WO2014012518A1

WO2014012518A1 - Switching power supply and chip for controlling the same

Info

Publication number: WO2014012518A1
Application number: PCT/CN2013/079706
Authority: WO
Inventors: Haiquan Zhang; Wenqing Wang; Xiaohua Yang
Original assignee: Shenzhen Byd Auto R & D Company Limited; Byd Company Limited
Priority date: 2012-07-19
Filing date: 2013-07-19
Publication date: 2014-01-23
Also published as: CN103580506A; CN103580506B

Abstract

A switching power supply and a chip for controlling the same are provided. The switching power supply comprises: a rectifying module (301); a transforming module (302); a switching module (303), connected with the transforming module (302); a chip (304) for controlling the switching power supply, connected with the transforming module (302) and the switching module (303) respectively, in which the chip (304) has a control terminal (COMP), a compensation module (406) and a power supply terminal (VDD), the control terminal is configured to output a turn off signal and to start the compensation module after being started and the compensation module is configured to stabilize and filter a voltage inside the chip (304) and to compensate the output voltage by controlling the switching module to turn on or off according to an output voltage of the transforming module; a starting resistor (R1); a first capacitor (C1); and a first MOS transistor (M1). With the switching power supply, the stand-by consumption is reduced without reducing the starting speed of the chip for controlling the switching power supply. Furthermore, as the number of the external elements is reduced, the size of the switching power supply is reduced and the cost is also decreased.

Description

SWITCHING POWER SUPPLY AND CHIP FOR CONTROLLING THE SAME

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to, and benefits of Chinese Patent Application Serial No.201210251094.0, filed with the State Intellectual Property Office of P. R. C. on July 19, 2012; the entire contents of which are incorporated herein by reference.

FIELD

Exemplary embodiments of the present disclosure relate generally to a power supply control field, and more particularly, to a switching power supply and a chip for controlling the same.

BACKGROUND

With a development of science, portable digital devices can be seen everywhere. However, rechargeable batteries in these portable digital devices cannot be used without charging apparatuses such as mobile phone chargers and power adapters. For example, for the mobile phone chargers, as the energy saving awareness of the people increases, the requirement on the stand-by power consumption of the mobile phone chargers also increases, and the mobile phone chargers having a stand-by power consumption of 30mW or even lOmW have been popularized in the industry.

Currently used chips often use S0T23-6 package, and all the six pins of the chips are used without idle ones. This kind of chips are mainly used for small power AC/DC (alternating current/direct current) conversion and act as a chip for controlling a switching power supply for the AC/DC conversion to control the output voltage and current according to peripheral design requirements.

However, with the switching power supply in the related art, the starting speed of the chip for controlling the switching power supply is low, the stand-by power consumption is high, or the cost is high.

SUMMARY

Embodiments of the present disclosure seek to solve at least one of the problems existing in the related art to at least some extent. According to a first aspect of the present disclosure, a witching power supply is provided. The switching power supply comprises: a rectifying module, configured to rectify an input alternating current to output a direct current; a transforming module, connected with the rectifying module and configured to transform a voltage of the direct current to generate an output voltage; a switching module, connected with the transforming module; a chip for controlling a switching power supply, connected with the transforming module and the switching module respectively, in which the chip for controlling the switching power supply has a control terminal, a compensation module and a power supply terminal, the control terminal is configured to output a turn off signal and to start the compensation module after being started and the compensation module is configured to stabilize and filter a voltage inside the chip for controlling the switching power supply and to compensate the output voltage by controlling the switching module to turn off according to the output voltage; a starting resistor, in which one end of the starting resistor is connected with the rectifying module; a first capacitor, in which one end of the first capacitor is connected with the power supply terminal, the other end of the first capacitor is grounded and a voltage of the power supply terminal is increased linearly when the first capacitor is charged; and a first MOS transistor, in which a gate of the first MOS transistor is connected with the control terminal, a source of the first MOS transistor is connected with the power supply terminal, a drain of the first MOS transistor is connected with the other end of the starting resistor, and the first MOS transistor is turned off when the turn off signal is received from the control terminal.

With the switching power supply according to embodiments of the present disclosure, the stand-by power consumption is reduced without reducing the starting speed of the chip for controlling the switching power supply. Furthermore, as the number of the external elements is reduced, the size of the switching power supply is reduced and the cost is also decreased.

According to a second aspect of the present disclosure, a chip for controlling a switching power supply comprising a switch transistor is provided. The chip comprises: a power supply control terminal; a control terminal connected with the switch transistor; a voltage division module, configured to divide a voltage of the power supply terminal to output a divided voltage after the chip is started; a compensation module, configured to stabilize and filter a voltage inside the chip and to compensate an output voltage of the switching power supply; and a starting control module, connected with the voltage division module, the compensation module and the control terminal respectively, and configured to control the control terminal to output a turn off signal to turn off the switch transistor according to the divided voltage, and to control the compensation module to start working.

With the chip for controlling the switching power supply according to embodiments of the present disclosure, by multiplexing the control terminal, the stand-by power consumption is reduced largely and the starting speed is increased. Furthermore, the chip for controlling the switching power supply according to embodiments of the present disclosure also has advantages of small size, low cost and easy packaging.

