A voltage conversion circuit and a supply voltage control circuit thereof

Abstract

Disclosed is a power supply voltage control circuit, which adopts an intelligent charging control circuit, uses an input voltage to charge a power supply capacitor, or uses the intelligent charging control circuit to charge the power supply capacitor when the output voltage is low, and uses an auxiliary winding to charge the power supply capacitor when the output voltage is high, so as to avoid the problems of high voltage resistance requirement of a power supply control chip and large circuit loss caused by a wide output voltage range of a voltage conversion circuit.

Description

Technical Field

[0001] Embodiments of the present invention relate to power supplies, and more specifically, to a power supply voltage control circuit. Background Technology

[0002] As smartphones become more feature-rich, they consume power faster and faster, leading to the development of fast charging technology. Figure 1 An existing voltage conversion circuit 10 for a fast charging power supply is shown. For example... Figure 1 As shown, the AC voltage Vac, after passing through the rectifier bridge 101, provides an input voltage Vin with a wavy waveform to the transformer T1 of the voltage conversion circuit 10. The power control chip 102 controls the duty cycle of the primary-side switch M1 coupled to the transformer T1 to control the energy conversion between the primary and secondary sides of the transformer T1, thereby controlling the output voltage Vout. The power control chip 102 is powered by the auxiliary winding Lt. The power supply voltage Vcc provided by the auxiliary winding Lt is proportional to the output voltage Vout, and the proportionality coefficient is determined by the turns ratio of the auxiliary winding Lt and the secondary winding Ls, i.e., Vcc:Vout=N(Lt):N(Ls), where N represents the number of turns of the winding. It should be understood that in order to maintain the normal operation of the power control chip 102, the power supply voltage Vcc has a minimum voltage limit, which is usually around 10V. When the output voltage Vout has a wide range, such as from 3.3V to 20V, in order to ensure that the power supply voltage Vcc still meets the minimum voltage requirement when the output voltage Vout = 3.3V, the turns ratio of the auxiliary winding Lt to the secondary winding Ls must be at least 3:1. With a turns ratio of 3:1 for the auxiliary winding Lt to the secondary winding Ls, the power supply voltage Vcc is 60V when the output voltage Vout = 20V. This necessitates a relatively high voltage withstand capability for the power supply control chip 102, but also results in significant power losses. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a power supply voltage control circuit that employs an intelligent charging control circuit. This circuit uses the input voltage to charge the power supply capacitor, or combines the intelligent charging control circuit with an auxiliary winding. When the output voltage is low, the power supply capacitor is charged using the intelligent charging control circuit and the input voltage; when the output voltage is high, the power supply capacitor is charged using the auxiliary winding. This avoids the problems of high voltage tolerance requirements for the power control chip and high circuit losses caused by the wide output voltage range of the voltage conversion circuit.

[0004] According to an embodiment of the present application, a power supply voltage control circuit is provided for charging a power supply capacitor to generate a power supply voltage, which is provided to a power supply control chip, which can be used to control a voltage conversion circuit to convert an input voltage to an output voltage. The power supply voltage control circuit includes a charging control circuit receiving the input voltage and the power supply voltage, and outputting a charging control signal based on the input voltage and the power supply voltage when the input voltage is less than a threshold voltage, wherein a pulse width of the charging control signal increases as the power supply voltage decreases; and a charging switch coupled between the input voltage and the power supply capacitor, having a control terminal receiving the charging control signal, and being turned on and off under the control of the charging control signal.

[0005] According to an embodiment of the present application, a power supply circuit is also provided, including the aforementioned power supply voltage control circuit, and further including a power supply capacitor having a charging terminal coupled to the charging switch, and having a ground terminal coupled to a reference ground.

[0006] According to an embodiment of the present application, a voltage conversion circuit is also provided, receiving an input voltage, and converting the input voltage to an output voltage, including a transformer having a primary winding and a secondary winding; a primary switch coupled to the primary winding; a power supply control chip outputting a primary control signal to a control terminal of the primary switch, to control the primary switch to be turned on and off; a power supply capacitor having a charging terminal providing a power supply voltage to the power supply control chip; a charging control circuit receiving the input voltage and the power supply voltage, and outputting a charging control signal based on the input voltage and the power supply voltage when the input voltage is less than a threshold voltage, wherein a pulse width of the charging control signal increases as the power supply voltage decreases; and a charging switch coupled between the input voltage and the charging terminal of the power supply capacitor, having a control terminal receiving the charging control signal, and being turned on and off under the control of the charging control signal. BRIEF DESCRIPTION OF DRAWINGS

