CN110572046A - DC/DC converter - Google Patents

DC/DC converter Download PDF

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Publication number
CN110572046A
CN110572046A CN201910812622.7A CN201910812622A CN110572046A CN 110572046 A CN110572046 A CN 110572046A CN 201910812622 A CN201910812622 A CN 201910812622A CN 110572046 A CN110572046 A CN 110572046A
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CN
China
Prior art keywords
resistor
operational amplifier
voltage
output
converter
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
CN201910812622.7A
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Chinese (zh)
Inventor
郑典清
蓝东升
冯刚
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Mornsun Guangzhou Science and Technology Ltd
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Mornsun Guangzhou Science and Technology Ltd
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Priority to CN201910812622.7A priority Critical patent/CN110572046A/en
Publication of CN110572046A publication Critical patent/CN110572046A/en
Withdrawn legal-status Critical Current

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Classifications

    • 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
    • H02M3/158—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 including plural semiconductor devices as final control devices for a single load
    • 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
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • H02M3/33592—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer

Abstract

the invention discloses a DC/DC converter, which comprises a BUCK converter, a push-pull converter, a control circuit, a voltage detection circuit, an isolation transmission circuit and a drive circuit, wherein the push-pull converter is used for rectifying a synchronous rectifier tube. The invention controls the working state of the synchronous rectifier tube of the push-pull converter by detecting the output voltage through the voltage detection circuit, and before the output voltage is not established to the voltage value of steady-state working, the secondary synchronous rectifier tube of the push-pull converter works in the diode rectification state to cut off the path of the current at the output end of the DC/DC converter flowing back to the input end, thereby protecting the power switch tube of the BUCK converter from being damaged, and simultaneously not influencing the efficiency of the DC/DC converter during steady-state working.

Description

DC/DC converter
Technical Field
The invention relates to a DC/DC converter, in particular to a DC/DC converter with a synchronous rectification BUCK + push-pull two-stage circuit topology.
Background
In a DC/DC isolation type high-power DC/DC railway power supply product with an input voltage range of 18-75V, in order to reduce the voltage stress of an input switching tube, reduce the number of turns of a transformer and improve the efficiency of a converter, a power supply circuit with a synchronous rectification BUCK + push-pull two-stage circuit topology is generally adopted.
The schematic diagram of the BUCK + push-pull two-stage circuit topology converter with synchronous rectification shown in fig. 1 includes a BUCK converter, a push-pull converter, a control circuit, an isolation transmission circuit and a driving circuit, wherein an input end of the BUCK converter is an input end of a DC/DC converter, a positive output end of the BUCK converter is connected with a positive input end of the push-pull converter, a negative output end of the BUCK converter is connected with a negative input end of the push-pull converter, an output end of the push-pull converter is an output end of the DC/DC converter, and the push-pull converter is rectified by a synchronous rectifier tube.
The BUCK converter generally comprises an input capacitor C1, a power switch tube Q1, a follow current tube Q2, an energy storage inductor L1 and an output end capacitor; the push-pull converter generally comprises an input capacitor, power switching tubes Q3 and Q4, a transformer T1, output end synchronous rectifying tubes Q5 and Q6 and an output end capacitor C3; the capacitor C2 is used as an output end capacitor of the BUCK converter and an input capacitor of the push-pull converter.
the control circuit at least comprises four signal terminals: a control signal output end HD of a BUCK converter power switch tube Q1, a control signal output end LD of a BUCK converter follow current tube Q2, a control signal output end PUSH of a PUSH-PULL converter power switch tube Q3, a control signal output end PULL of a PUSH-PULL converter power switch tube Q4, and a turn-on voltage VCC (not shown in fig. 1) of the control circuit. The output terminal HD and the output terminal LD of the control circuit output two complementary drive signals. The output end PUSH and the output end PULL output two complementary driving signals; the switching frequency of the driving signal output by the output terminal HD is 2 times that of the driving signal output by the output terminal PUSH. The driving signals output by the output terminals HD and LD are controlled by the output voltage Vo.
