WO2015003541A1

WO2015003541A1 - Power supply switching circuit and switching method between external power supply and battery power supply

Info

Publication number: WO2015003541A1
Application number: PCT/CN2014/079775
Authority: WO
Inventors: 詹昶; 陈松涛; 皮涛
Original assignee: 深圳市汇顶科技股份有限公司
Priority date: 2013-07-09
Filing date: 2014-06-12
Publication date: 2015-01-15
Also published as: CN103326458A; CN103326458B

Abstract

A power supply switching circuit and switching method between external power supply and battery power supply. The power supply switching circuit comprises: a switch, a first step-down transformer, a second step-down transformer, a third step-down transformer, a voltage reference module, a voltage divider, a comparator, and a level shift module. When a voltage of the external power supply is not less than a preset voltage threshold, the level shift module controls the switch to cut off a path from the battery to load; and when the voltage of the external power supply is less than the preset voltage threshold, the level shift module controls the switch to connect the path from the battery to the load. By using the power supply switching circuit and switching method, selection of system power supply can be implemented only by using one switch, thereby simplifying a structure of a control circuit and improving reliability of the circuit.

Description

Description: An external power supply and battery powered power switching circuit and switching method

The present invention relates to the field of electronic circuit technologies, and in particular, to an external power supply and a battery-powered power supply switching circuit and a switching method. Background technique

In an electronic system with both external power and battery power, the power switching circuit needs to control two sets of switches to control the connection and disconnection of the external power supply, as well as the connection and disconnection of the battery power. And use one of the power supplies to power the system based on the voltage relationship between the external power source and the battery power source. The status of the two sets of switches needs to be strictly guaranteed. Otherwise, if two power supplies are connected at the same time or disconnected at the same time, the system may be faulty. Summary of the invention

In view of the above, the technical problem to be solved by the present invention is to provide an external power supply and a battery-powered power supply switching circuit and a switching method, so that only one set of switches can be used to realize the selection of the system power supply, thereby simplifying the circuit structure and improving the circuit. reliability.

The technical solution adopted by the present invention to solve the above technical problems is as follows:

According to an aspect of the present invention, an external power supply and battery power supply switching circuit is provided, including: a switch, a first buck, a second buck, a third buck, a voltage reference module, a voltage divider, and a comparison And level shifting modules, where:

The input of the first buck is connected to the external power supply, the output is connected to the voltage reference module and the comparator; the input of the second buck is connected to the battery power, and the output is connected to the voltage reference module and the comparator; The input of the buck is connected to the external power supply, and the output is connected to the load; the input of the voltage divider Connect an external power supply, the output is connected to one input of the comparator; the input of the voltage reference module is connected to the output of the first buck and the second buck, and the output is connected to one input of the comparator; the comparator is based on the voltage The comparison result of the reference module and the voltage divider outputs a logic signal to the input end of the level shifting module; the switch has one end connected to the battery power source, the other end is connected to the load, the control end is connected to the level shifting module; and the output terminal of the level shifting module is connected to the switch The control terminal controls the on and off of the switch through logic signals.

Preferably, the first buck is a diode, a triode or a MOSFET.

Wherein, when the first buck is a diode, the anode of the diode is connected to an external power source, and the cathode is connected to the voltage reference module and the comparator; when the first buck is an NPN transistor, the collector and the base of the NPN transistor are connected externally The power supply, the emitter is connected to the voltage reference module and the comparator; when the first buck is a PNP transistor, the emitter of the PNP transistor is connected to the external power source, the base and the collector are connected to the voltage reference module and the comparator; When the buck is a 匪OS tube, the drain terminal, the gate terminal and the substrate of the 匪OS tube are connected to an external power source, and the source terminal is connected to the voltage reference module and the comparator; when the first buck is a PM0S tube, the PM0S tube The source is connected to an external power supply, and the drain, gate, and substrate are connected to a voltage reference module and a comparator.

Preferably, the second buck is a diode, a triode or a MOSFET.

