A Flyback Switching Power Supply with Wide Input Voltage

Abstract

The present invention discloses a flyback switching power supply with a wide input voltage, including a voltage input interface, a rectifier filter circuit, a high-frequency transformer, a first secondary rectifier filter circuit, a voltage output interface, a sampling circuit, an isolation circuit, a PWM control circuit, a switch circuit, a second secondary rectifier filter circuit, an auxiliary voltage output interface and a wide voltage startup circuit. The present invention increases the input voltage range of the flyback switching power supply and improves its stability by setting a more complex wide voltage startup circuit, overcomes the technical problem of a narrow input voltage range caused by only one or several resistors in series in the prior art, and enables the flyback switching power supply to be applicable to more electronic devices.

Description

Technical Field

[0001] The invention relates to the field of switching power supplies, and in particular to a flyback switching power supply with a wide input voltage. Background Art

[0002] A switching power supply uses electronic switching devices (such as transistors, field effect transistors, thyristors, etc.) to control the circuit so that the electronic switching devices are constantly "on" and "off", allowing the electronic switching devices to pulse modulate the input voltage, thereby achieving DC / AC, DC / DC voltage conversion, as well as adjustable output voltage and automatic voltage regulation. Flyback switching power supplies are widely used in almost all electronic devices due to their small size, light weight and high efficiency. With the continuous development of electronic technology, the application scenarios of switching power supplies are complex and varied, and the requirements for switching power supplies are getting higher and higher.

[0003] In the prior art, the composition of the flyback switching power supply is generally that after the input voltage is rectified and filtered, the PWM control IC and the switch device start working through the starting resistor. When the switch device is turned on, the high-frequency transformer stores energy, and when the switch device is turned off, the high-frequency transformer outputs energy. The output energy is rectified and filtered at the secondary to obtain the output voltage; the voltage output by the auxiliary power supply and the starting circuit simultaneously power the PWM control IC; the sampling circuit collects the output voltage, and at the same time feeds the output voltage back to the PWM control IC through the isolation circuit to adjust the PWM output duty cycle, thereby achieving the purpose of stabilizing the output voltage. Among them, the starting resistor of the switching power supply is generally composed of only one resistor or multiple resistors in series, and the input voltage range of the switching power supply is completely dependent on the minimum input current and maximum input current of the PWM control IC, and a wide range of input voltage cannot be achieved. After the switching power supply works normally, the starting circuit is still working, consuming power, and the greater the input voltage, the greater the power consumption. Summary of the invention

[0004] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, one object of the present invention is to provide a flyback switching power supply with a wide input voltage.

[0005] The technical solution adopted by the present invention is: a flyback switching power supply with a wide input voltage, including a voltage input interface, a rectifier filter circuit, a high-frequency transformer, a first secondary rectifier filter circuit, a voltage output interface, a sampling circuit, an isolation circuit, a PWM control circuit, a switch circuit, a second secondary rectifier filter circuit, an auxiliary voltage output interface and a wide voltage startup circuit;

[0006] The output end of the voltage input interface is connected to the input end of the rectification and filtering circuit, the output end of the rectification and filtering circuit is respectively connected to the input end of the wide voltage starting circuit and the input end of the high-frequency transformer, the output end of the wide voltage starting circuit is connected to the input end of the PWM control circuit, the output end of the high-frequency transformer is respectively connected to the input end of the first secondary rectification and filtering circuit and the input end of the second secondary rectification and filtering circuit, the output end of the first secondary rectification and filtering circuit is connected to the input end of the voltage output interface, the output end of the second secondary rectification and filtering circuit is connected to the input end of the auxiliary voltage output interface, the output end of the auxiliary voltage output interface is connected to the input end of the PWM control circuit, the output end of the voltage output interface is connected to the input end of the sampling circuit, the output end of the sampling circuit is connected to the input end of the isolation circuit, the output end of the isolation circuit is connected to the input end of the PWM control circuit, the output end of the PWM control circuit is connected to the input end of the switch circuit, and the output end of the switch circuit is connected to the input end of the high-frequency transformer;

[0007] The wide voltage starting circuit includes a first branch, a second branch, a twenty-eighth capacitor, an eighth voltage regulator and a first field effect transistor. One end of the first branch is connected to the output end of the rectification and filtering circuit, the other end of the first branch is respectively connected to one end of the twenty-eighth capacitor and the negative electrode of the eighth voltage regulator tube, the other end of the twenty-eighth capacitor and the positive electrode of the eighth voltage regulator tube are both grounded, one end of the second branch is connected to the output end of the rectification and filtering circuit, the other end of the second branch is connected to the drain of the first field effect tube, the gate of the first field effect tube is connected to the negative electrode of the eighth voltage regulator tube, and the source of the first field effect tube is connected to the input end of the PWM control circuit.

