CHARGING CIRCUIT AND CHARGING SYSTEM

A charging circuit can include: a first port for receiving a first input source; a second port coupled to a second input source or an external device; and a power stage circuit configured to operate as a charge pump in a first state, and to operate as a hybrid switching converter in a second state, where the hybrid switching converter and the charge pump share at least part of a plurality of power switches.

RELATED APPLICATIONS

This application claims the benefit of Chinese Patent Application No. 202110160944.5, filed on Feb. 5, 2021, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to the field of power electronics, and more particularly to charging circuits and systems.

BACKGROUND

A switched-mode power supply (SMPS), or a “switching” power supply, can include a power stage circuit and a control circuit. When there is an input voltage, the control circuit can consider internal parameters and external load changes, and may regulate the on/off times of the switch system in the power stage circuit. Switching power supplies have a wide variety of applications in modern electronics. For example, switching power supplies can be used to drive light-emitting diode (LED) loads.

DETAILED DESCRIPTION

Batteries in portable devices can be charged from a variety of power sources, such as adapters and wireless power sources. A buck charger is a fairly common battery charger topology that converts a DC input voltage to a DC output voltage. A feedback loop is required in the buck charger to control the switching time of the power switch in the buck circuit, in order to maintain a stable output current or voltage required for battery charging. However, the efficiency usually drops when the input voltage of the buck charger is much higher than the battery voltage. Charge pump circuits (e.g., switching capacitor voltage converters) are more efficient than buck chargers when the voltage of the input source is much higher than the battery voltage. However, since the input voltage and battery voltage cannot maintain a fixed ratio during the charging process, a controller may be required to monitor the battery voltage and adjust the voltage of the input source (e.g., an adapter), which increases the control complexity, in order to realize battery charging.

Referring now toFIG. 1, shown is a schematic circuit diagram of a first example charging system, in accordance with embodiments of the preset invention. In this particular example, charging system100can include charging circuit101, control circuit102, and battery BAT. Charging circuit101can include ports IN1and IN2and a power stage circuit, where port IN1receives a first input source and port IN2receives a second input source or is connected to an external device (e.g., earphones). In this embodiment, the first input source can be an adjustable input source to generate adjustable voltage Vin1at port IN1, and the second input source may be a fixed input source to generate fixed voltageVin2at port IN2. Output terminal OUT of the power stage circuit can be coupled to battery BAT.

In one embodiment, the charging system can also include adapter103connected to port IN1, and USB power source104connected to port IN2. Adapter103can generate adjustable voltage Vin1at port IN1to charge battery BAT via the power stage circuit, and USB power source104can generate fixed voltage Vin2at port IN2to charge battery BAT via the power stage circuit. It should be understood that other types of input sources are applicable in certain embodiments. In addition, the charging system can also include input capacitors Cin1and Cin2. Input capacitor Cin1can connect to port IN1, input capacitor Cin2can connect to port IN2. In another example, the charging system can also include an external device, and port IN2can connect to the external device, such that battery BAT is discharged to charge the battery in the external device.

In particular embodiments, the power stage circuit can operate as a charge pump in a first state, and operate as a hybrid switching converter in a second state, where the hybrid switching converter and the charge pump share at least part of the power switches. The first state is that port IN1is connected to the first input source (adjustable input source) to charge battery BAT. The second state can be divided into two modes. The first mode is that port IN2is connected to the second input source (fixed input source) to charge battery BAT, and the hybrid switching converter may operate in a buck mode at this time. The second mode can be that port IN2is connected to an external device to charge the external device by battery BAT, and the hybrid switching converter may operate in a boost mode at this time.

For example, the power stage circuit can include switch network1001, which can include a plurality of power switches that are coupled between port IN1and the reference ground to form a plurality of switch intermediate nodes. The power stage circuit also can include at least one flying capacitor, and the two ends of each flying capacitor may respectively be connected to the corresponding switch intermediate nodes. The flying capacitor(s) and switch network1001may form the charge pump. In this embodiment, the charge pump may have a fixed voltage conversion ratio. Here, the output voltage or output current (e.g., the voltage or current at output terminal OUT) generated by the charge pump can be adjusted by adjusting voltage Vin1generated by the first input source. In addition, battery BAT and capacitor CBATcan connect in parallel between output terminal OUT and the reference ground.