Wherein, when the second buck is a diode, the anode of the diode is connected to the battery power source, the cathode is connected to the voltage reference module and the comparator; when the second buck is an NPN transistor, the collector and the base of the NPN transistor are connected to the battery The power supply, the emitter is connected to the voltage reference module and the comparator; when the second buck is a PNP transistor, the emitter of the PNP transistor is connected to the battery power, the base and the collector are connected to the voltage reference module and the comparator; When the buck is a 匪OS tube, the drain terminal, the gate terminal and the substrate of the 匪OS tube are connected to the battery power source, and the source terminal is connected to the voltage reference module and the comparator; when the second step-down device is the PM0S tube, the PM0S tube The source is connected to an external power supply, and the drain, gate, and substrate are connected to a voltage reference module and a comparator.

Preferably, the third buck is a diode, a triode or a MOSFET.

Wherein, when the third buck is a diode, the anode of the diode is connected to an external power source, and the cathode is connected Load; when the third buck is an NPN transistor, the collector and base of the NPN transistor are connected to an external power source, and the emitter is connected to the load; when the third buck is a PNP transistor, the emitter of the PNP transistor is connected to an external power source, The base and the collector are connected to the load; when the third step-down device is the 匪OS tube, the drain terminal, the gate terminal and the substrate of the 匪OS tube are connected to the external power source, the source end is connected to the load; when the third step-down device is connected For the PM0S tube, the source of the PM0S tube is connected to an external power supply, and the drain terminal, the gate terminal, and the substrate are connected to the load.

Preferably, the switch comprises: two PM0S tubes MP1 and MP2 connected in series, the source end of the MP1 and the substrate are connected to the battery power supply, the drain end is connected to the drain end of the MP2, the gate end is connected with the control signal; the source end of the MP2 and the substrate are connected to the load The gate terminal is connected to the control signal. According to another aspect of the present invention, an external power supply and battery power supply switching method provided includes: controlling a switch to cut off a battery-to-load path when detecting that an external power supply voltage is not lower than a preset voltage threshold; When the voltage to the external power source is lower than the preset voltage threshold, the control switch connects the battery to the load path.

Preferably, the preset voltage threshold is less than the sum of the lowest battery operating voltage and the buck value of the third buck.

Preferably, the predetermined voltage threshold is achieved by the relative relationship between the output voltage of the voltage reference module and the output voltage of the voltage divider output.

The power switching circuit and the switching method provided by the invention remove the battery power to the outside when the external power source is dead, by introducing a step-down device between the external power source and the output voltage. The risk of power supply back-up, so only one switch is needed to control the battery power; when the battery power supplies the load, the threshold voltage of the control switch SW1 is set to avoid the generation of charging current from the external power source to the battery power source. Therefore, the selection of the system power supply can be realized by using only one set of switches, which simplifies the structure of the control circuit and improves the circuit reliability. DRAWINGS

FIG. 1 is a schematic structural diagram of a power switching circuit according to an embodiment of the present invention. 2 is a schematic structural diagram of a power switching circuit according to a preferred embodiment of the present invention.

FIG. 3 is a schematic structural diagram of another power switching circuit according to a preferred embodiment of the present invention. detailed description

The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It is understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Embodiment 1 is shown in FIG. 1 as an external power supply and a battery power supply switching circuit. The power switching circuit includes: a switch SW1, a first buck 10, a second buck 20, and a third buck 30. Voltage reference module 40, voltage divider 50, comparator 60 and level shifting module 70, wherein:

The input of the first buck 10 is connected to an external power supply, the output is connected to the voltage reference module 40 and the comparator 60; the input of the second buck 20 is connected to the battery power, and the output is connected to the voltage reference module 40 and Comparator 60; the input end of the third buck 30 is connected to an external power supply, and the output is connected to the load; the input of the voltage divider 50 is connected to an external power supply, and the output is connected to an input of the comparator 60; The input terminal is connected to the output terminals of the first buck 10 and the second buck 20, and the output terminal is connected to one input terminal of the comparator 60; the comparator 60 outputs a logic signal according to the comparison result of the voltage reference module 40 and the voltage divider 50. To the input of the level shifting module 70; the switch SW1, the end is connected to the battery power, the other end is connected to the load, the control end is connected to the level shifting module 70; the output of the level shifting module 70 is connected to the control end of the switch SW1, through the logic The signal controls the on and off of the switch SW1.