[0008] Further, the first branch includes a tenth resistor, a seventeenth resistor, a twenty-first resistor, and a twenty-fifth resistor connected in series, and the second branch includes an eighth resistor, an eleventh resistor, and a twenty-second resistor connected in series.

[0009] Furthermore, the flyback switching power supply also includes an overvoltage protection circuit, the input end of the overvoltage protection circuit is connected to the output end of the rectifier and filter circuit, and the output end of the overvoltage protection circuit is connected to the input end of the PWM control circuit.

[0010] Further, the overvoltage protection circuit includes a seventh resistor, a ninth resistor, a sixteenth resistor, a second transient suppression diode, a third transient suppression diode and a fortieth resistor connected in series, one end of the seventh resistor is connected to the output end of the rectifier and filter circuit, and one end of the fortieth resistor is grounded;

[0011] The overvoltage protection circuit also includes a fourth field effect transistor, a gate of the fourth field effect transistor is connected to the other end of the fortieth resistor, a drain of the fourth field effect transistor is grounded, and a source of the fourth field effect transistor is connected to the input end of the PWM control circuit.

[0012] Furthermore, the PWM control circuit includes a PWM control chip.

[0013] Furthermore, the PWM control chip is TNY278P.

[0014] The beneficial effects of the present invention are:

[0015] The present invention increases the input voltage range of the flyback switching power supply and improves its stability by setting a more complex wide-voltage starting circuit, thereby overcoming the technical problem of a narrow input voltage range caused by only one starting resistor or several resistors connected in series in the prior art, thereby making the flyback switching power supply applicable to more electronic devices.

[0016] In addition, the present invention also provides an overvoltage protection circuit. When the input voltage is too high, the starting voltage of the starting circuit is lowered, and the flyback switching power supply does not work, thereby ensuring that the switching power supply will not burn out the back-end circuit due to overvoltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of an embodiment of a flyback switching power supply with a wide input voltage in the present invention;

[0018] Figure 2 It is a circuit schematic diagram of another embodiment of a flyback switching power supply with a wide input voltage in the present invention. DETAILED DESCRIPTION

[0019] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0020] The present invention provides a flyback switching power supply with a wide input voltage, such as Figure 1 As shown, it includes a voltage input interface, a rectifier and filter circuit, a high-frequency transformer, a first secondary rectifier and filter circuit, a voltage output interface, a sampling circuit, an isolation circuit, a PWM control circuit, a switch circuit, a second secondary rectifier and filter circuit, an auxiliary voltage output interface and a wide voltage starting circuit;

[0021] The output end of the voltage input interface is connected to the input end of the rectification and filtering circuit, the output end of the rectification and filtering circuit is respectively connected to the input end of the wide voltage starting circuit and the input end of the high-frequency transformer, the output end of the wide voltage starting circuit is connected to the input end of the PWM control circuit, the output end of the high-frequency transformer is respectively connected to the input end of the first secondary rectification and filtering circuit and the input end of the second secondary rectification and filtering circuit, the output end of the first secondary rectification and filtering circuit is connected to the input end of the voltage output interface, the output end of the second secondary rectification and filtering circuit is connected to the input end of the auxiliary voltage output interface, the output end of the auxiliary voltage output interface is connected to the input end of the PWM control circuit, the output end of the voltage output interface is connected to the input end of the sampling circuit, the output end of the sampling circuit is connected to the input end of the isolation circuit, the output end of the isolation circuit is connected to the input end of the PWM control circuit, the output end of the PWM control circuit is connected to the input end of the switch circuit, and the output end of the switch circuit is connected to the input end of the high-frequency transformer;

[0022] In this embodiment, the wide voltage starting circuit includes a first branch, a second branch, a twenty-eighth capacitor, an eighth voltage regulator and a first field effect transistor, one end of the first branch is connected to the output end of the rectification and filtering circuit, the other end of the first branch is respectively connected to one end of the twenty-eighth capacitor and the negative electrode of the eighth voltage regulator tube, the other end of the twenty-eighth capacitor and the positive electrode of the eighth voltage regulator tube are both grounded, one end of the second branch is connected to the output end of the rectification and filtering circuit, the other end of the second branch is connected to the drain of the first field effect tube, the gate of the first field effect tube is connected to the negative electrode of the eighth voltage regulator tube, and the source of the first field effect tube is connected to the input end of the PWM control circuit.