The isolated transmission circuit at least comprises 4 signal terminals: an input signal end VIA, an input signal end VIB, an output signal end VOA and an output signal end VOB; the input signal VIA and the output signal VOA are time-synchronized driving signals, and the input signal VIB and the output signal VOB are time-synchronized driving signals. The isolation transmission circuit is used for transmitting the drive signal output by the output end PUSH of the control circuit and the output end PULL of the control circuit to the input end of the drive circuit in an isolation way.
The driving circuit at least comprises 5 signal terminals: the input signal terminal INA, the input signal terminal INB, the output signal terminal OUTA, the output signal terminal OUTB and the power supply signal terminal VDD1, wherein the input signal terminal INA and the output signal terminal OUTA are time-synchronous driving signals, and the input signal terminal INB and the output signal terminal OUTB are time-synchronous driving signals. The driving circuit is used for transmitting the driving signal of the isolation transmission circuit to the secondary side of the push-pull converter and driving the power switch tube Q5 and the power switch tube Q6, when the level signal of the input signal end INA or the input signal end INB of the driving circuit is higher than a first comparison reference voltage, the output signal end OUTA or the output signal end OUTB of the driving circuit outputs the driving signal with high level, and when the level signal of the input signal end INA or the input signal end INB of the driving circuit is lower than a second comparison reference voltage, the output signal end OUTA or the output signal end OUTB of the driving circuit stops outputting the driving signal with high level. Wherein the first comparison reference voltage is higher than the second comparison reference voltage.
The power switch Q1 and the follow current Q2 are typically electronic switches such as MOSFET transistors. When the power switch Q1 is turned on, the voltage at the input terminal VIN charges the energy storage inductor L1 through the power switch Q1 and provides energy to the capacitor C2. When the power switch Q1 is turned off, the follow current Q2 is turned on, and the current flowing through the energy storage inductor L1 continues to flow through the follow current Q2, and the capacitor C2 discharges, so that the output voltage V1 of the BUCK converter is maintained.
The input voltage of the push-pull converter is taken from the output voltage of the BUCK converter and is V1. The power switches Q3 and Q4 and the synchronous rectifiers Q5 and Q6 are typically electronic switches such as MOSFET transistors. The power switch Q3 of the push-pull converter and the synchronous rectifier Q5 are turned on or off at the same time, and the power switch Q4 of the push-pull converter and the synchronous rectifier Q6 are turned on or off at the same time. The input voltage V1 of the push-pull converter supplies energy to the output Vo through the transformer T1 when the power switch Q3 and the synchronous rectifier Q5 are turned on. When the power switch Q3 and the synchronous rectifier Q5 are turned off, the power switch Q4 and the synchronous rectifier Q6 start to be turned on, and the input voltage V1 supplies energy to the output Vo through the transformer T1.
In fig. 1, when current flows to the output end through the synchronous rectifier Q5 or the synchronous rectifier Q6, the conduction of the synchronous rectifier can replace a one-way diode, so that the voltage drop of the one-way diode is eliminated, the synchronous rectification effect is achieved, and the efficiency is improved. However, since the synchronous rectifier has a bidirectional conduction current capability, a current can also reversely flow back to the input end from the output end through the synchronous rectifier, so that when the converter in fig. 1 is applied to power supply of energy storage devices such as a battery and a capacitor, a large amount of energy can be stored in the output end Vo, and the power switch Q1 in the BUCK converter can be damaged. The specific analysis is as follows:
When the input terminal VIN is frequently switched, after the voltage of the input terminal VIN drops to 0V, the voltage of the output terminal Vo does not drop rapidly but drops slowly because the output terminal Vo stores a large amount of energy. At this time, the input terminal VIN voltage drops to 0V and then starts up again, and when the input terminal VIN voltage reaches the start voltage VCC of the control circuit, the output terminal PUSH and the output terminal PULL of the control circuit start to output the high-level driving signal. The driving circuit is started to work at the same time, and the power switch tube Q3, the power switch tube Q4, the synchronous rectifier tube Q5 and the synchronous rectifier tube Q6 start to work alternately and synchronously. At this time, the output terminal of the BUCK converter senses a voltage V11 from the output terminal Vo of the two-stage topology converter through the transformer T1, the magnitude of the sensed voltage V11 is related to the magnitude of the energy stored in the output terminal Vo, and the greater the stored energy is, the greater the sensed voltage V11 is.
