Secondary side protection detection circuit of power converter

Abstract

The present invention relates to a secondary-side protection detection circuit for a power converter, comprising a detection element, an adder amplifier circuit, an electronic switch, and a charge-discharge circuit. The detection element is connected to an output connection terminal of the power converter. The adder amplifier circuit comprises an operational amplifier, a first resistor, and a second resistor. The input terminal of the operational amplifier is connected to the detection element, and the output terminal of the operational amplifier is connected to a primary-side control element. The first and second resistors are connected in series between the input terminal and a power supply terminal of the operational amplifier. A connection node is defined between the first and second resistors. The electronic switch is connected between a ground terminal and the connection node and comprises a control terminal. The charge-discharge circuit is connected between the control terminal of the electronic switch and the power supply terminal of the operational amplifier.

Description

Technical Field

[0001] The present invention relates to a secondary side protection detection circuit, and more particularly to a secondary side protection detection circuit of a power converter. Background Art

[0002] The basic structure of conventional power converters is as follows Figure 4 As shown, the circuit architecture can basically include a transformer T. The primary winding 51 of the transformer T is connected in series with a drive switch Q. The gate of the drive switch Q can be connected to a signal output pin Y of a PWM controller 53 (i.e., a pulse width modulation controller). The PWM controller 53 has a protection mode trigger pin X. The primary winding 51 of the transformer T is also connected to the power input terminal of the power converter 50 to receive a DC input power source VDC. The secondary winding 52 of the transformer T can be connected to a positive power output terminal (+Vo) and a negative power output terminal (-Vo) of the power converter 50 via a secondary circuit 54. The positive power output terminal (+Vo) and the negative power output terminal (-Vo) are connected to a load 60. The negative power supply output terminal (-Vo) is connected in series with a detection resistor 55. The detection circuit 55 is connected to an amplifier circuit 56. The amplifier circuit 56 can be an inverting amplifier circuit or a non-inverting amplifier circuit composed of an operational amplifier (OPA). The amplifier circuit 56 is connected to the protection mode trigger pin X of the PWM controller 53 through a feedback isolation circuit 57. The feedback isolation circuit 57 can be a circuit composed of an optocoupler.

[0003] The operating principle of the power converter 50 is that the PWM controller 53 outputs a drive signal to the drive switch Q. The drive switch Q is activated according to the drive signal, causing the DC input power VDC to be converted by the transformer T and the secondary circuit 54 to generate a DC output power at the positive power output terminal (+Vo) and the negative power output terminal (-Vo). Therefore, the voltage generated by the current flowing through the detection resistor 55 (hereinafter referred to as the detection voltage) can reflect the current supplied by the power converter 50 to the load 60. The amplifier circuit 56 amplifies the detection voltage and provides it to the protection mode trigger pin X of the PWM controller 53 through the feedback isolation circuit 57. When the voltage received by the protection mode trigger pin X is greater than or equal to a protection mode threshold, it generally indicates that an abnormal condition has occurred in the load 60. The PWM controller 13 enters a protection mode. In this protection mode, the PWM controller 53 stops outputting a driving signal to the driving switch Q, causing the power converter 50 to stop operating and thereby stop outputting the DC input power to the load 60, thereby achieving a protective effect.

[0004] When the load connected to the power converter 50 is a capacitive load, that is, the input end of the load 60 is provided with an input capacitor Cin, a surge current will be generated at the start-up moment of the power converter 50 to charge the input capacitor Cin of the load 60. The surge current is reflected in the output voltage waveform of the amplifier circuit 56, which can be referred to as Figure 5 , the inrush current occurs from t0 to t1, and the power converter 50 enters a steady state after t1.

[0005] However, during the period from t0 to t1, the output voltage of the amplifier circuit 56 reaches a voltage value Vth. This voltage value Vth is fed back to the protection mode trigger pin X of the PWM controller 53 via the feedback isolation circuit 57, causing the PWM controller 53 to enter the protection mode. In other words, the power converter 50 enters the protection mode directly upon startup, and is unable to provide the DC output power to the load 60. Summary of the Invention

[0006] In view of this, the main object of the present invention is to provide a secondary side protection detection circuit for a power converter, so as to overcome the disadvantage that the conventional power converter directly enters the protection mode upon startup and is unable to provide power to the load.