Specifically, when the voltage of the external power source is not lower than the threshold voltage set by the circuit, the comparator 60 generates a logic signal net03 for outputting to the level shifting module 70, and the level shifting module 70 performs level shifting of the logic signal net03. The logic signal net04 controls the switch SW1 to turn off, turns off the path between the battery power supply and the load, and the external power supply supplies power to the load through the third buck 30. When the voltage of the external power source is lower than the threshold voltage set by the circuit, the comparator 60 generates a logic signal net03 output to the level shift. The module 70, the level shifting module 70 performs level shifting of the logic signal net03 to generate a logic signal net04 to control the switch SW1 to be turned on, and the battery power source supplies power to the load through the switch SW1.

In this embodiment, due to the reverse cut-off characteristic of the third buck, the voltage from the output voltage VDD2 to the external power source does not overflow. However, due to the two-phase conduction characteristic of the switch SW1, if the battery voltage is less than the difference between the voltage of the external power source and the voltage of the third step-down device, there is a risk that the external power source charges the battery through the third buck and the switch SW1. . Therefore, the circuit needs to set an appropriate threshold voltage VTM according to the operating voltage range of the battery, assuming that the operating voltage of the battery is at least VBAT _MIN and the step-down value of the buck is V _d . _{Wn The} threshold voltage _VTM can be determined by the following formula:

VTM < VBATMIN + V _D , ( 1 )

In the present embodiment, the setting of the threshold voltage VTM is realized by the relative relationship between the output reference voltage netO1 of the voltage reference module 40 and the output divided voltage net02 of the voltage divider 50. The reference voltage netOl is a relatively constant voltage; and the divided voltage net02 is the linear divided voltage of the external power supply. Assuming that the voltage of the external power supply is V _BUS , the partial voltage coefficient is l/k, ie net02 = (l/k) *VBUS , the threshold voltage VTM can be calculated by the following formula:

V _TH = (net01/net02) *V _BUS = k*net01 ( 2 )

As a preferred embodiment of the present embodiment, the first buck 10, the second buck 20, and the third buck 30 include, but are not limited to, diodes, transistors, or MOSFETs.

In summary, regardless of the voltage of the battery power supply, as long as the voltage of the external power supply is not lower than the threshold voltage VTM set by the circuit, the logic signal net04 controls the switch SW1 to be turned off, and the path between the battery power and the load is turned off. The external power supply supplies the output voltage VDD2 to the load through the third buck. Due to the reverse-cut characteristic of the third buck, the voltage from the output voltage VDD2 to the external power supply does not overflow, and at the same time, as long as the preset voltage threshold It is less than the sum of the lowest battery operating voltage and the buck value of the third buck, and the external power supply does not charge the battery through the switch SW1. Embodiment 2

FIG. 2 is a schematic structural diagram of a power switching circuit according to a preferred embodiment of the present invention. In this embodiment, three diodes are used to implement the functions of the buck, specifically including: a switch SW1, three diodes D l, D2, D3, a voltage reference module 40, a voltage divider 50, a comparator 60, and a level shifting module. 70, where:

One end of the switch SW1 is connected to the battery power supply, the other end is connected to the output voltage VDD2, the control signal net04 is from the level shifting module 70; the anode of the diode D1 is connected to the external power supply, the cathode is connected to the internal step-down voltage VDD1; the anode of the diode D2 is connected to the battery power supply, the cathode Connect the internal step-down voltage VDD 1 ; the anode of the diode D3 is connected to the external power supply, the cathode is connected to the output voltage VDD2; the input of the voltage divider 50 is connected to the external power supply, and the output divided voltage net02 is connected to one input of the comparator 60; The operating power of 40 is the internal step-down voltage VDD1, and the output reference voltage netO l is connected to the other input terminal of the comparator 60; the operating power of the comparator 60 is the internal step-down voltage VDD1, and the output logic signal net03 is connected to the level shifting module 70. The input terminal; the level shifting module 70 outputs the logic signal net03 after the level shifting, and the logic signal net04 controls the turning on and off of the switch SW1.

