High-voltage starting switching power supply

Abstract

This application relates to a high-voltage starting switching power supply, including a transformer and a power supply connected to the primary winding of the transformer, and a control chip including a charging capacitor, a STA module, and a main control module. The charging capacitor is electrically connected to the input terminal of the STA module, and the main control module is electrically connected to the output terminal of the STA module. The STA module is used to detect the input voltage of the control chip. A high-voltage starting branch and a power supply branch are electrically connected to the charging capacitor and the primary winding, respectively. A switching switch is electrically connected to the output terminal of the high-voltage starting branch and the STA module. The switching switch is turned off or on to charge the charging capacitor by the high-voltage starting branch or the power supply branch. A control switch is electrically connected to the output terminal of the main control module and the primary winding. The starting voltage has a preset value. The STA module outputs a first signal according to the input voltage to turn the switching switch on or off. When the input voltage is less than the preset value, the high-voltage starting branch charges the charging capacitor. When the input voltage is greater than the preset value, the power supply branch charges the charging capacitor.

Description

Technical Field

[0001] This invention relates to the field of switching circuit technology, and more specifically to a high-voltage start-up switching power supply. Background Technology

[0002] With the widespread use of electronic devices, the application of switching power supplies is expanding. The control chip in a switching power supply is typically powered by an auxiliary winding. When the power supply is first turned on, the secondary output is not yet established, and the voltage of the auxiliary winding is too low to supply power to the control chip, causing the power supply to malfunction upon initial power-on. Therefore, switching power supplies generally have a startup circuit to activate the control chip upon power-on, driving the transformer to quickly switch the voltage and enabling the switching power supply to operate normally.

[0003] When the power supply is first powered on, the control chip needs to obtain a startup voltage from the input terminal. A traditional and simple approach is to connect a relatively large startup resistor RST to the VCC capacitor at the input terminal. When the power supply is first powered on, the VCC capacitor is charged to complete the startup of the control chip. This startup circuit can meet the voltage startup requirement, but after the switching power supply has completed startup and the secondary voltage has been established to provide the operating voltage for the control chip, there is still current flowing through the startup resistor RST, resulting in unnecessary power consumption waste. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is how to provide the start-up voltage and operating voltage to the control chip of the switching power supply while avoiding power consumption waste.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A high-voltage starting switching power supply includes a transformer and a power source electrically connected to the primary winding of the transformer, wherein the secondary winding of the transformer is connected to a load, and the switching power supply comprises:

[0007] The control chip includes a charging capacitor, an STA module, and a main control module. The charging capacitor is electrically connected to the input terminal of the STA module, and the main control module is electrically connected to the output terminal of the STA module. The STA module is used to detect the input voltage of the control chip.

[0008] The high-voltage starting branch is used to provide the starting voltage to the control chip and is electrically connected to the charging capacitor and the primary coil.

[0009] The power supply branch is used to provide the operating voltage to the control chip and is electrically connected to the charging capacitor and the primary coil.

[0010] A switching switch is electrically connected to the output terminal of the high-voltage starting branch and the STA module. The switching switch is turned off or on to allow the high-voltage starting branch or the power supply branch to charge the charging capacitor.

[0011] A control switch is used to control the energy storage or disconnection of the primary coil, and is electrically connected to the output terminal of the main control module and the primary coil.

[0012] Wherein, the start-up voltage has a preset value, and the STA module outputs a first signal according to the input voltage to turn the switching switch on or off; when the input voltage is less than the preset value, the high-voltage start-up branch charges the charging capacitor; when the input voltage is equal to the preset value, the power supply branch charges the charging capacitor.

[0013] Furthermore, the high-voltage starting branch includes a transistor, a first diode, and a starting resistor. The transistor is connected in series with the control switch, and the first diode is connected in series with the starting resistor.

[0014] The transistor has a first pin connected to the primary coil, a second pin electrically connected to the control switch, and a third pin electrically connected to the switching switch. The charging capacitor is electrically connected to the second pin through the first diode and the start-up resistor.