[0023] In this embodiment, the first branch includes a tenth resistor, a seventeenth resistor, a twenty-first resistor, and a twenty-fifth resistor connected in series, and the second branch includes an eighth resistor, an eleventh resistor, and a twenty-second resistor connected in series.

[0024] In this embodiment, the flyback switching power supply further includes an overvoltage protection circuit, the input end of the overvoltage protection circuit is connected to the output end of the rectifier and filter circuit, and the output end of the overvoltage protection circuit is connected to the input end of the PWM control circuit.

[0025] In this embodiment, the overvoltage protection circuit includes a seventh resistor, a ninth resistor, a sixteenth resistor, a second transient suppression diode, a third transient suppression diode and a fortieth resistor connected in series, one end of the seventh resistor is connected to the output end of the rectifier and filter circuit, and one end of the fortieth resistor is grounded;

[0026] The overvoltage protection circuit also includes a fourth field effect transistor, a gate of the fourth field effect transistor is connected to the other end of the fortieth resistor, a drain of the fourth field effect transistor is grounded, and a source of the fourth field effect transistor is connected to the input end of the PWM control circuit.

[0027] When the input voltage is too high, the fourth field effect transistor is turned on, so that the starting voltage of the starting circuit is pulled down, and the flyback switching power supply does not work, ensuring that the switching power supply will not burn out the back-end circuit due to overvoltage.

[0028] like Figure 2 As shown in FIG. 1 , a circuit schematic diagram of a flyback switching power supply with a wide input voltage is shown. The voltage input interface is connected to the live wire terminal L and the neutral wire terminal N of the mains.

[0029] In this embodiment, the AC-AC voltage converter D1, the third capacitor C3, the eighth capacitor C8, the fourteenth resistor R14, the fifteenth resistor R15, the twentieth resistor R20, the twenty-third resistor R23, the twenty-seventh resistor R27 and the twenty-eighth resistor R28 form a rectification and filtering circuit.

[0030] In this embodiment, the tenth resistor R10, the seventeenth resistor R17, the twenty-first resistor R21, the twenty-fifth resistor R25, the twenty-eighth capacitor C28, the eighth voltage regulator D8, the eighth resistor R8, the eleventh resistor R11, the twenty-second resistor R22 and the first field effect transistor Q1 form a wide voltage starting circuit.

[0031] In this embodiment, the seventh resistor R7, the ninth resistor R9, the sixteenth resistor R16, the second transient suppression diode TVS2, the third transient suppression diode TVS3, the fourth field effect transistor Q4 and the fortieth resistor R40 form an overvoltage protection circuit.

[0032] In this embodiment, the third diode D3, the fifth capacitor C5, the second inductor L2, the sixth capacitor C6, the seventh diode D7, the eleventh capacitor C11, the third inductor L3, the twelfth capacitor C12, the twelfth diode D12, the fourteenth capacitor C14, the fourth inductor L4, and the fifteenth capacitor C15 form a first secondary rectification and filtering circuit.

[0033] In this embodiment, the forty-eighth resistor R48, the fiftieth resistor R50, the fifty-first resistor R51, the voltage regulator U3, the forty-sixth resistor R46 and the forty-seventh resistor R47 form a sampling circuit.

[0034] In this embodiment, the ninth diode D9 and the eighteenth capacitor C18 form a second secondary rectification and filtering circuit.

[0035] In this embodiment, T1 is a high frequency transformer.

[0036] In this embodiment, the isolation circuit includes an isolation optocoupler U2.

[0037] In this embodiment, the switch circuit includes a second field effect transistor Q2.

[0038] In this embodiment, the PWM control circuit includes a PWM control chip U1. The model of the PWM control chip U1 is TNY278P.