In this embodiment, the lithium battery is taken as an example. The typical lithium battery operating voltage is about 3V~4. 2V, assuming that the step-down value of the diode is 0. 7V, then by the formula VTM < VBATMTM + V, _:: It can be seen that the threshold voltage setting range is VTM < 3. 7V.

Regardless of the voltage of the battery power supply, as long as the voltage of the external power supply is not lower than the threshold voltage set by the circuit 3. 7V, the logic signal net04 controls the switch SW1 to be turned off, the path between VBAT and the load is turned off, and the external power supply passes through the diode. D3 output voltage VDD2 supplies power to the load. The output voltage VDD2 is equal to the difference between the external power supply voltage and the diode D3. For example, when the external power supply voltage is 3.7V, the output voltage is 3V.

When the voltage of the external power supply is lower than the threshold voltage set by the circuit, the logic signal net04 controls the switch SW1 to be turned on, and the battery power supplies the voltage to the load through the output voltage VDD2 of the switch SW1. Due to the reverse cut-off characteristic of the diode D3, the VDD2 is inverted to the voltage of the external power supply. However, due to the bi-directional characteristics of the switch SW1, the threshold voltage required to meet the above formula (1) is required to avoid the external power supply charging the battery through the switch SW1.

In this embodiment, the voltage of the internal step-down voltage VDD1 is equal to (V _BUS - 0.7 V) or (V _BAT - 0. 7V) The one with the higher voltage. Therefore, any of the external power source and the battery power source can be powered, and the voltage reference module 40 and the comparator 60 can be powered. The minimum voltage of VDD1 is only VBAT _MIN - 0.7V when the system is only powered by the battery. Therefore, it is ensured that the control function of the power switch can be realized. The minimum operating voltage of the voltage reference module 40 and the comparator 60 must be lower than VDD1. Minimum voltage. The minimum operating voltage of the voltage reference module 40 and the comparator 60 must be lower than 2. 3V.

Of course, the step-down value of the diode in this embodiment is merely an example, and other types of diodes may be selected in practice, and a triode and a MOS tube may be used instead.

Specifically, when an NPN transistor is used instead of the diode D1, the collector and the base of the NPN transistor are connected to an external power source, and the emitter is connected to the voltage reference module 40 and the comparator 60; when a PNP transistor is used instead of the diode D1, the PNP transistor The emitter is connected to the external power source, the base and the collector are connected to the voltage reference module 40 and the comparator 60; when the 匪OS tube is used instead of the diode D1, the drain terminal, the gate terminal and the substrate of the 匪OS tube are connected to the external power source, the source The terminal is connected to the voltage reference module 40 and the comparator 60; when the PMOS transistor is used instead of the diode D1, the source of the PM0S transistor is connected to an external power supply, and the drain terminal, the gate terminal and the substrate are both connected to the voltage reference module 40 and the comparator 60.

When the NPN transistor is used instead of the diode D2, the anode of the diode is connected to the battery power source, and the cathode is connected to the voltage reference module 40 and the comparator 60. When the NPN transistor is used instead of the diode D2, the collector and the base of the NPN transistor are connected to the battery power source, and the emission is performed. The pole is connected to the voltage reference module 40 and the comparator 60; when the PNP transistor is used instead of the diode D2, the emitter of the PNP transistor is connected to the battery power source, and the base and the collector are connected to the voltage reference module 40 and the comparator 60; When the diode replaces the diode D2, the drain terminal, the gate terminal and the substrate of the 匪OS tube are connected to the battery power source, and the source terminal is connected to the voltage reference module 40 and the comparator 60; when the PM0S tube is used instead of the diode D2, the source end of the PM0S tube An external power supply is connected, and the drain terminal, the gate terminal and the substrate are both connected to the voltage reference module 40 and the comparator 60.

