SWITCH POWER SUPPLY CIRCUIT AND TERMINAL DEVICE

This application provides a switch power supply circuit and a terminal device, and the switch power supply circuit uses a second switch transistor to replace a diode in an asynchronous switch power supply circuit. A turn-on impedance of the switch transistor is very small, only tens of milliohms, so that a turn-on voltage drop in the switch power supply circuit is reduced from hundreds of millivolts to tens of millivolts, power loss of the switch power supply circuit is greatly reduced, and output efficiency is improved. Moreover, this solution uses a discrete component to form a control circuit to control a switch status of the second switch transistor without additionally setting a pulse width modulation (PWM) controller, and costs of the discrete component are far lower than costs of the PWM controller, reducing hardware costs of a switch power supply and simplifying a circuit design.

TECHNICAL FIELD

This application relates to the field of power electronics technologies, and in particular, to a switch power supply circuit and a terminal device.

BACKGROUND

A switch power supply utilizes the modern power electronics technology to control a time ratio of turning on and turning off of a switch crystal UAN to maintain a stable output voltage. The switch power supply usually includes a pulse width modulation (PWM) control integrated circuit (IC) chip and a metal-oxide-semiconductor field-effect transistor (MOSFET). For example, common switch power supply circuits include boost circuits, buck circuits, and the like.

However, some switch power supply circuits have problems of large loss and low working efficiency.

SUMMARY

In view of this, this application provides a switch power supply circuit and a terminal device, to resolve the foregoing technical problems, and a technical solution disclosed in this application is as follows:

In a first aspect, this application provides a boost switch power supply circuit. The boost switch power supply circuit includes a first inductor, a first switch transistor, a second switch transistor, a control circuit and an output capacitor, where one end of the first inductor is connected to a positive input end of the boost switch power supply circuit, and the other end of the first inductor is connected to a first end of the first switch transistor; a second end of the first switch transistor is connected to a ground end, and a control end of the first switch transistor is connected to a drive signal controller; a first end of the second switch transistor is connected to a public node of the first inductor and the first switch transistor, a second end of the second switch transistor is connected to a positive output end of the boost switch power supply circuit, and a control end of the second switch transistor is connected to the control circuit; the control circuit includes a first voltage divider circuit and a second voltage divider circuit, and outputs a control signal for controlling a switch status of the second switch transistor; the first voltage divider circuit is connected in parallel between the first end and the second end of the first switch transistor; the second voltage divider circuit is connected between the second end of the second switch transistor and the ground end, the second voltage divider circuit includes at least two resistors connected in series, and a third switch transistor connected in series between the at least two resistors, a first end of the third switch transistor is connected to the control end of the second switch transistor, and a control end of the third switch transistor is connected to a middle node of the first voltage divider circuit; and the output capacitor is connected in parallel between the positive output end and the ground end. This solution uses a second switch transistor to replace a diode in an asynchronous boost switch power supply circuit. A turn-on voltage drop of the switch transistor is far lower than a turn-on voltage drop of the diode, reducing power loss of the boost switch power supply circuit. Moreover, the control circuit of the second switch transistor includes a discrete component, and finally implements that the second switch transistor is turned off when the first switch transistor (that is, a main loop switch transistor) is turned on, and the second switch transistor is turned on when the first switch transistor is turned off. Costs of the discrete component are far lower than costs of a PWM controller, and therefore the control circuit that includes the discrete component reduces hardware costs of the boost switch power supply circuit, and simplifies a circuit design of the boost switch power supply circuit.

In a possible implementation of the first aspect, the first voltage divider circuit includes at least two resistors connected in series.

In another possible implementation of the first aspect, the first voltage divider circuit includes a first resistor and a second resistor connected in series, and a public node of the first resistor and the second resistor is the middle node of the first voltage divider circuit.