Additional aspects and advantages of embodiments of present disclosure will be given in part in the following descriptions, become apparent in part from the following descriptions, or be learned from the practice of the embodiments of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and advantages of embodiments of the present disclosure will become apparent and more readily appreciated from the following descriptions made with reference to the drawings, in which:

Fig. 1 is a circuit diagram of a switching power supply according to scheme 1 in the related art;

Fig. 2 is a circuit diagram of a switching power supply according to scheme 2 in the related art;

Fig. 3 is a circuit diagram of a switching power supply according to an embodiment of the present disclosure;

Fig. 4A is a circuit diagram of a chip for controlling a switching power supply according to an embodiment of the present disclosure;

Fig. 4B is a circuit diagram of a compensation module in a chip for controlling a switching power supply according to an embodiment of the present disclosure;

Fig. 5 A is a schematic diagram of a chip for controlling a switching power supply according to an embodiment of the present disclosure;

Fig. 5B is a flow chart of a working process of a chip for controlling a switching power supply according to an embodiment of the present disclosure;

Fig. 6 is a timing diagram of working voltages of a control terminal and a power supply terminal of a chip for controlling a switching power supply according to an embodiment of the present disclosure; and

Fig. 7 is a circuit diagram of a switching power supply according to another embodiment of the present disclosure. DETAILED DESCRIPTION

Reference will be made in detail to embodiments of the present disclosure. The embodiments described herein with reference to drawings are explanatory, illustrative, and used to generally understand the present disclosure. The embodiments shall not be construed to limit the present disclosure. The same or similar elements and the elements having same or similar functions are denoted by like reference numerals throughout the descriptions.

Various embodiments and examples are provided in the following description to implement different structures of the present disclosure. In order to simplify the present disclosure, certain elements and settings will be described. However, these elements and settings are only by way of example and are not intended to limit the present disclosure. In addition, reference numerals may be repeated in different examples in the present disclosure. This repeating is for the purpose of simplification and clarity and does not refer to relations between different embodiments and/or settings. Furthermore, examples of different processes and materials are provided in the present disclosure. However, it would be appreciated by those skilled in the art that other processes and/or materials may be also applied. Moreover, a structure in which a first feature is "on" a second feature may include an embodiment in which the first feature directly contacts the second feature, and may also include an embodiment in which an additional feature is formed between the first feature and the second feature so that the first feature does not directly contact the second feature.

In the description, terms concerning attachments, coupling and the like, such as "connected" and "interconnected", refer to a relationship in which structures are secured or attached to one another through mechanical or electrical connection, or directly or indirectly through intervening structures, unless expressly described otherwise. Specific implications of the above phraseology and terminology may be understood by those skilled in the art according to specific situations.

In order to reduce the starting loss of chips, the following schemes are often used:

Scheme 1: Fig. 1 is a circuit diagram of a switching power supply in the related art. As shown in Fig. 1, an alternating current Vac is converted into a direct current by a rectification of a rectifying bridge and then transformed by a transformer to obtain desired output voltage and current. During the above process, the chip IC controls the values of the output voltage and current by sampling the voltage and current, so as to make the system output the voltage and current precisely. Currently, a resistance of an external starting resistor Rl is increased to reduce the starting power consumption of the circuit, so as to reduce the starting loss of the chip. However, considering the starting power consumption of the chip itself, the resistance of the external starting resistor Rl cannot be increased infinitely. This is because when the current provided by the system is too low, the chip will be unable to start. Therefore, there is a limit on the use of the starting resistor Rl. Furthermore, due to the existence of the starting resistor Rl, a portion of the power consumption will always be present, which belongs to the wasted energy and can be calculated according to the following formula: consumption — (VacxV2)

Rl

Scheme 2: Fig. 2 is a circuit diagram of a switching power supply in the related art. As shown in Fig. 2, a depletion type MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) Ml is added in the external starting circuit in Fig. 1 to form an external switching circuit, and the external switching circuit comprises the starting resistor Rl, the MOS transistor Ml, a diode D3 and a resistor R7. Depending on the operating characteristics of the MOS transistor Ml, only when the voltage V_GS of the MOS transistor Ml is less than -3V, the MOS transistor Ml is turned off and the chip IC is charged. After the chip IC is started, the depletion type MOS transistor Ml is turned off by using the external switching circuit so as to cut off the starting circuit, and thus the stand-by power consumption is reduced.

Scheme 3: Based on the S0T23-6 package, one or more additional pins for controlling the external depletion type transistor are provided to change the package form. In other words, a package comprising seven or eight pins is used.

As shown in Figs. 1 and 2, the functions of each pin of the above chip are as follows:

VDD - power supply terminal of chip

GND - grounded terminal of chip

COMP - control terminal of compensation module and external depletion type transistor CS - peak current detecting terminal

INV - output voltage feedback terminal

DRI - output driving terminal. There are many defects in the related art. With respect to the scheme 1, the external circuit can only reduce the value of the stand-by power consumption by increasing the resistance of the starting resistor Rl. However, when the chip is started, there is a starting power consumption of the chip itself, which causes the fact that the resistance of the starting resistor Rl cannot be increased infinitely, otherwise, the chip will be unable to start and the system cannot work normally. Furthermore, even if the chip is able to start when the resistance of the starting resistor Rl is very large, the starting power consumption cannot be eliminated totally, and the starting time (one of usual parameters) will be very long as the starting current is very low. Therefore, the other performances of the chip are reduced when some performances are achieved. With respect to the scheme 2, although the external switching circuit can be cut off after the chip is started, as a lot of elements are added, the cost is increased, the dimension of the printed circuit board is enlarged and the circuit layout is more difficult especially when a small switching power supply is required. With respect to the scheme 3, in addition to enlarged package and enlarged volume of the chip, the expensive cost due to the large package also makes it not favorable in price.

