed-loop control signal is output. In this embodiment, a preset output power is set, and the output power is compared with the preset output power. When the output power is greater than the preset output power, the circuit is overloaded; otherwise, the circuit is under light load. Among them, the preset output power can be set to 20% of the rated load of the DC conversion circuit, and the value of 20% can be adjusted according to the needs of the circuit. When the circuit load reaches more than 20% of the rated load, the circuit is judged to be overloaded, otherwise, the circuit is lightly loaded.

Further, referring to Figure 1, the DC-DC conversion unit 2 includes a DC-DC conversion circuit 2-1, an LC resonant circuit 2-2 and a rectifier filter circuit 2-3. The DC conversion circuit also includes a DC-DC conversion circuit for obtaining The current feedback signal at the input end of 2-1 is a current detection circuit 4, the DC input end 1 is connected to the input end of the DC-DC conversion circuit 2-1 through the current detection circuit 4, and the output end of the DC-DC conversion circuit 2-1 is through The LC resonant circuit 2-2 is connected to the input terminal of the rectifier filter circuit 2-3, and the output terminal of the rectifier filter circuit 2-3 is connected to the DC output terminal 3, the input terminal of the voltage feedback circuit 7, and the input terminal of the current feedback circuit 8 respectively. , the output terminal of the main control circuit 5 is connected to the control terminal of the DC-DC conversion circuit 2-1 to input the conversion control signal, and the output terminal of the current detection circuit 4 is connected to the input terminal of the main control circuit 5.

Among them, the current detection circuit 4 is set to detect the current at the input end of the DC-DC conversion circuit 2-1 to achieve front-end current feedback, and the main control circuit 5 can know the current situation at the input end of the DC-DC conversion circuit 2-1; An LC resonant circuit 2-2 is provided between the DC-DC conversion circuit 2-1 and the rectifier filter circuit 2-3, so that the main control circuit 5 can realize soft switching control of the DC-DC conversion circuit 2-1 and reduce the circuit load. The voltage spikes in the DC converter circuit help to further improve the conversion efficiency of the DC conversion circuit.

Preferably, with reference to Figures 1 and 2, Figure 2 exemplarily shows a circuit diagram of a DC input terminal, a current detection circuit and a DC-DC conversion unit. The DC input terminal 1 includes a first filter capacitor CE1, and the input DC voltage is passed through the first filter capacitor CE1. A first direct current DC1 is formed after filtering by a filter capacitor CE1. The current detection circuit 4 includes a current feedback resistor FR1. The current feedback resistor FR1 samples the first direct current DC1 (that is, the input current of the DC-DC conversion circuit 2-1) and transmits it to the input terminal of the main control circuit through the output terminal IS1. In this embodiment, the main control circuit includes a processor such as a microcontroller, and the processor is used as the main control center to control the operation of the DC conversion circuit.

Referring to Figures 1 and 2, the DC-DC conversion circuit 2-1 includes a first power tube M1, a second power tube M2 and a transformer T1. The negative terminal of the DC input terminal 1, that is, DC1- passes the current detection circuit 4 and the first power tube The negative output terminal of the tube M1 and the negative output terminal of the second power tube M2 are both connected. The control terminal PWM1 of the first power tube M1 and the control terminal PWM2 of the second power tube M2 are respectively used as the control terminals of the DC-DC conversion circuit. The main The output terminal of the control circuit outputs the conversion control signal to the control terminal PWM1 and the control terminal PWM2; the positive output terminal of the first power tube M1 is connected to the first input terminal A of the transformer T1, and the positive output terminal of the second power tube M2 is connected to the transformer T1. The second input terminal C is connected, the positive terminal of DC input terminal 1, DC1, is connected to the intermediate input terminal B of transformer T1 (that is, the central tap of transformer T1), and the output terminal of transformer T1 is connected to the input of the rectifier and filter circuit 2-3 end connection. In this embodiment, the DC-DC conversion circuit 2-1 is a DC-DC boost circuit, the conversion control signal is a complementary push-pull PWM signal, and a set of complementary push-pull PWM signals is used to control the first power tube M1 and the second power transistor M1. The power transistor M2 is alternately turned on to convert the first direct current DC1 into a second direct current, and increase the voltage value of the first direct current DC1 to achieve DC boosting. At the same time, the rectifier filter circuit 2-3 is set to filter out the voltage peak in the second DC power to generate a flat third DC signal. The third DC signal is output from the output terminals DC2 and DC2- of the rectifier filter circuit 2-3 to the DC output terminal, current The input terminal of the feedback circuit and the input terminal of the voltage feedback circuit.