In still another possible implementation of the first aspect, the second voltage divider circuit includes a third resistor and a fourth resistor connected in series, and a third switch transistor connected in series between the third resistor and the fourth resistor; and a first end of the third switch transistor is connected to the third resistor, a second end of the third switch transistor is connected to the fourth resistor, a control end of the third switch transistor is connected to the middle node of the first voltage divider circuit, and the first end of the third switch transistor is further connected to the control end of the second switch transistor. It can be learned that the first voltage divider circuit of this solution generates a control signal for controlling, based on a voltage at an SW node on an input end main loop, the third switch transistor in the second voltage divider circuit to be turned on and turned off, and further, the second voltage divider circuit provides a control signal for the second switch transistor to be turned on and turned off. Therefore, the control circuit that includes the discrete component controls the second switch transistor to be turned on and turned off, reducing hardware costs of the boost switch power supply circuit.

In yet still another possible implementation of the first aspect, the first switch transistor, the second switch transistor and the third switch transistor each are a metal-oxide-semiconductor field-effect transistor MOS transistor; and the first end is a drain of the MOS transistor, the second end is a source of the MOS transistor, and the control end is a gate of the MOS transistor.

In yet another possible implementation of the first aspect, the first switch transistor and the third switch transistor each are an NMOS transistor, and the second switch transistor is a PMOS transistor.

In a second aspect, this application provides a buck switch power supply circuit. The buck switch power supply circuit includes a first inductor, a first switch transistor, a second switch transistor, a control circuit and an output capacitor, where a first end of the first switch transistor is connected to a positive input end of the buck switch power supply circuit, a second end of the first switch transistor is connected to one end of the first inductor, and a control end of the first switch transistor is connected to a drive signal controller; the other end of the first inductor is connected to a positive output end of the buck switch power supply circuit; a first end of the second switch transistor is connected to a first public node of the first switch transistor and the first inductor, a second end of the second switch transistor is connected to a ground end, and a control end of the second switch transistor is connected to the control circuit; the control circuit includes a first voltage divider circuit and a second voltage divider circuit, and outputs a control signal for controlling a switch status of the second switch transistor; the first voltage divider circuit is connected in parallel between the first end and the second end of the second switch transistor; the second voltage divider circuit is connected between the other end of the first inductor and the ground end, the second voltage divider circuit includes at least two resistors connected in series, and a third switch transistor connected in series between the at least two resistors, a first end of the third switch transistor is connected to the control end of the second switch transistor, and a control end of the third switch transistor is connected to a middle node of the first voltage divider circuit; and the output capacitor is connected in parallel between the positive output end and the ground end. It can be learned that in the buck switch power supply circuit, the second switch transistor is used to replace a freewheeling diode. A turn-on impedance of the switch transistor is very small, only tens of milliohms, and a freewheeling current is usually a few amperes. Therefore, a turn-on voltage drop of the second switch transistor is tens of millivolts, but a turn-on voltage drop of the freewheeling diode is several hundred millivolts. Based on this, after the switch transistor is used to replace the freewheeling diode, power loss of the buck switch power supply circuit is greatly reduced, and output efficiency is improved. Moreover, in this solution, the control circuit that includes the discrete component controls the on and off states of the second switch transistor, so that when the first switch transistor is turned on, the second switch transistor is turned off; or when the first switch transistor is turned off, the second switch transistor is turned on. That is, this solution does not need to additionally set a PWM controller, costs of the discrete component are far lower than costs of the PWM controller, so that hardware costs of the buck switch power supply circuit are reduced, and a circuit design is simplified.

In a possible implementation of the second aspect, the first voltage divider circuit includes a first resistor and a second resistor, and the first resistor and the second resistor; and a public node of the first resistor and the second resistor is the middle node of the first voltage divider circuit.

In another possible implementation of the second aspect, the second voltage divider circuit includes a third resistor and a fourth resistor connected in series, and a third switch transistor connected in series between the third resistor and the fourth resistor; and a first end of the third switch transistor is connected to the third resistor, a second end of the third switch transistor is connected to the fourth resistor, a control end of the third switch transistor is connected to the middle node of the first voltage divider circuit, and the first end of the third switch transistor is further connected to the control end of the second switch transistor.

In still another possible implementation of the second aspect, the first switch transistor, the second switch transistor and the third switch transistor each are a metal-oxide-semiconductor field-effect transistor MOS transistor; and the first end is a drain of the MOS transistor, the second end is a source of the MOS transistor, and the control end is a gate of the MOS transistor.

