CN112787505A - DC-DC converter and control circuit and control method thereof - Google Patents
DC-DC converter and control circuit and control method thereof Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of DC power input into DC power output
- H02M3/02—Conversion of DC power input into DC power output without intermediate conversion into AC
- H02M3/04—Conversion of DC power input into DC power output without intermediate conversion into AC by static converters
- H02M3/10—Conversion of DC power input into DC power output without intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/145—Conversion of DC power input into DC power output without intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M3/155—Conversion of DC power input into DC power output without intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/156—Conversion of DC power input into DC power output without intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
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Abstract
The application discloses a DC-DC converter, a control circuit and a control method thereof, wherein the control circuit comprises a current detection circuit, an error amplifier, a mode switching circuit and a drive circuit, the current detection circuit obtains a detection signal by detecting the current flowing through a power transistor, the error amplifier is used for obtaining an error amplification signal according to the output voltage of the DC-DC converter and a reference voltage, the mode switching circuit is used for comparing the detection signal with a preset voltage, different reference signals are generated according to the comparison result, different driving signals are generated by the driving circuit according to the different reference signals and the error amplification signal so as to control the power transistor to work in a switching mode or a linear mode, when the DC-DC converter is operated in a light load state, the power transistor is operated in a linear mode, the ripple of the output voltage and the static current of the circuit and the EMI interference caused by the switch can be reduced.
Description
Technical Field
The invention relates to the technical field of power electronics, in particular to a DC-DC converter and a control circuit and a control method thereof.
Background
One or more DC-DC converters may be used in portable computers, mobile phones, personal digital assistants, and other portable or non-portable electronic devices. A DC-DC converter is a voltage converter that converts an input voltage to a fixed output voltage. Existing DC-DC converters can be used in a variety of load scenarios, with relatively high and low differences between different loads, and small and large loads varying according to specific applications, systems, and/or user requirements.
DC-DC converters can be classified into two types, linear mode voltage regulators and switch mode voltage regulators, depending on the operating mode, and different DC-DC converters are suitable for different loads. For example, the linear mode voltage regulator has the advantages of low noise, small quiescent current and the like when in small load; the switch mode voltage regulator can provide accurate output voltage under the condition of large load and has higher efficiency.
For the application scenario of load variation, the conventional approach is to use a linear mode regulator, such as LDO, for small loads and a switch mode regulator for large loads, switching between the two converters depending on the conditions. This approach requires the use of two DC-DC converters, requires more components, and requires additional pins for switching between converters, which is costly and complex.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide a DC-DC converter having both a linear mode and a switching mode, and a control circuit and a control method thereof.
According to a first aspect of the present invention, there is provided a control circuit of a DC-DC converter, the DC-DC converter comprising a power transistor and an inductance connected to each other, the control circuit for providing a drive signal to control a state of the power transistor, wherein the control circuit comprises: a current detection circuit for detecting a load current flowing through the power transistor to obtain a detection signal; the error amplifier is used for obtaining an error amplification signal according to the output voltage of the DC-DC converter and a reference voltage; the mode switching circuit is used for comparing the detection signal with a preset voltage and generating different reference signals according to a comparison result; and the driving circuit is used for controlling the power transistor to work in a switching mode or a linear mode according to the different reference signals and the error amplification signals, wherein the different reference signals at least comprise reference voltage or triangular wave signals.
Preferably, when the detection signal is greater than the preset voltage, the driving circuit generates a first driving signal according to the triangular wave signal and the error amplification signal, the power transistor operates in a switching mode in response to the first driving signal, and when the detection signal is less than the preset voltage, the driving circuit generates a second driving signal according to the reference voltage and the error amplification signal, and the power transistor operates in a linear mode in response to the second driving signal.
Preferably, when the detection signal is greater than the preset voltage, the driving circuit operates as a comparator, and when the detection signal is less than the preset voltage, the driving circuit operates as an error amplifier.