Further, referring to Figure 2, in this embodiment, the first power tube M1 and/or the second power tube M2 are exemplarily selected as MOS tubes. The gate of the MOS tube is the control end of the power tube, and the source of the MOS tube is the power tube. The negative output terminal of the MOS tube is the positive output terminal of the power tube. The rectifier filter circuit 2-3 includes a rectifier bridge and filter capacitor CE2, and the LC resonant circuit 2-2 includes a resonant inductor Ls and a resonant capacitor CBB1. The first output terminal D of the transformer T1 is connected to one end of the resonant inductor Ls, and the resonant inductor Ls The other end is connected to one end of the resonant capacitor CBB1, the other end of the resonant capacitor CBB1 is connected to the input end of the rectifier bridge, the output end of the rectifier bridge is connected to the input end of the filter capacitor CE2, and the output end of the filter capacitor CE2 (that is, DC2 and DC2 -) are respectively connected to the DC output terminal, the input terminal of the voltage feedback circuit, and the input terminal of the current feedback circuit. In this embodiment, the rectifier bridge includes diodes D1, D2, D3 and D4, and the resonant inductor Ls is the leakage inductance of the transformer T1.

When the LC resonant circuit 2-2 is not added, the first power tube M1 and the second power tube M2 in the DC-DC conversion circuit 2-1 work in the hard switching state. When the power tube works in the hard switching state, there will be A very high voltage spike is generated in the circuit, which will also increase the switching loss of the power tube. The generated voltage spike will be proportionally transmitted to the rectifier filter circuit 2-3 through the transformer T1, and at the same time, it will be transmitted to the rectifier filter circuit 2-3. It also brings higher losses, which in turn affects the conversion efficiency of the DC conversion circuit. After setting up the LC resonant circuit 2-2, the second DC current resonates in series through the resonant inductor Ls and the resonant capacitor CBB1, causing the power tubes (the first power tube M1 and the second power tube M2) to work in a soft switching state, reducing the The voltage spike in the circuit helps to further improve the conversion efficiency of the DC conversion circuit.

Further, with reference to Figures 1 and 3, Figure 3 is a circuit diagram of an embodiment of an open-loop control circuit and a voltage feedback circuit in the present invention. The voltage feedback circuit includes an operational amplifier IC1 and a reference voltage circuit. The DC-DC conversion unit The output terminal (i.e., DC2) is connected to the non-inverting input terminal of the operational amplifier IC1, the output terminal of the reference voltage circuit is connected to the inverting input terminal of the operational amplifier IC1, and the output terminal FB1 of the operational amplifier IC1 is connected to the input terminal of the main control circuit. Among them, the reference voltage circuit includes DC power supply VCC2, voltage dividing resistors R27 and R35, which provide a reference voltage for the operational amplifier IC1. The voltage value of the reference voltage can be set freely and is not limited here. In the closed-loop control state, the operational amplifier IC1 compares the output voltage of the output terminal DC2 (that is, the voltage of the third direct current) with the reference voltage to achieve voltage feedback. When the voltage of the output terminal DC2 is greater than the set reference voltage, the operational amplifier IC1 After the amplifier IC1 is isolated by the optocoupler PC1, it outputs a voltage feedback signal from the output terminal FB1 to the main control circuit. Then the main control circuit can know that the output voltage of the DC-DC conversion unit (ie, the third DC signal) is too high and can adjust it in time. The control signal is converted to control the voltage of the third direct current signal to return to stability.