In the following, a switching power supply according to embodiments of the present disclosure will be described with reference to the drawings.

Fig. 3 is a circuit diagram of a switching power supply according to an embodiment of the present disclosure. Referring to Fig. 3, the switching power supply comprises a rectifying module 301, a transforming module 302, a switching module 303, a chip 304 for controlling the switching power supply, a starting resistor Rl, a first capacitor CI and a first MOS transistor Ml.

The rectifying module 301 is configured to rectify an input alternating current to output a direct current. The transforming module 302 is connected with the rectifying module 301 and configured to transform a voltage of the direct current to generate an output voltage. The switching module 303 is connected with the transforming module 302. The chip 304 is connected with the transforming module 302 and the switching module 303 respectively. The chip 304 comprises a control terminal COMP, a compensation module and a power supply terminal VDD. The control terminal COMP is configured to output a turn off signal and to start the compensation module after being started. The compensation module is configured to stabilize and filter a voltage inside the chip 304 and to compensate the output voltage by controlling the switching module 303 to turn on or off according to the output voltage.

Further, as shown in Fig. 3, one end of the starting resistor Rl is connected with the rectifying module 301. One end of the first capacitor CI is connected with the power supply terminal VDD and a source of the first MOS transistor Ml respectively, and the other end of the first capacitor CI is grounded. When the first capacitor CI is charged, a voltage of the power supply terminal VDD is increased linearly. The first capacitor CI is also called a charging capacitor. A gate of the first MOS transistor Ml is connected with the control terminal COMP, the source of the first MOS transistor Ml is connected with the power supply terminal VDD, and a drain of the first MOS transistor is connected with the other end of the starting resistor Rl. The first MOS transistor Ml is turned off when the turn off signal is received from the control terminal.

With the chip 304 in the switching power supply of the present disclosure, based on the current S0T23-6 package, a control function is added to one pin (i.e. the control terminal) to make the control terminal have two different functions without increasing a number of pins, and the two different functions can act in different conditions without interfering with each other.

Specifically, as shown in Fig. 3, the functions of each pin of the chip 304 are as follows:

VDD - power supply terminal;

GND - grounded terminal;

COMP - control terminal of compensation module and external depletion type transistor;

CS - peak current detecting terminal;

INV - output voltage feedback terminal;

DRI - output driving terminal.

It should be understood that during the starting process of the chip 304, an external power supply circuit is required to provide power to the chip 304. Furthermore, only when the voltage of the power supply terminal VDD is greater than a certain threshold, the chip 304 is started. However, after the chip 304 is started, the voltage required by working is fed back from a secondary coil of the transforming module 302 rather than provided by the external power supply circuit. Therefore, after the chip 304 is started, the external power supply circuit is redundant and should be removed so as to reduce the stand-by power consumption of the switching power supply.

As shown in Fig. 3, during the starting process of the chip 304, the voltage of the control terminal COMP follows with the voltage of the power supply terminal VDD to guarantee the voltage drop V_Gs of the first MOS transistor Ml is very low (about 0V), which guarantees the drain and the source of the first MOS transistor Ml are in a fully on state. After the chip 304 is started, the voltage of the control terminal COMP is pulled down to 0V within a very short time so as to pull down the voltage of the gate of the first MOS transistor Ml, while the voltage of the source of the first MOS transistor Ml remains at a voltage value of the power supply terminal VDD. Using the voltage difference between the gate and the source of the first MOS transistor Ml, the first MOS transistor Ml is turned off and the external starting circuit no longer provides a current for the chip 304. This is the first function of the control terminal COMP, i.e. the function of controlling the external switch transistor. After the chip 304 is started, the control terminal COMP performs the second function, i.e. the linear compensation function. Specifically, after the chip 304 is started, the voltage inside the chip 304 is stabilized and filtered by using a gate capacitor of the first MOS transistor Ml, which guarantees a stability of the voltage of the control terminal COMP and the output voltage and a normal working of the external loop of the chip 304.

In the embodiments of the present disclosure, the chip 304 has the control terminal COMP. In the present disclosure, the control terminal COMP has two functions: firstly, it is used to output a control signal to control the first MOS transistor Ml to turn on or off; secondly, it is connected with a compensation capacitor to stabilize and filter the linear compensation voltage inside the chip 304. This is because, as the external loop works in a flyback manner, it is impossible to sample voltage continuously, and thus the linear compensation voltage should compensate the output voltage of the switching power supply periodically which requires the compensation capacitor to stabilize the linear compensation voltage, or else the external loop will not work stably. In one embodiment of the present disclosure, the compensation capacitor is the gate capacitor of the first MOS transistor Ml .