Preferably, the mode switching circuit includes: a comparator for comparing the detection signal with the preset voltage; the first end of the first switch tube is used for receiving the triangular wave signal, and the control end of the first switch tube is connected with the output end of the comparator and used for providing the triangular wave signal to the driving circuit when the first switch tube is conducted; and a second switch tube, a first end of which is used for receiving the reference voltage, a control end of which is connected with the output end of the comparator and is used for providing the reference voltage for the driving circuit when the comparator is conducted, wherein when the detection signal is greater than the preset voltage, the comparator conducts the first switch tube and turns off the second switch tube, and when the detection signal is less than the preset voltage, the comparator conducts the second switch tube and turns off the first switch tube.
Preferably, the comparator is implemented by a hysteresis comparator.
Preferably, the first switch tube is selected from an N-type metal oxide semiconductor field effect transistor, and the second switch tube is selected from a P-type metal oxide semiconductor field effect transistor.
Preferably, the control circuit further comprises: an oscillator for generating an oscillation signal; and a ramp generator for generating the triangular wave signal according to the oscillation signal.
According to a second aspect of the present invention, there is provided a control method of a DC-DC converter including a power transistor and an inductance connected to each other, wherein the control method includes: detecting a current flowing through the power transistor to obtain a detection signal; obtaining an error amplification signal according to the output voltage of the DC-DC converter and the reference voltage; comparing the detection signal with a preset voltage, and generating different reference signals according to a comparison result; and controlling the power transistor to work in a switch mode or a linear mode according to the different reference signals and the error amplification signals, wherein the different reference signals at least comprise a reference voltage or a triangular wave signal.
Preferably, the controlling the power transistor to operate in a switching mode or a linear mode according to the different reference signal and the error amplification signal includes: when the detection signal is greater than the preset voltage, a first driving signal is generated according to the triangular wave signal and the error amplification signal, the power transistor responds to the first driving signal and works in a switch mode, when the detection signal is less than the preset voltage, a second driving signal is generated according to the reference voltage and the error amplification signal, and the power transistor responds to the second driving signal and works in a linear mode.
According to a third aspect of the present invention, there is provided a DC-DC converter comprising a power transistor and an inductance connected to each other; and the control circuit controls the output voltage by controlling the state of the power transistor.
The DC-DC converter, the control circuit and the control method thereof of the embodiment of the invention have the following beneficial effects.
The control circuit comprises a current detection circuit, an error amplifier, a mode switching circuit and a driving circuit, wherein the current detection circuit obtains a detection signal by detecting current flowing through the power transistor, the error amplifier is used for obtaining an error amplification signal according to the output voltage of the DC-DC converter and a reference voltage, the mode switching circuit is used for comparing the detection signal with a preset voltage and generating different reference signals according to the comparison result, and the driving circuit generates different driving signals according to the different reference signals and the error amplification signal so as to control the power transistor to work in a switching mode or a linear mode. The traditional method can realize the switching between the linear mode and the switch mode only by using two DC-DC converters and a control circuit, but the invention can be realized only by using one control circuit, thereby greatly reducing the circuit cost.
In addition, the control circuit of the invention switches the linear mode and the switch mode according to the load state, for example, when the DC-DC converter operates in a small load state, the power transistor is controlled to operate in the linear mode, the ripple voltage of the output voltage of the DC-DC converter and the EMI interference of the circuit can be kept at a low level, and the quiescent current consumed by the control circuit can be reduced. When the DC-DC converter works in a heavy load state, the power transistor is controlled to work in a switching mode, and the efficiency of the DC-DC converter is improved.
Finally, the mode switching circuit of the embodiment of the invention provides different reference signals to the driving circuit through comparison of the detection signal and the preset voltage so as to realize switching between the linear mode and the switch mode, and compared with the existing DC-DC converter which simultaneously comprises the LDO circuit and the PWM circuit, the mode switching circuit needs fewer elements, does not need to add extra pins and has lower circuit cost.