[0007] The secondary side protection detection circuit of the power converter of the present invention comprises:

[0008] a detection element connected to an output connection terminal of the power converter;

[0009] An adder amplifier circuit includes an operational amplifier, a first resistor, and a second resistor. The operational amplifier includes:

[0010] an input terminal connected to the detection element;

[0011] an output terminal connected to a primary-side control element of the power converter; and

[0012] a power supply terminal;

[0013] The first resistor and the second resistor are connected in series between the input terminal and the power supply terminal of the operational amplifier, and a connection node is formed between the first resistor and the second resistor;

[0014] an electronic switch connected between a ground terminal and the connection node and comprising a control terminal; and

[0015] A charge-discharge circuit is connected to the control terminal of the electronic switch and the power supply terminal of the operational amplifier.

[0016] Preferably, in the aforementioned secondary side protection detection circuit, the adder amplifier circuit is an inverting adder circuit structure.

[0017] Preferably, in the secondary side protection detection circuit as described above, the adder amplifier circuit is a non-inverting adder circuit structure.

[0018] Preferably, in the secondary side protection detection circuit as described above, the input terminal of the operational amplifier connected to the detection element is an inverting input terminal, and the first resistor and the second resistor are connected in series between the inverting input terminal of the operational amplifier and the power terminal.

[0019] Preferably, as described above in the secondary side protection detection circuit, the electronic switch is an N-type metal oxide semiconductor field effect transistor, whose drain is connected to the connection node between the first resistor and the second resistor, its source is connected to the ground end, and its gate is the control end.

[0020] Preferably, as described above in the secondary side protection detection circuit, the charge and discharge circuit includes a resistor and a capacitor, the resistor of the charge and discharge circuit is connected between the control end of the electronic switch and the power supply end of the operational amplifier, and the capacitor is connected between the control end of the electronic switch and the ground end.

[0021] Preferably, in the secondary-side protection detection circuit as described above, the connection node between the first resistor and the second resistor is defined as a first connection node, and a second connection node is provided between the resistor and the capacitor of the charge-discharge circuit; the secondary-side protection detection circuit includes an auxiliary discharge circuit, which includes: a diode whose anode is connected to the second connection node and whose cathode is connected to the power supply terminal of the operational amplifier; and a resistor connected between the control terminal of the electronic switch and the ground terminal.

[0022] According to the circuit architecture of the secondary-side protection detection circuit of the present invention, even if an inrush current occurs at the moment of startup of the power converter, the present invention utilizes the circuit structure of the adder amplifier circuit to ensure that the voltage polarity obtained by the operational amplifier from the detection element is opposite to the voltage polarity of the voltage at its power supply terminal. This overall reduces the output voltage of the operational amplifier at its output terminal, so that the voltage at the protection mode trigger pin of the primary-side control element is less than the protection mode threshold. Therefore, the inrush current does not cause the primary-side control element to enter protection mode, thereby overcoming the problems described in the prior art. Furthermore, in steady state, the energy stored in the charge-discharge circuit is sufficient to turn on the electronic switch, placing the connection node between the first resistor and the second resistor at a low potential or grounded, rendering the adder amplifier circuit a conventional amplifier circuit capable of performing conventional protection monitoring of the steady-state current passing through the detection element.

[0023] On the other hand, the present invention can be completed by using only simple components such as operational amplifiers, resistors, capacitors, electronic switches, etc., without using a digital control circuit including a microcontroller, thereby significantly reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 : A schematic diagram of a circuit in which an embodiment of a secondary side protection detection circuit of the present invention is connected to a power converter.

[0025] Figure 2 : A circuit diagram of an embodiment of a secondary side protection detection circuit of the present invention.

[0026] Figure 3 : Schematic diagram of the voltage waveform fed back to the primary-side control element of an embodiment of the secondary-side protection detection circuit of the present invention.

[0027] Figure 4 : Schematic diagram of the connection circuit between a conventional voltage range power converter and an amplifier circuit.