the output voltage V1 of the BUCK converter is VIN × D, and D is the duty ratio of the driving signal output by the control circuit HD. When the BUCK converter is just started, the control circuit is in a soft start state, D is slowly increased from zero, at the moment, D is small, the induction voltage V11 is larger than VIN multiplied by D, and the BUCK converter is in a reverse working state, namely a boost working state. The power switch Q1 will bear a large reverse current from the source to the drain, the larger the induced voltage V11, the larger the reverse current, and when the current exceeds the current that the power switch Q1 can bear, the power switch Q1 will be damaged.
therefore, in order to solve the problem that the power switch Q1 is damaged when the input terminal VIN is frequently switched, a technical solution for preventing the output current from flowing backwards needs to be provided.
Disclosure of Invention
in view of this, the technical problem to be solved by the present invention is to provide a DC/DC converter, which adopts a BUCK + push-pull two-stage circuit topology with synchronous rectification, and when the input voltage is frequently switched, the output current will not flow backwards, so that the power switch tube in the BUCK converter is not damaged.
In order to solve the technical problems, the invention has the conception that: the working state of the synchronous rectifier tube on the secondary side of the push-pull converter is controlled by detecting the output voltage, and before the output voltage is not established to a voltage value of steady-state working, the synchronous rectifier tube on the secondary side of the push-pull converter works in a diode rectification state to cut off a path for backward flowing of current at the output end of the DC/DC converter to the input end, so that a power switch tube of the BUCK converter is protected from being damaged, and the efficiency of the DC/DC converter is not influenced during steady-state working.
Based on the inventive concept, the technical scheme of the invention is as follows:
A DC/DC converter comprises a BUCK converter, a push-pull converter, a control circuit, an isolation transmission circuit and a drive circuit, and is characterized in that: the voltage detection circuit comprises a power supply end VDD2, an input end IN1, a first output end OUT1 and a second output end OUT2, wherein the power supply end VDD2 is a power supply input end of the voltage detection circuit and supplies power to the voltage detection circuit; the input end IN1 is connected with the output end of the DC/DC converter and is used for detecting the output voltage Vo; the first output terminal OUT1 is connected to the input signal terminal INA of the driving circuit to control the input signal terminal INA of the driving circuit, and the second output terminal OUT2 is connected to the input signal terminal INB of the driving circuit to control the input signal terminal INB of the driving circuit.
Preferably, the power supply terminal VDD2 of the voltage detection circuit can be supplied with power alone, or can be connected to the power supply signal terminal VDD1 of the driving circuit, and can also be connected to the output voltage Vo.
As a specific embodiment of the voltage detection circuit, the voltage detection circuit includes: the voltage detection circuit comprises a voltage stabilizing diode Z1, a resistor R1, a resistor R2, a resistor R3, an operational amplifier IC2, a diode D1 and a diode D2; one end of a resistor R1 serves as an input end IN1 of the voltage detection circuit, the other end of a resistor R1 is connected with one end of a resistor R2, the connection point of the resistor R1 is connected with the positive input end of the operational amplifier IC2, the other end of the resistor R2 is connected with the output ground, the anode of a voltage stabilizing diode Z1 is connected with the output ground, the cathode of the voltage stabilizing diode Z1 is connected with one end of a resistor R3, the connection point of the resistor R1 is connected with the negative phase input end of the operational amplifier IC2, the other end of the resistor R3 and the power supply end of the operational amplifier IC2 are connected with the power supply end of the voltage detection circuit, the ground end of the operational amplifier IC2 is connected with the output ground, the output end of the operational amplifier IC2 is connected with the cathode of a diode D1 and the cathode of a diode D2, the anode of a diode D1 serves as.
Preferably, the diodes D1 and D2 are schottky diodes.
Preferably, the regulated voltage value of the voltage stabilizing diode Z1 is lower than the minimum voltage value of the power supply end of the voltage detection circuit.