Drawings
The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:
fig. 1 shows a schematic structural diagram of an electronic device according to a first embodiment of the invention;
fig. 2 shows a circuit schematic of a DC-DC converter according to a second embodiment of the invention;
fig. 3 shows a schematic diagram of the mode switching circuit in fig. 2.
Detailed Description
Various embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Like elements in the various figures are denoted by the same or similar reference numerals. For purposes of clarity, the various features in the drawings are not necessarily drawn to scale.
It should be understood that in the following description, "circuitry" may comprise singly or in combination hardware circuitry, programmable circuitry, state machine circuitry, and/or elements capable of storing instructions executed by programmable circuitry. When an element or circuit is referred to as being "connected to" another element or element/circuit is referred to as being "connected between" two nodes, it may be directly coupled or connected to the other element or intervening elements may be present, and the connection between the elements may be physical, logical, or a combination thereof. In contrast, when an element is referred to as being "directly coupled" or "directly connected" to another element, it is intended that there are no intervening elements present.
The invention is further illustrated with reference to the following figures and examples.
Fig. 1 shows a schematic structural diagram of an electronic device according to a first embodiment of the present invention. As shown in fig. 1, the electronic apparatus 100 includes a power supply 101, a DC-DC converter 102, and a load 103. The electronic device 100 may be a notebook computer, a mobile phone, a personal data assistant, or other devices. The power source 101 may be various power sources such as a lithium ion battery, and is used for providing an input voltage Vin to the DC-DC converter 102. The DC-DC converter 102 converts an input voltage Vin to a fixed output voltage Vout and supplies it to a load 103. For convenience of explanation, only one DC-DC converter and load are shown in fig. 1, but it is understood that the electronic apparatus 100 may actually have a plurality of DC-DC converters and a plurality of loads.
Fig. 2 shows a circuit schematic of a DC-DC converter according to a second embodiment of the invention. As shown in fig. 2, the DC-DC converter 102 includes a main circuit and a control circuit 201. The main circuit comprises an inductor L1, a power transistor M1, a freewheeling diode D1 (or a synchronous rectification transistor is adopted), a sampling resistor Rs and an output filter capacitor Co. The control circuit 201 controls the output voltage Vout of the DC-DC converter by controlling the state of the power transistor M1 in the main circuit or simultaneously controlling the states of other transistors. The power transistor M1 may be various transistors such as NPN darlington transistor, NPN bipolar transistor, PNP bipolar transistor, and N-type MOSFET and P-type MOSFET, etc. The control circuit 201 is packaged as a chip IC, for example. In some embodiments, the power transistor M1 in the main circuit is also packaged in the chip IC.
In the main circuit, a sampling resistor Rs, a power transistor M1 and an inductor L1 are connected in series between an input voltage Vin and an output voltage Vout in sequence. In this embodiment, the power transistor M1 is an N-type MOSFET (metal oxide semiconductor field effect transistor). The cathode of the freewheeling diode D1 is connected between the inductor L1 and the drain of the power transistor M1, and the anode of the freewheeling diode D1 is grounded.
The control circuit 201 includes a current detection circuit 211, an error amplifier 212, a drive circuit 213, and a mode switching circuit 214.
The current detection circuit 211 is realized by, for example, an operational amplifier having an inverting input terminal connected to the intermediate node of the power transistor M1 and the sampling resistor Rs and a non-inverting input terminal connected to the other end of the sampling resistor Rs, thereby obtaining a detection signal Vs amplified by the operational amplifier 211 corresponding to the load current flowing through the power transistor M1. In this embodiment, the detection signal Vs Is Rs n, where Is the load current flowing through the power transistor M1, Rs Is the resistance of the sampling resistor, and n Is the amplification factor of the operational amplifier 211.