[0028] Figure 5 : Schematic diagram of the voltage waveform fed back to the primary-side control element from a conventional amplifier circuit.

[0029] Brief description of the figures:

[0030] 10,50: Power converter 11,51: Primary winding

[0031] 12,52: Secondary winding 13,53: PWM controller

[0032] 14,54: Secondary circuit 20,60: Load

[0033] 55: Detection resistor 30: Secondary side protection detection circuit

[0034] 31: Detection element 32: Adder amplifier circuit

[0035] 320: Operational amplifier 321: Power supply terminal

[0036] 322: output terminal 33: charging and discharging circuit

[0037] 34: auxiliary discharge circuit 350: control terminal

[0038] 40,57: Feedback isolation circuit 56: Amplification circuit

[0039] Q1: electronic switch Y: signal output pin

[0040] X: Protection mode trigger pin T: Transformer

[0041] Q: Drive switch VDC: DC input power

[0042] (+Vo): Positive power output terminal (-Vo): Negative power output terminal

[0043] R4: first resistor R5: second resistor

[0044] N1, N2: connection nodes R1, R2, R3, R6, R7: resistors

[0045] C1: capacitor VCC1: operating voltage

[0046] D2: diode Cin: input capacitor

[0047] V sense :Detection voltage DETAILED DESCRIPTION

[0048] The following is a detailed description of the technical means used by the present invention to achieve the intended purpose of the invention, with reference to the drawings and preferred embodiments of the present invention.

[0049] The secondary side protection detection circuit of the present invention is used in a power converter. It should be noted that the circuit architecture and working principle of the power converter are not the focus of the present invention and are only briefly described below.

[0050] Please refer to Figure 1 The power converter 10 can be a switching power converter with a wide input voltage range, or a step-up power converter, thus enabling a wide range of applications. For example, the power converter 10 circuit architecture can essentially include a transformer T, a drive switch Q, a PWM controller 13 (i.e., a pulse width modulation controller), and a secondary circuit 14. The PWM controller 13 includes a signal output pin Y and a protection mode trigger pin X. The primary winding 11 of the transformer T is connected in series with a drive switch Q. The drive switch Q can be, for example, a metal oxide semiconductor field effect transistor (MOSFET), the gate of which can be connected to the signal output pin Y of the PWM controller 13. The primary winding 11 of the transformer T is also connected to the power input of the power converter 10 to receive a DC input power source VDC. The secondary winding 12 of the transformer T is connected to multiple output terminals of the power converter 10 via the secondary circuit 14. These multiple output terminals may include a positive power output terminal (+Vo) and a negative power output terminal (-Vo). The positive power output terminal (+Vo) and the negative power output terminal (-Vo) are connected to a load 20. The operating principle of the power converter 10 can be referred to in the prior art and will not be repeated here. In short, when the voltage received by the protection mode trigger pin X of the PWM controller 13 is greater than or equal to a protection mode threshold, the PWM controller 13 enters a protection mode. In this protection mode, the PWM controller 13 stops outputting a drive signal to the drive switch Q, causing the power converter 10 to stop operating and thereby stop outputting the DC input power to the load 20, thereby achieving a protective function.

[0051] Please refer to Figure 1 and Figure 2 The secondary-side protection detection circuit 30 of the present invention includes a detection element 31, an adder amplifier circuit 32, an electronic switch Q1, and a charge-discharge circuit 33, and may further include an auxiliary discharge circuit 34. The secondary-side protection detection circuit 30 can be connected to the protection mode trigger pin X of the PWM controller 13 via a feedback isolation circuit 40 to trigger the PWM controller 13 to enter protection mode at an appropriate time, as described in detail below.

[0052] The detection element 31 is connected to one of the output connection terminals of the power converter 10. In the embodiment of the present invention, the detection element 31 is connected in series between the negative power output terminal (-Vo) and the secondary winding 12 of the transformer T. The detection element 31 can be a resistor, and the smaller the resistance value, the better to minimize its power consumption.