[0007] For a better understanding of the present application, the present application will be described in detail according to the following drawings:

[0008] Figure 1 A prior art voltage conversion circuit 10 for fast charging power supply is shown;

[0009] Figure 2 A circuit structure schematic diagram of a voltage conversion circuit 20 according to an embodiment of the present application is shown;

[0010] Figure 3 A waveform schematic diagram of signals of a charging control circuit 23 according to an embodiment of the present application is shown; and

[0011] Figure 4 A circuit structure schematic diagram of a voltage conversion circuit 40 according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0012] Specific embodiments of the present invention will now be described in detail. It should be noted that the embodiments described herein are for illustrative purposes only and are not intended to limit the invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other instances, well-known circuits, materials, or methods have not been specifically described to avoid obscuring the invention.

[0013] Throughout this specification, references to "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases "in an embodiment," "in an embodiment," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. Moreover, those skilled in the art will understand that the accompanying drawings provided herein are for illustrative purposes and are not necessarily drawn to scale. The same reference numerals indicate the same elements. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0014] Figure 2 A schematic diagram of the circuit structure of a voltage conversion circuit 20 according to an embodiment of the present invention is shown. The voltage conversion circuit 20 includes: a transformer T1 having a primary winding Lp and a secondary winding Ls; a primary-side switch M1 coupled to the primary winding Lp; a power control chip 21 that outputs a primary-side control signal G1 to the control terminal of the primary-side switch M1 to control the on / off state of the primary-side switch M1; a power supply capacitor Cvcc that provides a power supply voltage Vcc to the power control chip 21; a charging control circuit 23 that receives an input voltage Vin and a power supply voltage Vcc, and outputs a charging control signal Gc based on the power supply voltage Vcc and the input voltage Vin when the input voltage Vin is less than a threshold voltage Vth, wherein the pulse width of the charging control signal Gc increases as the power supply voltage Vcc decreases; and a charging switch S1 coupled between the input voltage Vin and the charging terminal of the power supply capacitor Cvcc, having a control terminal that receives the charging control signal Gc and is switched on and off under the control of the charging control signal Gc.

[0015] exist Figure 2The charging control circuit 23 includes: a first comparison circuit 230, which receives an input voltage Vin and a threshold voltage Vth, and generates a pulse signal Clk based on the input voltage Vin and the threshold voltage Vth, wherein the pulse signal Clk is valid when the input voltage Vin drops to the threshold voltage Vth; a calculation circuit 232, which receives a power supply voltage Vcc and a reference voltage Vref, and outputs a compensation signal Vdi based on the difference between the power supply voltage Vcc and the reference voltage Vref; a sample-and-hold circuit 231, which has a clock terminal to receive the pulse signal Clk and an input terminal to receive the compensation signal Vdi, samples the compensation signal Vdi when the pulse signal Clk is valid, and outputs a sample-and-hold signal Vdo based on the compensation signal Vdi; and a second comparison circuit 233, which receives the sample-and-hold signal Vdo and the input voltage Vin, and outputs a charging control signal Gc based on the comparison result between the sample-and-hold signal Vdo and the input voltage Vin.

[0016] In one embodiment, the first comparison circuit 230 includes: a comparator 2301 that receives an input voltage Vin and a threshold voltage Vth, and outputs an input voltage comparison signal CP1 based on the input voltage Vin and the threshold voltage Vth; and a pulse circuit 2302 that receives the input voltage comparison signal CP1 and outputs a pulse signal Clk based on the input voltage comparison signal CP1, wherein the pulse signal Clk is valid when the input voltage Vin drops to the threshold voltage Vth. It should be understood that any circuit capable of generating a valid signal characterizing the drop of the input voltage Vin to the threshold voltage Vth can be used as the first comparison circuit.

