TWI790873B - Secondary side protection detection circuit of power converter - Google Patents

Abstract

A secondary side protection detection circuit of 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 terminal of the power converter, the The adder amplifying circuit includes an operational amplifier, a first resistor and a second resistor, the input end of the operational amplifier is connected to the detection element, and the output end is connected to the primary side control element, the first and second resistors connected in series between the input terminal of the operational amplifier and the power supply terminal, there is a connection node between the first and second resistors, the electronic switch is connected between a ground terminal and the connection node and includes a control terminal, the The charging and discharging circuit is connected with the control terminal of the electronic switch and the power supply terminal of the operational amplifier.

Description

Secondary side protection detection circuit of power converter

The invention relates to a secondary side protection detection circuit, in particular to a secondary side protection detection circuit of a power converter.

The basic structure of a conventional power converter is shown in FIG. 4 . The circuit structure basically includes a transformer T. The primary side 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 PWM A signal output pin Y of the controller 53 (ie, a pulse width modulation controller), the PWM controller 53 has a protection mode trigger pin X. The primary side 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 VDC, and the two ends of the secondary side winding 52 of the transformer T can be connected to the power supply through the secondary side circuit 54. A positive power output terminal (+Vo) and a negative power output terminal (−Vo) of the power converter 50 are used for connecting a load 60 . Wherein, the negative power supply output terminal (-Vo) is connected in series with a detection resistor 55, and the detection circuit 55 is connected to an amplifying circuit 56, which may be an inverting amplifying circuit composed of an operational amplifier (OPA) or a non-inverting amplifying circuit. Phase amplifying circuit, the amplifying circuit 56 is connected to the protection mode trigger pin X of the PWM controller 53 through a feedback isolation circuit 57, and the feedback isolation circuit 57 may be a circuit composed of an optocoupler.

The working principle of the power converter 50 is that the PWM controller 53 outputs a driving signal to the driving switch Q, and the driving switch Q is activated according to the driving signal, so that the DC input power VDC passes through the transformer T and the secondary After the conversion of the side circuit 54, a DC output power is generated at the positive power supply output terminal (+Vo) and the negative power supply output terminal (-Vo), so the current passing through the detection resistor 55 is generated in the detection resistor 55. The voltage (hereinafter referred to as the detection voltage) can reflect the current supplied by the power converter 50 to the load 60. After the amplifying circuit 56 amplifies the detection voltage, the feedback isolation circuit 57 provides It is supplied to the protection mode trigger pin X of the PWM controller 53 . When the voltage received by the protection mode trigger pin X is greater than or equal to a protection mode threshold value, it usually means that the load 60 has an abnormal condition, and the PWM controller 53 enters a protection mode. In this protection mode, the PWM control The switch 53 stops outputting the driving signal to the driving switch Q, so that the power converter 50 stops operating, thereby stopping outputting the DC input power to the load 60, thereby achieving the function of protection.

When the load connected to the power converter 50 is a capacitive load, that is to say, the input terminal of the load 60 is provided with an input capacitor Cin, at the moment of starting the power converter 50, an input capacitor Cin to the load 60 will be generated. A surge current for charging, the surge current reflected in the output voltage waveform of the amplifying circuit 56 can refer to FIG. 5 , the surge current occurs from t0 to t1, and the power converter 50 enters a steady state after t1.

However, during the period from t0 to t1, the output voltage of the amplifying circuit 56 will reach a voltage value Vth, and after the voltage value Vth is fed back to the protection mode trigger pin X of the PWM controller 53 through the feedback isolation circuit 57, it will be Causes the PWM controller 53 to enter the protection mode. That is to say, the power converter 50 directly enters the protection mode once it starts up, so that it cannot provide the DC output power to the load 60 .

In view of this, the main purpose of the present invention is to provide a secondary-side protection detection circuit of a power converter, so as to overcome the conventional disadvantage that the power converter directly enters the protection mode upon startup, thereby failing to provide power to the load.