It should be understood that depending on the number and/or the connection manner of the power switches and the flying capacitor(s) in switch network1001, output voltages with different voltage conversion ratios can be generated at output terminal OUT. In particular embodiments, any suitable switching capacitor topology can be utilized as the charge pump. The power stage circuit can also include inductor L, which can connect between port IN2and the corresponding power switch in switch network1001. Inductor L, the flying capacitor(s), and at least part of the power switches in switch network1001may form the hybrid switching converter. The output voltage or output current generated by the hybrid switching converter can be adjusted by adjusting the duty cycle of the power switches in the hybrid switching converter.

Charging circuit101can also include switches QBLK1and QBLK2. When the power stage circuit operates as the charge pump in the first state, switch QBLK1can be controlled to be in an on state to receive the first input source, while the switch QBLK2can be controlled to be in an off state, in order to prevent voltage Vin1generated by the first input source or other voltages in charging circuit101from being transmitted to port IN2and affecting the power source or device connected to port IN2. When the power stage circuit operates as the hybrid switching converter in the second state, switch QBLK2can be controlled to be in an on state to receive the second input source, while switch QBLK1can be controlled to be in an off state, in order to prevent voltage VIN2generated by the second input source or other voltages in charging circuit101from being transmitted to port IN1and affecting the power source or device connected to port IN1.

Control circuit102can generate a corresponding control signal according to current feedback signal Ifb representing the output current or voltage feedback signal Vfb representing the output voltage to control the operating state of the power stage circuit, in order to meet the charging and discharging requirements. For batteries, there are generally two modes for charging: constant current charging mode, and constant voltage charging mode. For example, when the voltage of battery BAT is lower than a first threshold (e.g., 3V), battery BAT may need to be charged at the constant current charging mode with a smaller current. When the voltage of battery BAT is higher than the first threshold, battery BAT can be charged at the constant current charging mode with a larger current. When the voltage of battery BAT is higher than a second threshold (e.g., 4.2V), battery BAT can be fully charged, and battery BAT may start to enter the constant voltage charging mode.

In the example ofFIG. 1, sampling resistor Rs can connect in series between output terminal OUT of the power stage circuit and battery BAT. Current feedback signal Ifb can be obtained by obtaining the voltage difference between the two ends of sampling resistor Rs, and different desired charging currents can be achieved by setting different current reference signals. In addition, voltage feedback signal Vfb can be obtained by sampling the voltage across capacitor CBAT, in order to perform constant voltage charging control on battery BAT.

Referring now toFIG. 2, shown is a schematic circuit diagram of a second example charging system, in accordance with embodiments of the present invention. In this example charging system, charging circuit101can also include switch QBATconnected in series between output terminal OUT of the power stage circuit and battery BAT. For example, switch QBATcan be a MOSFET with a variable substrate; that is, the direction of the anode of its body diode can be selectively changed to adapt to different situations. Also, the current sampling can be performed by using switch QBATto replace sampling resistor Rs inFIG. 1. In this example, when the voltage of battery BAT is higher than the first threshold, switch QBATcan be controlled to be in a fully conducting state. When battery BAT is not fully charged, current feedback signal Ifb can be obtained by sampling the current of switch QBAT, in order to perform constant current charging on battery BAT. When battery BAT is fully charged, voltage feedback signal Vfb can be obtained by obtaining the voltage of the first terminal (e.g., at output terminal OUT) of switch QBAT, in order to perform constant voltage charging on battery BAT.

In addition, when the voltage of battery BAT is lower than the first threshold, that is, when battery BAT is under-voltage, control circuit102can control the voltage at output terminal OUT to be equal to a desired voltage by acquiring the voltage at the first terminal (e.g., at output terminal OUT) of switch QBATas voltage feedback signal Vfb, in order to normally power the additional load (not shown inFIG. 2) connected to output terminal OUT. At this time, switch QBATcan be controlled to operate in a linear state (e.g., operate as a low-dropout [LDO] regulator) by controlling the driving voltage of switch QBATto generate a small constant current to charge battery BAT, in order to avoid excessive current for charging battery BAT. In addition, charging circuit101can also include output capacitor COUT, which can connect between output terminal OUT and the reference ground.