In yet still another possible implementation of the second aspect, the first switch transistor, the second switch transistor, and the third switch transistor each are an NMOS transistor.

According to a third aspect, this application further provides a terminal device. The terminal device includes the boost switch power supply circuit according to any one of the implementations of the first aspect or the buck switch power supply circuit according to any one of the implementations of the second aspect; and the boost switch power supply circuit or the buck switch power supply circuit is configured to supply power to a to-be-powered module in the terminal device, and the to-be-powered module includes a speaker power amplifier or an LCD backlight module.

It should be understood that descriptions of technical features, technical solutions, beneficial effects, or similar statements in this application do not imply that all features and advantages can be implemented in any single embodiment. On the contrary, it may be understood that descriptions of the features or the beneficial effects mean that at least one embodiment includes a specific technical feature, technical solution, or beneficial effect. Therefore, the descriptions of the technical features, the technical solutions, or the beneficial effects in this specification may not necessarily be specific to a same embodiment. The technical features, technical solutions, or beneficial effects described in embodiments may be further combined in any proper manner. A person skilled in the art may understand that a specific embodiment may be implemented without using one or more specific technical features, technical solutions, or beneficial effects of the embodiment. In other embodiments, additional technical features and beneficial effects may further be identified in a specific embodiment that does not reflect all the embodiments.

DESCRIPTION OF EMBODIMENTS

In this specification, the claims, and the brief description of drawings of this application, the terms “first”, “second”, “third”, and the like are intended to distinguish between different objects but do not limit a particular order.

In embodiments of this application, the word “example” or “for example” is used to represent giving an example, an illustration, or a description. Any embodiment or design solution described by using “as an example” or “for example” in this application should not be explained as being more preferred or having more advantages than another embodiment or design solution. To be precise, the terms, such as “as an example” or “for example”, are intended to present a related concept in a specific manner.

A switch power supply circuit includes a synchronous switch power supply circuit and an asynchronous switch power supply circuit, for example, a synchronous boost circuit, an asynchronous boost circuit, a synchronous buck circuit and an asynchronous buck circuit. Compared with the synchronous switch power supply circuit, the asynchronous boost circuit and the asynchronous buck circuit are connected with the output end through the diode, and the asynchronous switch power supply circuit is simple in circuit structure and control logic, so that the asynchronous switch power supply circuit is widely used.

However, the inventor of this application finds in research that power loss of the asynchronous switch power supply circuit is large, and working efficiency is low.

For example, in an asynchronous boost circuit shown inFIG.1A, an inductor L1and a first switch transistor Q1are connected in series and then connected in parallel with an input power supply Vin, and one end at which L1and Q1are connected is further connected to a positive output end through a diode D1.

When Q1is turned on, the input power supply Vin and L1form a closed loop, and L1stores energy, and at this time D1is reverse biased and is in an off state. When Q1is turned off, a left-negative and right-positive induced voltage is generated in L1because a current of the inductor L1cannot be changed sharply, and the induced voltage is superimposed on the input power supply. At this time, D1is forward biased and turned on, and the input power supply and the induced voltage form a loop through D1and a load. Since a turn-on voltage of D1is high, power loss of the asynchronous boost circuit is large, and working efficiency is low.

If a synchronous boost circuit is adopted, as shown inFIG.1B, difference fromFIG.1Ais that D1on an output main loop is replaced with a second switch transistor Q2. However, Q1and a PWM control IC of Q1are usually integrated in a switch power supply chip, and cannot provide a control signal to the outside, in other words, a switch status of Q2cannot be controlled by the PWM control IC of Q1. Therefore, use of a synchronous boost circuit requires an additional PWM controller (that is, a PWM control IC) to control turning on and turning off of Q2, resulting in an increase in hardware costs.

In order to solve the above technical problems, the inventor proposes the switch power supply circuit of this application, and uses a second switch transistor to replace the diode in the asynchronous switch power supply circuit. A turn-on voltage drop of the switch transistor is far lower than a turn-on voltage drop of the diode, reducing power loss of the switch power supply circuit. In addition, a control circuit that includes a discrete component controls on and off states of the second switch transistor, so that when a first switch transistor (that is, a main loop switch transistor) is turned on, the second switch transistor is turned off, or when the first switch transistor is turned off, the second switch transistor is turned on. Costs of the discrete component are far lower than costs of a PWM controller, and therefore the control circuit that includes the discrete component reduces hardware costs of the switch power supply circuit, and simplifies a circuit design of the switch power supply circuit.