[0039] When the input voltage of the voltage input interface is too high, the fourth field effect tube Q4 is turned on, the power supply VCC terminal of the PWM control chip U1 is pulled down, the cathode voltage of the diode D17 is pulled down, and the cathode voltage of the sixteenth diode D16 connected to the wide voltage startup circuit is also pulled down, the startup voltage of the wide voltage startup circuit is pulled down, and the flyback switching power supply does not work, ensuring that the switching power supply will not cause the back-end circuit to burn due to overvoltage. Assuming that the protection voltage of the switching power supply is 800V and the conduction voltage of the fourth field effect tube Q4 is 4V, then the voltage divider circuit composed of the seventh resistor R7, the ninth resistor R9, the sixteenth resistor R16 and the fortieth resistor R40, the voltage divider voltage value on the fortieth resistor R40 must be greater than 4V, thereby ensuring that when the input voltage of the switching power supply exceeds 800V, the startup voltage of the wide voltage startup circuit is pulled down, and the PWM control chip does not work. The sixteenth diode D16 is set to ensure that when the overvoltage protection circuit is working, the wide voltage startup circuit does not work, avoiding the switching power supply from falling into a closed loop of opening and closing, causing device damage.

[0040] When the input voltage of the voltage input interface is normal, the wide voltage startup circuit can work normally. The tenth resistor R10, the seventeenth resistor R17, the twenty-first resistor R21, the twenty-fifth resistor R25, the twenty-eighth capacitor C28 and the eighth voltage regulator D8 form a voltage divider circuit, and the eighth voltage regulator D8 ensures that the first field effect tube Q1 can be turned on. The rectified voltage UA is supplied to the PWM control chip U1 through the eighth resistor R8, the eleventh resistor R11, the twenty-second resistor R22 and the first field effect tube Q1. The power supply voltage does not exceed the voltage regulator voltage of the eighth voltage regulator D8, ensuring that the power supply of the control chip U1 will not be over-voltage.

[0041] The input voltage range of the switching power supply depends on the resistance values ​​of the eighth resistor R8, the eleventh resistor R11 and the twenty-second resistor R22. When selecting the resistance values ​​of the eighth resistor R8, the eleventh resistor R11 and the twenty-second resistor R22, it is only necessary to ensure that when the input voltage is low, the starting current flowing into the PWM control chip U1 can be satisfied, so that the PWM control chip U1 can start normally; within the overvoltage protection voltage range, when the maximum voltage is input, it can be ensured that the PWM control chip U1 can also work normally.

[0042] After the output voltage of the PWM control chip U1 is greater than the conduction voltage of the second field effect tube Q2, the second field effect tube Q2 is turned on, and the voltage UA after rectification stores energy for the high-frequency transformer T1; when the output voltage of the PWM control chip U1 is a low voltage, the high-frequency transformer T1 outputs energy, and outputs voltages VOUT, VOUT1 and VOUT2 to the voltage output interface respectively through the first secondary rectification and filtering circuit, and outputs the auxiliary voltage VAUX to the auxiliary voltage output interface through the second secondary filtering and rectifying circuit, and the auxiliary voltage VAUX supplies power to the PWM control chip U1. After the auxiliary voltage VAUX supplies power to the PWM control chip U1 normally, the voltage value of the auxiliary voltage VAUX exceeds the voltage regulation value of the fourth voltage regulator D4, so that the third triode Q3 is turned on, and the first field effect tube Q1 in the wide voltage startup circuit is turned off, and no longer supplies power to the PWM control chip U1, thereby reducing the power consumption of the switching power supply.

[0043] The sampling circuit collects the output voltage of the voltage output interface and feeds it back to the PWM control chip U1 through the isolation optocoupler U2. The PWM control chip U1 adjusts the PWM output duty cycle to ensure the stability of the output voltage.

[0044] In this embodiment, in order to improve the integration of components, the switch circuit (the second field effect transistor Q2) can be integrated into the PWM control chip U1.

