Anti-backflow circuit in DC-DC converter

Abstract

The utility model discloses an anti-backflow circuit in a DC-DC converter, and relates to the field of voltage conversion, and the anti-backflow circuit in the DC-DC converter comprises a main control module which is used for detecting the voltage difference of a resistor RSENSE to control the conduction of an MOS tube M3 so as to avoid the backflow phenomenon in the DC-DC converter; the MOS tube M3 is used as a switch of a DC-DC converter loop; the resistor RSENSE is used as a resistor of a series loop of the DC-DC converter, and the voltage drop of the resistor RSENSE reflects the relationship between the input voltage VCC and the output voltage VOUT; compared with the prior art, the anti-backflow circuit provided by the utility model has the beneficial effects that the anti-backflow circuit designed by the utility model effectively avoids the situation of current backflow when the MOS tube is conducted, ensures the use safety of the DC-DC converter, and is suitable for different DC-DC converters of a synchronous boost type, a synchronous buck type and the like.

Description

Technical Field

[0001] The utility model relates to the field of voltage conversion, in particular to an anti-backflow circuit in a DC-DC converter. Background Art

[0002] The DC-DC conversion power supply topology includes synchronous step-down DC-DC converters and synchronous step-up DC-DC converters.

[0003] See also Figure 1 (The existing technology does not have an anti-backflow protection circuit within the dotted box). The traditional synchronous step-down DC-DC converter consists of MOS tubes M1, M2 and inductor L1 to form a switching path. Capacitor CL1 and resistor RL1 are the load RC network. Switching path 1: From VCC through M1, L1 to Vout, this process charges the inductor L1 and discharges the output at the same time (providing load energy). Switching path 2: From Vout through L1, M2 in the reverse direction, it discharges. MOS tubes M1 and M2 cannot be turned on at the same time. If these two path processes do not have a circuit to prevent backflow, then under certain application conditions, such as when the Vout voltage is higher than VCC and M1 is open at this time, the process of charging the capacitor and discharging the load at the same time cannot be achieved, and the current will instead flow back from Vout to VCC.

[0004] See also Figure 2 (The existing technology does not include the backflow protection circuit within the dashed box.) The principle of backflow protection for synchronous boost DC-DC converters is the same as that for the aforementioned buck converters. After the output voltage Vout has been boosted to a relatively high voltage, it primarily supplies power to the load. If current backflow occurs (from Vout through M5 and L2 back to VCC), the output voltage will drop. If Vout is connected to a battery load, this will cause abnormal battery discharge, resulting in energy loss and waste.

[0005] Therefore, the existing DC-DC conversion power supply topology lacks anti-backflow protection circuit and needs to be improved. Utility Model Content

[0006] The purpose of the present utility model is to provide a backflow prevention circuit in a DC-DC converter to solve the problems raised in the above background technology.

[0007] To achieve the above objectives, the present invention provides the following technical solutions:

[0008] A backflow prevention circuit in a DC-DC converter, comprising:

[0009] The main control module is used to detect the voltage difference on the resistor RSENSE to control whether the MOS tube M3 is turned on or off to avoid backflow in the DC-DC converter;

[0010] MOS tube M3 is used as a switch in the DC-DC converter circuit;

[0011] Resistor RSENSE is used as the resistance of the DC-DC converter series circuit. Its voltage drop reflects the relationship between the input voltage VCC and the output voltage VOUT.

[0012] The resistor RSENSE is connected to the main control module, the main control module is connected to the G pole of the MOS tube M3, and the S pole and D pole of the MOS tube M3 are connected to the input side and output side of the DC-DC converter.

[0013] As a further solution of the present invention: the main control module includes:

[0014] The reference voltage acquisition module is used to obtain the reference voltage and output it to the MOS tube control module;

[0015] The resistor voltage drop acquisition module is used to obtain the voltage drop of the resistor RSENSE and output it to the MOS tube control module;

[0016] The MOS tube control module is used to compare the reference voltage and the voltage drop of the resistor RSENSE to control whether the MOS tube M3 is turned on or not.