Fig. 4A is a circuit diagram of a chip for controlling a switching power supply according to an embodiment of the present disclosure. As shown in Fig. 4A, the chip 304 comprises a voltage division module 401 and a starting control module 402.

The voltage division module 401 is connected with the power supply terminal VDD and configured to divide the voltage of the power supply terminal VDD to output a divided voltage. The starting control module 402 is connected with the voltage division module 401 and the control terminal COMP respectively and configured to control the control terminal COMP to output the turn off signal according to the divided voltage output from the voltage division module 401.

Specifically, as shown in Fig. 4, the voltage division module 401 comprises a second resistor R2 and a third resistor R3. One end of the second resistor R2 is connected with the power supply terminal VDD, the other end of the second resistor R2 is connected with one end of the third resistor R3, the other end of the third resistor R3 is grounded.

The starting control module 402 comprises a comparator CMP, an inverter 403, a second PMOS transistor M2, a processing unit 404 and a third PMOS transistor M3. A first input end of the comparator CMP is connected with the other end of the second resistor R2, and a second input end of the comparator CMP is connected with a reference voltage end REF. An input end of the inverter 403 is connected with an output end of the comparator CMP. A drain of the second PMOS transistor M2 is connected with the power supply terminal VDD, and a gate of the second PMOS transistor M2 is connected with an output end of the inverter 403. An input end of the processing unit 404 is connected with the output end of the comparator CMP for processing an output signal of the comparator CMP to generate a pulse signal. A gate of the third PMOS transistor M3 is connected with an output end of the processing unit 404, a drain of the third PMOS transistor M3 is connected with a source of the second PMOS transistor M2, and a source of the third PMOS transistor M3 is grounded.

Furthermore, as shown in Fig. 4A, the chip 304 may also comprise a delay unit 405, a fourth PMOS transistor M4 and the compensation module 406. An input end of the delay unit 405 is connected with the output end of the comparator CMP for delaying the output signal of the comparator CMP to generate a delay signal. A gate of the fourth PMOS transistor M4 is connected with the delay unit 405, a drain of the fourth PMOS transistor M4 is connected with the compensation module 406, and a source of the fourth PMOS transistor M4 is connected with the control terminal COMP. The fourth PMOS transistor M4 is turned on to start the compensation module 406 under a control of the delay signal.

Specifically, as shown in Fig. 4A, during the starting process of the chip 304, the voltage of the power supply terminal VDD increases from 0V, a voltage V_A of an output end A of the voltage division module 401 also increases from 0V and is less than the reference voltage V_REF before the chip 304 is started. Thus, at this time, a signal EN output from the comparator CMP is a low level signal, and a signal ENR obtained by inverting the signal EN with the inverter 304 is a high level signal. The high level signal ENR turns on the second PMOS transistor M2, and then the voltage of the control terminal COMP increases with the voltage of the power supply terminal VDD. When the voltage of the power supply terminal VDD increases to the starting threshold (for example, 16V) of the chip 304, the voltage V_A is greater than the reference voltage V_REF, and the comparator CMP is inverted. At this time, the signal EN is a high level signal, and then the signal ENR is inverted to obtain a low level signal to turn off the second PMOS transistor M2. Thus, the control terminal COMP is disconnected from the power supply terminal VDD, and the voltage of the control terminal COMP no longer varies with the voltage of the power supply terminal VDD. Then, the high level signal EN is processed by the processing unit 404 to generate the pulse signal ENS (for example, a high level pulse with a very small width), the pulse signal ENS turns on the third PMOS transistor M3 for a short time to pull down the voltage of the control terminal COMP to about 0V (before pulling down, the voltage of the control terminal COMP is almost equal to the starting threshold of the chip 304 (for example, 16V)). At the end of the above operation, the signal EN is delayed by the delay unit 405 (i.e. a rising edge of the signal EN is delayed for a short time) to generate a delay signal END, the delay signal END turns on the fourth PMOS transistor M4 to connect the control terminal COMP with the compensation module 406. Thus, the function transformation of the control terminal COMP is completed, and then the compensation module 406 works normally and stably due to the gate capacitor of the first MOS transistor Ml. During the whole transformation process, the three switch transistors inside the chip 304 turn on or off as follows: the second PMOS transistor M2 enters an off state from an off state, and then the third PMOS transistor M3 turns on for a short time, and finally the fourth PMOS transistor M4 enters an on state from an off state.

In other words, in one embodiment of the present disclosure, during the starting process of the chip 304, the voltage of the power supply terminal VDD increases from 0V. During this increasing process, the voltage of the control terminal COMP follows with the voltage of the power supply terminal VDD until the chip 304 is started (i.e. the voltage of the control terminal COMP reaches the starting threshold such as 16V). After the chip 304 is started, the voltage of the control terminal COMP decreases to 0V immediately, whereas the voltage of the power supply terminal VDD remains at about 13V to make the voltage drop V_GS of the first MOS transistor Ml remain at about -13V. Thus, the first MOS transistor Ml enters the off state from the on state to disconnect the chip 304 from the external starting circuit and reduce the stand-by power consumption of the switching power supply.