[0017] exist Figure 2 In this embodiment, the charging control circuit 23 controls the on / off state of the charging switch S1 to control the charging of the power supply capacitor Cvcc, thereby establishing a power supply voltage Vcc on the power supply capacitor Cvcc. That is, the charging control circuit 23, the charging switch S1, and the power supply capacitor Cvcc constitute a power supply circuit, providing the power supply voltage Vcc to power the power control chip 21, enabling the power control chip 21 to operate normally and provide the primary-side control signal G1 to control the on / off state of the primary-side switch M1, thereby controlling the energy conversion between the primary and secondary sides of the transformer T1, converting the input voltage Vin into an output voltage Vout that meets the requirements of the downstream load. Specifically, when the primary-side switch M1 is on, the secondary-side switch Ds is off, the current flowing through the primary winding Lp increases, the primary winding Lp stores energy, and the output power supply capacitor Co supplies power to the load. When the primary-side switch M1 is off, the secondary switch Ds is on, the energy of the primary winding Lp is transferred to the secondary winding Ls, the secondary winding Ls supplies power to the load, and simultaneously charges the output capacitor Co to maintain the output voltage Vout.

[0018] Figure 3The waveforms of the signals of the charging control circuit 23 according to an embodiment of the present application are shown in the following figures. The working principle of the charging control circuit 23 is explained below in conjunction with Figure 2 and Figure 3 .

[0019] As shown in Figure 3 , the input voltage Vin has a doughnut waveform after the rectification of the alternating voltage Vac. The threshold voltage Vth is compared with the input voltage Vin, and when the input voltage Vin is less than the threshold voltage Vth, the input voltage comparison signal CP1 outputted by the comparator 2301 is high, and vice versa. The pulse circuit 2302 receives the input voltage comparison signal CP1 and generates an effective pulse signal Clk at the rising edge of the input voltage comparison signal CP1. After receiving the effective pulse signal Clk, the sample-and-hold circuit 231 samples the compensation signal Vdi. The compensation signal Vdi is the difference between the reference voltage Vref and the power supply voltage Vcc, i.e. Vdi = Vref - Vcc. The sample-and-hold circuit 231 holds the sampled signal and outputs a sample-and-hold signal Vdo. The sample-and-hold signal Vdo is compared with the input voltage Vin to obtain a charging control signal Gc. When the sample-and-hold signal Vdo is greater than the input voltage Vin, the charging control signal Gc is high, and vice versa. When the charging control signal Gc is high, the charging switch S1 is turned on, the charging end of the power supply capacitor Cvcc is coupled to the input voltage Vin, and the power supply capacitor Cvcc can be charged. The charging current Is is shown in Figure 3 , and its waveform is related to the input voltage Vin. Specifically, Is = (Vin - Vcc) / Rdson, where Rdson is the on-resistance of the charging switch S1.

[0020] When the input polarity of the comparator is changed, the high and low levels of the output signal will also change accordingly, resulting in a corresponding change in the control logic of the entire circuit. It should be understood that Figure 2 and Figure 3 The embodiments are only used to illustrate the principles of the application, and in other embodiments, the connection structure of the circuit and the level form of the signals can be adaptively changed.

[0021] From Figure 3It can be seen that the lower the value of the power supply voltage Vcc, the greater the value of the sample-and-hold signal Vdo, and the longer the high level of the charging control signal Gc obtained after comparison with the input voltage Vin, which means that the longer the on duration of the charging switch S1 and the longer the charging duration of the power supply capacitor Cvcc, so that the power supply voltage Vcc rises faster. The value of the reference voltage Vref is the target value of the power supply voltage Vcc. When the value of the power supply voltage Vcc rises to the reference voltage Vref, the difference between the two is 0, and the value of the sample-and-hold signal Vdo is 0, which is lower than the input voltage Vin, so that the charging control signal Gc is at a low level, the charging switch S1 is turned off, and the power supply capacitor Cvcc is not charged. Only when the value of the power supply voltage Vcc is lower than the reference voltage Vref, the value of the sample-and-hold signal Vdo is the difference between the two, and the charging control signal Gc is generated after comparison with the input voltage Vin to control the charging switch S1, thereby controlling the charging of the power supply capacitor Cvcc.

[0022] It should be understood that the input voltage Vin not only includes the actual input voltage Vin, but also includes the voltage signal obtained by dividing the actual output voltage Vin. In Figure 3 In the embodiment, the input voltage Vin has a steamed bun waveform, i.e. the waveform of an alternating voltage with a sine waveform after full-bridge rectification. It should be understood that the input voltage Vin of the present application can also have other waveforms, such as a triangular wave, etc.

[0023] Figure 2 The voltage conversion circuit 20 in the power supply control circuit 20 has a Flyback topology. It should be understood that the power supply voltage control circuit including the charging control circuit 23 and the charging switch S1 can be used in any voltage conversion circuit 20 with other topologies, such as Buck topology, Boost topology, etc.

