TWI672897B - Voltage converter - Google Patents

Abstract

The invention provides a voltage converter comprising a transformer, a power switch, a first control circuit and a current detecting circuit. The transformer includes a primary side winding, a secondary side winding, and an auxiliary winding. The transformer is used to convert the input voltage to an output voltage. The first end of the power switch is coupled to the primary side winding, and the second end of the power switch is coupled to the first control circuit. The first control circuit is configured to generate a first control signal according to the current detection voltage to control the operation of the power switch and generate the second control signal. The current detecting circuit is coupled to the third end of the power switch, the first control circuit and the auxiliary winding, and is configured to sense the current detecting voltage according to the second control signal to provide to the first control circuit.

Description

Voltage converter

The present invention is directed to a voltage converter, and more particularly to a voltage converter that provides different output voltages.

With the development of technology, there are more and more types of electronic products, such as notebook computers, mobile communication devices, personal portable assistants, multimedia players, etc. These electronic products need to use a voltage converter to convert high-voltage AC power or DC power. A stable DC power source that meets the requirements as a source of power for charging or operation. Furthermore, as the hardware specifications of electronic products continue to increase, the demand for power supplies for electronic products is also increasing. For example, an e-sport notebook computer designed for video games has a very high demand for power supply. Therefore, how to adapt to various power supply requirements of voltage converters has become one of the goals of the industry.

Accordingly, it is a primary object of the present invention to provide a voltage converter of different output voltages.

The invention discloses a voltage converter, comprising: a transformer comprising a primary side winding, a secondary side winding and an auxiliary winding for converting an input voltage into an output voltage; a power switch, one of the power switches The first end is coupled to the primary side winding; a first control circuit is coupled to the second end of the power switch for generating a first control signal according to a current detection voltage to control the operation of the power switch And generating a second control signal; and a current detecting circuit coupled to the third end of the power switch, the first control circuit and the auxiliary winding, for sensing the current detection according to the second control signal A voltage is measured to provide to the first control circuit.

Certain terms are used throughout the description and following claims to refer to particular elements. Those of ordinary skill in the art should understand that a hardware manufacturer may refer to the same component by a different noun. The scope of this specification and the subsequent patent application do not use the difference in name as the way to distinguish the components, but the difference in function of the components as the criterion for distinguishing. The term "including" as used throughout the scope of the specification and subsequent patent applications is an open term and should be interpreted as "including but not limited to". In addition, the term "coupled" is used herein to include any direct and indirect electrical connection. Therefore, if a first device is coupled to a second device, it means that the first device can be directly electrically connected to the second device or indirectly electrically connected to the second device through other devices or connection means.

Please refer to FIG. 1. FIG. 1 is a schematic diagram of a voltage converter 1 according to an embodiment of the present invention. The voltage converter 1 is used to provide an output voltage VO to a load. The load can be any electronic product that requires power, and the output voltage VO can be used as a power source for charging or normal operation of the electronic product. The output voltage VO is a first output voltage value V1 or a second output voltage value V2. For example, the first output voltage value V1 is smaller than the second output voltage value V2. The power supply device 1 includes a transformer 10, a first control circuit 20, a current detecting circuit 30, a second control circuit 40, an output voltage switching circuit 50, a feedback circuit 60, a power switch SW1, and a resistor. RA, capacitance Co and CA, and diodes DA and DO. Transformer 10 converts an input voltage VI to an output voltage VO. The transformer 10 includes a primary side winding NP, a secondary side winding NS, and an auxiliary winding NA. The first end of the primary winding NP is coupled to an input terminal IN for receiving an input voltage VI, and the second end of the primary winding NP is coupled to the power switch SW1. The first end of the secondary winding NS is coupled to the diode DO, and the second end of the secondary winding NS is coupled to a second ground GND2. The first end of the auxiliary winding NA is coupled to the diode DA, and the second end of the auxiliary winding NA is coupled to the first ground GND1. The anode of the diode DA is coupled to the first end of the auxiliary winding NA, and the cathode of the diode DA is coupled to the resistor RA. The first end of the resistor RA is coupled to the cathode of the diode DA, and the second end of the resistor RA is coupled to the power switch SW1 and the current detecting circuit 30. The anode of the diode DO is coupled to the first end of the secondary winding NS, and the cathode of the diode DO is coupled to an output terminal OUT. The first end of the capacitor CO is coupled to the output terminal OUT, and the second end of the capacitor CO is coupled to a second ground GND2.

