Flyback Converter with Improved Over-Voltage Protection

Abstract

The present invention discloses a flyback converter with improved overvoltage protection, comprising a primary-side winding configured to receive an input voltage; a secondary-side winding coupled to the primary-side winding and connected to a rectifier circuit to generate a DC output voltage; a primary-side regulation controller; an auxiliary winding configured to provide operating power to the primary-side regulation controller; an external detection circuit connected between the auxiliary winding and the primary-side regulation controller; an internal detection circuit disposed within the primary-side regulation controller and coupled to the external detection circuit, for activating or deactivating an overvoltage protection circuit by detecting a current value flowing through the external detection circuit and comparing it with a preset current value of the internal detection circuit; and a switching device connected to the primary-side winding and the primary-side regulation controller for receiving a switching signal generated by the primary-side regulation controller and changing the current flowing through the primary-side winding.

Description

Technical Field

[0001] The present invention relates to the technical field related to flyback converters, and in particular to a flyback converter with improved overvoltage protection. Background Art

[0002] Flyback converters are widely used as power conversion devices in various electronic products due to their advantages such as high efficiency, low losses, small size, and light weight. For a flyback converter to operate properly and stably, its protection mechanisms, such as overvoltage protection, are crucial.

[0003] Traditionally, flyback converters use primary-side input voltage detection as an overvoltage protection mechanism, with a fixed voltage protection point. The overvoltage protection circuit must maintain a constant detection mode, consuming power at all times.

[0004] In recent years, people have become increasingly concerned about the energy consumption of electronic devices, as increasingly stringent energy-saving standards have been enacted. Charging devices used in personal computers and other electronic devices, such as smartphones and tablets, typically utilize flyback converters for AC / DC conversion. To meet the increasingly stringent green energy and environmental requirements of future electronic devices, an overvoltage protection mechanism with more refined energy-saving specifications is needed. Summary of the Invention

[0005] Based on the above needs, the present invention provides a flyback converter with improved overvoltage protection, comprising a primary-side winding configured to receive an input voltage: a secondary-side winding coupled to the primary-side winding and connected to a rectifier circuit to generate a DC output voltage; a primary-side regulation controller; an auxiliary winding configured to provide operating power to the primary-side regulation controller; an external detection circuit connected between the auxiliary winding and the primary-side regulation controller; an internal detection circuit disposed within the primary-side regulation controller and coupled to the external detection circuit, for activating or deactivating an overvoltage protection circuit by detecting a current value flowing through the external detection circuit and comparing it with a preset current value of the internal detection circuit; and a switching device connected to the primary-side winding and the primary-side regulation controller for receiving a switching signal generated by the primary-side regulation controller and changing the current flowing through the primary-side winding.

[0006] The external detection circuit is coupled to the internal detection circuit via a pin.

[0007] The internal detection circuit includes: an operational amplifier having a positive input terminal connected to ground, a negative input terminal coupled to a first transistor and the pin, and an output terminal coupled to the first transistor; a current mirror having an input terminal coupled to the first transistor, receiving and outputting the current value flowing through the external detection circuit; a current source coupled to the current mirror, providing the preset current value; and a buffer having an input terminal coupled to the output terminal of the current mirror and the current source, and an output terminal coupled to the overvoltage protection circuit, for activating or deactivating the overvoltage protection circuit by comparing the current value flowing through the external detection circuit with the preset current value.

[0008] The first transistor is an N-type metal oxide semiconductor field effect transistor (NMOSFET).

[0009] The current mirror includes: a second transistor, which is a P-type metal oxide semiconductor field effect transistor (PMOSFET); and a third transistor, which is a P-type metal oxide semiconductor field effect transistor (PMOSFET). The gates of the second transistor and the third transistor are coupled to each other and to the drains of the second transistor and the first transistor. The sources of the second transistor and the third transistor are coupled to a supply voltage.

[0010] A negative input terminal of the operational amplifier is coupled to the source of the first transistor.

[0011] The output terminal of the operational amplifier is coupled to the gate of the first transistor.

[0012] The external detection circuit is a voltage divider circuit.