When the NPN transistor is used instead of the diode D3, the collector and the base of the NPN transistor are connected to the external power source, and the emitter is connected to the load. When the PNP transistor is used instead of the diode D3, the emitter of the PNP transistor is connected to the external power source, the base and the collector are connected. To the load; when using 匪0S tube instead of diode D3 When the drain end, the gate end and the substrate of the 匪OS tube are connected to the external power source, the source end is connected to the load; when the PM0S tube is used instead of the diode D3, the source end of the PM0S tube is connected to the external power source, the drain end, the gate end and the lining The bottom is connected to the load. Embodiment 3

FIG. 3 is a schematic structural diagram of a power switching circuit according to a preferred embodiment of the present invention. This embodiment further exemplifies the scheme of the switch SW1 on the basis of the second embodiment, and the same part as the second embodiment is not heavy here. Said. The switch SW1 comprises: two series connected PM0S tubes MP1 and MP2, the source end of the MP1 and the substrate are connected to the battery power supply, the drain end is connected to the drain end of the MP2, and the gate end is connected to the control signal net04a of the level shifting module 70 _; the source end of the MP2 The load is connected to the substrate, and the gate terminal is connected to the control signal net04b of the level shifting module 70. The control signal net04 in Fig. 2 is split into two in-phase control signals net04a and net04b in Fig. 3. When the voltage of the external power supply is lower than the threshold voltage, the control signals net04a and net04b are both low level of 0V voltage, the switch SW1 is turned on, and the battery power supplies power to the load through the switch SW1. When the voltage of the external power supply is not lower than the threshold voltage, net04a is the high level of the VBAT voltage, net04b is the high level of the VDD2 voltage, the switch SW1 is turned off, the path between the battery power supply and the load is turned off, and the external power supply passes through the diode. D3 supplies power to the load.

It should be noted that, in this embodiment, since the PM0S tube is used to constitute the switch, the high level is turned off and the low level is turned on. When the PM0S tube is used, since the voltage domain of net03 is VDD1, the high level of net03 does not necessarily turn off the switch. Therefore, level shifting must be performed by level shifting module 70 to move MP4 control signal net 04a to The battery power supply is in the same voltage domain, and the MP2 control signal net04b is moved to the same voltage domain as the load power supply VDD2.

The preferred embodiments of the present invention have been described above with reference to the drawings, and are not intended to limit the scope of the invention. A person skilled in the art can implement the invention in various variants without departing from the scope and spirit of the invention. For example, the features of one embodiment can be used in another embodiment to obtain a further embodiment. Any modifications, equivalent substitutions and improvements made within the technical concept of the invention are intended to be included within the scope of the invention. Industrial applicability

The power switching circuit and the switching method provided by the invention remove the battery power to the outside when the external power source is dead, by introducing a step-down device between the external power source and the output voltage. The risk of power supply back-up, so only one switch is needed to control the battery power; when the battery power supplies the load, the threshold voltage of the control switch SW1 is set to avoid the generation of charging current from the external power source to the battery power source. Therefore, the selection of the system power supply can be realized by using only one set of switches, which simplifies the structure of the control circuit and improves the circuit reliability.

Claims

claims

1. An external power supply and battery-powered power supply switching circuit, including: a switch, a first voltage reducer, a second voltage reducer, a third voltage regulator, a voltage reference module, a voltage divider, a comparator and a level transfer module , in:

The input terminal of the first voltage regulator is connected to the external power supply, and the output terminal is connected to the voltage reference module and comparator; the input terminal of the second voltage regulator is connected to the battery power supply, and the output terminal is connected to the voltage reference module and comparator. device; the input terminal of the third voltage reducer is connected to an external power supply, and the output terminal is connected to a load; the input terminal of the voltage divider is connected to an external power supply, and the output terminal is connected to an input terminal of the comparator; the voltage reference The input end of the module is connected to the output end of the first voltage reducer and the second voltage reducer, and the output end is connected to an input end of the comparator; the comparator outputs according to the comparison result between the voltage reference module and the voltage divider. The logic signal is sent to the input end of the level transfer module; one end of the switch is connected to the battery power supply, the other end is connected to the load, and the control end is connected to the level transfer module; the output end of the level transfer module is connected to the switch The control terminal controls the on and off of the switch through logic signals.