[0024] Figure 4 A circuit structure schematic diagram of a voltage conversion circuit 40 according to an embodiment of the present application is shown. The voltage conversion circuit 40 includes a transformer T1 having a primary winding Lp and a secondary winding Ls; a primary switch M1 coupled to the primary winding Lp; a power supply control chip 21 outputting a primary control signal G1 to a control end of the primary switch M1 to control the on-off of the primary switch M1; a power supply capacitor Cvcc providing a power supply voltage Vcc to the power supply control chip 21; a charging control circuit 23 receiving an input voltage Vin and the power supply voltage Vcc, and outputting a charging control signal Gc based on the input voltage Vin and the power supply voltage Vcc when the input voltage Vin is less than a threshold voltage Vth, wherein the pulse width of the charging control signal Gc increases with the decrease of the power supply voltage Vcc; and a charging switch S1 coupled between the input voltage Vin and a charging end of the power supply capacitor Cvcc, having a control end receiving the charging control signal Gc, and being turned on and off under the control of the charging control signal Gc.

[0025] In Figure 4 The transformer T1 further comprises an auxiliary winding Lt. The auxiliary winding Lt is coupled to the charging terminal of the power supply capacitor Cvcc through a diode Dt. When the voltage provided by the auxiliary winding Lt is higher than the voltage that the charging control circuit 23 can achieve by controlling the charging switch S1 to charge the power supply capacitor Cvcc, i.e. the reference voltage Vref, the auxiliary winding Lt charges the power supply capacitor Cvcc. Those skilled in the art can set a reasonable value of the reference voltage Vref and the turns ratio between the auxiliary winding Lt and the secondary winding Ls according to the application requirements after understanding the principles of the present application, so that the power supply capacitor Cvcc can be charged by the charging control circuit 23 to maintain the power supply of the power supply control chip 21 when the output voltage Vout is low, and the power supply capacitor Cvcc can be charged by the auxiliary winding Lt to maintain the power supply voltage Vcc when the output voltage Vout is high.

[0026] When the output voltage Vout is low, the charging control circuit 23 is used to control the charging of the power supply capacitor Cvcc, and the turns ratio between the auxiliary winding Lt and the secondary winding Ls does not need to be high, and the turns ratio between the two can be as low as 1:1, or even 1:2, or lower. When the turns ratio between the auxiliary winding Lt and the secondary winding Ls is 1:2, even if the output voltage Vout reaches 20V, the power supply voltage Vcc is only 10V. That is, when the turns ratio between the auxiliary winding Lt and the secondary winding Ls is low, even if the output voltage Vout is high, the voltage provided by the auxiliary winding Lt will not be too high to cause the power supply control chip 21 to bear a high voltage, and the circuit loss caused by high voltage is also reduced.

[0027] In an embodiment, the charging control circuit 23 is integrated into the power supply control chip 21. In an embodiment, the charging control circuit 23 and the charging switch S1 are both integrated into the power supply control chip 21.

[0028] The charging switch S1 can include any controllable switch such as a JFET (Junction Field Effect Transistor), a MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor), etc.

[0029] It should be understood that the circuit and working process given in the present application are only illustrative. Any circuit that can realize the functions and working processes of the circuit of the present application does not deviate from the spirit or essence of the present application.

[0030] While the application has been described with reference to several exemplary embodiments, it is to be understood that the use of other words or terminologies used herein is intended to convey a practical, and conceptual meaning and not a limiting meaning as used in any particular exemplary embodiment. It is therefore submitted that the foregoing disclosure of exemplary embodiments of the application are intended for illustrative purposes only and not for limiting the scope of the application as contemplated by the appended claims and their equivalents.