The first end of the power switch SW1 is coupled to the second end of the primary winding NP. The second end of the power switch SW1 is coupled to the first control circuit 20 for receiving a control signal S1. The third end of the power switch SW1 is coupled to the current detecting circuit 30. The power switch SW1 can control the signal transmission path between the first end and the third end according to the potential of the control signal S1 to present an on state (short circuit) or a non-conduction state (open circuit). The power switch SW1 can be a power transistor. For example, the power switch SW1 may be a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET), a bipolar Junction Transistor (BJT), or other components having similar functions, but not This is limited to this. When the power switch SW1 is turned on, the primary side winding current ICS flows through the primary side winding NP and the power switch SW1, and the primary side winding NP stores energy. At this time, the output voltage VO is generated by the capacitor CO to supply power to the load. When the power switch SW1 is not turned on, the energy stored in the primary winding NP is transmitted to the secondary winding NS to supply power to the capacitor CO.

The first control circuit 20 can be an integrated circuit device. The first control circuit 20 is coupled to the power switch SW1, the current detecting circuit 30, the feedback circuit 60, and the auxiliary winding NA. The first control circuit 20 includes pins CS, FB, GD1, GD2, SGND, Vcc, and the like. The first control circuit 20 can receive a power supply voltage VCC via the pin Vcc and perform related operations accordingly. The first control circuit 20 can receive a current detection voltage VCS via the pin CS and generate control signals S1 and S2 according to the current detection voltage VCS. The first control circuit 20 can output the control signal S1 via the pin GD1 to control the operation of the power switch SW1. The first control circuit 20 can output the control signal S2 via the pin GD2 to control the operation of the current detecting circuit 30. The pin FB of the first control circuit 20 is coupled to the output voltage switching circuit 50 via the feedback circuit 60 to detect the output voltage VO of the voltage converter 1. The first control circuit 20 receives a feedback signal via the pin FB.

The first control circuit 20 includes comparators 202, 204, 206, a timer 208, and a driver 210. The first input of the comparator 202 is for receiving the current detection voltage VCS, the second input of the comparator 202 is for receiving a reference voltage VR1, and one of the outputs of the comparator 202 is for outputting a comparison signal. The comparator 202 is configured to compare the signals received by the first input terminal and the second input terminal to generate a comparison signal. The comparison signal may be a voltage signal or a current signal, but is not limited thereto. Timer 208 is used to count the time. For example, timer 208 can count for a predetermined time. For example, the timer 208 can generate a time count signal to the comparator 202 every predetermined time. The timer 208 can start counting according to the indication of the comparator 202, and generate a time counting signal to the comparator 202 after the counting reaches a predetermined time period.

In one embodiment, the comparator 202 compares the signals received by the first input and the second input according to the time counting signal generated by the timer 208 to generate a comparison signal. For example, the comparator 202 determines whether the current detection voltage VCS is greater than the reference voltage VR1 according to the time counting operation of the timer 208 and determines whether the current detection voltage VCS is greater than the reference voltage VR1 for a predetermined time, and accordingly generates a comparison signal. . The driver 210 is coupled to the output of the comparator 202 for receiving the comparison signal and generating a driving signal S2 to the current detecting circuit 30 for controlling the operation of the current detecting circuit 30. When the comparator 202 determines that the current detection voltage VCS is greater than the reference voltage VR1 and the current detection voltage VCS is greater than the reference voltage VR1 for a predetermined time according to the time count of the timer 208, the comparator 202 generates and outputs a comparison signal to the driver. 210. The driver 210 generates the control signal S2 to the auxiliary switch SW2 of the current detecting circuit 30, so that the auxiliary switch SW2 is switched to the conductive state according to the control signal S2. When the comparator 202 determines that the current detection voltage VCS is less than the reference voltage VR1, the comparator 202 generates and outputs a comparison signal to the driver 210, and the driver 210 generates the control signal S2 to the auxiliary switch SW2 of the current detecting circuit 30, so as to assist The switch SW2 is switched to the non-conducting state in response to the control signal S2.