Fig. 4B is a circuit diagram of a compensation module in a chip for controlling a switching power supply according to an embodiment of the present disclosure. As shown in Fig. 4B, a current IDC is a variable current generated according to different loads inside the chip 304. A square wave TDSF is a secondary degaussing wave of the transforming module 302 sampled by the chip 304 for controlling a switch transistor M5 to turn on or off, and the duty ratio and turn-on time of the square wave TDSF are related to the load. A node CCOMP is connected with an external compensation capacitor C2 via the switch transistor M4 to generate a periodical switch current which makes the voltage of a resistor R4 change continuously. In order to ensure that the voltage of an input end of an operational amplifier is stable, the external compensation capacitor C2 is added. Then, a current ICOMP required by the linear compensation is generated by amplifying the voltage of the input end of the operational amplifier, and connected to the output voltage feedback terminal INV to pull down the value of INV and increase the output voltage, thus compensating the voltage drop of the output load line. This is the linear compensation process.

Fig. 5 A is a schematic diagram of a chip for controlling a switching power supply according to an embodiment of the present disclosure. As shown in Fig. 5A, before the chip 304 is started, the starting control module 402 is disconnected from the compensation module 406, and the voltage of the control terminal COMP follows with the voltage of the power supply terminal VDD. After the chip 304 is started, the voltage of the control terminal COMP no long follows with the voltage of the power supply terminal VDD and is pulled down to 0V immediately, and then the starting control module 402 is connected with the compensation module 406, in other words, the control terminal COMP is connected to the compensation module 406 via the starting control module 402. A sampling module 1 samples a voltage feedback signal output from the switching power supply. The voltage feedback signal is compared and amplified by an error amplifier 2 and then sent to a control module 4 together with a secondary degaussing time of the switching power supply sampled by a degaussing time sampling module 3. The control module 4 outputs a reference voltage signal of a power switch transistor of the switching power supply to the compensation module 406 according to the secondary degaussing time and the amplified voltage feedback signal and outputs a switch signal to control a turn-on time and working frequency of an external power switch transistor. Then, the switch signal is processed by a logic processing module 5 and sent to a driving module 6. The driving module 6 outputs a driving signal to the DRI terminal to control the external power switch transistor to turn on or off. Furthermore, a feedforward module 7 sends the voltage feedback signal to the control module 4 and the peak current detecting terminal CS. A starting unit 8 presets the starting threshold for turning on or off the chip 304 and realizes an under-voltage protection function. A reference and bias module 9 provides a power supply and an enable signal for a low voltage circuit and provides a reference and a bias.

Fig. 5B is a flow chart of a working process of a chip for controlling a switching power supply according to an embodiment of the present disclosure. As shown in Fig. 5B, before the chip 304 is started, the voltage of the power supply terminal VDD is 0V, and the voltage of the control terminal COMP is 0V. During the starting process of the chip 304, the voltage of the power supply terminal VDD increases slowly. When the voltage of the power supply terminal VDD is less than the starting threshold (for example, 16V), an enable signal "0" is output, i.e. a low level signal is output, and the voltage of the power supply terminal VDD continues increasing. At this time, the starting control module 402 controls the voltage of the control terminal COMP to follow with the voltage of the power supply terminal VDD, i.e. the voltage of the control terminal COMP is equal to the voltage of the power supply terminal VDD. When the voltage of the power supply terminal VDD is not less than the starting threshold, an enable signal "1" is output, i.e. a high level signal is output. At this time, the chip 304 has been started, the voltage of the control terminal COMP decreases to 0V immediately (i.e. the voltage of the control terminal COMP is 0V), and the compensation module 406 enters a normal linear compensation state. From this, the starting control module 402 is configured to control the voltage of the control terminal COMP so as to control the first MOS transistor Ml to turn on or off, and the compensation module 406 is configured to provide linear voltage compensation.

Fig. 6 is a timing diagram of working voltages of a control terminal and a power supply terminal of a chip for controlling a switching power supply according to an embodiment of the present disclosure. As shown in Fig. 6, a horizontal axis represents time T, and vertical axis represents voltages of the control terminal COMP and the power supply terminal VDD respectively. The voltage of the control terminal COMP increases with the voltage of the power supply terminal VDD during the starting process of the chip 304. After the chip 304 is started, the voltage of the power supply terminal VDD comes back to a normal working value, whereas the voltage of the control terminal COMP is pulled down to 0V immediately. Then, according to the load, the voltage of the control terminal COMP is changed so as to change a value of the linear voltage compensation under different loads. However, even if in the case of maximum compensation, the voltage of the control terminal COMP will not be greater than IV. Therefore, the small change in the voltage of the control terminal COMP will not affect the normal turning off of the first MOS transistor (i.e. the external depletion type transistor) Ml. In one embodiment, the small change in the voltage of the control terminal COMP is 0.5V. After the chip 304 is started, the external depletion type transistor is turned off until the switching power supply is turned off and the chip 304 stops working.