Another specific embodiment of the voltage detection circuit is characterized in that: the voltage detection circuit comprises an operational amplifier IC1, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, an operational amplifier IC2, a diode D1 and a diode D2; one end of a resistor R1 is used as an input end of the voltage detection circuit, the other end of the resistor R1 is connected with a resistor R2, the connection point of the resistor R2 is connected with the positive input end of an operational amplifier IC2, the other end of the resistor R2 is connected with an output ground, the anode of the operational amplifier IC1 is connected with an output ground, the cathode of the operational amplifier IC1 is connected with one end of a resistor R4, the other end of the resistor R4 is connected with one end of a resistor R3, the connection point of the resistor R465 is connected with the negative input end of the operational amplifier IC2, the other end of the resistor R3 and the power supply end of the operational amplifier IC2 are connected with the power supply end of the voltage detection circuit, one end of a resistor R6 is connected with the output ground, the other end of the resistor R6 is connected with one end of a resistor R5, the connection point is connected with the reference end of the operational amplifier IC1, the other end of the resistor R5 is connected with the negative input end of the operational amplifier IC2, the ground end of, an anode of the diode D2 serves as a second output terminal OUT2 of the voltage detection circuit.
Preferably, the diodes D1 and D2 are schottky diodes.
Preferably, when the reference terminal voltage of the operational amplifier IC1 is higher than the internal reference voltage value, when the reference terminal voltage of the operational amplifier IC1 is higher than the internal reference voltage value, a current flows from the cathode to the anode of the operational amplifier IC1, and when the reference terminal voltage of the operational amplifier IC1 is lower than the internal reference voltage value, the cathode of the operational amplifier IC1 is turned off.
Preferably, the voltage value of the negative phase input terminal of the operational amplifier IC2 is the regulated voltage value of the operational amplifier IC1, and the regulated voltage value is lower than the minimum voltage value of the power supply terminal VDD2 of the voltage detection circuit.
The working principle of the invention is briefly analyzed as follows:
When the input end is frequently switched, the voltage detection circuit detects the output voltage in real time. When the output voltage is not established to the steady-state working voltage value, the output end of the operational amplifier IC2 of the voltage detection circuit outputs a low level, the high-level pulse voltage of the output ends VOA and VOB of the isolation transmission circuit is pulled down through a diode D1 and a diode D2 and is lower than the second comparison reference level of the driving circuit, the driving circuit does not work, and the synchronous rectifier tube of the push-pull converter works in a diode rectification state. Because of the unidirectional conductivity of the diode, the current at the output end cannot flow back to the primary side.
When the output voltage value is established to the steady-state working voltage value, the output end of the operational amplifier IC2 of the voltage detection circuit outputs a high level, the high level voltage value is larger than the voltages of the VOA and VOB of the isolation transmission circuit output end, the diodes D1 and D2 are in the cut-off state, the normal work of the driving circuit is not influenced, the synchronous rectifier tube of the push-pull converter works in the synchronous rectification state, the control circuit finishes soft start at the moment, the V1 is VIN multiplied by D, the BUCK converter works in the charging state, the power switch tube Q1 has no reverse BOOST heavy current from the source electrode to the drain electrode, and the power switch tube Q1 cannot be damaged.
the invention has the beneficial effects that:
when the input end of the DC/DC converter adopting the BUCK + push-pull two-stage circuit topology with synchronous rectification is used for frequent switching, and steady-state work is not established, the synchronous rectification tube of the push-pull converter works in a diode rectification state, and a path for backward flowing of current at the output end of the DC/DC converter to the input end is cut off, so that a power switch tube of the BUCK converter is protected from being damaged.
Drawings
FIG. 1 is a schematic diagram of a prior art BUCK + push-pull two-stage circuit topology converter with synchronous rectification;
FIG. 2 is a schematic block diagram of the DC/DC converter of the present invention;
FIG. 3 is a schematic diagram of a voltage detection circuit in the DC/DC converter of the first embodiment;
fig. 4 is a schematic diagram of a voltage detection circuit in the DC/DC converter of the second embodiment.