The secondary side protection detection circuit of the power converter of the present invention includes: a detection element connected to an output terminal of the power converter; an adder amplifier circuit including an operational amplifier, a first resistor and a first resistor Two resistors, the operational amplifier includes: an input end connected to the detection element; an output end connected to the 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 of the operational amplifier and the power supply terminal, and there is a connection node between the first resistor and the second resistor; an electronic switch , which is connected between a ground terminal and the connection node and includes a control terminal; and a charge-discharge circuit, which connects the control terminal of the electronic switch and the power supply terminal of the operational amplifier.

According to the circuit structure of the secondary side protection detection circuit of the present invention, although there is a surge current at the moment the power converter is started, the present invention uses the circuit structure of the adder amplifier circuit, and the operational amplifier obtains from the detection element The voltage polarity and the voltage polarity of the power supply terminal are opposite to each other, which can reduce the output voltage of the operational amplifier at its output terminal as a whole, so that the voltage of the protection mode trigger pin of the primary side control element is lower than the protection mode threshold value, so the surge current will not This causes the primary side control element to enter a protection mode, thereby overcoming the problems described in the prior art. On the other hand, in a steady state, the energy storage of the charging and discharging circuit is enough to turn on the electronic switch, which can make the connection node between the first resistor and the second resistor be at a low potential or ground, so that the adder The amplifying circuit becomes a general amplifying circuit, that is, it can carry out conventional protection monitoring on the steady-state current passing through the detecting element.

On the other hand, the present invention can be completed by using only simple components such as operational amplifiers, resistors, capacitors, electronic switches, etc., and does not need to use digital control circuits including microcontrollers, so that the cost is greatly reduced.

10,50: power converter

11,51: primary side winding

12,52: Secondary side winding

13,53: PWM controller

14,54: Secondary side circuit

20,60: load

55: Detection resistor

30:Secondary side protection detection circuit

31: Detection component

32: Adder amplifier circuit

320: operational amplifier

321: power terminal

322: output terminal

33: Charge and discharge circuit

34: Auxiliary discharge circuit

350: control terminal

40,57: feedback isolation circuit

56: Amplifying circuit

Q1: Electronic switch

Y: Signal output pin

X: protection mode trigger pin

T: Transformer

Q: Drive switch

VDC: DC input power

(+Vo): Positive power output

(-Vo): Negative power supply output

R4: first resistor

R5: second resistor

N1, N2: connection nodes

R1, R2, R3, R6, R7: Resistors

C1: Capacitor

VCC1: working voltage

D2: Diode

Cin: input capacitor

V _sense : detection voltage

FIG. 1 : A schematic circuit diagram of an embodiment of a secondary side protection detection circuit of the present invention connected to a power converter.

FIG. 2 is a schematic circuit diagram of an embodiment of the secondary side protection detection circuit of the present invention.

FIG. 3 is a schematic diagram of a voltage waveform fed back to a primary side control element by an embodiment of the secondary side protection detection circuit of the present invention.

Figure 4: A schematic diagram of a connection circuit between a conventional voltage range power converter and an amplifying circuit.

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

The secondary side protection detection circuit of the present invention is used in a power converter. It should be noted that the circuit structure and working principle of the power converter are not the focus of the present invention, and are only briefly described as follows.

Please refer to FIG. 1 , the power converter 10 can be a switching power converter with a wide input voltage range, or a step-up power converter, so the present invention can be widely applied. For example, the circuit structure of the power converter 10 basically includes a transformer T, a driving switch Q, a PWM controller 13 (ie: pulse width modulation controller) and a secondary side circuit 14, the PWM The controller 13 includes a signal output pin Y and a protection mode trigger pin X. The primary side winding 11 of the transformer T is connected in series with a driving switch Q. The driving switch Q can be a MOSFET, for example, and its gate can be connected to the signal output pin Y of the PWM controller 13 . The primary side winding 11 of the transformer T is also connected to the power input terminal of the power converter 10 to receive a DC input power VDC, and the two ends of the secondary side winding 12 of the transformer T can be connected through the secondary side circuit 14 The plurality of output connections of the power converter 10 may include a positive power output (+Vo) and a negative power output (-Vo), the positive power output (+Vo) and the negative The power output terminal (-Vo) is for connecting a load 20 . The working principle of the power converter 10 can be referred to 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 the protection mode, the PWM controller 13 stops outputting the driving signal to the driving switch Q, so that the power converter 10 stops operating, thereby stopping outputting the DC input power to the load 20, so as to achieve the function of protection.