Fig. 7 is a circuit diagram of a switching power supply according to another embodiment of the present disclosure. As shown in Fig. 7, a switching power supply with a typical flyback AC/DC conversion circuit is provided. The switching power supply comprises an external capacitor C2, one end of the external capacitor C2 is connected with the control terminal COMP and the gate of the first MOS transistor Ml respectively, the other end of the external capacitor C2 is grounded, and the output voltage is compensated when the external capacitor C2 is charged. For example, the switching power supply may be applied to a mobile phone charger. During the starting process of the chip 304, the voltage of the control terminal COMP follows with the voltage of the power supply terminal VDD, i.e. the voltage of the control terminal COMP is equal to the voltage of the power supply terminal VDD, the voltage of the gate of the first MOS transistor Ml is equal to the voltage of the source of the first MOS transistor Ml, the voltage V_GS is about 0V, the first MOS transistor Ml is turned on normally, the first capacitor CI at the power supply terminal VDD is charged by a starting current through the first MOS transistor Ml, and the voltage of the power supply terminal VDD increases linearly until the chip 304 is started. Then, the voltage of the power supply terminal VDD goes back to the normal working value, and the chip 304 enters the normal working state. At this time, the voltage of the control terminal COMP is pulled down to 0V to make the voltage V_GS of the first MOS transistor Ml become a negative value (for example, about -13V), and thus the first MOS transistor Ml is turned off (i.e. the source and the drain of the first MOS transistor Ml is in the off state) to cut off the starting current. After the chip 304 is started, the voltage of the power supply terminal VDD is provided by the voltage fed back from the secondary coil of the transforming module 302, the voltage of the control terminal COMP increases slowly to a compensation voltage level to supply the normal voltage compensation for the chip 304. Furthermore, in one embodiment, considering that the capacitance of the gate capacitor of the first MOS transistor Ml is too low, the external capacitor C2 is added to make the linear compensation more stable.

With the switching power supply according to embodiments of the present disclosure, by integrating more functions into the chip 304, the availability of pins is increased, thus changing the fact that one pin only has one function. At the same time, while maintaining the function and performance of the chip, a new function is developed, without changing the package form (still using the SOT23-6 package in the related art) or increasing the number of packaged pins.

Therefore, compared with the scheme 1 in the related art, the switching power supply according to embodiments of the present disclosure will neither have too long starting time due to the limit of starting power consumption, nor be unable to start due to the extremely large resistance of the starting resistor. In other words, the switching power supply according to embodiments of the present disclosure has advantages of low power consumption and very short starting time.

Compared with the scheme 2 in the related art, the switching power supply according to embodiments of the present disclosure has a smaller size due to the removal of many elements, such as the external resistors and stabilivolt tubes. Therefore, with the development of the size reducing of chargers and adapters, the switching power supply according to embodiments of the present disclosure has an advantage over the switching power supply in the related art because it has the smaller size.

Compared with the scheme 3 in the related art, the switching power supply according to embodiments of the present disclosure neither changes the package form (still using the SOT23-6 package in the related art) nor increases the number of packaged pins. Therefore, the switching power supply according to embodiments of the present disclosure has an advantage of low cost.

Furthermore, a chip for controlling a switching power supply comprising a switch transistor is provided.

As shown in Fig. 4A, the chip 304 comprises a power supply terminal VDD, a control terminal COMP, a voltage division module 401, a compensation module 406 and a starting control module 402.

The control terminal COMP is connected with the switch transistor. The voltage division module 401 is configured to divide a voltage of the power supply terminal VDD to output a divided voltage after the chip 304 is started. The compensation module 406 is configured to stabilize and filter a voltage inside the chip 304 and to compensate an output voltage of the switching power supply. The starting control module 402 is connected with the voltage division module 401, the compensation module 406 and the control terminal COMP respectively, and configured to control the control terminal COMP to output a turn off signal to turn off the switch transistor according to the divided voltage and to control the compensation module 406 to start working. During the starting process of the chip 304, the voltage of the control terminal COMP follows with the voltage of the power supply terminal VDD to guarantee the voltage drop V_GS of the switch transistor is very low (about 0V), which guarantees the drain and the source of the switch transistor are in a fully on state. After the chip 304 is started, the switch transistor is turned off using a voltage difference between a gate and a source of the switch transistor. This is the first function of the control terminal COMP, i.e. the function of controlling the external switch transistor. After the chip 304 is started, the control terminal COMP performs the second function, i.e. the linear compensation function. Specifically, after the chip 304 is started, the voltage inside the chip 304 is stabilized and filtered by using a gate capacitor of the switch transistor.

Specifically, in one embodiment, the voltage division module 401 may comprise a second resistor R2 and a third resistor R3. One end of the second resistor R2 is connected with the power supply terminal VDD, the other end of the second resistor R2 is connected with one end of the third resistor R3, and the other end of the third resistor R3 is grounded.

Further, the starting control module 402 may comprise a comparator CMP, an inverter 403, a second PMOS transistor M2, a processing unit 404 and a third PMOS transistor M3. A first input end of the comparator CMP is connected with the other end of the second resistor R2, and a second input end of the comparator CMP is connected with a reference voltage end REF. An input end of the inverter 403 is connected with an output end of the comparator CMP. A drain of the second PMOS transistor M2 is connected with the power supply terminal VDD, and a gate of the second PMOS transistor M2 is connected with an output end of the inverter 403. An input end of the processing unit 404 is connected with the output end of the comparator CMP for processing an output signal of the comparator CMP to generate a pulse signal. A gate of the third PMOS transistor M3 is connected with an output end of the processing unit 404, a drain of the third PMOS transistor M3 is connected with a source of the second PMOS transistor M2, and a source of the third PMOS transistor M3 is grounded.