The first input of the comparator 204 is for receiving the current detection voltage VCS, and the second input of the comparator 204 is for receiving a reference voltage VR2. In one embodiment, when the current detection voltage VCS is greater than the reference voltage VR2, the comparator 204 generates an overvoltage control signal to activate the overvoltage protection function, thereby controlling the first control circuit 20 to switch to the shutdown state. The first input of the comparator 206 is for receiving the current detection voltage VCS, and the second input of the comparator 206 is for receiving a reference voltage VR3. In one embodiment, when the current detection voltage VCS is greater than the reference voltage VR3, the comparator 206 generates the control signal S1 to the pin GD1 to control the power switch SW1 to switch to the non-conduction state. In short, the comparator 204 and the comparator 206 perform an overvoltage protection function according to the reference voltages VR2 and VR3, respectively, to limit the operation of the first control circuit 20 and the power switch SW1, thereby achieving protection of the voltage converter itself and the power supply thereof. product.

The current detecting circuit 30 includes an auxiliary switch SW2 and resistors RC1, RC2. The first end of the resistor RC1 is coupled to the third end of the power switch SW1, the second end of the resistor RA, the first end of the auxiliary switch SW2, and the pin CS of the first control circuit 20. The second end of the resistor RC1 is coupled to the first ground GND1. As shown in FIG. 1, the first end of the auxiliary winding NA is coupled to the third end of the power switch SW1 via the diode DA and the resistor RA. The current detecting voltage VCS is output to the pin CS of the first control circuit 20 via the first end of the resistor RC1. The first end of the auxiliary switch SW2 is coupled to the third end of the power switch SW1, the second end of the resistor RA, and the pin CS of the first control circuit 20, and the second end of the auxiliary switch SW2 is coupled to the first control circuit 20 The pin GD2 is used to receive the control signal S2. The third end of the auxiliary switch SW2 is coupled to the resistor RC2. The auxiliary switch SW2 can control the signal transmission path between the first end and the third end according to the potential of the control signal S2 to present an on state (short circuit) or a non-conduction state (open circuit). The first end of the resistor RC2 is coupled to the third end of the auxiliary switch SW2, and the second end of the resistor RC2 is coupled to the first ground GND1.

The second control circuit 40 can be an integrated circuit device. The second control circuit 40 includes pins GD3, Vdd, and SYSTEM. The second control circuit 40 can receive a power supply voltage VDD via the pin Vdd and perform related operations accordingly. The second control circuit 40 can receive the system signal SS via the pin SYSTEM. The system signal SS is used to instruct the voltage converter 1 to provide the output voltage VO as the first output voltage value V1 or the second output voltage value V2. The second control circuit 40 generates a control signal S3 based on the system signal SS. The second control circuit 40 can output the control signal S3 to the output voltage switching circuit 50 via the pin GD3.