Control circuit102can control the power stage circuit to operate as the charge pump when detecting that port IN1is connected to an adjustable input source (e.g., an adapter), and may generate adjustment signal Vaj according to current feedback signal Ifb or voltage feedback signal Vfb, in order to adjust voltage Vin1generated by the first input source at port IN1to meet the charging requirement of battery BAT. In addition, control circuit102can generate control signals according to the preset control logic to control the switching states of the power switches, such that the voltage conversion ratio of the charge pump is constant. Control circuit102can control the power stage circuit to operate as the hybrid switching converter in a buck mode when detecting that port IN2is connected to a fixed input source (e.g., a USB power source), and may adjust the duty cycle of power switches according to current feedback signal Ifb or voltage feedback signal Vfb, in order to generate control signals to control the switching states of the power switches to meet the charging requirements of battery BAT.

When the battery is fully charged, control circuit102can control the power stage circuit to operate as the hybrid switching converter in a boost mode when detecting that port IN2is connected to an external device, and may adjust the duty cycle of power switches according the voltage generated at port IN2and the current flowing through port IN2, in order to generate control signals to control the switching states of the power switches to meet the charging requirements of external devices. Of course, if necessary, the duty cycle of the power switches also can be adjusted according to the discharge current of battery BAT, such that the discharge current does not exceed a current limit value.

Referring now toFIG. 3, shown is a schematic circuit diagram of a first example charging circuit, in accordance with embodiments of the present invention. In this particular example, the charge pump with the voltage conversion ratio of 2:1, that is, Vin1/Vout=2, is utilized. Of course, charge pumps with other voltage conversion ratios (e.g., 3:1, 4:1, . . . , N:1, etc.) are also suitable in certain embodiments. While the charging circuit with switch QBATis exemplified herein, it should be understood that the charging circuit without switch QBATmay also be applicable in certain embodiments. In this particular example, switch network1001can include power switches Q1-Q4sequentially connected in series between port IN1and the reference ground to form switch intermediate nodes n1-n3. The power stage circuit can include flying capacitor CFLYconnected between intermediate node n1and switch intermediate node n3. Switch intermediate node n2can be used as output terminal OUT, and can be coupled to battery BAT. In this example, output terminal OUT can connect to battery BAT via switch QBAT. For example, inductor L can be coupled between port IN2and switch intermediate node n1, and inductor L, flying capacitor CFLY, and power switches Q2-Q4may form the hybrid switching converter. In another example, inductor L can be coupled between port IN2and the first end of power switch Q1, and inductor L, flying capacitor CFLY, and power switches Q1-Q4may form the hybrid switching converter.

The power stage circuit can also include switch QBLK1connected to port IN1, and switch QBLK2connected to port IN2. For example, switch QBLK1can connect between port IN1and power switch Q1, and switch QBLK2can connect between the second end of inductor L and switch intermediate node n1. It should be understood that in other embodiments, switches QBLK2may be connected between port IN2and the first end of inductor L. When the power stage circuit operates as the charge pump, switch QBLK1can be turned on, and switch QBLK2may be turned off. When the power stage circuit operates as the hybrid switching converter, switch QBLK1can be turned off, and switch QBLK2may be turned on.

In this embodiment, the voltage conversion ratio of the charge pump can be controlled to remain constant, and there may be no need to adjust the duty cycle of the power switches according to the voltage feedback signal or the current feedback signal. Therefore, when the charge pump is operating, an external adjustable input source (e.g., an adapter) may need to be connected to port IN1to meet the requirements of the charging voltage and charging current of the battery at different stages, such that the desired charging voltage and charging current can be obtained by adjusting voltage Vin1generated by the first input source. It should be understood that other suitable control methods can also be used to control the operating states of the charge pump to adjust output voltage Vout in certain embodiments.