[0015] The switching switch is turned off or on to turn the transistor on or off; when the input voltage is less than the preset value, the transistor is on; when the input voltage is greater than the preset value, the transistor is off. At the same time, the STA module outputs a second signal to start the main control module.

[0016] Furthermore, the transistor is a depletion-mode gallium nitride MOS transistor, and the control switch and the switching switch are both enhancement-mode MOS transistors. The first pin is the drain of the transistor, the second pin is the source of the transistor, and the third pin is the gate of the transistor. The drain of the control switch is electrically connected to the source of the transistor, the drain of the switching switch is electrically connected to the gate of the transistor, and the source of the control switch and the source of the switching switch are grounded.

[0017] Furthermore, the anode of the first diode is electrically connected to the gate of the transistor, the positive terminal of the charging capacitor is electrically connected to the cathode of the first diode, and the negative terminal of the charging capacitor is grounded.

[0018] Furthermore, the high-voltage start-up branch also includes a protection resistor, which is connected in series between the anode of the first diode and the gate of the transistor.

[0019] Furthermore, the STA module includes a startup determination circuit, which includes a comparator, a NOT gate circuit, a voltage divider branch, and an adjustment switch;

[0020] The input terminals of the switching switch and the NOT gate are both electrically connected to the output terminal of the comparator. The inverting input terminal of the comparator is connected to the preset value. The input voltage is divided by the voltage divider branch and then connected to the non-inverting input terminal of the comparator. The voltage divider branch includes several resistors connected in series. The adjusting switch is turned on or off so that at least one of the resistors is connected to the voltage divider branch or short-circuited.

[0021] Furthermore, the voltage divider branch includes a first resistor, a second resistor, and a third resistor connected in series, and the regulating switch is connected in parallel across the third resistor. The regulating switch is turned on or off to short-circuit or connect the third resistor.

[0022] The comparator controls the NOT gate circuit to output a third signal to turn the adjustment switch on or off; when the third signal is high, the third resistor is short-circuited; when the third signal is low, the third resistor is connected to the voltage divider branch.

[0023] Furthermore, the regulating switch is an enhancement-mode MOS transistor, the gate of the regulating switch is electrically connected to the output terminal of the NOT gate circuit, and the source of the regulating switch is grounded.

[0024] Furthermore, the power supply branch includes an auxiliary coil and a second diode. The anode of the second diode is electrically connected to the high-voltage terminal of the auxiliary coil, the cathode of the second diode is connected to the positive terminal of the charging capacitor, and the low-voltage terminal of the auxiliary coil is grounded.

[0025] Furthermore, the control chip also includes a detection module, which detects the magnitude of the load output voltage of the secondary coil and sends a feedback signal to the main control module. The main control module outputs a pulse-width modulated control signal based on the feedback signal to control the control switch to be turned on or off.

[0026] The beneficial effects of this invention are as follows: By setting up a high-voltage start-up branch and a power supply branch within the switching power supply to provide start-up voltage and operating voltage to the control chip respectively, and by using an STA module and a switching switch, the STA module detects the input voltage of the control chip and controls the switching switch to switch between the high-voltage start-up branch and the power supply branch to charge the charging capacitor of the control chip. When the input voltage is less than a preset value of the start-up voltage, the high-voltage start-up branch charges the charging capacitor; when the input voltage is greater than the preset value, the power supply branch charges the charging capacitor. This allows the high-voltage start-up branch to be shut down promptly after the switching power supply starts up, and to be restarted to provide start-up voltage to the control chip when the input voltage is less than the preset value, thereby reducing energy loss.