The output voltage switching circuit 50 includes a voltage regulator 502, an auxiliary switch SW3, and resistors RS1 to RS3. The first end of the resistor RS1 is coupled to the output terminal OUT, and the second end of the resistor RS1 is coupled to the resistor RS3. The first end of the auxiliary switch SW3 is coupled to the output terminal OUT, and the second end of the auxiliary switch SW3 is coupled to the pin GD3 of the second control circuit 40 for receiving the control signal S3. The third end of the auxiliary switch SW3 is coupled to the resistor RS2. The auxiliary switch SW3 can control the signal transmission path between the first end and the third end according to the potential of the control signal S3 to present an on state (short circuit) or a non-conduction state (open circuit). The first end of the resistor RS2 is coupled to the third end of the auxiliary switch SW3, and the second end of the resistor RS2 is coupled to the resistor RS3. The first end of the resistor RS3 is coupled to the second end of the resistor RS1, the second end of the resistor RS2, the voltage regulator 502 and the feedback circuit 60, and the second end of the resistor RS3 is coupled to the second ground GND2. The voltage regulator 502 is coupled to the first end of the resistor RS3 and the second ground GND2 for controlling one of the resistors RS3 across the voltage VRS3 such that the voltage across the voltage VRS3 of the resistor RS3 has a fixed voltage difference. The voltage regulator 502 can be a TL431 voltage regulator chip, but is not limited thereto. In one embodiment, when the system signal SS indicates that the output voltage VO is the first output voltage value V1, the second control circuit 40 generates the control signal S3 such that the auxiliary switch SW3 is in a non-conducting state in response to the control signal S3. When the system signal SS indicates that the output voltage VO is the second output voltage value V2, the second control circuit 40 generates the control signal S3, so that the auxiliary switch SW3 is switched to the on state according to the control signal S3. In addition, the feedback circuit 60 includes a photocoupler 602, resistors R1 R R2, and capacitors C1 C C3. The photocoupler 602 can be a PC817 optocoupler, but is not limited thereto.

Please refer to FIG. 2, which is a related signal waveform diagram of the voltage converter 1 of FIG. The voltage VGS_Q1 is the gate voltage of the power switch SW1, the voltage VGS_Q2 is the gate voltage of the auxiliary switch SW2, and the voltage VGS_Q3 is the gate voltage of the auxiliary switch SW3. In the present embodiment, the voltage converter 1 can provide the output voltage VO as a first output voltage value V1 (eg, 19 volts) or a second output voltage value V2 (eg, 25 volts). First, during the period T0 to T1, the voltage converter 1 is not yet powered up, and the power switch SW1, the auxiliary switch SW2, and the auxiliary switch SW3 are all in a non-conducting state (off state), and the output voltage VO is zero.

At time T1, voltage converter 1 is powered up. At this time, the power switch SW1, the auxiliary switch SW2, and the auxiliary switch SW3 are still in a non-conducting state, and the winding voltage VNP of the primary winding NP, the winding voltage VNS of the secondary winding NS, and the output voltage VO gradually rise. As shown in Fig. 2, the output voltage VO gradually rises during the period from time T1 to time T2. As shown in FIG. 3, during the period from time T1 to time T2, since the auxiliary switch SW2 is in a non-conduction state, the resistor RC2 is in an open state. In this way, the total resistance of the load resistor coupled between the power switch SW1 and the first ground GND1 is the resistance value of the resistor RC1. Furthermore, since the second control circuit 40 has not yet started to operate, the auxiliary switch SW3 is in a non-conducting state and the resistor RS2 is in an open state. In this case, the output voltage dividing resistor of the output voltage switching circuit 50 is the resistor RS1 and the resistor RS3. The total voltage dividing resistance value (ie, the total resistance value between the output terminal OUT and the second ground GND2) in the output voltage switching circuit 50 is a series resistance value of the resistor RS1 and the resistor RS3. Next, at time T2, the first control circuit 20 starts operating and the first control circuit 20 outputs a control signal S1 to control the power switch SW1 to switch to the on state. As shown in Fig. 2, during the period from T2 to T3, the output voltage VO continues to rise.

At time T3, the power switch SW1 is still in an on state. The second control circuit 40 starts operating and outputs a control signal S3 to control the power switch SW3 to switch to the on state. As shown in FIG. 4, since the power switch SW3 is switched to the on state according to the control signal S3, the output voltage dividing resistor of the output voltage switching circuit 50 is the resistor RS1, the resistor RS2, and the resistor RS3. The total voltage dividing resistance value (ie, the total resistance value between the output terminal OUT and the second ground GND2) in the output voltage switching circuit 50 is an equivalent resistance value in which the resistor RS1 is connected in parallel with the resistor RS2 and then connected in series with the resistor RS3. The parallel resistance value after the resistor RS1 is connected in parallel with the resistor RS2 is smaller than the resistance value of the single resistor RS1. As shown in FIG. 2, during the period from time T3 to time T4, the output voltage VO continues to rise, and the power switch SW1 is continuously maintained in the on state. For example, the voltage across the control resistor RS3 of the regulator 502, VRS3, is 2.5 volts. Output voltage VO = (2.5 volts ∕ resistance RS3) * (resistance RS1 ‖ resistance RS2) + 2.5 volts.