[0013] An input terminal of the current mirror is coupled to the drain of the first transistor.

[0014] The primary side regulation controller is an integrated circuit controller.

[0015] The switching device is a metal oxide semiconductor field effect transistor (MOSFET) which serves as a main switch controlled by a primary side regulation controller. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The components, features and advantages of the present invention can be understood through the detailed description of the preferred embodiments outlined in the specification and the accompanying drawings:

[0017] Figure 1 An application circuit showing a flyback converter with improved overvoltage protection according to a preferred embodiment of the present invention is depicted.

[0018] Figure 2The diagram depicts the charge and discharge waveforms detected by the pins DRV(OUT), FB, and CS of the PSR controller in the flyback converter according to a preferred embodiment of the present invention.

[0019] Figure 3 The overvoltage detection circuit of the flyback converter according to a preferred embodiment of the present invention is described. During the ton period of the flyback converter, an external detection circuit generates a path through which a current flows.

[0020] Figure 4 A circuit diagram of an overvoltage detection circuit located inside a PSR controller according to a preferred embodiment of the present invention is depicted.

[0021] Description of main component symbols:

[0022] Bridge Rectification 101

[0023] Transformer 103

[0024] Primary side regulation controller 105

[0025] RCD clamping component 104

[0026] Current detection circuit 107

[0027] External detection circuit 109

[0028] Operational Amplifier 211

[0029] Current Source 213

[0030] Buffer 215 DETAILED DESCRIPTION

[0031] Some preferred embodiments of the present invention will now be described in more detail. However, it should be appreciated that the preferred embodiments of the present invention are provided to illustrate and not to limit the present invention. Furthermore, the present invention may be implemented in a wide variety of other embodiments in addition to those expressly described, and the scope of the present invention is not expressly limited unless otherwise specified in the appended claims.

[0032] The present invention aims to provide a flyback converter with improved overvoltage protection, thereby resolving the problem that the voltage protection point in a conventional flyback converter is fixed.

[0033] Please refer to Figure 1According to a preferred embodiment of the present invention, a flyback converter application circuit with improved overvoltage protection is provided. Its input voltage is derived from the mains input, filtered by a bridge rectifier 101 and an input capacitor C1, and then rectified into a DC voltage, which is then output to the input of a transformer 103. The application circuit includes a primary-side regulating (PSR) controller 105, a primary-side main switch Q3, a transformer 103, an auxiliary power rectifier diode D1, an auxiliary power rectifier filter capacitor C2, a startup resistor R_ON, two demagnetization (or quasi-resonant) detection voltage divider resistors R1 and R2, an RCD clamping element 104 comprising a resistor RSN, a capacitor CSN, and a diode D2, an output rectifier diode DO, and an output filter capacitor CO. The PSR controller 105 first charges the auxiliary power rectifier filter capacitor C2 through the starting resistor R_ON. When the voltage reaches the starting threshold voltage of the PSR controller 105, its output terminal DRV begins to output a turn-on voltage signal to control the conduction of the primary-side main switch Q3. When the primary-side main switch Q3 is turned on, it is affected by the current limiting and soft-start control voltage level of the PSR controller 105, turning off the main switch Q3 until the next turn-on signal is activated, repeating the on / off cycle. On the secondary side, due to the conduction of the main switch Q3, the AC voltage of the output winding (secondary winding) Ns of the transformer 103 gradually increases. The voltage is filtered by the output diode DO and the output filter capacitor CO to a DC output Vo. In addition, the AC voltage of the auxiliary power winding Na of the primary-side transformer gradually increases. The voltage is filtered by the auxiliary power rectifier diode D1 and the filter capacitor C2 to a DC output, providing the power required by the PSR controller 105 and replacing the power supply function of the starting resistor R_ON.

[0034] In a preferred embodiment, the PSR adjustment controller 105 is an integrated circuit controller (controller IC).

[0035] In a preferred embodiment, the main switch Q3 (switching device) is a metal oxide semiconductor field effect transistor (MOSFET).