In this embodiment, for the hybrid switching converter, the duty cycle of the power switches may be adjusted according to the voltage feedback signal or the current feedback signal, in order to adjust output voltage Vout and output current Iout to meet the requirements of the charging voltage and charging current of the battery at different stages. It should be understood that when the external device is charged by the battery, the voltage and current at port IN2are output voltage Vout and output current Iout adjusted by the hybrid switching converter, respectively, in order to meet the charging requirements of the external device.

Referring now toFIG. 4, shown is a schematic block diagram of an example control circuit, in accordance with embodiments of the present invention. The control circuit will be described in detail below with reference toFIGS. 3 and 4. As shown inFIG. 4, control circuit102can include error amplifier EA1, error amplifier EA2, regulator105, pulse-width modulation (PWM) generating circuit106, and driving circuit107. Error amplifier EA1can generate error signal Err1according to current reference signal Iref representing the desired value of output current Iout and current feedback signal Ifb representing output current Iout. Error amplifier EA2can generate error signal Err2according to voltage reference signal Vref representing the desired value of output voltage Vout and voltage feedback signal Vfb representing output voltage Vout. Regulator105can generate adjustment signal Vaj according to error signal Err1or error signal Err2when the power stage circuit operates as the charge pump, in order to adjust voltage Vin1generated by the first input source. When the power stage circuit operates as the hybrid switching converter, regulator105may not operate.

In this embodiment, in the first mode, output current Iout can be controlled to be constant, and regulator105can generate adjustment signal Vaj according to error signal Err1to adjust voltage Vin1output by adapter103(e.g., the first input source). Thereby, output current Iout flowing through output terminal OUT of the power stage circuit may be equal to the desired charging current. In the second mode, output voltage Vout can be controlled to be constant, adjustment signal Vaj is generated according to error signal Err2to adjust voltage Vin1output by adapter103, such that output voltage Vout at output terminal OUT of the power stage circuit is equal to the desired charging voltage. For example, error signal Err1can be generated according to current feedback signal Ifb representing output current Iout flowing through output terminal OUT of the power stage circuit and current reference signal Iref, and error signal Err2can be generated according to voltage feedback signal Vfb representing output voltage Vout at output terminal OUT of the power stage circuit and voltage reference signal Vref.

In this embodiment, adjustment signal Vaj may be positively correlated with error signal Err1or error signal Err2. When error signal Err1or error signal Err2is positive and its value is larger, adjustment signal Vaj may correspondingly be larger, thereby rapidly increasing voltage Vin1output by adapter103to increase the output current or voltage, and otherwise decreasing voltage Vin1output by adapter103to reduce the output current or voltage. It should be understood that any other suitable battery charging control method can be applied in certain embodiments. PWM generating circuit106can directly generate the switching control signal Vg according to the preset control logic when the power stage circuit operates as the charge pump, in order to control the switching states of the power switches in the charge pump, such that the charge pump maintains a fixed voltage conversion ratio.

PWM generating circuit106can generate switching control signal Vg according to error signal Err1or error signal Err2to adjust the duty cycle of the power switches in the hybrid switching converter when the power stage circuit operates as the hybrid switching converter. For example, when battery BAT is charged via the hybrid switching converter, in the first mode, output current Tout can be controlled to be constant, and the duty cycle of the power switches in the hybrid switching converter may be adjusted according to error signal Err1, such that output current Tout flowing through output terminal OUT of the power stage circuit is equal to the desired charging current. In the second mode, output voltage Vout can be controlled to be constant, and the duty cycle of the power switches in the hybrid switching converter may be adjusted according to error signal Err2, such that output voltage Vout at output terminal OUT of the power stage circuit is equal to the desired charging voltage. For example, error signal Err1can be generated according to current feedback signal Ifb representing output current Tout flowing through output terminal OUT of the power stage circuit and current reference signal Iref, and error signal Err2can be generated according to voltage feedback signal Vfb representing output voltage Vout at output terminal OUT of the power stage circuit and voltage reference signal Vref.