[0053] The adder amplifier circuit 32 includes an operational amplifier (OPA) 320 and a plurality of resistors electrically connected to the OPA 320. The OPA 320 includes an input terminal, a power terminal 321, and an output terminal 322. The input terminal of the OPA 320 is connected to the detection element 31, and the output terminal 322 of the OPA 320 is connected to the primary-side control element of the power converter 10. In an embodiment of the present invention, the primary-side control element is the PWM controller 13. The output terminal 322 of the OPA 320 is connected to the protection mode trigger pin X of the PWM controller 13 via the feedback isolation circuit 40. The feedback isolation circuit 40 may include an optocoupler, for example.

[0054] Generally speaking, the operational amplifier 320 and the plurality of resistors can realize an inverting adder circuit structure or a non-inverting adder circuit structure through different connection structures. The adder amplifier circuit 32 of the present invention takes an inverting adder circuit structure as an example. The operational amplifier 320 includes an inverting input terminal (-) and a non-inverting input terminal (+). In the above description, the input terminal of the operational amplifier 320 connected to the detection element 31 is the inverting input terminal (-), so that the operational amplifier 320 can receive the detection voltage (i.e., voltage rise) V of the detection element 31. sense , the detection voltage V of the detection element 31 sense That is, it reflects the output current of the power converter 10 .

[0055] like Figure 2As shown, the multiple resistors included in the adder amplifier circuit 32 include a first resistor R4 and a second resistor R5. The first resistor R4 and the second resistor R5 are connected in series between the inverting input terminal (-) of the operational amplifier 320 and the power supply terminal 321. That is, one end of the first resistor R4 is connected to the power supply terminal 321 of the operational amplifier 320, the other end of the first resistor R4 is connected to one end of the second resistor R5, and the other end of the second resistor R5 is connected to the inverting input terminal (-) of the operational amplifier 320. A connection node N1 is defined between the first resistor R4 and the second resistor R5. Figure 2 In the embodiment of the inverting adder circuit structure shown, the non-inverting input terminal (+) of the operational amplifier 320 is grounded via a resistor R3. A resistor R1 is connected between the output terminal 322 and the inverting input terminal (-) of the operational amplifier 320. The inverting input terminal (-) of the operational amplifier 320 is connected to the detection element 31 via a resistor R2. The power supply terminal 321 of the operational amplifier 320 receives an operating voltage VCC1. For example, the power supply terminal 321 of the operational amplifier 320 can be connected to a secondary-side auxiliary winding (not shown) to obtain the operating voltage VCC1 from the secondary-side auxiliary winding.

[0056] The electronic switch Q1 is connected to a ground terminal and to a power supply terminal 321 of the operational amplifier 320 via a resistor among the multiple resistors of the adder amplifier circuit 32. For example, the electronic switch Q1 can be connected to the power supply terminal 321 of the operational amplifier 320 via the first resistor R4. When the electronic switch Q1 is in the on state, the connection node N1 can be at a low potential or grounded. Conversely, when the electronic switch Q1 is in the off state, the first resistor R4 and the second resistor R5 are connected in series, and the power supply terminal 321 of the operational amplifier 320 is at a high potential. The electronic switch Q1 includes a control terminal 350. The electronic switch Q1 can be operated in the on state or the off state depending on the voltage at the control terminal 350. The electronic switch Q1 may be a transistor, such as an N-type metal oxide semiconductor field effect transistor (N-type MOSFET), whose drain is connected to the connection node N1 between the first resistor R4 and the second resistor R5, whose source is connected to the ground terminal, and whose gate is the control terminal 350.

[0057] The charge-discharge circuit 33 is connected to the control terminal 350 of the electronic switch Q1 and the power terminal 321 of the operational amplifier 320. As the name suggests, the charge-discharge circuit 33 includes an energy storage element. The function of the charge-discharge circuit 33 is to charge the energy storage element of the charge-discharge circuit 33 when the power terminal 321 of the operational amplifier 320 receives the operating voltage VCC1. The operating voltage VCC1 simultaneously charges the energy storage element of the charge-discharge circuit 33, causing the voltage provided by the energy storage element to the control terminal 350 of the electronic switch Q1 to gradually increase, and the voltage can be increased to a level sufficient to operate the electronic switch Q1 in the on state. In an embodiment of the present invention, the charge-discharge circuit 33 includes a resistor R6 and a capacitor C1. The resistor R6 of the charge-discharge circuit 33 is connected between the control terminal 350 of the electronic switch Q1 and the power supply terminal 321 of the operational amplifier 320. The capacitor C1 is the energy storage element described above. The capacitor C1 is connected between the control terminal 350 of the electronic switch Q1 and the ground terminal. Therefore, the resistor R6 and the capacitor C1 can form a charge-discharge path. The operating voltage VCC1 can charge the capacitor C1 through the resistor R6. A connection node N2 is defined between the resistor R6 and the capacitor C1.