Referring to Figures 1, 2 and 3, the open-loop control circuit includes a switch tube Q2 and a signal input terminal OPEN_PWM for receiving an open-loop control signal. The signal input terminal OPEN_PWM is connected to the control terminal of the switch tube Q2. The positive terminal of the switch tube Q2 The output terminal is connected to the non-inverting input terminal of the operational amplifier IC1, and the negative output terminal of the switch tube Q2 is connected to the ground. In this embodiment, the negative output terminal of the switch tube Q2 is connected to the negative terminal DC2- of the output terminal of the rectifier and filter circuit 2-3, that is, grounded; and the switch tube Q2 is an NPN transistor, and the base of the NPN transistor is the switching tube. At the control end, the collector of the NPN transistor is the positive output terminal of the switch tube, and the emitter of the NPN transistor is the negative output terminal of the switch tube.

In this embodiment, when the current feedback signal reflects that the load of the DC conversion circuit is light load, that is, the output current of the rectifier filter circuit is small, at this time, the main control circuit outputs a low level (that is, the closed-loop control signal ) to the signal input terminal OPEN_PWM to control the DC conversion circuit in a closed-loop control state. The voltage feedback circuit can normally reflect the voltage of the third DC signal. The main control circuit outputs a push-pull PWM signal (that is, the conversion control signal) according to the voltage feedback signal. to the DC-DC conversion circuit to control the stability of the third DC signal. At this time, the duty cycle of the push-pull PWM signal is continuously adjusted to stabilize the third DC signal.

When the current feedback signal reflects that the load condition of the DC conversion circuit is heavy load, that is, the output current of the rectifier filter circuit is relatively large, at this time, the main control circuit outputs a high level (open-loop control signal) to the signal input terminal OPEN_PWM To control the DC conversion circuit to be in an open-loop control state, the open-loop control signal pulls down the level of the non-inverting input terminal of the operational amplifier IC1 through the switch Q2 to shield the voltage feedback of the third DC signal so that the main control circuit cannot detect it. Voltage feedback signal. At this time, because the main control circuit cannot detect the voltage feedback signal, it outputs the push-pull PWM signal to the maximum duty cycle for open-loop control. The maximum duty cycle at this time does not exceed 50%. The maximum duty cycle The specific value of can be set freely; it is worth noting that under open-loop control, it is necessary to ensure that the third DC voltage must be within the design range of the circuit. Since the push-pull PWM signal is always the maximum duty cycle during open-loop control, compared with During closed-loop control, the push-pull PWM signal is continuously adjusted, while open-loop control can fully transfer energy and improve the maximum utilization of the circuit, thus increasing the conversion efficiency of the circuit. In addition, this open-loop control scheme is suitable for loads carried by DC conversion circuits that have lower voltage error requirements, such as LED lights.

In addition, the DC conversion circuit also includes a power supply circuit, which is used to supply power to the main control circuit. The power supply circuit can be a power supply circuit composed of a three-terminal voltage regulator such as 78L12, 78L05, or an isolation transformer and a power management chip (UC3843, UC3844 etc.); it can also be a power supply winding added to the transformer T1 in the DC-DC conversion circuit to provide power for the main control circuit. Here, the specific implementation scheme of the power circuit is not limited.

Example 2

A DC conversion device includes the high conversion efficiency DC conversion circuit described in Embodiment 1. The DC conversion device has a high conversion efficiency due to its DC conversion circuit with high conversion efficiency. For a detailed description of the DC conversion circuit, refer to Embodiment 1 and will not be described again.

Example 3

A control method for a DC conversion circuit, applied to the high conversion efficiency DC conversion circuit described in Embodiment 1, including:

Determine whether the DC conversion circuit is overloaded according to the current feedback signal;

If it is determined to be overloaded, the main control circuit outputs an open-loop control signal to the open-loop control circuit;

The open-loop control circuit interrupts the voltage feedback of the voltage feedback circuit according to the open-loop control signal;

The main control circuit performs open-loop control on the DC-DC conversion unit.