[0036] When the flyback converter energizes the transformer 103 during the ton period, the input voltage Vin can be detected by the primary-to-auxiliary winding turns ratio Np / Na of the transformer 103 and the voltage Vaux measured on the auxiliary winding Na.

[0037] The auxiliary winding Na is combined with the voltage divider resistors R1 and R2 (voltage divider circuit) and connected to the FB pin to serve as an external detection circuit 109 for quasi-resonant (QR) mode detection and overvoltage protection (OVP).

[0038] The current detection circuit 107 is connected to the drain of the MOSFET transistor (main switch Q3) and the CS pin to detect the MOSFET transistor current signal.

[0039] refer to Figure 2 , which shows the charge and discharge waveforms detected by the pins DRV(OUT), FB, and CS of the PSR controller 105 in the flyback converter from top to bottom. It can be seen from the figure that when the flyback converter is in the ton period, the voltage detected by the FB pin is -(Na / Np)×V DC_BNI (Because the auxiliary winding Na is in anti-phase with the primary winding), it is a fixed negative value.

[0040] refer to Figure 1 and Figure 2 When designing the overvoltage detection circuit of the flyback converter, if a feedback circuit is used to lock the voltage value V FB is zero volts (will be Figure 4 Discussion), when the flyback converter is in the ton period, the external detection circuit 109 of the overvoltage protection (OVP) will generate a current I FB Through the FB pin, the voltage divider resistor R1 and the auxiliary winding Na, I FB The value of is (1 / R1)×(Na / Np)×Vpri. When the flyback converter is in the toff period, the external detection circuit 109 of the overvoltage protection (OVP) generates no current.

[0041] refer to Figure 3 , which shows that the overvoltage detection circuit of the flyback converter generates a current I during the flyback converter ton period. FB Through the FB pin, the voltage divider resistor R1 and the auxiliary winding Na, the current I FB Indicated by dotted arrows.

[0042] Please refer to Figure 4 , which is a circuit diagram of the overvoltage detection circuit proposed by the present invention located inside the PSR controller 105. As shown in the figure, the circuit includes an operational amplifier 211, a transistor Q4 (a first transistor), and a current mirror including a plurality of transistors Q1 (a second transistor) and Q2 (a third transistor). The positive input terminal (+) of the operational amplifier 211 is grounded, and the negative input terminal (-) of the operational amplifier 211 is coupled to the source of the transistor Q4 and the FB pin of the PSR controller 105, and is coupled to the external detection circuit 109 ( Figure 1), so the voltage at the FB pin is locked at zero volt. The gate of transistor Q4 is coupled to the output of the operational amplifier. The current I FB The current I generated at the drain of transistor Q4 is FB The level is Where Na / Np is the ratio of the auxiliary winding to the primary winding, Vpri is the voltage of the primary winding, and R1 is the voltage divider resistor (refer to Figure 1 、 Figure 3 ).

[0043] The drain of the transistor Q1 is coupled to the drain of the transistor Q4 to receive the current I FB The gates of the transistors Q1 and Q2 are coupled to each other and to the drains of the transistors Q1 and Q4 . The sources of the transistors Q1 and Q2 are coupled to the supply voltage Vcc.

[0044] In a preferred embodiment, the first transistor is an N-type metal oxide semiconductor field effect transistor (NMOSFET).

[0045] In a preferred embodiment, the second transistor is a P-type metal oxide semiconductor field effect transistor (PMOSFET).

[0046] In a preferred embodiment, the third transistor is a P-type metal oxide semiconductor field effect transistor (PMOSFET).

[0047] Current I M Based on the current I FB And generated at the drain of transistor Q2, which means that the current mirror receives the current I FB Parallel mirror current I FB The generated current I M Therefore, the current I M Depending on the parameters of transistors Q1 and Q2, the current I M With current I FB There is a proportional relationship between them. If transistors Q1 and Q2 are exactly the same, the current I M Equal to the current I FB .

[0048] A current source 213 has a preset current value IVINOVP_TH, one terminal of which is coupled to the drain of the transistor Q2 and the other terminal of which is grounded.