[0058] The overall circuit architecture of the secondary side protection detection circuit 30 of the present invention applied to the power converter 10 has been described above. The following describes the circuit operation of the secondary side protection detection implemented by the present invention with reference to current waveforms.

[0059] Please refer to Figure 1 When the load 20 connected to the power converter 10 is a capacitive load, that is, an input capacitor Cin is provided at the input end of the load 20, an inrush current will be generated at the startup moment of the power converter 10 to charge the input capacitor Cin of the load 20. At this time, the electronic switch Q1 is not turned on yet, and the adder amplifier circuit 32 performs its adding function. Although the inrush current generates a large detection voltage V when passing through the detection element 31 sense , but the detection voltage V sense The voltage polarity is opposite to the working voltage VCC1. Therefore, the present invention can reduce the output voltage V of the operational amplifier 320 at its output terminal 321 by setting the first capacitor R4 and the second capacitor R5. op , which is expressed as follows:

[0060]

[0061] In the above formula, the detection voltage V sense is a negative voltage, and the working voltage VCC1 is a positive voltage. That is, even if the surge current passes through the detection element 31 and generates a larger detection voltage V sense , but after being processed by the operational amplifier 320, the reduction amplitude can be expressed as follows:

[0062]

[0063] Thus, the voltage output by the operational amplifier 320 still keeps the voltage received by the protection mode trigger pin X lower than the protection mode threshold, so that the startup moment of the power converter 10 will not trigger the PWM controller 13 to enter the protection mode.

[0064] When the power converter 10 is in steady state, the steady-state current passing through the detection element 31 is less than the inrush current. At this time, the capacitor C1 of the charge-discharge circuit 33 is charged by the operating voltage VCC1 to a level sufficient to allow the electronic switch Q1 to operate in the on state. When the electronic switch Q1 is in the on state, the connection node N1 between the first resistor R4 and the second resistor R5 of the adder amplifier circuit 32 is grounded. The adder amplifier circuit 32 does not perform its adding function (i.e., it is equivalent to a general inverting amplifier). The operational amplifier 320 only amplifies the detection voltage V generated when the steady-state current passes through the detection element 31. sense In this way, even if a short circuit fault occurs in the load 20, a short circuit current will flow through the detection element 31. When the short circuit current flows through the detection element 31, the detection voltage V sense The voltage is directly amplified by the operational amplifier 320 without reducing the voltage amplitude as described above. The voltage output by the operational amplifier 320 causes the voltage received by the protection mode trigger pin X to be greater than or equal to the protection mode threshold, thereby triggering the PWM controller 13 to enter the protection mode to provide a short-circuit protection function.

[0065] In summary, the voltage waveform of the output terminal 322 of the operational amplifier 320 can be referred to Figure 3 The power converter 10 is started at t0. Although the inrush current is generated at the start-up instant (t0 to t1), the adder amplifier circuit 32 plays its adding function, and Figure 5 compared to, Figure 3 The voltage at the output terminal 321 of the operational amplifier 320 decreases as a whole. As time goes by, the capacitor C1 of the charge-discharge circuit 33 is charged to a level sufficient to allow the electronic switch Q1 to operate in the on state at t2. Therefore, after t2, the current passing through the detection element 31 is a steady-state current. The combination of the capacitance value of the capacitor C1 of the charge-discharge circuit 33 and the resistance value of the resistor R6 can determine the timing of turning on the electronic switch Q1, which can also determine the time length from t0 to t2. Figure 3The waveform shows that a short-circuit current begins to occur at t3. At t4, the output terminal 322 of the operational amplifier 320 reaches a voltage value Vth. When the voltage value Vth is fed back to the protection mode trigger pin X of the PWM controller 13 through the feedback isolation circuit 40, the PWM controller 13 can be triggered to enter the protection mode to provide a short-circuit protection function.