A circuit structure and a working process of the switch power supply circuit based on an asynchronous boost circuit provided in this application are described below with reference toFIG.2toFIG.5.

FIG.2is a schematic circuit principle diagram of a boost switch power supply according to an embodiment of this application. As shown inFIG.2, the boost switch power supply circuit includes an inductor L1, a first switch transistor Q1, a second switch transistor Q2, an output capacitor Co, a load RL, and a control circuit.

The inductor L1is connected to an input power supply Vin in parallel after being connected in series to the first switch transistor Q1, one end of L1is connected to a positive electrode of the input power supply Vin, the other end of L1is connected to a first end of Q1, a second end of Q1is connected to a negative electrode of Vin, and a control end of Q1is connected to a PWM controller.

A first end of the second switch transistor Q2is connected to a public node SW of L1and Q1, and a second end of the second switch transistor Q2is connected to a positive output end of the switch power supply (that is, a positive electrode of an output power supply), and a control end of Q2is connected to the control circuit.

The output capacitor Co is connected in parallel between the positive output end and GND for filtering an output voltage Vout to ensure stability of output voltage.

The control circuit includes a first voltage divider circuit and a second voltage divider circuit. The first voltage divider circuit is connected in parallel between the first end and the second end of Q1, and is configured to divide a voltage of the node SW to ground (GND). The second voltage divider circuit is connected in parallel to the output capacitor Co, that is, in parallel to the output side Vout, and is configured to provide a control voltage for controlling Q2to be turned on and turned off.

The first voltage divider circuit includes at least two voltage divider resistors connected in series as shown inFIG.2, and may include R1and R2connected in series. A public node A of R1and R2is connected to the second voltage divider circuit.

The second voltage divider circuit includes at least two voltage divider resistors and a switch transistor. For example, as shown inFIG.2, the second voltage divider circuit may include resistors R3, R4, and a third switch transistor Q3. A first end and a second end of Q3are connected in series between R3and R4, and a control end of Q3is connected to the public node A of the first voltage divider circuit. Moreover, the public node A at which the first end of Q3is connected to R3is connected to a control end of Q2.

In an example embodiment, as shown inFIG.2, Q1is an NMOS transistor, and Q2is a PMOS transistor. The first end, the second end and the control end of Q1and Q2each are sequentially a drain, a source and a gate of an NMOS transistor.

In other embodiments of this application, Q1may use other types of switch transistors, and similarly, Q2may alternatively use other types of switch transistors, and types of Q1and Q2are not specifically limited in this application.

In other embodiments of this application, there may be more than two, for example, three or more voltage divider resistors in the first voltage divider circuit, and similarly, there may be more than two, for example, three or more voltage divider circuits in the second voltage divider circuit. The quantity of the voltage divider resistors in the first voltage divider circuit and the second voltage divider circuit each and a resistance value of each resistor may be determined based on actual conditions.

Working processes of the boost switch power supply in different stages provided in embodiments of this application will be described below with reference toFIG.3andFIG.4.

(1) Energy Storage Stage of the Inductor L1

Refer toFIG.3. Q1is in an on state. The input power supply Vin forms a closed loop through the inductor L1and Q1, and since the inductor L1has a characteristic of allowing passing through of a direct current while blocking an alternating current, a current is generated in the closed loop. L1converts electric energy into magnetic energy for storage, and a current direction is shown by an arrow inFIG.3.

At the same time, since Q1is turned on, and the SW node is at an equal potential as GND, there is no current in the first voltage divider circuit, that is, a voltage of a node B is 0 V. A gate voltage of Q3is 0 V, and Q3is in an off state. Q3is in the off state, so that a positive electrode voltage of the node A is equal to a positive electrode voltage of Vout, that is, a voltage of the gate and a voltage of the source of Q2is equal, and Q2is in an off state.