At time T4, the output voltage VO reaches the first output voltage value V1, and the first control circuit 20 generates a corresponding control signal S1 to control the power switch SW1 to start switching operation, such as Pulse Width Modulation (PWM) switching. . In this way, during the period from time T4 to T5, as shown in FIG. 2, the output voltage VO is maintained at the first output voltage value V1, the power switch SW3 is maintained in the on state, and the current detection voltage VCS is maintained below the reference voltage VR3. .

At time T5, the second control circuit 40 receives the system signal SS via the pin SYSTEM to instruct switching the output voltage VO to the second output voltage value V2. The second control circuit 40 outputs a corresponding control signal S3 according to the system signal SS to control the power switch SW3 to switch to the non-conduction state. At this time, the resistor RC2 becomes an open state. As shown in FIG. 3, the output voltage dividing resistor of the output voltage switching circuit 50 is a resistor RS1 and a resistor RS3. The total voltage dividing resistance value of the output voltage switching circuit 50 becomes the series resistance value of the resistor RS1 and the resistor RS3. Since the resistance value of each resistor is greater than the equivalent resistance value of each resistor in parallel with other resistors, the resistance value of the resistor RS1 will be greater than the equivalent resistance of the resistor RS1 and the resistor RS2 in parallel during the time T3 to T5. That is to say, the series resistance value of the resistor RS1 and the resistor RS3 in the output voltage switching circuit 50 will be greater than the series resistance value of the resistor RS1 in parallel with the resistor RS2 and then in series with the resistor RS3 during the time T3 to T5. At the same time, since the voltage regulator 502 maintains the voltage across the voltage VRS3 of the resistor RS3 at a fixed value (for example, 2.5 volts), the current flowing through the resistor RS3 does not change (for example, the current flowing through the resistor RS3 = 2.5 volts/RS3). In this case, for the output voltage switching circuit 50, when the total voltage dividing resistance value becomes large and the current does not change, the voltage across the output terminal OUT to the resistor RS3 (ie, the voltage across the resistor RS1) Will increase, as a result, the output voltage VO will also increase. As shown in Fig. 2, during the period from time T5 to time T6, the output voltage VO continues to increase, and the current detection voltage VCS also continues to increase. In other words, the output voltage switching circuit 50 is switched from a first output voltage mode to a second output voltage mode by the control of the second control circuit 40, and the output voltage VO can be continuously increased by the first output voltage value V1, thereby providing the first The output of the second output voltage value V2.

At time T6, the comparator 202 determines that the current detection voltage VCS is greater than the reference voltage VR1. As shown in Fig. 2, it is assumed that the length of time during the period from time T6 to time T7 is D (e.g., the length of time D can be 200 microseconds (μs)). During the period from time T6 to time T7, the comparator 202 determines that the current detection voltage VCS is greater than the reference voltage VR1 according to the time count of the timer 208 for a predetermined time D. Due to unexpected or unwanted system overvoltage problems, the voltage typically rises sharply and the duration is extremely short. For example, when the photocoupler 602 of the feedback circuit 60 is short-circuited, the output voltage VO will rise rapidly, and the winding voltage VNS of the secondary winding NS will rise rapidly, and the winding voltage VNA induced to the auxiliary winding NA will also rise rapidly. And the duration is extremely short. That is to say, when the current detection voltage VCS is greater than the reference voltage VR1 for a predetermined time D, this means that the rise of the current detection voltage VCS is generated by switching the output voltage, and is not an unexpected or unwanted system overvoltage. problem.