[0027] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0028] Figure 1 This is a circuit diagram of a switching power supply according to an embodiment of the present invention;

[0029] Figure 2 for Figure 1 The diagram shows the internal circuitry of the STA module. Detailed Implementation

[0030] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0031] Please see Figure 1 and Figure 2 This embodiment provides a high-voltage starting switching power supply, which is a flyback switching power supply. The flyback switching power supply has a transformer and a power supply VIN electrically connected to the primary winding N1 of the transformer. The secondary winding N2 of the transformer is connected to a load (not shown). In this embodiment, the flyback switching power supply includes a control chip, a high-voltage starting branch providing a starting voltage to the control chip, a power supply branch providing an operating voltage to the control chip, a switching switch Q3, and a control switch Q2. The switching switch Q3 is turned on or off to switch between the high-voltage starting branch and the power supply branch for starting. The control switch Q2 is used to control the primary winding N1 to be turned on or off.

[0032] Specifically, the control chip includes a charging capacitor C1, an STA module, and a main control module PWM. The charging capacitor C1 is electrically connected to the input terminal of the STA module, and the main control module PWM is electrically connected to the output terminal of the STA module. The STA module is used to detect the input voltage VCC of the control chip. The high-voltage starting branch is electrically connected to the charging capacitor C1 and the primary coil N1. The power supply branch is electrically connected to the charging capacitor C1 and the primary coil N1. The switching switch Q3 is electrically connected to the high-voltage starting branch and the output terminal of the STA module. The switching switch Q3 is turned off or on to allow the high-voltage starting branch or the power supply branch to charge the charging capacitor C1. The control switch Q2 is electrically connected to the output terminal of the main control module PWM and the primary coil N1. The starting voltage has a preset value VREF. The STA module outputs a first signal S1 according to the input voltage VCC to turn the switching switch Q3 on or off. When the input voltage VCC is less than the preset value VREF, the high-voltage starting branch charges the charging capacitor C1; when the input voltage is greater than the preset value VREF, the power supply branch charges the charging capacitor C1.

[0033] In this embodiment, the high-voltage starting branch includes transistor Q1, a first diode D2, and a starting resistor R2. Transistor Q1 is connected in series with control switch Q2, and the first diode D2 is connected in series with starting resistor R2. Transistor Q1 has a first pin (unlabeled) connected to the primary coil N1, a second pin (unlabeled) electrically connected to control switch Q2, and a third pin (unlabeled) electrically connected to switching switch Q3. Charging capacitor C1 is electrically connected to the second pin through the first diode D2 and starting resistor R2.

[0034] Switch Q3 is turned off or on to turn transistor Q1 on or off; when the input voltage is less than the preset value VREF, transistor Q1 is turned on; when the input voltage is greater than the preset value VREF, transistor Q1 is turned off. At the same time, the STA module outputs a second signal to start the PWM of the main control module.

[0035] The aforementioned transistor Q1 is a depletion-mode gallium nitride MOSFET, while control switch Q2 and switching switch Q3 are both enhancement-mode MOSFETs. The first pin of Q2 is the drain of transistor Q1, the second pin is the source of transistor Q1, and the third pin is the gate of transistor Q1. The drain of control switch Q2 is electrically connected to the source of transistor Q1, and the drain of the switching switch is electrically connected to the gate of transistor Q1. The source of control switch Q2 and the source of the switching switch are grounded (GND). The structure, principle, and connection method of depletion-mode and enhancement-mode MOSFETs are well known to those skilled in the art and will not be elaborated upon here.

[0036] In this embodiment, transistor Q1 is a gallium nitride (GaN) transistor, which has advantages such as a large bandgap, high electron mobility, and strong breakdown electric field. It can be used in high-temperature, high-voltage, and high-frequency operating environments, improving the safety factor and extending the service life of the switching power supply. This allows transistor Q1 and control switch Q2 to operate in high-frequency applications, improving efficiency. Furthermore, since the gallium nitride (GaN) transistor can withstand 600V high voltage, control switch Q2 can be a low-voltage MOSFET.

[0037] The anode of the first diode D2 is electrically connected to the gate of the transistor Q1, the positive terminal of the charging capacitor C1 is electrically connected to the cathode of the first diode D2, and the negative terminal of the charging capacitor C1 is grounded to GND.