(2) Discharge Stage of the Inductor L1

Refer toFIG.4. Q1is in an off state. An energy storage current of L1disappears. Because of a self-inductance characteristic of the inductor L1, a left-negative and right-positive induced voltage VL is generated, and a voltage of the node SW is increased. At the same time, an induced current from left to right is generated in L1, and a direction of the induced current is shown in a direction of an arrow inFIG.4, preventing the energy storage current from decreasing. At this time, the input power supply Vin, the inductor L1and the first voltage divider circuit form a closed loop, the induced current of L1flows through the first voltage divider circuit, and the voltage VB of the node B is increased.

In an example embodiment, Q3is an NMOS transistor, a source of Q3is connected to GND, a gate of Q3is connected to the node B, that is, a voltage difference VGSbetween the gate and the source of Q2is VB. When VB is greater than or equal to a threshold voltage value VGSth1of the gate and the source of the NMOS transistor, Q3is turned on, and VGsth1is about 0.7 V. That is, after VB is greater than or equal to 0.7 V, Q3is turned on.

In an example embodiment, Q2is a PMOS transistor, and is turned on when a voltage difference VGS2between the gate and the source of the PMOS transistor is greater than or equal to a threshold voltage value VGSth2. VGSth2is about −2 V, that is, when a gate voltage of the PMOS transistor is lower than a source voltage by 2 V and above, the PMOS transistor is turned on.

As shown inFIG.4, the gate of Q2is connected to the node A, and the source is connected to the positive output end of the switch power supply, that is, the positive electrode of Vout. When Q3is turned on, the voltage of the node A is pulled down to 0 V, that is, the gate voltage VGof Q2is 0 V. At this time, the voltage difference VGSbetween the gate and the source of Q2is −Vout, and −Vout is less than VGSth2, so that Q2is triggered to be turned on. The input power supply Vin and the induced voltage VL of the inductor L1are superposed to supply power to the load RL.

It should be noted that processes of triggering Q2and Q3to be turned on is short. After both Q2and Q3are turned on, the first voltage divider circuit and the second voltage divider circuit are connected in parallel between the node SW and the ground end GND. Resistance value ratios of R1, R2, R3and R4are appropriately configured, to ensure that Q2and Q3remain in the on state when Q1is in the off state.

In an example embodiment, the resistance value ratio of R1to R2is about 1:500, a resistance value ratio of R3to R4is about 1:4. Specific resistance values of R1to R4are not limited provided that the resistance values of R1to R4satisfy the above ratio.

When the input voltage Vin=4 V, the output voltage Vout=15 V, and Q2and Q3are turned on, a body diode of Q2has a turn-on voltage drop, so that the voltage of the node SW is about 15.5 V. For example, R1=1 kΩ, R2=510 kΩ, R3=10 kΩ, R4=39 kΩ. The voltages of nodes VA and VB are as follows:

R1and R2are connected in series between the node SW and GND, that is, R1and R2divide the voltage of the node SW, and a voltage drop VB on R2is about 15.46 V, that is, the gate voltage of Q3is about 15.46 V. R3and R4divide Vout=15 V, and a voltage drop on R4is about 12 V, that is, a source voltage of Q3is about 12 V. Therefore, a voltage difference Vas between the gate and the source of Q3is about 3.46 V, which is greater than the turn-on threshold 0.7 V of the NMOS transistor, so that Q3remains the on state.

A turn-on resistance of Q3is only tens of milliohms, which is negligible compared to the kilo-ohm resistance values of R3and R4, so that the voltage of the node A is equal to the voltage drop on R4, and is about 12 V, that is, the gate voltage of Q2is about 12 V. The source voltage of Q2is the output voltage Vout=15 V, so that the voltage difference Vas between the gate and the source of Q2is about −3 V, which is greater than the turn-on threshold −2 V of the PMOS transistor. Therefore, Q2can maintain the on state.

When Q1is switched from the off state to the on state, the voltage of the node SW becomes 0 V, the voltage difference between the gate and the source of Q3does not satisfy the turn-on threshold 0.7 V of the NMOS transistor, and therefore Q3is turned off. Further, after Q3is turned off, the voltage of the node A becomes Vout, and at this time, the gate voltage of Q2is equal to the source voltage, so that Q2is also turned off.