The error amplifier 212 is used for comparing the output voltage Vout with a reference voltage Vref and obtaining an error amplified signal Vc therebetween. In one embodiment, the error amplifier 212 may be implemented by an error amplifier having an inverting input for receiving a feedback signal indicative of the output voltage Vout. The voltage of the feedback signal may be equal to the output voltage Vout or less than the output voltage Vout. In one embodiment, the feedback signal may be obtained by using a voltage dividing network formed by series resistors as a feedback resistor network. The non-inverting input terminal of the error amplifier is used for receiving a reference voltage Vref. The reference voltage Vref may come from a variety of sources, such as by a bandgap reference circuit.
The driving circuit 213 is configured to compare the error amplified signal Vc with a reference to generate a driving signal, which is used to control the state of the power transistor M1.
The mode switching circuit 214 is used to compare the detection signal Vs with a predetermined voltage and provide different references to the driving circuit 213 according to the comparison result.
In the present embodiment, the mode switching circuit 214 is configured to determine the load state of the DC-DC converter according to the comparison result between the detection signal Vs and the preset voltage, and control the operating state of the power transistor M1 according to the determination result.
When the DC-DC converter operates in a heavy load state and the detection signal Vs is greater than the preset voltage, the mode switching circuit 214 provides a triangular wave signal RAMP to the driving circuit 213, and at this time, the driving circuit 213 operates as a comparator, compares the error amplification signal Vc with the triangular wave signal RAMP, generates a first driving signal having a certain duty ratio according to a crossing point of the triangular wave signal RAMP and the error amplification signal Vc, and the power transistor M1 is turned on and off in response to the duty ratio of the first driving signal to adjust the output voltage Vout.
For example, if the output voltage Vout at the load terminal is greater than the reference voltage Vref, a voltage difference exists between the two input terminals of the error amplifier 212, and the voltage difference causes the error amplified signal Vc output by the error amplifier 212 to increase, and the duty ratio of the first driving signal decreases. Conversely, if the output voltage Vout at the load terminal is smaller than the reference voltage Vref, the voltage difference causes the error amplified signal Vc output by the error amplifier 212 to decrease, and the duty ratio of the first driving signal increases.
When the power transistor M1 operates as a switch in response to the first driving signal, the DC-DC converter operates in a switching mode with a switching frequency determined by the triangular wave signal, with an efficiency higher than 90%.
When the DC-DC converter operates in a light load state, the detection signal Vs is smaller than the preset voltage, the mode switching circuit 214 provides a reference voltage REF to the driving circuit 213, at this time, the driving circuit 213 operates as an error amplifier, generates a second driving signal according to a voltage difference between the error amplified signal Vc and the reference voltage REF, and the power transistor M1 operates in a linear region as a variable resistor to adjust the magnitude of the output voltage Vout by adjusting the magnitude of the on-current in response to the second driving signal, so as to make the error amplified signal Vc approach the reference voltage REF at this time as much as possible.
For example, if the output voltage Vout of the load RL exceeds the required voltage value, the voltage difference between the two input terminals of the error amplifier 212 increases the error amplified signal Vc, the increase of the error amplified signal Vc causes the driving circuit 213 to output a driving signal to the power transistor M1, and the power transistor M1 decreases the current to decrease the output voltage Vout. Conversely, if the output voltage Vout of the load RL is lower than the desired voltage value, the voltage difference between the two input terminals of the error amplifier 212 is smaller, and the error amplified signal Vc is smaller, so that the driving circuit 213 outputs a driving signal to the power transistor M1, and the power transistor M1 increases the current to increase the output voltage Vout.
When the power transistor M1 operates in the linear region in response to the second driving signal, the ripple voltage of the output voltage of the DC-DC converter and the EMI interference of the circuit can be kept at a low level due to the absence of high frequency switching, and the quiescent current consumed by the control circuit can be reduced.