2. The power switching circuit according to claim 1, characterized in that the first voltage reducer is a diode, a triode or a MOS tube.

3. The power switching circuit according to claim 2, wherein,

When the first voltage reducer is a diode, the anode of the diode is connected to the external power supply, and the cathode is connected to the voltage reference module and the comparator;

When the first voltage reducer is an NPN transistor, the collector and base of the NPN transistor are connected to the external power supply, and the emitter is connected to the voltage reference module and the comparator;

When the first voltage reducer is a PNP transistor, the emitter of the PNP transistor is connected to the external power supply, and the base and collector are connected to the voltage reference module and the comparator;

When the first voltage reducer is an NMOS tube, the drain end, gate end and substrate of the NMOS tube are all connected to the external power supply, and the source end is connected to the voltage reference module and the comparator;

When the first voltage reducer is a PMOS tube, the source end of the PMOS tube is connected to the external power supply, and the drain end, Both the gate terminal and the substrate are connected to the voltage reference module and the comparator.

4. The power switching circuit according to claim 1, wherein the second voltage reducer is a diode, a transistor or a MOS transistor.

5. The power switching circuit according to claim 4, wherein,

When the second voltage reducer is a diode, the anode of the diode is connected to the battery power supply, and the cathode is connected to the voltage reference module and the comparator;

When the second voltage reducer is an NPN transistor, the collector and base of the NPN transistor are connected to the battery power supply, and the emitter is connected to the voltage reference module and the comparator;

When the second voltage regulator is a PNP transistor, the emitter of the PNP transistor is connected to the battery power supply, and the base and collector are connected to the voltage reference module and the comparator;

When the second voltage reducer is an NMOS tube, the drain end, gate end and substrate of the NMOS tube are all connected to the battery power supply, and the source end is connected to the voltage reference module and the comparator;

When the second voltage reducer is a PMOS tube, the source end of the PMOS tube is connected to an external power supply, and the drain end, gate end and substrate are all connected to the voltage reference module and the comparator.

6. The power switching circuit according to claim 1, wherein the third voltage reducer is a diode, a transistor or a MOS transistor.

7. The power switching circuit according to claim 6, wherein,

When the third voltage reducer is a diode, the anode of the diode is connected to the external power supply, and the cathode is connected to the load;

When the third voltage reducer is an NPN transistor, the collector and base of the NPN transistor are connected to the external power supply, and the emitter is connected to the load;

When the third voltage reducer is a PNP transistor, the emitter of the PNP transistor is connected to the external power supply, and the base and collector are connected to the load;

When the third voltage reducer is a NMOS tube, the drain end, gate end and substrate of the NMOS tube are all connected to the external power supply, and the source end is connected to the load;

When the third voltage reducer is a PMOS tube, the source end of the PMOS tube is connected to the external power supply, and the drain end, Both the gate terminal and the substrate are connected to the load.

8. The power switching circuit according to any one of claims 1 to 7, wherein the switch includes: two PMOS tubes MP1 and MP2 connected in series, the source end and substrate of MP1 are connected to the battery power source, and the drain end The drain terminal of MP2 is connected, and the gate terminal is connected to the control signal; the source terminal and substrate of MP2 are connected to the load, and the gate terminal is connected to the control signal.

9. A method for switching between external power supply and battery power supply, the method includes:

When it is detected that the voltage of the external power supply is not lower than the preset voltage threshold, the control switch cuts off the path from the battery to the load; when it is detected that the voltage of the external power supply is lower than the preset voltage threshold, the control switch connects the path from the battery to the load. .

10. The power switching method according to claim 9, wherein the preset voltage threshold is less than the sum of the lowest value of the battery operating voltage and the voltage reduction value of the third voltage regulator.

11. The power switching method according to claim 9 or 10, wherein the preset voltage threshold is realized through the relative relationship between the output voltage of the voltage reference module and the output voltage output by the voltage divider.