In the boost switch power supply circuit provided in this embodiment, the second switch transistor Q2is used to replace the diode D1connected between the inductor and the positive output end. A turn-on impedance of the switch transistor is very small, only tens of milliohms and an output current is usually a few amperes, so that a turn-on voltage drop is reduced from hundreds of millivolts to tens of millivolts. Therefore, after the second switch transistor Q2is used to replace the diode D1, power loss of the boost switch power supply circuit is greatly reduced, and output efficiency is improved. Moreover, this solution uses the discrete component to form the control circuit to control the on and off states of the second switch transistor Q2, so that when the first switch transistor (that is, the main loop switch transistor) is turned on, the switch transistor is turned off. Therefore, this solution does not need to additionally set a PWM controller, costs of the discrete component are far lower than costs of the PWM controller, reducing hardware costs of the boost switch power supply circuit and simplifying the circuit design.

Similar to the asynchronous boost circuit, an asynchronous buck circuit also has problems of large power loss and low working efficiency. As shown inFIG.5, two input ends of a switch power supply circuit are connected to one end of an inductor L1through Q1, and the other end of the L1is connected to an output end, and a freewheeling diode D1is reversely connected between a ground end (GND) and a public node of Q1and L1. An output capacitor Co is connected in parallel to the output end to ensure that an output voltage at the output end is stable, and a load RLis connected to two ends of Co.

When Q1is turned on, L1stores energy and D1is turned off. When Q1is turned off, L1is discharged through D1, and D1is turned on, but a turn-on voltage drop of D1is large, which reaches hundreds of millivolts, resulting in large power loss and low output efficiency of the whole switch power supply circuit.

In order to solve problems of large power loss and low output efficiency of a switch power supply based on an asynchronous buck circuit, the inventor of this application provides a switch power supply circuit based on a buck circuit, a switch transistor is used to replace the freewheeling diode D1, and the power loss is reduced. Moreover, a control circuit that includes a discrete component drives the switch transistor to be turned on and off, a PWM controller does not need to be additionally added, hardware costs are reduced, and a circuit design is simplified.

As shown inFIG.6, a buck switch power supply circuit according to an embodiment of this application includes: a first switch transistor Q1, an energy storage inductor L1, a second switch transistor Q2, an output capacitor Co, a load RL, and a control circuit that includes a discrete component. It can be seen that this solution uses the second switch transistor Q2to replace the freewheeling diode D1inFIG.5, and the control circuit that includes the discrete component drives to control Q2to turn on and turn off.

A first end of Q2is connected to a second end of Q1, a second end of Q2is connected to a ground end GND, and a control end is connected to the control circuit.

The output capacitor Co is connected in parallel between two output ends to ensure stability of an output voltage Vout. The load RLis connected in parallel to two ends of the output capacitor Co.

In an embodiment of this application, the control circuit includes a first voltage divider circuit and a second voltage divider circuit. The second voltage divider circuit includes a third switch transistor Q3.

One end of the first voltage divider circuit is connected to a public node SW of Q1and L1, and the other end of the first voltage divider circuit is connected to the ground end GND. A middle node (that is, a first middle node) of the first voltage divider circuit is connected to a control end of the third switch transistor Q3. The first voltage divider circuit provides a drive control voltage for Q3by dividing a voltage of the SW node.

In an example embodiment, the first voltage divider circuit may include at least two voltage divider resistors sequentially connected in series, and the two voltage divider resistors R1and R2are used as an example for description. A public node B (that is, the first middle node) of R1and R2is connected to the control end of Q3.

One end of the second voltage divider circuit is connected to one end that is of L1and that is connected to a positive output end, and the other end of the second voltage divider circuit is connected to GND. A middle node (that is, a second middle node) of the second voltage divider circuit is connected to the control end of the second switch transistor Q2. The second voltage divider circuit is configured to provide a drive control voltage to Q2.