[0045] The flyback switching power supply of the present invention increases the input voltage range of the flyback switching power supply by setting the above-mentioned wide voltage starting circuit. In the typical circuit of the existing flyback switching power supply, the input voltage range is 85-265V, and the input voltage range is narrow. The flyback switching power supply of the present invention can expand the input voltage range to 70-500V. When the input voltage is the minimum voltage of 70V, the voltage after rectification is 100V, the minimum starting current of the PWM control chip is 10uA (the minimum starting current can be queried in the PWM control chip manual), and the sum of the resistance values ​​of the eighth resistor R8, the eleventh resistor R11 and the twenty-second resistor R22 is selected not to exceed 10MΩ; when the input voltage is the maximum voltage of 500V, the voltage after rectification is 700V, and the current passing through the eighth resistor R8, the eleventh resistor R11 and the twenty-second resistor R22 is 70uA, and the PWM control chip can work normally. Obviously, the input voltage range of the switching power supply of the present invention is more than twice as wide as that of the existing switching power supply, which not only improves the stability of the flyback switching power supply, but also makes the flyback switching power supply applicable to more electronic devices.

[0046] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art can make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A flyback switching power supply with a wide input voltage, characterized in that: It includes a voltage input interface, a rectifier filter circuit, a high-frequency transformer, a first secondary rectifier filter circuit, a voltage output interface, a sampling circuit, an isolation circuit, a PWM control circuit, a switch circuit, a second secondary rectifier filter circuit, an auxiliary voltage output interface, an overvoltage protection circuit and a wide voltage startup circuit; The output end of the voltage input interface is connected to the input end of the rectification and filtering circuit, the output end of the rectification and filtering circuit is respectively connected to the input end of the wide voltage starting circuit and the input end of the high-frequency transformer, the output end of the wide voltage starting circuit is connected to the input end of the PWM control circuit, the output end of the high-frequency transformer is respectively connected to the input end of the first secondary rectification and filtering circuit and the input end of the second secondary rectification and filtering circuit, the output end of the first secondary rectification and filtering circuit is connected to the input end of the voltage output interface, the output end of the second secondary rectification and filtering circuit is connected to the input end of the auxiliary voltage output interface, the output end of the auxiliary voltage output interface is connected to the input end of the PWM control circuit, the output end of the voltage output interface is connected to the input end of the sampling circuit, the output end of the sampling circuit is connected to the input end of the isolation circuit, the output end of the isolation circuit is connected to the input end of the PWM control circuit, the output end of the PWM control circuit is connected to the input end of the switch circuit, and the output end of the switch circuit is connected to the input end of the high-frequency transformer; The wide voltage startup circuit includes a first branch, a second branch, a twenty-eighth capacitor, an eighth voltage regulator tube and a first field effect tube, one end of the first branch is connected to the output end of the rectification and filtering circuit, the other end of the first branch is respectively connected to one end of the twenty-eighth capacitor and the negative electrode of the eighth voltage regulator tube, the other end of the twenty-eighth capacitor and the positive electrode of the eighth voltage regulator tube are both grounded, one end of the second branch is connected to the output end of the rectification and filtering circuit, the other end of the second branch is connected to the drain of the first field effect tube, the gate of the first field effect tube is connected to the negative electrode of the eighth voltage regulator tube, and the source of the first field effect tube is connected to the input end of the PWM control circuit; The first branch includes a tenth resistor, a seventeenth resistor, a twenty-first resistor and a twenty-fifth resistor connected in series, and the second branch includes an eighth resistor, an eleventh resistor and a twenty-second resistor connected in series; The input end of the overvoltage protection circuit is connected to the output end of the rectifier and filter circuit, and the output end of the overvoltage protection circuit is connected to the input end of the PWM control circuit; The overvoltage protection circuit comprises a seventh resistor, a ninth resistor, a sixteenth resistor, a second transient suppression diode, a third transient suppression diode and a fortieth resistor connected in series, one end of the seventh resistor is connected to the output end of the rectifier and filter circuit, and one end of the fortieth resistor is grounded; The overvoltage protection circuit further includes a fourth field effect transistor, the gate of the fourth field effect transistor is connected to the other end of the fortieth resistor, the drain of the fourth field effect transistor is grounded, and the source of the fourth field effect transistor is connected to the input end of the PWM control circuit; The flyback switching power supply further includes a sixteenth diode, a first end of the sixteenth diode is connected to the fourth field effect transistor, and a second end of the sixteenth diode is connected to the twenty-eighth capacitor; wherein the sixteenth diode is used to make the wide voltage startup circuit inoperative when the overvoltage protection circuit is operating; The PWM control circuit includes a PWM control chip, and the PWM control chip is TNY278P; the flyback switching power supply expands the input voltage range to 70V to 500V.

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