When battery BAT charges the external device via the hybrid switching converter, in the first mode, output current Tout can be controlled to be constant, and the duty cycle of the power switches in the hybrid switching converter is adjusted according to error signal Err1, such that output current Tout flowing through port IN2is equal to the desired charging current. In the second mode, output voltage Vout can be controlled to be constant, and the duty cycle of the power switches in the hybrid switching converter may be adjusted according the error signal Err2, such that output voltage Vout at port IN2is equal to the desired charging voltage. For example, error signal Err1can be generated according to current feedback signal Ifb representing output current Tout flowing through port IN2and current reference signal Iref, and error signal Err2can be generated according to voltage feedback signal Vfb representing output voltage Vout at port IN2and voltage reference signal Vref. Of course, it can also be realized by limiting the discharge current of battery BAT. It should be understood that any suitable control method can be utilized to adjust the duty cycle of the power switches in the hybrid switching converter (e.g., comparing the error signal with a ramp signal to generate a PWM control signal, or using a fixed on-time to adjust the off-time to adjust the switching frequency) in certain embodiments.

Drive circuit107can generate control signals G1-G4of power switches Q1-Q4according to switching control signal Vg. When the power stage circuit operates as the charge pump, switching control signal Vg is the preset control logic and may not be affected by error signal Err1or error signal Err2; that is, control signals G1-G4of power switches Q1-Q4may remain unchanged. When the power stage circuit operates as the hybrid switching converter, switching control signal Vg can change according to the change of error signal Err1or error signal Err2. In this example, by integrating both the charge pump and the hybrid switching converter in the power stage circuit, different modes can be adopted in different charging occasions, thereby ensuring that the charging system has good efficiency without adding additional power devices.

Referring now toFIG. 5, shown is a schematic circuit diagram of the first example charging circuit in a first state, in accordance with embodiments of the present invention. In this particular example, in the first state, switch QBLK2can be turned off, thereby blocking the influence of voltage VIN1output by the first input source and other voltages in the charging circuit on port IN2, and switch QBLK1may be turned on, such that the charging circuit is a charge pump that receives voltage VIN1output by the first input source, and can include power switches Q1-Q4and flying capacitor CFLY. In this example, a general control logic can control the charge pump; that is, the control signals of power switches Q2and Q4are the same, the control signals of power switches Q1and Q3are the same, and the phase difference between the control signals of power switch Q1and power switch Q2is 180°. Therefore, the charge pump may have two stages of operation. In the first stage, power switches Q1and Q3can be turned on, and power switches Q2and Q4may be turned off. In this stage, flying capacitor CFLYcan connect in series with output capacitor COUT; that is, Vin1−VCFLY=Vout. In the second stage, power switches Q2and Q4can be turned on, and power switches Q1and Q3may be turned off. In this stage, flying capacitor CFLYcan connect in parallel with output capacitor COUT; that is, VCFLY=Vout. Thus, it can be concluded that: VCFLY=Vout=(½)*Vin1, and Iout=2*Iin1.

Referring now toFIGS. 6A and 6B, shown are schematic circuit diagrams of the first example charging circuit in a second state, in accordance with embodiments of the present invention. In the second state, switch QBLK1can be turned off, thereby blocking the influence of voltage VIN2output by the second input source and other voltages in the charging circuit on port IN1, and switch QBLK2may be turned on, such the charging circuit is a hybrid switching converter, that can include inductor L, power switches Q2-Q4, and flying capacitor CFLY. In this example, power switch Q1can be controlled to be off in this state.

According to the different components connected to port IN2, the hybrid switching converter may have two operating modes. When port IN2is connected to the second input source, output voltage Vout can be the voltage on output capacitor COUT, and output current Iout the current flowing to battery BAT, as shown inFIG. 6A. At this time, the hybrid switching converter may operate in the buck mode. When port IN2is connected to an external device, battery BAT can be used as an input source, output voltage Vout may be the voltage on input capacitor Cin2, output current Iout can be the current flowing to port IN2, and battery BAT may be discharged to charge the external device, as shown inFIG. 6B. At this time, the hybrid switching converter may operate in the boost mode.