The second voltage divider circuit may include at least two voltage divider resistors and a third switch transistor Q3, and two voltage divider resistors R3and R4are used as an example. R3, Q3and R4are connected in series, one end of R3is connected to L1as an end of the second voltage divider circuit, the other end of R3is connected to a first end of Q3, a second end of Q3is connected to one end of R4, and the other end of R4is connected to GND. The public node A (that is, the second node) of Q3and R3is connected to the control end of Q2.

In an example embodiment, as shown inFIGS.6, Q1, Q2and Q3each are an NMOS transistor, and the first end, the second end and the control end are sequentially a drain, a source and a gate.

In other embodiments of this application, Q1, Q2and Q3may alternatively use other types of switch transistors, which is not limited in this application.

In addition, in other embodiments of this application, there may be more than two voltage divider resistors included in the first voltage divider circuit, and similarly, there may be more than two voltage divider resistors included in the second voltage divider circuit, which is not limited in this application.

A working process of the buck switch power supply according to this embodiment of this application will be described below with reference toFIG.7andFIG.8.

(1) Energy Storage Stage of the Inductor L1

Refer toFIG.7. When Q1is in an on state, the input power supply Vin, the inductor L1, the output capacitor Co and the load RLform a closed loop. L1stores energy, a current flowing through the L1increases linearly, and simultaneously L1charges the Co to supply power to RL.

Q3is an NMOS transistor, a source of Q3is connected to GND through the resistor R4, a gate of Q3is connected to the node B, and when a voltage difference between the gate and the source of Q3is greater than a turn-on threshold of the NMOS transistor, about 0.7 V, Q3is turned on.

After Q1is turned on, the node SW is at a high level, a current flows in the first voltage divider circuit, and a voltage VB of the node B is a voltage drop on the resistor R2, that is, the high level is greater than the turn-on threshold of the NMOS transistor, so that Q3is turned on.

After Q3is turned on, the node A in the second voltage divider circuit is pulled down to a low level, a gate of Q2is connected to the node A, a source of Q2is connected to GND, a voltage difference between the gate and the source of Q2is substantially 0, so that Q2is turned off.

(2) Discharge Stage of the Inductor L1

Refer toFIG.8. When Q1is in an off state, the node SW is 0 V, at this time, there is no current flowing in the first voltage divider circuit, there is no voltage drop on the resistor R2, and a voltage of the node B is 0 V, so that Q3is turned off. After Q3is turned off, there is no current flowing in the second voltage divider circuit. Therefore, a voltage at the node A is equal to a voltage at the positive output end, that is, the node A is at a high level.

The gate of Q2is connected to the node A, the source is connected to the GND. When Q3is turned off, the node A is at the high level, and a voltage difference between the gate and the source of Q2is greater than the turn-on threshold of the NMOS transistor, so that Q2is turned on.

The inductor L1, the output capacitor Co, the load RLand the second switch transistor Q2form a closed loop, L1discharges through Q2, a current flowing through L1decreases linearly, and an output voltage is maintained stable through the output capacitor Co and an inductor current.

By appropriately configuring resistance value ratios of R1to R4, Q2is turned off when L1stores energy, and Q2is turned on when L1is discharged.

In an example embodiment, the resistance value ratio of R1to R2is about 1:3, and the resistance value ratio of R3to R4is about 6:1, for example, R1=100 kΩ, R2=330 kΩ, R3=330 k≤2, and R4=51 kΩ. The input voltage Vin=4 V and the output voltage Vout=1.8 V are taken as an example for description.

As shown inFIG.7, when Q1is turned on, the voltage of the node SW is equal to the input voltage, which is 4 V, the first voltage divider circuit divides the voltage of the node SW, and the voltage drop on the resistor R2is 3.07 V, that is, the gate voltage of Q3is 3.07 V. The source of Q3is connected to GND through R4, a source voltage of Q3is approximately 0 V, so that the voltage difference between the gate and the source of Q3is approximately 3.07 V, which satisfies the turn-on condition of Q3.

After Q3is turned on, the voltage of the node A is approximately equal to the voltage drop on R4of about 0.24 V (R3and R4divide the output voltage Vout, and the voltage drop on R4is about 0.24 V). At this time, the voltage difference between the gate and the source of Q2is about 0.24 V, so that Q2is turned off. That is, when Q1is in the on state, Q3is turned on and Q2is turned off.