Specifically, a preset current value is set, and the current value of the current feedback signal is compared with the preset current value. When the current value of the current feedback signal is greater than the preset current value, the circuit is in an overload state. When the current value of the current feedback signal When the value is less than the preset current value, the circuit is in a light load state.

When the DC conversion circuit is at light load, the voltage feedback is not interrupted. At this time, the DC conversion circuit is in a closed-loop control state. The output voltage of the DC-DC conversion unit is obtained through the voltage feedback circuit to obtain the voltage feedback signal. The main control circuit is based on the voltage The feedback signal output controls the conversion control signal of the DC-DC conversion unit to control the third DC signal to remain stable. In this embodiment, the conversion control signal is a complementary push-pull PWM signal, and the duty cycle of the push-pull PWM signal is continuously adjusted. to stabilize the third DC signal.

In the case of outputting an open-loop control signal, the open-loop control circuit interrupts the voltage feedback of the voltage feedback circuit according to the open-loop control signal. At this time, the DC conversion circuit is in an open-loop control state. Referring to Embodiment 1, it can be seen that at this time, it is deduced that The duty cycle of the PWM signal is the maximum duty cycle. At this time, the maximum duty cycle does not exceed 50%. The DC conversion circuit works at the maximum conversion efficiency, which improves the utilization of the circuit, effectively improves the conversion efficiency of the circuit, and overcomes the problem. There is a technical problem in the known technology that the DC/DC conversion circuit cannot meet the requirement of high conversion efficiency.

On the other hand, you can also control whether to output an open-loop control signal based on the current feedback signal and voltage feedback signal, obtain the output power (P=UI) based on the current feedback signal and voltage feedback signal, and then determine the DC based on the output power and the preset output power. Convert the load condition of the circuit, that is, determine whether the circuit is lightly loaded or overloaded. When the circuit is overloaded, an open-loop control signal is output, and when the circuit is lightly loaded, a closed-loop control signal is output. In this embodiment, a preset output power is set, and the output power is compared with the preset output power. When the output power is greater than the preset output power, the circuit is overloaded; otherwise, the circuit is under light load. Among them, the preset output power can be set to 20% of the rated load of the DC conversion circuit, and the value of 20% can be adjusted according to the needs of the circuit. When the circuit load reaches more than 20% of the rated load, the circuit is judged to be overloaded, otherwise, the circuit is lightly loaded.

The above is a detailed description of the preferred implementation of the present invention, but the present invention is not limited to the embodiments. Those skilled in the art can also make various equivalent modifications or substitutions without violating the spirit of the present invention. , these equivalent modifications or substitutions are included in the scope defined by the claims of this application.

Claims (10)