[0038] In this embodiment, the working principle of the high-voltage start-up branch is as follows: When the power supply VIN is powered on, transistor Q1 is normally turned on, and the charging capacitor C1 is quickly charged through the start-up branch connected to the primary coil N1 to generate a charging current I1. When the power supply VIN is just powered on, the control chip has not yet started, the control switch Q2 is turned off, the charging capacitor C1 is charged through the high-voltage start-up branch, and the input voltage VCC gradually rises. At the same time, the STA module detects the input voltage VCC. When the input voltage VCC reaches the preset value VREF, the STA module outputs the first control signal S1 to control the switching switch Q3 to turn on, the gate of transistor Q1 is pulled low to ground, transistor Q1 is turned off, and the high-voltage start-up is completed.

[0039] In this embodiment, the high-voltage start-up branch also includes a protection resistor R1, which is connected in series between the anode of the first diode D2 and the gate of transistor Q1. A closed loop forms a self-feedback relationship between the protection resistor R1, the start-up resistor R2, and the transistor Q1. When transistor Q1 is turned on, its gate-source voltage must meet the turn-on condition to ensure a constant voltage across the start-up resistor R2. Therefore, the charging current I1 is almost constant. The magnitude of the charging current I1 is determined by the gate-source voltage of transistor Q1, the resistance of the start-up resistor R2, and the capacitance of the charging capacitor C1. That is, after determining the gate-source voltage of transistor Q1, the magnitude of the charging current I1 can be controlled by changing the resistance of the start-up resistor R2 or the capacitance of the charging capacitor C1, thereby adjusting the start-up time of the switching power supply.

[0040] It should be noted that after the high voltage start-up is completed, the control method of transistor Q1 and control switch Q2 connected in series can control the on and off of transistor Q1 by controlling the on and off of control switch Q2. At this time, transistor Q1 is used as a high voltage resistant switching transistor, which makes the circuit design more flexible.

[0041] Specifically, after the high-voltage startup of the control chip is completed, the power supply branch charges the charging capacitor C1 to provide the operating voltage for the control chip. Simultaneously, the STA module outputs the second signal S2 to the main control module PWM. Since transistor Q1 is connected in series with the control switch Q2, when the control switch Q2 is turned on, the source of transistor Q1 is pulled down to a low voltage, and transistor Q1 turns on again. At this time, transistor Q1 and the control switch Q2 form a high-voltage switching transistor group, used to control the primary coil N1 to conduct and store energy or to turn it off. When the control switch Q2 is turned off, transistor Q1 is also turned off. This establishes the control system of the switching power supply.

[0042] To enable the control chip to adjust the appropriate operating frequency and duty cycle, the control chip also includes a detection module (not shown). The detection module detects the magnitude of the load output voltage VOUT of the secondary coil N2 and sends a feedback signal to the main control module PWM. The main control module PWM outputs a pulse-width modulated control signal SW based on the feedback signal to control the switch Q2 to turn on or off. The working principle and connection method of the detection module are well known to those skilled in the art, and therefore will not be described in detail here.

[0043] Specifically, when the control signal SW output by the main control module PWM is high, the control switch Q2 is turned on, the source of transistor Q1 is pulled down to a low voltage, and transistor Q1 is turned on again. At this time, transistor Q1 is used as a high-voltage control switch, and the primary coil N1 is turned on to store energy. When the control signal SW output by the main control module PWM is low, the control switch Q2 is turned off. Since the switching switch Q3 is still on, the gate of transistor Q1 is grounded to GND, so transistor Q1 is turned off very quickly. The primary coil N1 is disconnected, and the secondary coil N2 is turned on to provide the load output voltage VOUT. This cycle is repeated to achieve stable output.

[0044] As described above, the power supply branch is used to provide operating voltage to the control chip. In this embodiment, the power supply branch includes an auxiliary coil N3 and a second diode D1. The anode of the second diode D1 is electrically connected to the high-voltage terminal of the auxiliary coil N3, and the cathode of the second diode D1 is connected to the positive terminal of the charging capacitor C1. The low-voltage terminal of the auxiliary coil N3 is grounded to GND. Using the auxiliary coil N3 to charge the charging capacitor C1 is a conventional technique in the art, and therefore will not be described in detail here.