[0017] As a further solution of the present invention: the reference voltage acquisition module includes a comparator OP1 and a multiplexer MUX. The non-inverting terminal of the comparator OP1 is connected to the reference voltage, the inverting terminal of the comparator OP1 is connected to one end of an external variable resistor R and the S pole of a MOS transistor MN1, the other end of the external variable resistor R is grounded, the D pole of the MOS transistor MN1 is connected to the D pole of the MOS transistor MP1, the G pole of the MOS transistor MP1, and the G pole of the MOS transistor MP2, the S pole of the MOS transistor MP1 is connected to the S pole of the MOS transistor MP2 and the power supply voltage VCC, the D pole of the MOS transistor MP2 is grounded via multiple resistors connected in series, the D pole of the MOS transistor MP2 is connected to an input terminal of the multiplexer MUX, the connection points between the multiple resistors connected in series are respectively connected to different input terminals of the multiplexer MUX, the multiplexer MUX is connected to a chip select signal SEL, and the output terminal of the multiplexer MUX is connected to the MOS transistor control module.

[0018] As a further solution of the present invention: the resistance voltage drop acquisition module includes a Schmitt trigger COMP2, the non-inverting end and the inverting end of the Schmitt trigger COMP2 are respectively connected to the two ends of the resistor RSENSE, and the output end of the Schmitt trigger COMP2 is connected to the MOS tube control module.

[0019] As a further solution of the present invention: the MOS tube control module includes a Schmitt trigger COMP1, the non-inverting end of the Schmitt trigger COMP1 is connected to the reference voltage acquisition module, the inverting end of the Schmitt trigger COMP1 is connected to the resistance voltage drop acquisition module, and the output end of the Schmitt trigger COMP1 is connected to the G pole of the MOS tube M3.

[0020] Compared with the prior art, the beneficial effect of the present invention is that the anti-backflow circuit designed in the present invention effectively avoids the current backflow when the MOS tube is turned on, ensures the safe use of the DC-DC converter, and is suitable for different DC-DC converters such as synchronous boost type and synchronous buck type. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a circuit diagram of a synchronous step-down DC-DC converter equipped with an anti-backflow circuit.

[0022] Figure 2 This is a circuit diagram of a synchronous step-up DC-DC converter equipped with a backflow prevention circuit.

[0023] Figure 3 The figure is a schematic diagram of a backflow prevention circuit in a DC-DC converter.

[0024] Figure 4 This is the circuit diagram of the main control module. DETAILED DESCRIPTION

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0026] See also Figure 3 , a backflow prevention circuit in a DC-DC converter, comprising:

[0027] The main control module is used to detect the voltage difference on the resistor RSENSE to control whether the MOS tube M3 is turned on or off to avoid backflow in the DC-DC converter;

[0028] MOS tube M3 is used as a switch in the DC-DC converter circuit;

[0029] Resistor RSENSE is used as the resistance of the DC-DC converter series circuit. Its voltage drop reflects the relationship between the input voltage VCC and the output voltage VOUT.

[0030] The resistor RSENSE is connected to the main control module, the main control module is connected to the G pole of the MOS tube M3, and the S pole and D pole of the MOS tube M3 are connected to the input side and output side of the DC-DC converter.

[0031] In a specific embodiment, the voltage VIN is the power supply outside the chip. Figure 1 The synchronous step-down DC-DC converter shown in the figure is used for explanation. The voltage VIN is the input voltage VCC. The current-sense resistor Rsense is connected in series in the power supply path. By measuring the voltage difference across the resistor, the current in the power supply VCC path can be detected in real time. This current can reflect the output current in real time, thereby judging the change and magnitude of the load power. Based on the judgment result, the MOS tube M3 in the output path is controlled to turn on and off, which can achieve reverse current flow at the output end. The judgment method is as follows:

[0032] Voltage polarity detection: When the voltage on the right side of the current-sense resistor Rsense is higher than the voltage on the left side, it means that backflow from the output to the input has occurred. At this time, the main control module inside the chip detects this state and outputs a control signal to control the MOS tube M3 to turn off. At this time, the backflow path can be cut off, thereby preventing backflow.

[0033] Voltage dropout detection: In certain specific applications, such as battery-powered and solar-powered applications, the voltage polarity remains normal, but the voltage dropout is as small as a certain voltage value. This indicates that the input energy is very low and the chip loop has entered discontinuous mode. At this point, the synchronous MOS transistor may be abnormally turned on, resulting in abnormal discharge from the output Vout to GND. In this case, simply turning off the MOS transistor M3 can prevent backflow. Therefore, a threshold can be set for protection based on actual application requirements.