1. A DC conversion circuit with high conversion efficiency, characterized in that it includes a DC input terminal, a DC-DC conversion unit, a DC output terminal, and a voltage feedback for obtaining the voltage feedback signal of the output terminal of the DC-DC conversion unit. circuit, a current feedback circuit for obtaining the current feedback signal at the output end of the DC-DC conversion unit, an open-loop control circuit and a main control circuit; the main control circuit is used to control the DC according to the voltage feedback signal output -Conversion control signal for the operation of the DC conversion unit, the main control circuit is used to control whether to output an open-loop control signal according to the current feedback signal, and the open-loop control circuit is used to interrupt the open-loop control signal according to the open-loop control signal Voltage feedback of voltage feedback circuit; The DC input terminal is connected to the input terminal of the DC-DC conversion unit, and the output terminal of the DC-DC conversion unit is respectively connected to the DC output terminal, the input terminal of the voltage feedback circuit, and the current feedback circuit. The input terminal is connected, the output terminal of the voltage feedback circuit and the output terminal of the current feedback circuit are connected to the input terminal of the main control circuit, and the output terminal of the main control circuit is connected to the DC-DC conversion unit The control terminal is connected to input the conversion control signal, the output terminal of the main control circuit is connected to the input terminal of the open-loop control circuit, and the output terminal of the open-loop control circuit is connected to the input terminal of the voltage feedback circuit. connect. 2. The DC conversion circuit with high conversion efficiency according to claim 1, characterized in that the DC-DC conversion unit includes a DC-DC conversion circuit and a rectifier filter circuit, and the DC input terminal is connected to the DC-DC The input end of the conversion circuit is connected, the output end of the DC-DC conversion circuit is connected with the input end of the rectifier filter circuit, and the output end of the rectifier filter circuit is respectively connected with the DC output end and the voltage feedback circuit. The input terminal is connected to the input terminal of the current feedback circuit, and the output terminal of the main control circuit is connected to the control terminal of the DC-DC conversion circuit. 3. The DC conversion circuit with high conversion efficiency according to claim 2, characterized in that the DC conversion circuit further includes an LC resonant circuit, and the output end of the DC-DC conversion circuit communicates with the LC resonant circuit through the LC resonant circuit. The input terminal of the rectifier filter circuit is connected. 4. The DC conversion circuit with high conversion efficiency according to claim 2, characterized in that the DC conversion circuit further includes a current detection circuit for obtaining a current feedback signal at the input end of the DC-DC conversion circuit, so The DC input terminal is connected to the input terminal of the DC-DC conversion circuit through the current detection circuit, and the output terminal of the current detection circuit is connected to the input terminal of the main control circuit. 5. The DC conversion circuit with high conversion efficiency according to any one of claims 2 to 4, characterized in that the DC-DC conversion circuit includes a first power tube, a second power tube and a transformer, and the DC input The negative terminal of the terminal is connected to the negative output terminal of the first power tube and the negative output terminal of the second power tube. The control terminal of the first power tube and the control terminal of the second power tube serve as the control terminals of the first power tube and the second power tube respectively. The control end of the DC-DC conversion circuit; the positive output end of the first power tube is connected to the first input end of the transformer, and the positive output end of the second power tube is connected to the second input end of the transformer. The positive terminal of the DC input terminal is connected to the intermediate input terminal of the transformer, and the output terminal of the transformer is connected to the input terminal of the rectifier and filter circuit. 6. The DC conversion circuit with high conversion efficiency according to any one of claims 1 to 4, characterized in that the main control circuit is also used to control whether to output the current feedback signal and the voltage feedback signal according to the current feedback signal and the voltage feedback signal. The open loop control signal. 7. The DC conversion circuit with high conversion efficiency according to any one of claims 1 to 4, characterized in that the voltage feedback circuit includes an operational amplifier and a reference voltage circuit, and the output end of the DC-DC conversion unit is connected to The non-inverting input terminal of the operational amplifier is connected, the output terminal of the reference voltage circuit is connected to the inverting input terminal of the operational amplifier, and the output terminal of the operational amplifier is connected to the input terminal of the main control circuit. 8. The DC conversion circuit with high conversion efficiency according to claim 7, wherein the open-loop control circuit includes a switch tube and a signal input terminal for receiving the open-loop control signal, and the signal input terminal It is connected to the control terminal of the switch tube, the positive output terminal of the switch tube is connected to the non-inverting input terminal of the operational amplifier, and the negative output terminal of the switch tube is connected to the ground. 9. A DC conversion device, characterized by comprising the high conversion efficiency DC conversion circuit according to any one of claims 1 to 8. 10. A control method for a DC conversion circuit, characterized in that it is applied to the high conversion efficiency DC conversion circuit according to any one of claims 1 to 8, including: Determine whether the DC conversion circuit is overloaded according to the current feedback signal; If it is determined to be overloaded, the main control circuit outputs an open-loop control signal to the open-loop control circuit; The open-loop control circuit interrupts the voltage feedback of the voltage feedback circuit according to the open-loop control signal; The main control circuit performs open-loop control on the DC-DC conversion unit.