[0045] like Figure 2 As shown, the STA module includes a startup determination circuit, which comprises a comparator CMP, a NOT gate, a voltage divider branch, and an adjustment switch Q4. The input terminals of the switching switch Q3 and the NOT gate are both electrically connected to the output terminal of the comparator CMP. The inverting input terminal of the comparator CMP is connected to a preset value VREF. The input voltage VCC is divided by the voltage divider branch and then connected to the non-inverting input terminal of the comparator CMP. The voltage divider branch includes several resistors connected in series. The adjustment switch Q4 is turned on or off to ensure that at least one resistor is connected to the voltage divider branch or short-circuited.

[0046] Specifically, the input voltage VCC is divided by the voltage divider branch to form a voltage divider voltage VA. The voltage divider voltage VA is connected to the non-inverting input of the comparator CMP. The inverting input of the comparator CMP is connected to the preset value VREF. After comparing the voltage divider voltage VA with the preset value VREF, the comparator CMP controls the NOT gate circuit to output the third signal S3 to make the regulating switch Q4 turn on or off.

[0047] In this embodiment, the voltage divider branch includes a first resistor R3, a second resistor R4, and a third resistor R5 connected in series. An adjusting switch Q4 is connected in parallel across the third resistor R5. The adjusting switch Q4 is turned on or off to short-circuit or connect the third resistor R5. The comparator CMP controls the NOT gate circuit to output a third signal S3 to turn the adjusting switch Q4 on or off. When the third signal S3 is high, the third resistor R5 is short-circuited; when the third signal S3 is low, the third resistor R5 is connected to the voltage divider branch.

[0048] The aforementioned regulating switch Q4 is an enhancement-mode MOSFET. The gate of the regulating switch Q4 is electrically connected to the output terminal of the NOT gate circuit, and the source of the regulating switch Q4 is grounded to GND.

[0049] The working principle of the judgment circuit in this embodiment is as follows: When the power supply VIN is first powered on, the input voltage VCC rises slowly, the voltage divider VA is less than VREF, the comparator CMP outputs the first signal S1 at a low level, the switch Q3 is not turned on, the start-up branch quickly charges the charging capacitor C1, and the input voltage VCC rises; the first signal S1 outputs a high level through the NOT gate circuit to the gate of the regulating switch Q4, the regulating switch Q4 is turned on, the voltage divider resistor R5 is short-circuited, and the voltage divider VA = (R4) / (R3+R4) rises; when VA is greater than the preset value VREF, the comparator CMP outputs the first signal S1 from a low level to a high level, and the switch Q3 is turned on. When the gate voltage of transistor Q1 is pulled low to ground, transistor Q1 is turned off, and the high-voltage startup branch completes the startup process. At this time, the first signal S1 outputs a low level through the NOT gate circuit to the gate of the regulating switch Q4. The regulating switch Q4 is turned off, and the voltage divider resistor R5 is connected to the voltage divider branch. The voltage divider resistor R5 participates in the voltage division. At this time, VA = (R4 + R5) / (R3 + R4 + R5). If you want to re-enable the startup branch to charge the VCC capacitor, you need to satisfy VA = (R4 + R5) / (R3 + R4 + R5) less than VREF. The comparator CMP outputs the first signal S1 from high level to low level, and transistor Q1 is turned on again to charge the charging capacitor C1.