[0034] Here corresponds to Figure 1 The synchronous step-down DC-DC converter is described, so Figure 4 There is an inductor L1 corresponding to Figure 1 The structure and principle of synchronous boost DC-DC converter are similar and will not be described in detail.

[0035] In this example: See Figure 4 , the main control module includes:

[0036] The reference voltage acquisition module is used to obtain the reference voltage and output it to the MOS tube control module;

[0037] The resistor voltage drop acquisition module is used to obtain the voltage drop of the resistor RSENSE and output it to the MOS tube control module;

[0038] The MOS tube control module is used to compare the reference voltage and the voltage drop of the resistor RSENSE to control whether the MOS tube M3 is turned on or not.

[0039] In this example: See Figure 4 The reference voltage acquisition module includes a comparator OP1 and a multiplexer MUX. The non-inverting terminal of the comparator OP1 is connected to a reference voltage, the inverting terminal of the comparator OP1 is connected to one end of an external variable resistor R and the S terminal of a MOS transistor MN1, the other end of the external variable resistor R is grounded, the D terminal of the MOS transistor MN1 is connected to the D terminal of a MOS transistor MP1, the G terminal of the MOS transistor MP1, and the G terminal of the MOS transistor MP2, the S terminal of the MOS transistor MP1 is connected to the S terminal of the MOS transistor MP2 and a power supply voltage VCC, the D terminal of the MOS transistor MP2 is grounded via multiple resistors connected in series, the D terminal of the MOS transistor MP2 is connected to an input terminal of the multiplexer MUX, the connection points between each of the multiple resistors connected in series are connected to different input terminals of the multiplexer MUX, the multiplexer MUX is connected to a chip select signal SEL, and the output terminal of the multiplexer MUX is connected to the MOS transistor control module.

[0040] The G terminals of MOS transistors MP1 and MP2 are connected, so their on-state current is the same. The current flowing through the external variable resistor R is equal to the current flowing through the multiple resistors connected in series. Therefore, by adjusting the resistance of the external variable resistor R, the voltage fed back to the multiple resistors connected in series to the multiplexer MUX can be changed. External variable resistors R with different resistance values can generate different reference voltages VR1, VR2, VR3, ..., and VRn (theoretically, n can be any value as long as there are enough voltage divider resistors). This allows for flexible generation of different reference voltages VRn, making the overall circuit suitable for different application conditions.

[0041] The signal "SEL" in the figure above is the chip select signal. If it is a two-choice chip select, only one chip select is required. If four-choice chip select is required, two chip selects are required, and so on. VREF is the reference voltage, which is a constant ideal value, usually 1.2V. R_reg is the feedback terminal of the external resistor R. VR1, VR2, VR3...VRn are the reference voltages obtained after resistor voltage division. The appropriate voltage is selected by the multiplexer to be used as the input reference voltage of Schmitt trigger COMP1.

[0042] In this example: See Figure 4 The resistance voltage drop acquisition module includes a Schmitt trigger COMP2, the non-inverting end and the inverting end of the Schmitt trigger COMP2 are respectively connected to the two ends of the resistor RSENSE, and the output end of the Schmitt trigger COMP2 is connected to the MOS tube control module.

[0043] The non-inverting terminal and the inverting terminal of the Schmitt trigger COMP2 are respectively connected to the two ends of the resistor RSENSE, and the voltage drop of the resistor RSENSE is fed back to the MOS tube control module, that is, the voltage relationship between the input voltage VCC and the output VOUT is fed back to the MOS tube control module.

[0044] In this example: See Figure 4 The MOS tube control module includes a Schmitt trigger COMP1, the non-inverting end of the Schmitt trigger COMP1 is connected to the reference voltage acquisition module, the inverting end of the Schmitt trigger COMP1 is connected to the resistance voltage drop acquisition module, and the output end of the Schmitt trigger COMP1 is connected to the G pole of the MOS tube M3.