[0066] Furthermore, considering that the operating power converter 10 may be powered off and then immediately restarted (for example, if the DC input power source VDC becomes momentarily unstable), the present invention provides an auxiliary discharge circuit 34. The auxiliary discharge circuit 34 includes a diode D2 and a resistor R7. The anode of the diode D2 is connected to the connection node N2 between the resistor R6 of the charge-discharge circuit 33 and the capacitor C1, and the cathode of the diode D2 is connected to the power supply terminal 321 of the operational amplifier 320. In other words, the diode D2 can be connected across the resistor R6 of the charge-discharge circuit 33, and the resistor R7 of the auxiliary discharge circuit 34 is connected between the control terminal 350 of the electronic switch Q1 and the ground terminal.

[0067] When the power converter 10 is powered off, the capacitor C1 of the charge-discharge circuit 33 and the parasitic capacitance of the electronic switch Q1 can be discharged through the discharge path provided by the diode D2 and another discharge path provided by the resistor R7. Utilizing multiple discharge paths, the discharge is accelerated, thereby accelerating the turn-off of the electronic switch Q1 and minimizing the energy stored in the capacitor C1. Consequently, when the power converter 10 is powered off and immediately restarted, the electronic switch Q1 is ensured to be in the off state, allowing the adder amplifier circuit 32 to smoothly reset to its initial state for performing the adding function. Furthermore, because the energy stored in the capacitor C1 is minimized, the time it takes for the capacitor C1 to charge to the point where it can turn on the electronic switch Q1 is correspondingly maximized, providing more time to suppress the effects of the inrush current.

[0068] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A secondary side protection detection circuit for a power converter, characterized in that: Include: a detection element connected to an output connection terminal of the power converter; An adder amplifier circuit includes an operational amplifier, a first resistor, and a second resistor. The operational amplifier includes: an input terminal connected to the detection element; an output terminal connected to a primary-side control element of the power converter; and a power supply terminal; The first resistor and the second resistor are connected in series between the input terminal and the power supply terminal of the operational amplifier, and a connection node is formed between the first resistor and the second resistor; an electronic switch connected between a ground terminal and the connection node and comprising a control terminal; and A charge-discharge circuit is connected to the control terminal of the electronic switch and the power supply terminal of the operational amplifier.

2. The secondary side protection detection circuit of the power converter according to claim 1, wherein: The adder amplifier circuit is an inverting adder circuit structure.

3. The secondary side protection detection circuit of the power converter according to claim 1, wherein: The adder amplifier circuit is a non-inverting adder circuit structure.

4. The secondary side protection detection circuit of the power converter according to claim 2, wherein: The input terminal of the operational amplifier connected to the detection element is an inverting input terminal. The first resistor and the second resistor are connected in series between the inverting input terminal of the operational amplifier and the power terminal.

5. The secondary side protection detection circuit of the power converter according to claim 4, wherein: The electronic switch is an N-type metal oxide semiconductor field effect transistor, a drain of which is connected to the connection node between the first resistor and the second resistor, a source of which is connected to the ground end, and a gate of which is the control end.

6. The secondary side protection detection circuit of the power converter according to any one of claims 2, 4 or 5, wherein: The charge-discharge circuit includes a resistor and a capacitor. The resistor of the charge-discharge circuit is connected between the control end of the electronic switch and the power supply end of the operational amplifier. The capacitor is connected between the control end of the electronic switch and the ground end.

7. The secondary side protection detection circuit of the power converter according to claim 6, wherein: The connection node between the first resistor and the second resistor is defined as a first connection node, and a second connection node is defined between the resistor and the capacitor of the charge-discharge circuit; The secondary side protection detection circuit includes an auxiliary discharge circuit, which includes: a diode, an anode of which is connected to the second connection node, and a cathode of which is connected to the power supply terminal of the operational amplifier; and A resistor is connected between the control terminal of the electronic switch and the ground terminal.

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