Detailed Description
Fig. 2 is a schematic block diagram of a DC/DC converter of the present invention, which is different from the prior art in fig. 1 in that a path of an output current flowing backward to a primary side is to be cut off, and therefore, the DC/DC converter further includes a voltage detection circuit, an input end of the voltage detection circuit detects an output voltage Vo at an output end of the DC/DC converter, and outputs a detection voltage signal through a first output end OUT1 and a second output end OUT2 thereof, and the driving circuit determines whether to cut off the path of the output current flowing backward to the primary side by comparing the detection voltage signal with a first comparison reference voltage and a second comparison reference voltage, so as to protect a power switching tube in the BUCK converter from being damaged.
In order that those skilled in the art will more readily understand the present invention, reference will now be made to the specific embodiments.
First embodiment
Fig. 3 is a schematic diagram of a voltage detection circuit in a DC/DC converter according to a first embodiment of the present invention, and other circuits are the same as those in fig. 1 and 2 and are not drawn.
The voltage detection circuit of the embodiment is composed of a zener diode Z1, a resistor R1, a resistor R2, a resistor R3, an operational amplifier IC2, a diode D1 and a diode D2.
One end of the resistor R1 is an input end of the voltage detection circuit and is connected with the output voltage Vo, the other end of the resistor R1 is connected with the resistor R2, the other end of the resistor R2 is connected with the output ground, the other end of the resistor R1 is connected with one end of the resistor R2, the connection point of the resistor R2 is connected with the positive input end of the operational amplifier IC2, the other end of the resistor R2 is connected with the output ground, the cathode of the voltage stabilizing diode Z1 is connected with one end of the resistor R3, the connection point of the resistor R6342 is connected with the negative input end of the operational amplifier IC2, the other end of the resistor R3 and the power supply end of the operational amplifier IC2 are connected with the power supply end of the voltage detection circuit, the grounding end of the operational amplifier IC2 is connected with the output ground, the output end of the operational amplifier IC2 is connected with the cathode of the diode D1 and the cathode of the diode D2, the anode of the diode D1 serves as a first output.
Preferably, in the present embodiment, the diodes D1 and D2 are schottky diodes, so as to obtain a lower forward conduction voltage drop.
Further, the first comparison reference level V of the driving circuit is set in the present embodimentDISHIs 2.2V, and a second comparison reference level VDISLThe voltage is 0.8V, and the misoperation of the driving circuit can be effectively avoided through the return difference design.
The working principle is as follows:
As shown in fig. 3, the operational amplifier IC2 in this embodiment is preferably LM2904 of TI, and when the input voltage VIN of the DC/DC converter reaches the control circuit operating voltage VCC, the control circuit starts to operate, the output terminals HD, LD, PUSH and PULL of the control circuit output a high-level driving signal, the voltage V1 of the positive output terminal U1 of the BUCK converter starts to rise, the PUSH-PULL converter starts to operate, the output voltage Vo rises, the output voltage Vo is divided by the resistors R1 and R2, and a voltage V2 is generated across the resistor R2.
When the voltage V2 does not rise to the regulated voltage value of the zener diode Z1, the output terminal voltage of the operational amplifier IC2 is at a low level, and the high-level pulse voltage of the output signal terminal VOA and the output signal terminal VOB of the isolation transmission circuit is pulled down by the diode D1 and the diode D2 and is lower than the second comparison reference voltage VDISLThe driving circuit does not work, the output signal end OUTA and the output signal end OUTB of the driving circuit do not output driving signals, and the synchronous rectifier Q5 and the synchronous rectifier Q6 work in a diode rectification state. Due to the unidirectional conductivity of the diode, the current energy stored at the output Vo of the DC/DC converter cannot be reversely sunk to the positive output U1 of the BUCK converter through the transformer T1.
When the voltage V2 rises to the regulated voltage value of the zener diode Z1, the output terminal voltage of the operational amplifier IC2 is at a high level, the high level voltage value is greater than the voltage of the output signal terminal VOA and the output signal terminal VOB of the isolation transmission circuit, the diode D1 and the diode D2 are in an off state, the normal operation of the driving circuit is not affected, and the synchronous rectifier Q5 and the synchronous rectifier Q6 start to operate in a synchronous rectification state. At this time, the control circuit completes soft start, and the DC/DC converter operates in a steady state, in which the voltage V11 sensed by the positive output terminal U1 of the BUCK converter is less than V1 — VIN × D. The power switch tube Q1 works in a forward BUCK charging state, but not in a reverse BOOST state, and the power switch tube Q1 has no reverse charging current, so that the damage risk caused by the backward flow of the current in the power switch tube Q1 in the BUCK converter is solved.