Furthermore, as shown in Fig. 4A, the chip 304 may further comprise a delay unit 405 and a fourth PMOS transistor M4. An input end of the delay unit 405 is connected with the output end of the comparator CMP for delaying the output signal of the comparator CMP to generate a delay signal. A gate of the fourth PMOS transistor M4 is connected with the delay unit 405, a drain of the fourth PMOS transistor M4 is connected with the compensation module 406, and a source of the fourth PMOS transistor M4 is connected with the control terminal COMP. The fourth PMOS transistor M4 is turned on to start the compensation module 406 under a control of the delay signal.

In other words, during the starting process of the chip 304, the voltage of the power supply terminal VDD increases from 0V, a voltage V_A of an output end A of the voltage division module 401 also increases from 0V and is less than the reference voltage V_REF before the chip 304 is started. Thus, at this time, a signal EN output from the comparator CMP is a low level signal, and a signal ENR obtained by inverting the signal EN with the inverter 304 is a high level signal. The high level signal ENR turns on the second PMOS transistor M2, and then the voltage of the control terminal COMP increases with the voltage of the power supply terminal VDD. When the voltage of the power supply terminal VDD increases to the starting threshold (for example, 16V) of the chip 304, the voltage V_A is greater than the reference voltage V_REF, and the comparator CMP turns over. At this time, the signal EN is a high level signal, and then the signal ENR is inverted to obtain a low level signal to turn off the second PMOS transistor M2. Thus, the control terminal COMP is disconnected from the power supply terminal VDD, and the voltage of the control terminal COMP no longer varies with the voltage of the power supply terminal VDD. Then, the high level signal EN is processed by the processing unit 404 to generate the pulse signal ENS (for example, a high level pulse with a very small width), the pulse signal ENS turns on the third PMOS transistor M3 for a short time to pull down the voltage of the control terminal COMP to about 0V (before pulling down, the voltage of the control terminal COMP is almost equal to the starting threshold of the chip 304 (for example, 16V)). At the end of the above operation, the signal EN is delayed by the delay unit 405 (i.e. a rising edge of the signal EN is delayed for a short time) to generate a delay signal END, the delay signal END turns on the fourth PMOS transistor M4 to connect the control terminal COMP with the compensation module 406. Thus, the function transformation of the control terminal COMP is completed, and then the compensation module 406 works normally and stably due to the gate capacitor of the first MOS transistor Ml. During the whole transformation process, the three switch transistors inside the chip 304 turn on or off as follows: the second PMOS transistor M2 enters an off state from an off state, and then the third PMOS transistor M3 turns on for a short time, and finally the fourth PMOS transistor M4 enters an on state from an off state.

With the chip for controlling the switching power supply according to embodiments of the present disclosure, by multiplexing the control terminal COMP, the stand-by power consumption is reduced greatly and the starting speed is increased. Furthermore, the chip for controlling the switching power supply according to embodiments of the present disclosure has advantages of small size, low cost and easy packaging.

Although the device, system, and method of the present disclosure is embodied in software or code executed by general purpose hardware as discussed above, as an alternative the device, system, and method may also be embodied in dedicated hardware or a combination of software/general purpose hardware and dedicated hardware. If embodied in dedicated hardware, the device or system can be implemented as a circuit or state machine that employs any one of or a combination of a number of technologies. These technologies may include, but are not limited to, discrete logic circuits having logic gates for implementing various logic functions upon an application of one or more data signals, application specific integrated circuits having appropriate logic gates, programmable gate arrays (PGA), field programmable gate arrays (FPGA), or other components, etc. Such technologies are generally well known by those skilled in the art and, consequently, are not described in detail herein.

It can be understood that all or part of the steps in the method of the above embodiments can be implemented by instructing related hardware via programs, the program may be stored in a computer readable storage medium, and the program includes one step or combinations of the steps of the method when the program is executed.

In addition, each functional unit in the present disclosure may be integrated in one progressing module, or each functional unit exists as an independent unit, or two or more functional units may be integrated in one module. The integrated module can be embodied in hardware, or software. If the integrated module is embodied in software and sold or used as an independent product, it can be stored in the computer readable storage medium.

The computer readable storage medium may be, but not limited to read-only memories, magnetic disks, or optical disks.

Reference throughout this specification to "an embodiment," "some embodiments," "one embodiment", "another example," "an example," "a specific example," or "some examples," means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present disclosure. Thus, the appearances of the phrases such as "in some embodiments," "in one embodiment", "in an embodiment", "in another example," "in an example," "in a specific example," or "in some examples," in various places throughout this specification are not necessarily referring to the same embodiment or example of the present disclosure. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

Although explanatory embodiments have been shown and described, it would be appreciated by those skilled in the art that the above embodiments can not be construed to limit the present disclosure, and changes, alternatives, and modifications can be made in the embodiments without departing from spirit, principles and scope of the present disclosure.