Please refer to FIG. 1 and FIG. 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 charging and discharging circuit 33, or further includes an auxiliary discharging circuit 34. The secondary side protection detection circuit 30 can pass through a feedback isolation circuit (feedback The isolation) 40 is connected to the protection mode trigger pin X of the PWM controller 13 to trigger the PWM controller 13 to enter the protection mode at an appropriate time, which will be described in detail later.

The detection element 31 is connected to one of the output terminals of the power converter 10. In an embodiment of the present invention, the detection element 31 is connected in series between the negative power supply output terminal (-Vo) and the secondary side of the transformer T. Between the windings 12, the detection element 31 can be a resistor, the resistance of which should be as small as possible to minimize its power consumption.

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

Generally speaking, the operational amplifier 320 and the complex resistor can realize an inverting adder circuit structure or a non-inverting adder circuit structure through different connection structures. The adder amplifying circuit 32 of the present invention is based on an inverting adder The circuit structure is an example. The operational amplifier 320 includes an inverting input terminal (-) and a non-inverting input terminal (+). In the foregoing, the input terminal of the operational amplifier 320 connected to the detection element 31 is the inverting The input terminal (-) enables the operational amplifier 320 to receive the detection voltage (i.e. voltage boost) V _sense of the detection element 31, and the detection voltage V _sense of the detection element 31 reflects the power converter 10. Output current.

As shown in FIG. 2, the complex resistors included in the adder amplifier circuit 32 include a first resistor R4 and a second resistor R5, and the first resistor R4 and the second resistor R5 are connected in series in the Between the inverting input terminal (-) of the operational amplifier 320 and the power supply terminal 321, that is to say, one end of the first resistor R4 is connected to the power supply terminal 321 of the operational amplifier 320, and the other end of the first resistor R4 is connected to Should One end of the second resistor R5, the other end of the second resistor R5 is connected to the inverting input terminal (-) of the operational amplifier 320, there is a connection node between the first resistor R4 and the second resistor R5 N1. The embodiment of the inverting adder circuit structure shown in Figure 2, the non-inverting input end (+) of this operational amplifier 320 is grounded through a resistor R3, the output end 322 of this operational amplifier 320 is connected with the inverting input end (+). -) is connected to a resistor R1, the inverting input terminal (-) of the operational amplifier 320 is connected to the detection element 31 through a resistor R2, and the power supply terminal 321 of the operational amplifier 320 receives an operating voltage VCC1, for example That is, the power terminal 321 of the operational amplifier 320 can be connected to a secondary side auxiliary winding (not shown in the figure), so as to obtain the working voltage VCC1 from the secondary side auxiliary winding.

The electronic switch Q1 is connected to a ground terminal and a resistor among the plurality of resistors through the adder amplifier circuit 32 is connected to the power supply terminal 321 of the operational amplifier 320. For example, the electronic switch Q1 can be connected to the power supply terminal 320 through the first resistor R4. Connect the power supply terminal 321 of the operational amplifier 320, when the electronic switch Q1 operates in the on state, the connection node N1 can be at a low potential or ground; on the contrary, when the electronic switch Q1 operates in the off state, the first The resistor R4 and the second resistor R5 are connected in series, and the power terminal 321 of the operational amplifier 320 is at a high potential. The electronic switch Q1 includes a control terminal 350 , and the electronic switch Q1 can be operated in an on state or an off state according to the voltage of the control terminal 350 . Wherein, the electronic switch Q1 can be a transistor, such as an N-type metal oxide semiconductor field effect transistor (N-type MOSFET), and its drain is connected to the connection between the first resistor R4 and the second resistor R5 The source of the node N1 is connected to the ground terminal, and the gate is connected to the control terminal 350 .