Claims

1. A power supply voltage control circuit for charging a power supply capacitor to generate a power supply voltage for a power supply control chip, the power supply control chip being configured to control a voltage conversion circuit to convert an input voltage to an output voltage, the power supply voltage control circuit comprising: a charging control circuit configured to receive the input voltage and the power supply voltage, and output a charging control signal based on the input voltage and the power supply voltage when the input voltage is less than a threshold voltage, wherein a pulse width of the charging control signal increases as the power supply voltage decreases; and a charging switch coupled between the input voltage and the power supply capacitor, and having a control terminal configured to receive the charging control signal and to be turned on and off under control of the charging control signal; wherein the charging control circuit comprises: a first comparison circuit configured to receive the input voltage and the threshold voltage, and to generate a pulse signal based on the input voltage and the threshold voltage, the pulse signal being active when the input voltage falls below the threshold voltage; a calculation circuit configured to receive the power supply voltage and a reference voltage, and to output a compensation signal based on a difference between the power supply voltage and the reference voltage; and a sample-and-hold circuit having a clock terminal configured to receive the pulse signal, and having an input terminal configured to receive the compensation signal, the sample-and-hold circuit being configured to sample the compensation signal when the pulse signal is active, and to output a sample-and-hold signal based on the compensation signal; and a second comparison circuit configured to receive the sample-and-hold signal and the input voltage, and to output the charging control signal based on a comparison between the sample-and-hold signal and the input voltage. The first comparison circuit comprises:

2. The supply voltage control circuit of claim 1, wherein, a comparator configured to receive the input voltage and the threshold voltage, and to output an input voltage comparison signal based on the input voltage and the threshold voltage; and a pulse circuit configured to receive the input voltage comparison signal, and to output the pulse signal based on the input voltage comparison signal, the pulse signal being active when the input voltage falls below the threshold voltage. 3.A power supply circuit comprising the power supply voltage control circuit of any one of claims 1-2, and further comprising a power supply capacitor having a charging terminal coupled to the charging switch, and having a ground terminal coupled to a reference ground. The charging terminal of the power supply capacitor is coupled to an auxiliary winding of the voltage conversion circuit.

4. The power supply circuit of claim 3, wherein, 5.A voltage conversion circuit configured to receive an input voltage, and to convert the input voltage to an output voltage, the voltage conversion circuit comprising: a transformer having a primary winding and an auxiliary winding; a primary switch coupled to the primary winding; a power supply control chip configured to output a primary control signal to a control terminal of the primary switch to control turning on and off of the primary switch; a power supply capacitor having a charging terminal configured to provide a power supply voltage to the power supply control chip; a charging control circuit configured to receive the input voltage and the power supply voltage, and to output a charging control signal based on the input voltage and the power supply voltage when the input voltage is less than a threshold voltage, wherein a pulse width of the charging control signal increases as the power supply voltage decreases; and a charging switch coupled between the input voltage and the charging terminal of the power supply capacitor, and having a control terminal configured to receive the charging control signal and to be turned on and off under control of the charging control signal; wherein the charging control circuit comprises: a first comparison circuit configured to receive the input voltage and the threshold voltage, and to generate a pulse signal based on the input voltage and the threshold voltage, the pulse signal being active when the input voltage falls below the threshold voltage; and a calculation circuit configured to receive the power supply voltage and a reference voltage, and to output a compensation signal based on a difference between the power supply voltage and the reference voltage; and a sample-and-hold circuit having a clock terminal configured to receive the pulse signal, and having an input terminal configured to receive the compensation signal, the sample-and-hold circuit being configured to sample the compensation signal when the pulse signal is active, and to output a sample-and-hold signal based on the compensation signal; and a second comparison circuit configured to receive the sample-and-hold signal and the input voltage, and to output the charging control signal based on a comparison between the sample-and-hold signal and the input voltage. The computing circuit receives a power supply voltage and a reference voltage, and outputs a compensation signal based on a difference between the power supply voltage and the reference voltage; The sample-and-hold circuit has a clock terminal receiving a pulse signal, has an input terminal receiving the compensation signal, samples the compensation signal when the pulse signal is active, and outputs a sample-and-hold signal based on the compensation signal; and The second comparison circuit receives the sample-and-hold signal and the input voltage, and outputs a charging control signal based on a comparison result of the sample-and-hold signal and the input voltage.

6. The voltage conversion circuit of claim 5, wherein, The first comparison circuit includes: The comparator receives the input voltage and a threshold voltage, and outputs an input voltage comparison signal based on the input voltage and the threshold voltage; and The pulse circuit receives the input voltage comparison signal, and outputs a pulse signal based on the input voltage comparison signal, wherein the pulse signal is active when the input voltage drops to the threshold voltage.

7. The voltage conversion circuit of claim 5, wherein the transformer further comprises an auxiliary winding coupled to a charge terminal of the power supply capacitor through a diode.

8. The voltage conversion circuit of claim 5, wherein, The charging control circuit and the charging switch are integrated in a power supply control chip.

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