[0045] The multiplexer MUX outputs a fixed voltage (adjusted by an external variable resistor R) to the non-inverting terminal of the Schmitt trigger COMP1. The Schmitt trigger COMP2 outputs a voltage that feeds back the relationship between the current voltage VCC and VOUT to the inverting terminal of the trigger COMP1. When the relationship between the voltages VCC and VOUT is normal, the non-inverting terminal of the Schmitt trigger COMP1 is higher than the inverting terminal voltage and outputs a high level. Otherwise, it outputs a low level to control the conduction state of the MOS tube V3 and prevent backflow. The fixed voltage output by the multiplexer MUX can be adjusted by an external variable resistor R, which has a wider range of applications.

[0046] The working principle of the present invention is as follows: the main control module is used to detect the voltage difference across the resistor RSENSE to control whether the MOS transistor M3 is turned on or off, thereby avoiding the backflow phenomenon in the DC-DC converter; the MOS transistor M3 is used to serve as a switch in the DC-DC converter circuit; the resistor RSENSE is used to serve as the resistor of the DC-DC converter series circuit, and its voltage drop reflects the relationship between the input voltage VCC and the output voltage VOUT.

[0047] It is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered in all respects as exemplary and non-restrictive.

[0048] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A backflow prevention circuit in a DC-DC converter, characterized in that: The anti-backflow circuit in the DC-DC converter includes: The main control module is used to detect the voltage difference on the resistor RSENSE to control whether the MOS tube M3 is turned on or off to avoid backflow in the DC-DC converter; MOS tube M3 is used as a switch in the DC-DC converter circuit; Resistor RSENSE is used as the resistance of the DC-DC converter series circuit. Its voltage drop reflects the relationship between the input voltage VCC and the output voltage VOUT. The resistor RSENSE is connected to the main control module, the main control module is connected to the G pole of the MOS tube M3, and the S pole and D pole of the MOS tube M3 are connected to the input side and output side of the DC-DC converter.

2. The anti-backflow circuit in the DC-DC converter according to claim 1, characterized in that: The main control module includes: The reference voltage acquisition module is used to obtain the reference voltage and output it to the MOS tube control module; The resistor voltage drop acquisition module is used to obtain the voltage drop of the resistor RSENSE and output it to the MOS tube control module; The MOS tube control module is used to compare the reference voltage and the voltage drop of the resistor RSENSE to control whether the MOS tube M3 is turned on or not.

3. The anti-backflow circuit in the DC-DC converter according to claim 2, characterized in that: The reference voltage acquisition module includes a comparator OP1 and a multiplexer MUX. The non-inverting terminal of the comparator OP1 is connected to a reference voltage, the inverting terminal of the comparator OP1 is connected to one end of an external variable resistor R and the S-pole of a MOS transistor MN1, the other end of the external variable resistor R is grounded, the D-pole of the MOS transistor MN1 is connected to the D-pole of a MOS transistor MP1, the G-pole of the MOS transistor MP1, and the G-pole of the MOS transistor MP2, the S-pole of the MOS transistor MP1 is connected to the S-pole of the MOS transistor MP2 and a power supply voltage VCC, the D-pole of the MOS transistor MP2 is grounded via multiple resistors connected in series, the D-pole of the MOS transistor MP2 is connected to an input terminal of the multiplexer MUX, the connection points between each of the multiple resistors connected in series are respectively connected to different input terminals of the multiplexer MUX, the multiplexer MUX is connected to a chip select signal SEL, and the output terminal of the multiplexer MUX is connected to the MOS transistor control module.

4. The anti-backflow circuit in the DC-DC converter according to claim 2, characterized in that: The resistance voltage drop acquisition module includes a Schmitt trigger COMP2, the in-phase terminal and the inverting terminal of the Schmitt trigger COMP2 are respectively connected to the two ends of the resistor RSENSE, and the output terminal of the Schmitt trigger COMP2 is connected to the MOS tube control module.

5. The anti-backflow circuit in the DC-DC converter according to claim 2, characterized in that: The MOS tube control module includes a Schmitt trigger COMP1, the in-phase end of the Schmitt trigger COMP1 is connected to the reference voltage acquisition module, the inverting end of the Schmitt trigger COMP1 is connected to the resistance voltage drop acquisition module, and the output end of the Schmitt trigger COMP1 is connected to the G pole of the MOS tube M3.

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