Fig. 3 shows a schematic diagram of the mode switching circuit of fig. 2. As shown in fig. 3, the mode switching circuit includes a comparator 401, a switching transistor M2 and a switching transistor M3, the switching transistor M2 is implemented by an N-type MOSFET, and the switching transistor M3 is implemented by a P-type MOSFET. The comparator 401 compares the detection signal Is with the preset voltage Vth. When the detection signal Is greater than the preset voltage Vth, the output signal of the comparator 401 Is at a high level, the switching tube M2 Is turned on, the switching tube M3 Is turned off, and the switching tube M2 provides the triangular wave signal RAMP as a reference to the subsequent driving circuit 213; when the detection signal Is smaller than the preset voltage Vth, the comparator 401 inverts to output a low level, the switching tube M3 Is turned on, the switching tube M2 Is turned off, and the switching tube M3 provides the reference voltage REF as a reference to the driving circuit 213 at the subsequent stage.
In order to realize smooth conversion of the DC-DC converter 102, i.e. the DC-DC converter 102 can smoothly switch from the linear mode to the switching mode and from the switching mode to the linear mode, the mode switching circuit 214 Is in the hysteresis operation mode when the detection signal Is reaches the preset voltage Vth, for example, the comparator 401 can adopt a hysteresis comparator.
The concept "hysteresis" can also be used to describe the operation of the comparator, i.e. the comparator 401 can be selected from hysteresis comparators. An ideal comparator will oscillate between high and low levels if the voltages at the two inputs are equal. The "hysteresis comparator" can avoid the output oscillation of the comparator in this case, and outputs a low level when the voltages of the two input terminals are equal and outputs a high level when the voltages of the two input terminals are different by Δ V.
Further, the control circuit 201 further includes an oscillator 215 and a RAMP generator 216, the oscillator 215 is configured to generate an oscillation signal, and the RAMP generator 216 is configured to generate a triangular wave signal RAMP according to the oscillation signal.
In summary, in the DC-DC converter, the control circuit and the control method thereof according to the embodiments of the present invention, the control circuit includes a current detection circuit, an error amplifier, a mode switching circuit and a driving circuit, the current detection circuit obtains a detection signal by detecting a current flowing through the power transistor, the error amplifier obtains an error amplification signal according to an output voltage of the DC-DC converter and a reference voltage, the mode switching circuit compares the detection signal with a preset voltage, generates different reference signals according to a comparison result, and the driving circuit generates different driving signals according to the different reference signals and the error amplification signal to control the power transistor to operate in a switching mode or a linear mode. The traditional method can realize the switching between the linear mode and the switch mode only by using two DC-DC converters and a control circuit, but the invention can be realized only by using one control circuit, thereby greatly reducing the circuit cost.
In addition, the control circuit of the invention switches the linear mode and the switch mode according to the load state, for example, when the DC-DC converter operates in a small load state, the power transistor is controlled to operate in the linear mode, the ripple voltage of the output voltage of the DC-DC converter and the EMI interference of the circuit can be kept at a low level, and the quiescent current consumed by the control circuit can be reduced. When the DC-DC converter works in a heavy load state, the power transistor is controlled to work in a switching mode, and the efficiency of the DC-DC converter is improved.
Finally, the mode switching circuit of the embodiment of the invention provides different reference signals to the driving circuit through comparison of the detection signal and the preset voltage so as to realize switching between the linear mode and the switch mode, and compared with the existing DC-DC converter which simultaneously comprises the LDO circuit and the PWM circuit, the mode switching circuit needs fewer elements, does not need to add extra pins and has lower circuit cost.
In accordance with the present invention, as set forth above, these embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. The scope of the invention should be determined from the following claims.