The charging and discharging circuit 33 is connected to the control terminal 350 of the electronic switch Q1 and the power supply terminal 321 of the operational amplifier 320. As the name suggests, the charging and discharging circuit 33 has an energy storage element. The power supply terminal 321 of the electronic switch Q1 receives the operating voltage VCC1, and the operating voltage VCC1 charges the energy storage element of the charging and discharging circuit 33 at the same time, so that the voltage provided by the energy storage element to the control terminal 350 of the electronic switch Q1 gradually increases, and can raised enough to allow the electronic switch Q1 to operate in the on state. In an embodiment of the present invention, the charging and discharging circuit 33 includes a resistor R6 and a capacitor C1, The resistor R6 of the charging and discharging 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 as described above, and the capacitor C1 is connected to the Between the control terminal 350 of the electronic switch Q1 and the ground terminal, the resistor R6 and the capacitor C1 can form a charging and discharging path, and the working voltage VCC1 can charge the capacitor C1 through the resistor R6, wherein, There is a connection node N2 between the resistor R6 and the capacitor C1.

The overall circuit structure of the secondary-side protection detection circuit 30 of the present invention applied to the power converter 10 has been described above. The circuit operation of the secondary-side protection detection implemented by the present invention will be described below with current waveforms.

Please refer to FIG. 1, when the load 20 connected to the power converter 10 is a capacitive load, that is to say, the input terminal of the load 20 is provided with an input capacitor Cin, at the moment of starting the power converter 10, the The input capacitor Cin of the load 20 is charged with a surge current. At this time, the electronic switch Q1 is not turned on yet, and the adder amplifier circuit 32 exerts its adding function. Although the surge current generates a large detection voltage V _sense , but the voltage polarity of the detection voltage V _sense is opposite to the operating voltage VCC 1 , so the present invention can reduce the operational amplifier 320 by setting the first capacitor R4 and the second capacitor R5. The output voltage V _op of the output terminal 321 is expressed as follows:

In the above formula, the detection voltage V _sense is a negative voltage, and the working voltage VCC 1 is a positive voltage, that is, even if the surge current passes through the detection element 31 to generate a relatively large detection voltage V _sense , But after it is processed by the operational amplifier 320, the reduced magnitude can be expressed as follows:

In this way, the voltage output by the operational amplifier 320 still makes the voltage received by the protection mode trigger pin X lower than the protection mode threshold value, so that the power converter 10 will not trigger the PWM controller 13 to enter the protection mode at the moment of startup. model.

When the power converter 10 is in a steady state, the steady state current passing through the detection element 31 is smaller than the inrush current. At this time, the capacitor C1 of the charging and discharging circuit 33 is charged by the operating voltage VCC1 enough to allow the electronic switch Q1 operates in the on state. When the electronic switch Q1 is operated in the conduction state, the connection node N1 between the first resistor R4 and the second resistor R5 of the adder amplifier circuit 32 is grounded, and the adder amplifier circuit 32 does not perform its addition function (ie: Equivalent to a general inverting amplifier), the operational amplifier 320 only has to amplify the detection voltage V _sense generated when the steady-state current passes through the detection element 31 . In this way, even if a short-circuit fault occurs in the load 20, a short-circuit current will pass through the detection element 31, and the detection voltage V _sense generated when the short-circuit current passes through the detection element 31 is directly amplified by the operational amplifier 320, and Without reducing the voltage amplitude as mentioned 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 value, thereby triggering the PWM controller 13 to enter the protection mode, to Provides short circuit protection.