Therefore, at time T7, when the comparator 202 determines that the current detection voltage VCS is greater than the reference voltage VR1 during T6 to T7, the comparator 202 generates and outputs a comparison signal to the driver 210 to notify the driver 210 to turn on the auxiliary switch SW2. The driver 210 generates the control signal S2 to the auxiliary switch SW2 so that the auxiliary switch SW2 switches to the on state in response to the control signal S2. Therefore, as shown in FIG. 5, the total resistance of the load resistor coupled between the switch SW1 and the first ground GND1 is the parallel resistance value of the resistor RC1 and the resistor RC2 in parallel. Since the equivalent resistance of the resistors in parallel is smaller than the resistance value of the respective resistors, the total resistance value of the load resistor coupled between the switch SW1 and the first ground GND1 is changed compared to the resistance value of the resistor RC1. Small (resistance value of resistor RC1 and resistor RC2 < resistance value of resistor RC1), so that the current detection voltage VCS will drop, and a higher output voltage VO can be allowed to make the current detection voltage The VCS reaches the trigger voltage for overvoltage protection. After time T7, the output voltage VO continues to rise until the second output voltage value V2 is reached. In other words, the voltage converter 1 of the embodiment of the present invention provides the output voltage VO of the first output voltage value V1 during the time T4 to T5 according to the system requirements. After time T5, the second control circuit 40 controls the output voltage switching circuit 50 to switch according to system requirements, so that the voltage converter 1 can provide the output voltage VO of the second output voltage value V1 after time T7.

In summary, the voltage converter 1 of the embodiment of the present invention can switch and output different output voltages according to system requirements. Moreover, through the cooperation of the first control circuit 20 and the current detecting circuit 30, the current detecting voltage VCS can be timely adjusted when the low output voltage is switched to the high output voltage without separately adjusting the output voltage for performing the overvoltage. The setting of the protection function comparator 204 and the reference voltages VR2 and VR3 applied by the comparator 206.  The above are only the preferred embodiments of the present invention, and all changes and modifications made to the scope of the present invention should be within the scope of the present invention.  

1‧‧‧Voltage Converter

10‧‧‧Transformers

20‧‧‧First control circuit

202, 204, 206‧‧‧ comparator

208‧‧‧Timer

210‧‧‧ drive

30‧‧‧ Current detection circuit

40‧‧‧Second control circuit

50‧‧‧Output voltage switching circuit

502‧‧‧ Voltage Regulator

60‧‧‧Return circuit

602‧‧‧Photocoupler

C1～C3, CA, CO‧‧‧ capacitor

CS, FB, GD1~GD3, SGND, SYSTEM, Vcc, Vdd‧‧‧ pins

DA, DO‧‧‧ diode

GND1‧‧‧First ground

GND2‧‧‧Second ground

ICS‧‧‧ primary side winding current

IN‧‧‧ input

NA‧‧‧Auxiliary winding

NP‧‧‧ primary winding

NS‧‧‧ secondary winding

OUT‧‧‧ output

R1～R2, RA, RC1～RC2, RS1～RS3‧‧‧ resistance

S1～S3‧‧‧ control signal

SS‧‧‧ system signal

SW1‧‧‧ power switch

SW2～SW3‧‧‧Auxiliary switch

VCC, VDD‧‧‧ power supply voltage

VCS‧‧‧ current detection voltage

VGS_Q1, VGS_Q2, VGS_Q3‧‧‧ voltage

VI‧‧‧Input voltage

VNA‧‧‧Auxiliary winding voltage

VNP, VNS‧‧‧ winding voltage

VO‧‧‧ output voltage

VR1 ~ VR3‧‧‧ reference voltage

VRS3‧‧‧ cross pressure

FIG. 1 is a schematic diagram of a voltage converter according to an embodiment of the present invention.  Figure 2 is a waveform diagram of the associated signal of the voltage converter of Figure 1.  3 to 5 are schematic diagrams showing an equivalent circuit of the voltage converter in operation of the embodiment of the present invention.  