Second embodiment
Fig. 4 is a schematic diagram of a voltage detection circuit in a DC/DC converter according to a second embodiment of the present invention, and other circuits are the same as those in fig. 1 and 2, and therefore are not drawn.
The voltage detection circuit of the present embodiment includes: operational amplifier IC1, resistor R1, resistor R2, resistor R3, resistor R4, resistor R5, resistor R6, operational amplifier IC2, diode D1 and diode D2.
One end of a resistor R1 is used as an input end of the voltage detection circuit to be connected with the output voltage Vo, the other end of the resistor R1 is connected with a resistor R2, the connection point of the resistor R2 is connected with a positive input end of an operational amplifier IC2, the other end of the resistor R2 is connected with an output ground, the anode of the operational amplifier IC1 is connected with the output ground, the cathode of the operational amplifier IC1 is connected with one end of a resistor R4, the other end of the resistor R4 is connected with one end of a resistor R3, the connection point of the resistor R465 is connected with a negative input end of the operational amplifier IC2, the other end of the resistor R3 and the power supply end of the operational amplifier IC2 are connected with the power supply end of the voltage detection circuit, one end of a resistor R6 is connected with the output ground, the other end of the resistor R6 is connected with one end of a resistor R5, the connection point is connected with the reference end of the operational amplifier IC1, the other end of the resistor R5 is connected with the negative input end of the operational amplifier IC2, an anode of the diode D2 serves as a second output terminal OUT2 of the voltage detection circuit.
Preferably, the voltage value of the negative phase input terminal of the operational amplifier IC2 is the regulated voltage value of the operational amplifier IC1, which is lower than the minimum voltage value of the supply terminal VDD2 of the voltage detection circuit.
As shown in fig. 4, the working principle of this embodiment is substantially the same as that of the first embodiment, and the difference is that the implementation manner of the voltage stabilization value at the negative phase input end of the operational amplifier IC2 is different, the second embodiment uses the operational amplifier IC1, the resistor R4, the resistor R5, and the resistor R6 to implement the adjustable voltage stabilization value, the operational amplifier IC1 can use the IC AZ431, the voltage accuracy of the IC AZ431 can reach ± 0.4%, for example, a resistor with an accuracy of ± 0.1% is selected, the voltage stabilization value can achieve an accuracy of ± 1%, and the voltage stabilization value accuracy of the voltage regulator tube is generally ± 5%, so that the second embodiment can achieve more accurate detection and control of the output voltage Vo, and finally achieve the purpose of reducing the reverse current value.
It should be noted that the control logic of the present embodiment and the second embodiment is: when the level signal of the input signal terminal INA or the input signal terminal INB of the driving circuit is higher than the first comparison reference voltage, the output signal terminal OUTA or the output signal terminal OUTB of the driving circuit outputs the driving signal of high level, and when the level signal of the input signal terminal INA or the input signal terminal INB of the driving circuit is lower than the second comparison reference voltage, the output signal terminal OUTA or the output signal terminal OUTB of the driving circuit stops outputting the driving signal of high level. It is also conceivable to use the opposite control logic, and in this case, as long as the output voltage Vo is not established to the steady state, the driving is not operated, and no high-level driving signal is output.
The foregoing is merely a preferred embodiment of the present invention, and it should be noted that the above-described preferred embodiment should not be construed as limiting the present invention. For those skilled in the art, it is obvious that several equivalent changes, modifications and decorations can be made without departing from the spirit and scope of the present invention, and these equivalent changes, modifications and decorations should also be regarded as the protection scope of the present invention, and no detailed description is given here.