To sum up the above, the voltage waveform of the output terminal 322 of the operational amplifier 320 can be referred to FIG. 3 . The power converter 10 starts at t0. The adder amplifying circuit 32 performs its adding function. Compared with FIG. 5 , FIG. 3 shows that the voltage at the output terminal 321 of the operational amplifier 320 decreases as a whole. As time progresses, the capacitor C1 of the charge-discharge circuit 33 is charged enough at t2 to allow the electronic switch Q1 to operate in a conduction state, so after t2, the current passing through the detection element 31 is a steady-state current, wherein, Through the combination of the capacitance of the capacitor C1 and the resistance of the resistor R6 of the charge-discharge circuit 33 , the timing of turning on the electronic switch Q1 can be determined, that is, the time length from t0 to t2 can be determined. Moreover, the waveform of FIG. 3 shows that a short-circuit current begins to occur at t3, and the output terminal 322 of the operational amplifier 320 reaches a voltage value Vth at t4, and the voltage value Vth passes through the feedback isolation circuit. When the circuit 40 is fed back to the protection mode trigger pin X of the PWM controller 13, the PWM controller 13 can be triggered to enter the protection mode to provide short-circuit protection.

In addition, considering that the power converter 10 in operation may be powered off and started immediately (for example, the DC input power supply VDC is momentarily unstable), the present invention provides the auxiliary discharge circuit 34, which includes one or two Pole D2 and a resistor R7, the anode of the diode D2 is connected to the connection node N2 between the resistor R6 of the charging and discharging 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 That is to say, 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.

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 communicate with the other discharge path provided by the resistor R7 via the discharge path provided by the diode D2. Discharging, using multiple discharge paths to achieve the effect of accelerating the discharge, thereby accelerating the turn-off of the electronic switch Q1 and minimizing the energy storage of the capacitor C1. Thereby, when the power converter 10 is powered off and started immediately, it can ensure that the electronic switch Q1 is in the off state, so that the adder amplifier circuit 32 can be successfully reset to the initial state of adding function; on the other hand , because the energy storage of the capacitor C1 has been minimized, correspondingly maximizing the time for the capacitor C1 to be charged to turn on the electronic switch Q1, that is, there is more time to suppress the impact of the surge current.

30:Secondary side protection detection circuit

32: Adder amplifier circuit

320: operational amplifier

321: power terminal

322: output terminal

33: Charge and discharge circuit

34: Auxiliary discharge circuit

350: control terminal

Q1: Electronic switch

R4: first resistor

R5: second resistor

N1, N2: connection nodes

R1, R2, R3, R6, R7: Resistors

C1: Capacitor

VCC1: working voltage

D2: Diode

V _sense : detection voltage

Claims (7)

A secondary side protection detection circuit of a power converter, comprising: a detection element connected to an output terminal of the power converter; An adder amplifying circuit includes an operational amplifier, a first resistor and a second resistor, and the operational amplifier includes: an input terminal connected to the detection element; an output terminal connected to the primary side control element of the power converter; and a power terminal; The first resistor and the second resistor are connected in series between the input terminal of the operational amplifier and the power supply terminal, and there is a connection node between the first resistor and the second resistor; an electronic switch connected between a ground terminal and the connection node and including a control terminal; and A charging and discharging circuit is connected to the control terminal of the electronic switch and the power supply terminal of the operational amplifier. 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. The secondary side protection detection circuit of a power converter as claimed in claim 1, wherein the adder amplifier circuit is a non-inverting adder circuit structure. The secondary side protection detection circuit of the power converter as described in claim 2, wherein the input end of the operational amplifier connected to the detection element is an inverting input end, and the first resistor and the second resistor It is connected in series between the inverting input terminal of the operational amplifier and the power supply terminal. 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, and its drain is connected between the first resistor and the second resistor The source of the connection node is connected to the ground terminal, and the gate is connected to the control terminal. The secondary side protection detection circuit of the power converter according to any one of claims 2, 4 and 5, wherein the charging and discharging circuit includes a resistor and a capacitor, and the resistor of the charging and discharging circuit is connected to the electronic Between the control terminal of the switch and the power supply terminal of the operational amplifier, the capacitor is connected between the control terminal of the electronic switch and the ground terminal. The secondary side protection detection circuit of the power converter as described in claim 6, wherein the connection node between the first resistor and the second resistor is defined as a first connection node, and the charging and discharging circuit There is a second connection node between the resistor and the capacitor; The secondary side protection detection circuit includes an auxiliary discharge circuit, and the auxiliary discharge circuit includes: a diode, the anode of which is connected to the second connection node, and the cathode of which 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.

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