Claims (9)

A voltage converter comprising:
a transformer comprising a primary side winding, a secondary side winding and an auxiliary winding for converting an input voltage into an output voltage;
a power switch, a first end of the power switch is coupled to the primary side winding;
a first control circuit coupled to the second end of the power switch for generating a first control signal according to a current detection voltage to control operation of the power switch and generating a second control signal; and a current The detecting circuit is coupled to the third end of the power switch, the first control circuit and the auxiliary winding for sensing the current detecting voltage according to the second control signal to be provided to the first control circuit. The voltage converter of claim 1, wherein the current detecting circuit comprises:
a first resistor, a first end of the first resistor is coupled to the third end of the power switch, the first control circuit and the auxiliary winding, and the current detecting voltage is first through the first resistor The first end of the first resistor is coupled to a first ground, wherein the first end of the auxiliary winding is coupled to the power switch via a diode and a resistor The third end;
a first auxiliary switch, a first end of the first auxiliary switch is coupled to the third end of the power switch, the first control circuit and the auxiliary winding, and one of the first auxiliary switches is second terminated The first control circuit is configured to receive the second control signal; and a second resistor, the first end of the second resistor is coupled to the third end of the first auxiliary switch, and the second resistor is The second end is coupled to the first ground. The voltage converter of claim 2, wherein the first control circuit comprises:
a timer for counting a predetermined time;
a comparator includes a first input terminal, a second input terminal, and an output terminal, wherein the comparator is configured to compare the signals received by the first input terminal and the second input terminal according to the counting of the timer to generate a comparison signal, wherein the first input terminal is configured to receive the current detection voltage, the second input terminal is configured to receive a reference voltage, and the output terminal is configured to output the comparison signal; and a driver coupled to the The output of the comparator is configured to generate the second control signal according to the comparison signal. The voltage converter of claim 3, wherein the comparator generates and outputs the current detection voltage when the current detection voltage is greater than the reference voltage and the current detection voltage is greater than the reference voltage for the predetermined time. Comparing the signal to the driver, the driver generates the second control signal to the first auxiliary switch, and the first auxiliary switch is in an on state according to the second control signal. The voltage converter of claim 3, wherein the comparator generates and outputs the comparison signal to the driver when the current detection voltage is less than the reference voltage, and the driver generates the second control signal accordingly. The first auxiliary switch and the first auxiliary switch are in a non-conducting state according to the second control signal. The voltage converter described in claim 1 of the patent scope, further comprising:
a second control circuit for generating a third control signal according to a system signal; and an output voltage switching circuit comprising:
a third resistor, a first end of the third resistor is coupled to one of the first ends of the secondary winding;
a fourth resistor, the first end of the fourth resistor is coupled to the second end of the third resistor, and the second end of the fourth resistor is coupled to a second ground;
a voltage regulator coupled to the first end of the fourth resistor and the second ground for controlling a voltage across the fourth resistor such that the voltage across the fourth resistor has a fixed voltage difference;
a second auxiliary switch, a first end of the second auxiliary switch is coupled to the first end of the second side winding and the first end of the third resistor, and the second end of the second auxiliary switch Connected to the second control circuit for receiving the third control signal; and a fifth resistor, the first end of the fifth resistor is coupled to the third end of the second auxiliary switch, the fifth resistor One second end is coupled to the second end of the third resistor, the first end of the fourth resistor, and the voltage regulator. The voltage converter of claim 6, wherein the second control circuit generates the third control signal and the second auxiliary when the system signal indicates that the output voltage is a first output voltage value The switch is in a non-conducting state due to the third control signal. The voltage converter of claim 7, wherein the second control circuit generates the third control signal and the second auxiliary when the system signal indicates that the output voltage is a second output voltage value The switch is in an on state due to the third control signal, wherein the first output voltage value is less than the second output voltage value. The voltage converter of claim 6, wherein the voltage converter further comprises:
a first diode, an anode of the first diode is coupled to the first end of the secondary winding, and a cathode of the first diode is coupled to the first of the third resistor And the first end of the second auxiliary switch; and a first capacitor, the first end of the first capacitor is coupled to the cathode of the first diode, the first end of the third resistor And the first end of the second auxiliary switch, the second end of the first capacitor is coupled to the second ground.