Claims (9)

1. A DC/DC converter comprises a BUCK converter, a push-pull converter, a control circuit, an isolation transmission circuit and a drive circuit, and is characterized in that: the voltage detection circuit comprises a power supply end VDD2, an input end IN1, a first output end OUT1 and a second output end OUT2, wherein the power supply end VDD2 is a power supply input end of the voltage detection circuit and supplies power to the voltage detection circuit; the input end IN1 is connected with the output end of the DC/DC converter and is used for detecting the output voltage Vo; the first output terminal OUT1 is connected to the input signal terminal INA of the driving circuit to control the input signal terminal INA of the driving circuit, and the second output terminal OUT2 is connected to the input signal terminal INB of the driving circuit to control the input signal terminal INB of the driving circuit.
2. The DC/DC converter according to claim 1, wherein: the power supply end VDD2 of the voltage detection circuit can be independently powered, and can also be connected with the power supply signal end VDD1 of the driving circuit, and can also be connected with the output voltage Vo.
3. The DC/DC converter according to claim 1, wherein: the voltage detection circuit comprises a voltage stabilizing diode Z1, a resistor R1, a resistor R2, a resistor R3, an operational amplifier IC2, a diode D1 and a diode D2; one end of a resistor R1 serves as an input end IN1 of the voltage detection circuit, the other end of a resistor R1 is connected with one end of a resistor R2, the connection point of the resistor R1 is connected with the positive input end of the operational amplifier IC2, the other end of the resistor R2 is connected with the output ground, the anode of a voltage stabilizing diode Z1 is connected with the output ground, the cathode of the voltage stabilizing diode Z1 is connected with one end of a resistor R3, the connection point of the resistor R1 is connected with the negative phase input end of the operational amplifier IC2, the other end of the resistor R3 and the power supply end of the operational amplifier IC2 are connected with the power supply end of the voltage detection circuit, the ground end of the operational amplifier IC2 is connected with the output ground, the output end of the operational amplifier IC2 is connected with the cathode of a diode D1 and the cathode of a diode D2, the anode of a diode D1 serves as.
4. The DC/DC converter according to claim 3, wherein: diodes D1 and D2 are schottky diodes.
5. The DC/DC converter according to claim 3, wherein: the regulated voltage value of the voltage stabilizing diode Z1 is lower than the minimum voltage value of the power supply end of the voltage detection circuit.
6. The DC/DC converter according to claim 1, wherein: the voltage detection circuit comprises an operational amplifier IC1, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, an operational amplifier IC2, a diode D1 and a diode D2; one end of a resistor R1 is used as an input end of the voltage detection circuit, the other end of the resistor R1 is connected with a resistor R2, the connection point of the resistor R2 is connected with the positive input end of an operational amplifier IC2, the other end of the resistor R2 is connected with an output ground, the anode of the operational amplifier IC1 is connected with an output ground, the cathode of the operational amplifier IC1 is connected with one end of a resistor R4, the other end of the resistor R4 is connected with one end of a resistor R3, the connection point of the resistor R465 is connected with the negative input end of the operational amplifier IC2, the other end of the resistor R3 and the power supply end of the operational amplifier IC2 are connected with the power supply end of the voltage detection circuit, one end of a resistor R6 is connected with the output ground, the other end of the resistor R6 is connected with one end of a resistor R5, the connection point is connected with the reference end of the operational amplifier IC1, the other end of the resistor R5 is connected with the negative input end of the operational amplifier IC2, the ground end of, an anode of the diode D2 serves as a second output terminal OUT2 of the voltage detection circuit.
7. The DC/DC converter according to claim 6, wherein: diodes D1 and D2 are schottky diodes.
8. The DC/DC converter according to claim 7, wherein: when the voltage at the reference terminal of the operational amplifier IC1 is higher than the internal reference voltage value, a current flows from the cathode to the anode of the operational amplifier IC1, and when the voltage at the reference terminal of the operational amplifier IC1 is lower than the internal reference voltage value, the cathode of the operational amplifier IC1 is turned off.
9. The DC/DC converter according to claim 8, wherein: the voltage value of the negative phase input end of the operational amplifier IC2 is the regulated voltage value of the operational amplifier IC1, and the regulated voltage value is lower than the minimum voltage value of the power supply end VDD2 of the voltage detection circuit.
CN201910812622.7A 2019-08-30 2019-08-30 DC/DC converter Withdrawn CN110572046A (en)

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