[0050] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0051] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A high-voltage starting switching power supply, comprising a transformer and a power source electrically connected to the primary winding of the transformer, wherein the secondary winding of the transformer is connected to a load, characterized in that, include: The control chip includes a charging capacitor, an STA module, and a main control module. The charging capacitor is electrically connected to the input terminal of the STA module, and the main control module is electrically connected to the output terminal of the STA module. The STA module is used to detect the input voltage of the control chip. A high-voltage startup branch is used to provide a startup voltage to the control chip and is electrically connected to the charging capacitor and the primary coil. The high-voltage startup branch includes a transistor, a first diode, and a startup resistor. The transistor is connected in series with a control switch, and the first diode is connected in series with the startup resistor. The transistor has a first pin connected to the primary coil, a second pin electrically connected to the control switch, and a third pin electrically connected to a switching device. The charging capacitor is electrically connected to the second pin through the first diode and the startup resistor. The switching device turns the transistor on or off by turning it off or off. The transistor is a depletion-mode gallium nitride MOSFET. The power supply branch is used to provide the operating voltage to the control chip and is electrically connected to the charging capacitor and the primary coil. A switching switch is electrically connected to the output terminal of the high-voltage starting branch and the STA module. The switching switch is turned off or on to enable the high-voltage starting branch or the power supply branch to charge the charging capacitor. and A control switch is used to control the primary coil to be turned on or off, and is electrically connected to the output terminal of the main control module and the primary coil. The starting voltage has a preset value. The STA module outputs a first signal based on the input voltage to turn the switching switch on or off. When the input voltage is less than the preset value, the transistor turns on, and the high-voltage starting branch charges the charging capacitor. When the input voltage is greater than the preset value, the transistor turns off, and the STA module outputs a second signal to start the main control module, and the power supply branch charges the charging capacitor.

2. The switching power supply as described in claim 1, characterized in that, Both the control switch and the switching switch are enhancement-mode MOSFETs. The first pin is the drain of the transistor, the second pin is the source of the transistor, and the third pin is the gate of the transistor. The drain of the control switch is electrically connected to the source of the transistor, and the drain of the switching switch is electrically connected to the gate of the transistor. The source of the control switch and the source of the switching switch are grounded.

3. The switching power supply as described in claim 2, characterized in that, The anode of the first diode is electrically connected to the gate of the transistor, the positive terminal of the charging capacitor is electrically connected to the cathode of the first diode, and the negative terminal of the charging capacitor is grounded.

4. The switching power supply as described in claim 3, characterized in that, The high-voltage start-up branch also includes a protection resistor, which is connected in series between the anode of the first diode and the gate of the transistor.

5. The switching power supply as described in claim 1, characterized in that, The STA module includes a start-up determination circuit, which includes a comparator, a NOT gate circuit, a voltage divider branch, and an adjustment switch. The input terminals of the switching switch and the NOT gate are both electrically connected to the output terminal of the comparator. The inverting input terminal of the comparator is connected to the preset value. The input voltage is divided by the voltage divider branch and then connected to the non-inverting input terminal of the comparator. The voltage divider branch includes several resistors connected in series. The adjusting switch is turned on or off so that at least one of the resistors is connected to the voltage divider branch or short-circuited.

6. The switching power supply as described in claim 5, characterized in that, The voltage divider branch includes a first resistor, a second resistor, and a third resistor connected in series. The regulating switch is connected in parallel across the third resistor. The regulating switch can be turned on or off to short-circuit or connect the third resistor. The comparator controls the NOT gate circuit to output a third signal to turn the adjustment switch on or off; when the third signal is high, the third resistor is short-circuited; when the third signal is low, the third resistor is connected to the voltage divider branch.

7. The switching power supply as described in claim 6, characterized in that, The regulating switch is an enhancement-mode MOS transistor, the gate of the regulating switch is electrically connected to the output terminal of the NOT gate circuit, and the source of the regulating switch is grounded.

8. The switching power supply as described in claim 1, characterized in that, The power supply branch includes an auxiliary coil and a second diode. The anode of the second diode is electrically connected to the high-voltage terminal of the auxiliary coil, and the cathode of the second diode is connected to the positive terminal of the charging capacitor. The low-voltage terminal of the auxiliary coil is grounded.

9. The switching power supply as described in claim 1, characterized in that, The control chip also includes a detection module, which detects the magnitude of the load output voltage of the secondary coil and sends a feedback signal to the main control module. The main control module outputs a pulse-width modulated control signal based on the feedback signal to control the control switch to be turned on or off.

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