Claims (10)
1. A control circuit of a DC-DC converter comprising a power transistor and an inductance connected to each other, the control circuit for providing a drive signal to control a state of the power transistor, wherein the control circuit comprises:
a current detection circuit for detecting a load current flowing through the power transistor to obtain a detection signal;
the error amplifier is used for obtaining an error amplification signal according to the output voltage of the DC-DC converter and a reference voltage;
the mode switching circuit is used for comparing the detection signal with a preset voltage and generating different reference signals according to a comparison result; and
a driving circuit for controlling the power transistor to operate in a switching mode or a linear mode according to the different reference signals and the error amplification signal,
wherein the different reference signals include at least a reference voltage or a triangular wave signal.
2. The control circuit of claim 1, wherein the driving circuit generates a first driving signal according to the triangular wave signal and the error amplifying signal when the detection signal is greater than the preset voltage, the power transistor operates in a switching mode in response to the first driving signal,
when the detection signal is smaller than the preset voltage, the driving circuit generates a second driving signal according to the reference voltage and the error amplification signal, and the power transistor responds to the second driving signal and works in a linear mode.
3. The control circuit of claim 2, wherein the driving circuit operates as a comparator when the detection signal is greater than the preset voltage, and
when the detection signal is smaller than the preset voltage, the driving circuit works as an error amplifier.
4. The control circuit of claim 1, wherein the mode switching circuit comprises:
a comparator for comparing the detection signal with the preset voltage;
the first end of the first switch tube is used for receiving the triangular wave signal, and the control end of the first switch tube is connected with the output end of the comparator and used for providing the triangular wave signal to the driving circuit when the first switch tube is conducted; and
a second switch tube, a first end for receiving the reference voltage, a control end connected with the output end of the comparator, for providing the reference voltage to the driving circuit when conducting,
wherein, when the detection signal is greater than the preset voltage, the comparator switches on the first switch tube and switches off the second switch tube,
when the detection signal is smaller than the preset voltage, the comparator switches on the second switch tube and switches off the first switch tube.
5. The control circuit of claim 4, wherein the comparator is implemented by a hysteresis comparator.
6. The control circuit of claim 4, wherein the first switch transistor is selected from an N-type metal oxide semiconductor field effect transistor and the second switch transistor is selected from a P-type metal oxide semiconductor field effect transistor.
7. The control circuit of claim 1, further comprising:
an oscillator for generating an oscillation signal; and
and the ramp generator is used for generating the triangular wave signal according to the oscillation signal.
8. A control method of a DC-DC converter including a power transistor and an inductance connected to each other, wherein the control method comprises:
detecting a current flowing through the power transistor to obtain a detection signal;
obtaining an error amplification signal according to the output voltage of the DC-DC converter and the reference voltage;
comparing the detection signal with a preset voltage, and generating different reference signals according to a comparison result; and
controlling the power transistor to work in a switch mode or a linear mode according to the different reference signals and the error amplification signal,
wherein the different reference signals include at least a reference voltage or a triangular wave signal.
9. The control method of claim 8, wherein the controlling the power transistor to operate in a switching mode or a linear mode according to the different reference signal and the error amplification signal comprises:
when the detection signal is greater than the preset voltage, generating a first driving signal according to the triangular wave signal and the error amplification signal, wherein the power transistor responds to the first driving signal and works in a switching mode,
and when the detection signal is smaller than the preset voltage, generating a second driving signal according to the reference voltage and the error amplification signal, wherein the power transistor responds to the second driving signal and works in a linear mode.
10. A DC-DC converter, comprising:
a power transistor and an inductor connected to each other; and
the control circuit of any of claims 1-7, the control circuit to control the output voltage by controlling a state of the power transistor.
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| CN201911094408.9A CN112787505A (en) | 2019-11-11 | 2019-11-11 | DC-DC converter and control circuit and control method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2023104060A1 (en) * | 2021-12-08 | 2023-06-15 | 中兴通讯股份有限公司 | Driving detection method, switching power supply, electronic device, and storage medium |
| WO2024067031A1 (en) * | 2022-09-29 | 2024-04-04 | 荣耀终端有限公司 | Power switching circuit and electronic device |
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Application publication date: 20210511 |