Referring now toFIG. 7, shown is a waveform diagram of an example operation of the first example charging circuit in the second state, in accordance with embodiments of the present invention. The operating principle of the hybrid switching converter will be described in detail below with reference toFIGS. 6 and 7. As shown inFIG. 7, in the second state, control signals G2and G4of power switches Q2and Q4are the same, and the duty cycle is D. Control signal G3of power switch Q3can be complementary to control signals G2and G4(e.g., power switch Q3and power switch Q2(or Q4) are turned on alternately).

There are two stages when the hybrid switching converter operates in the buck mode. As shown inFIG. 6A, in first stage t0-t1, power switches Q2and Q4can be turned on, power switch Q3turned off, and flying capacitor CFLYcan connect in parallel with output capacitor COUTand capacitor CBAT; that is, VCFLY=Vout. In addition, in first stage t0-t1, the second input source may store energy in inductor L, and inductor current iL can increase. In second stage t1-t2, power switches Q2and Q4can be turned off, power switch Q3may be turned on, and flying capacitor CFLYcan connect in series with output capacitor COUT. In second stage t1-t2, inductor L may release energy and inductor current iL can decrease. Combining the above two stages, according to the volt-second balance principle of inductor L, the following Formula (1) can be obtained.

From Formula (1), it can be concluded that: Vout/Vin2=1/(2−D), where D is the duty cycle of power switches Q2and Q4. That is, the variation range of output voltage Vout is 0.5Vin2˜Vin2. In addition, it can also be concluded that: Iout/Iin2=2−D; that is, the variation range of output current Iout is Iin2−2Iin2.

There are also two stages when the hybrid switching converter operates in the boost mode. As shown inFIG. 6B, in first stage t0-t1, power switches Q2and Q4can be turned on, power switch Q3may be turned off, and flying capacitor CFLYcan connect in parallel with output capacitor COUTand capacitor CBAT. As such, the voltage VCFLYacross flying capacitor CFLYis equal to voltage VCBATacross capacitor CBAT; that is, VCFLY=VCBAT. In addition, in first stage t0-t1, battery BAT may store energy in inductor L, and inductor current iL can increase. In second stage t1-t2, power switches Q2and Q4can be turned off, power switch Q3may be turned on, and flying capacitor CFLYcan connect in series with capacitor CBAT. In second phase t1-t2, inductor L may release energy and inductor current iL can decrease. Combining the above two stages, according to the volt-second balance principle of inductor L, the following Formula (2) can be obtained.

From Formula (2), it can be concluded that: Vout=(2−D)×VCBAT, where D is the duty cycle of power switches Q2and Q4. That is, the variation range of output voltage Vout is VCBAT˜2VCBAT. In addition, it can also be concluded that: Iout/IB=1/(2−D); that is, the variation range of output current Iout is 0.5IB˜IB.

Referring now toFIG. 8, shown is a schematic circuit diagram of a second example charging circuit, in accordance with embodiments of the present invention. In this particular example, inductor L can be coupled between port IN2and the first end of power switch Q1(e.g., between port IN2and switch QBLK2). The structure and composition of the rest of the charging circuit are substantially the same as those in the example ofFIG. 3. In addition, when the structure of the charging circuit is as shown inFIG. 8, the operating principle of the charge pump is substantially the same as the above, and the operating principle of the hybrid switching converter is slightly different. When the charging circuit operates as the hybrid switching converter, power switch Q1may always be controlled to be in an on state, and the switching states of power switches Q2-Q4can be the same as those in the charging circuit shown inFIG. 3, which does not affect the operation of hybrid switching converter.

The charging system according to the particular embodiments can include a dual-input charging circuit, which can operate as the charge pump when an adjustable input source is input, and may operate as the switching converter when a fixed input source is input to get higher efficiency. In addition, the charging system has fewer power switches than other approaches, thereby reducing system cost. In particular embodiments, the power switch can use any suitable electrically controllable switching devices, such as metal-oxide-semiconductor field-effect transistors (MOSFET), bipolar-junction transistors (BJT), or insulated-gate bipolar transistor (IGBT).