[0049] A buffer 215, whose input terminal is coupled to the current source 213 and the drain of the transistor Q2, and whose output terminal is coupled to the input terminal of the OVP protection circuit for activating or deactivating the OVP protection circuit. The buffer 215 can generate a current I MThe digital signal 0 or 1 is output with the preset current value IVINOVP_TH. When the input voltage Vin undergoes a large transient change, the output voltage Vpri exceeds the rated value, which will be reflected in the current I FB and the current I M On, current I FB The level is Therefore, when the current I M When the current is greater than the rated preset current value IVINOVP_TH, the buffer 215 outputs a digital signal 1 and the overvoltage protection circuit is triggered to provide protection for the PSR controller 105. Otherwise, the buffer 215 outputs a digital signal 0 and the overvoltage protection circuit is in a dormant state.

[0050] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention and its benefits are described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the above embodiments or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the claims of the present invention.

Claims

1. A flyback converter with improved overvoltage protection ， It is characterized by: Should Flyback Converter include : A primary winding is configured to receive an input voltage: A secondary winding is coupled to the primary winding and connected to a rectifier circuit to generate a DC output voltage; a primary-side regulation controller; an auxiliary winding configured to provide operating power for the primary-side regulation controller; An external detection circuit is connected between the auxiliary winding and the primary side regulation controller; An internal detection circuit is disposed within the primary-side regulation controller and coupled to the external detection circuit, and detects a current value flowing through the external detection circuit and compares it with a preset current value of the internal detection circuit to activate or deactivate an overvoltage protection circuit; and a switching device connected to the primary-side winding and the primary-side regulation controller for receiving a switching signal generated by the primary-side regulation controller and changing a current flowing through the primary-side winding; and The internal detection circuit includes: an operational amplifier having a positive input terminal grounded, a negative input terminal coupled to a first transistor and a pin, and an output terminal coupled to the first transistor; a current mirror having an input terminal coupled to the first transistor, receiving and outputting the current value flowing through the external detection circuit; a current source, coupled to the current mirror, and providing the preset current value; a buffer having an input terminal coupled to the output terminal of the current mirror and the current source, and an output terminal coupled to the overvoltage protection circuit, for activating or deactivating the overvoltage protection circuit by comparing the current value flowing through the external detection circuit with the preset current value; The external detection circuit is coupled to the internal detection circuit via the pin.

2. The flyback converter with improved overvoltage protection according to claim 1, wherein: When the flyback converter energizes the transformer during the ton period, the input voltage Vin is detected by the turns ratio Np / Na between the primary winding and the auxiliary winding of the transformer and the voltage Vaux measured on the auxiliary winding.

3. The flyback converter with improved overvoltage protection according to claim 2, wherein: The first transistor is an N-type metal oxide semiconductor field effect transistor (NMOSFET).

4. The flyback converter with improved overvoltage protection according to claim 3, wherein: The current mirror comprises: a second transistor, wherein the second transistor is a P-type metal oxide semiconductor field effect transistor (PMOSFET); a third transistor, the third transistor being a P-type metal oxide semiconductor field effect transistor (PMOSFET), The gates of the second transistor and the third transistor are coupled to each other and to the drains of the second transistor and the first transistor. The sources of the second transistor and the third transistor are coupled to a supply voltage.

5. The flyback converter with improved overvoltage protection according to claim 3, wherein: The negative input terminal of the operational amplifier is coupled to the source of the first transistor.

6. The flyback converter with improved overvoltage protection according to claim 3, wherein: The output terminal of the operational amplifier is coupled to the gate of the first transistor.

7. The flyback converter with improved overvoltage protection according to claim 3, wherein: An input terminal of the current mirror is coupled to the drain of the first transistor.

8. The flyback converter with improved overvoltage protection according to claim 1, wherein: The external detection circuit is a voltage divider circuit.

9. The flyback converter with improved overvoltage protection according to claim 1, wherein: The primary side regulation controller is an integrated circuit controller.

10. The flyback converter with improved overvoltage protection according to claim 1, wherein: The switching device is a metal oxide semiconductor field effect transistor (MOSFET).

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