Claims

WHAT IS CLAIMED IS:

1. A switching power supply, comprising:

a rectifying module, configured to rectify an input alternating current to output a direct current;

a transforming module, connected with the rectifying module and configured to transform a voltage of the direct current to generate an output voltage;

a switching module, connected with the transforming module;

a chip for controlling the switching power supply, connected with the transforming module and the switching module respectively, wherein the chip for controlling the switching power supply has a control terminal, a compensation module and a power supply terminal, the control terminal is configured to output a turn off signal and to start the compensation module after being started, and the compensation module is configured to stabilize and filter a voltage inside the chip for controlling the switching power supply and to compensate the output voltage by controlling the switching module to turn on or off according to the output voltage;

a starting resistor, wherein one end of the starting resistor is connected with the rectifying module;

a first capacitor, wherein one end of the first capacitor is connected with the power supply terminal, the other end of the first capacitor is grounded, and a voltage of the power supply terminal is increased linearly when the first capacitor is charged; and

a first MOS transistor, wherein a gate of the first MOS transistor is connected with the control terminal, a source of the first MOS transistor is connected with the power supply terminal, a drain of the first MOS transistor is connected with the other end of the starting resistor, and the first MOS transistor is turned off when the turn off signal is received from the control terminal.

2. The switching power supply according to claim 1, wherein the chip for controlling the switching power supply comprises:

a voltage division module, connected with the power supply terminal and configured to divide the voltage of the power supply terminal to output a divided voltage; and

a starting control module, connected with the voltage division module and the control terminal respectively and configured to control the control terminal to output the turn off signal according to the divided voltage.

3. The switching power supply according to claim 2, wherein the voltage division module comprises:

a second resistor, in which one end of the second resistor is connected with the power supply terminal; and

a third resistor, in which one end of the third resistor is connected with the other end of the second resistor, and the other end of the third resistor is grounded.

4. The switching power supply according to claim 2 or 3, wherein the starting control module comprises:

a comparator, in which a first input end of the comparator is connected with the other end of the second resistor, and a second input end of the comparator is connected with a reference voltage end;

an inverter, in which an input end of the inverter is connected with an output end of the comparator;

a second PMOS transistor, in which a drain of the second PMOS transistor is connected with the power supply terminal, and a gate of the second PMOS transistor is connected with an output end of the inverter;

a processing unit, in which an input end of the processing unit is connected with the output end of the comparator for processing an output signal of the comparator to generate a pulse signal; and

a third PMOS transistor, in which a gate of the third PMOS transistor is connected with an output end of the processing unit, a drain of the third PMOS transistor is connected with a source of the second PMOS transistor, and a source of the third PMOS transistor is grounded.

5. The switching power supply according to claim 4, wherein the chip for controlling the switching power supply further comprises:

a delay unit, in which an input end of the delay unit is connected with the output end of the comparator for delaying the output signal of the comparator to generate a delay signal; and

a fourth PMOS transistor, in which a gate of the fourth PMOS transistor is connected with the delay unit, a drain of the fourth PMOS transistor is connected with the compensation module, a source of the fourth PMOS transistor is connected with the control terminal, and the fourth PMOS transistor is turned on to start the compensation module under a control of the delay signal.

6. The switching power supply according to claim 1, further comprising: an external capacitor, wherein one end of the external capacitor is connected with the control terminal and the gate of the first MOS transistor respectively, the other end of the external capacitor is grounded, and the output voltage is compensated when the external capacitor is charged.

7. The switching power supply according to claim 1, wherein after the chip is started, the first

MOS transistor is turned off using a voltage difference between the gate and the source of the first MOS transistor.

8. The switching power supply according to claim 1, wherein after the chip is started, the voltage inside the chip is stabilized and filtered by using a gate capacitor of the first MOS transistor.

9. The switching power supply according to claim 1, wherein the first capacitor is a charging capacitor.

10. A chip for controlling a switching power supply comprising a switch transistor, wherein the chip comprises:

a p o wer supply terminal ;

a control terminal connected with the switch transistor;

a voltage division module, configured to divide a voltage of the power supply terminal to output a divided voltage after the chip is started;

a compensation module, configured to stabilize and filter a voltage inside the chip and to compensate an output voltage of the switching power supply; and

a starting control module, connected with the voltage division module, the compensation module and the control terminal respectively, and configured to control the control terminal to output a turn off signal to turn off the switch transistor according to the divided voltage, and to control the compensation module to start working.

11. The chip according to claim 10, wherein the voltage division module comprises:

12. The chip according to claim 11, wherein the starting control module comprises:

a comparator, in which a first input end of the comparator is connected with the other end of the second resistor, and a second input end of the comparator connected with a reference voltage end;

13. The chip according to claim 12, further comprising:

a delay unit, wherein an input end of the delay unit is connected with the output end of the comparator for delaying the output signal of the comparator to generate a delay signal; and

a fourth PMOS transistor, wherein a gate of the fourth PMOS transistor is connected with the delay unit, a drain of the fourth PMOS transistor is connected with the compensation module, a source of the fourth PMOS transistor is connected with the control terminal, and the fourth PMOS transistor is turned on to start the compensation module under a control of the delay signal.

14. The chip according to claim 10, wherein after the chip is started, the switch transistor is turned off using a voltage difference between a gate and a source of the switch transistor.

15. The chip according to claim 10, wherein after the chip is started, the voltage inside the chip is stabilized and filtered by using a gate capacitor of the switch transistor.