As shown inFIG.8, when Q1is turned off, the voltage of the node SW is 0 V, and the voltage of the node B is 0 V, so that Q3is turned off. After Q3is turned off, the voltage of the node A is pulled up to the output voltage of 1.8 V by the resistor R3, that is, the gate voltage of Q2is 1.8 V. The source of Q2is connected to GND, and the voltage difference between the gate and the source of Q2is 1.8 V, so that Q2is turned on. That is, when Q1is in the off state, Q3is turned off and Q2is turned on.

According to the buck switch power supply circuit provided in this embodiment, the second switch transistor Q2is used to replace the freewheeling diode D1. A turn-on impedance of the switch transistor is very small, only tens of milliohms, and a freewheeling current is usually a few amperes. Therefore, a turn-on voltage drop of Q2is tens of millivolts, but a turn-on voltage drop of the freewheeling diode D1is several hundred millivolts. Based on this, after the switch transistor is used to replace the freewheeling diode, the power loss of the buck switch power supply circuit is greatly reduced, and the output efficiency is improved. Moreover, in this solution, the control circuit that includes the discrete component controls the on and off states of the second switch transistor, so that when the first switch transistor is turned on, the second switch transistor is turned off; or when the first switch transistor is turned off, the second switch transistor is turned on. That is, this solution does not need to additionally set a PWM controller, costs of the discrete component are far lower than costs of the PWM controller, so that hardware costs of the buck switch power supply circuit are reduced, and a circuit design is simplified.

In another aspect, an embodiment of this application further provides a terminal device using the foregoing switch power supply circuit. As shown inFIG.9, the terminal device may include a processor, a memory, a display and a speaker.

It may be understood that the structure shown in this embodiment of this application does not constitute a specific limitation on the terminal device. In some other embodiments, the terminal device may include more or fewer components than those shown in the figure, or some components may be combined, or some components may be split, or components may be arranged in different manners. The components shown in the figure may be implemented in hardware, software, or a combination of software and hardware.

The display is configured to display an image, a video, and the like. The display may be a liquid crystal display (LCD), an organic light-emitting diode (OLED), or the like. When the display is LCD, a backlight power supply of the LCD uses the boost switch power supply or the buck switch power supply provided in the foregoing embodiments.

The speaker is configured to convert an audio electric signal into a sound signal, and the speaker is driven to operate through a power amplifier. In this embodiment of this application, a drive power supply of the power amplifier of the speaker uses the boost switch power supply or the buck switch power supply provided in the foregoing embodiments.

The memory may be configured to store computer-executable program code, and the executable program code includes instructions. The processor runs the instructions stored in the memory, to perform various function applications and data processing of the terminal device.

According to the terminal device provided in this embodiment, the foregoing switch power supply is used as drive power supply of the LCD or the drive power supply of the power amplifier of the speaker in the terminal device, and the switch power supply uses the second switch transistor that replaces a diode. A turn-on impedance of the switch transistor is very small, only tens of milliohms, so that a turn-on voltage drop is reduced from hundreds of millivolts to tens of millivolts, power loss of the switch power supply circuit is greatly reduced, and output efficiency is improved. Moreover, this solution uses a discrete component to form a control circuit to control a switch status of the second switch transistor without additionally setting a PWM controller, costs of the discrete component are far lower than costs of the PWM controller, reducing hardware costs of a switch power supply and simplifying a circuit design.

Based on the descriptions of the implementations, a person skilled in the art may clearly understand that for the purpose of convenient and brief descriptions, division into the foregoing functional modules is merely used as an example for descriptions. During actual application, the functions may be allocated to different functional modules for implementation based on a requirement. In other words, an inner structure of an apparatus is divided into different functional modules to implement all or some of the functions described above. For a detailed working process of the foregoing system, apparatus, and units, refer to a corresponding process in the foregoing method embodiments, and details are not described herein again.

The units described as separate components may or may not be physically separate, and components displayed as units may or may not be physical units, and may be at one position, or may be distributed on a plurality of network units. Some or all of the units may be selected based on actual requirements to achieve the objectives of solutions of embodiments.