JP2011030376A - Overcurrent protection circuit and dc stabilized power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem in a conventional overcurrent protection circuit that, although a peak current of output current is made to flow only during a predetermined period so as to meet the international safety standard by providing a time constant circuit for delaying a response time by a predetermined time on the output side of an overcurrent detecting comparator, the output voltage cannot be controlled at a high speed due to the effect of the time constant circuit since overcurrent prevention control is executed by way of the time constant circuit when the predetermined period passes and shifts to a period when overcurrent prevention control is executed. <P>SOLUTION: The current protection circuit is so configured as to perform overcurrent prevention control by comparing an output current with a predetermined set value for determining overcurrent. It includes a first overcurrent detection circuit 42 which detects an overcurrent that exceeds a first overcurrent level and outputs an overcurrent detection signal, and a masking circuit 41 which masks the overcurrent detection signal from the first overcurrent detection circuit 42 for a predetermined period. The masking circuit 41 releases masking after a predetermined period passes. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an overcurrent protection circuit and a DC stabilized power supply device, and more particularly to an overcurrent protection circuit for a device in which a peak current that greatly exceeds a rated current flows only for a predetermined time, and a DC including the overcurrent protection circuit The present invention relates to a stabilized power supply.

  2. Description of the Related Art Conventionally, a DC stabilized power supply device called an AC adapter that receives AC power from a commercial AC power supply and supplies DC power to an electronic device has been conventionally used. In particular, notebook personal computers are cited as main applications, but some of them are employed as power sources for printers. These AC adapters are designed in compliance with the versatility of the shape and the safety standards of each country. For example, in a power supply application of a printer, it is required to allow a current several times the rated current in addition to the rated current, in less than 1 second, or for a short time of about several seconds. However, there are output voltage, output current, and output power limit standards (requirements for limit current of IEC 60950-1: 2005 (EN 60950-1: 2006): see 2.5) as requirements of international safety standards. The general AC adapter must satisfy this standard.

  In view of the above safety, for example, in Japanese Patent Application Laid-Open No. 63-103616 (hereinafter referred to as Prior Art 1) cited as Patent Document 1, in order to satisfy the international safety standard, the power source peak current at the time of starting up the printer, etc. Addressed overcurrent protection circuits have been proposed. This prior art 1 is configured to detect the output current of the DC stabilized power supply apparatus and compare the detected value with a predetermined set value to determine the overcurrent of the DC stabilized power supply apparatus and perform overcurrent prevention control. In the overcurrent protection circuit, the first comparator that detects that the output current of the DC-stabilized power supply device has exceeded the upper limit of the average current (hereinafter referred to as a first overcurrent level), and the output current is A second comparator is provided for detecting that the upper limit of the peak current larger than the first overcurrent level (hereinafter referred to as the second overcurrent level) has been exceeded, and the output signal of the first comparator is output by a time constant circuit. It is designed to be delayed by a predetermined time τ.

JP-A-63-103616

  In the prior art 1, by providing a time constant circuit for delaying the response time by a predetermined time τ on the output side of the first comparator, the peak current of the output current flows for the predetermined time τ so as to satisfy the international safety standard. However, when the predetermined time τ elapses and the first overcurrent level overcurrent prevention control is entered, the overcurrent prevention control is performed via the time constant circuit. There was a problem that output voltage control (overcurrent prevention control) could not be performed at high speed due to the influence of the constant circuit.

  In view of the above problems, an object of the present invention is not to be affected by the time constant circuit when a peak current of an output current is detected and a period in which overcurrent prevention control is performed after a predetermined time τ has elapsed. An object of the present invention is to provide an overcurrent protection circuit capable of operating output voltage control at a high speed, and a DC stabilized power supply device including the overcurrent protection circuit.

An overcurrent protection circuit according to the present invention is configured to perform overcurrent prevention control by determining an overcurrent by comparing an output current with a predetermined set value, and has exceeded a first overcurrent level. A first overcurrent detection circuit that detects an overcurrent and outputs an overcurrent detection signal; and a masking circuit that masks the overcurrent detection signal from the first overcurrent detection circuit for a predetermined time, and The masking circuit is configured to release the mask after the predetermined time has elapsed.
The overcurrent protection circuit of the present invention includes a feedback signal photocoupler connected to the output side of the first overcurrent detection circuit and feeding back the overcurrent detection signal to the control circuit of the DC stabilized power supply device, The feedback signal photocoupler is configured to feed back the overcurrent detection signal that has been unmasked from the masking circuit.
In the overcurrent protection circuit of the present invention, the masking circuit includes a time constant circuit including a resistor and a capacitor, and a transistor, and the time constant circuit is configured to perform the predetermined time based on a charging voltage of the capacitor. By turning on the transistor, the current corresponding to the output signal of the overcurrent detection circuit is caused to flow to the output of the overcurrent detection circuit, thereby blocking the current flowing through the photodiode of the feedback signal photocoupler and the overcurrent detection. The signal is masked only for the predetermined time.
In the overcurrent protection circuit of the present invention, the masking circuit includes a time constant circuit including a resistor and a capacitor, and a transistor, and the predetermined time elapses based on a charging voltage of the capacitor of the time constant circuit. Thereafter, the mask is released by turning off the transistor, and a current is passed through the photodiode of the feedback signal photocoupler.
In addition, the DC stabilized power supply device of the present invention is characterized by comprising control means for performing overcurrent prevention control for suppressing overcurrent after the output signal of the masking circuit is stopped.
Moreover, the DC stabilized power supply device of the present invention is characterized by including the overcurrent protection circuit.

  According to the present invention, when the peak current of the output current is detected and the period when the overcurrent prevention control is performed after the lapse of the predetermined time τ, the output voltage can be controlled at high speed without being affected by the time constant circuit. Can be operated.

1 shows a specific embodiment of a stabilized DC power supply device according to the present invention. 1 shows a detailed configuration of an overcurrent protection circuit of a stabilized DC power supply device according to the present invention. It is explanatory drawing of the masking time which showed the voltage relationship of each part of the time constant circuit in an overcurrent protection circuit of the direct current | flow stabilized power supply device by this invention. It is explanatory drawing of the masking time which showed the relationship between the charge state of the capacitor | condenser of the time constant circuit in an overcurrent protection circuit, and masking time of the direct current | flow stabilized power supply device by this invention. It is a time sequence which showed operation | movement of the overcurrent protection circuit of the direct current | flow stabilized power supply device by this invention.

  In the overcurrent protection circuit according to the prior art 1, a time constant circuit for delaying the output signal by a predetermined time τ is provided on the output side of the first comparator, and the output voltage from this time constant circuit is directly used as an overcurrent signal. However, in the overcurrent protection circuit according to this embodiment of the present invention, the output voltage of the time constant circuit is not directly used as the output signal of the overcurrent protection circuit as in the prior art 1, but the first overcurrent protection circuit. The time constant circuit provided on the output side of the current detection circuit (corresponding to the first comparator of the prior art 1) masks the output signal from the first overcurrent detection circuit for a predetermined time τ and invalidates it. The difference is that the output signal of the current protection circuit.

  Specifically, a first overcurrent detection circuit that detects an overcurrent exceeding the first overcurrent level, a feedback signal photocoupler connected to the output side of the first overcurrent detection circuit, A masking circuit is provided that masks an overcurrent detection signal from one overcurrent detection circuit for a predetermined time τ, and delays a start time for current to flow through the feedback signal photocoupler by a predetermined time τ. The predetermined time τ masked by the masking circuit is defined in relation to the time constant of the time constant circuit in the masking circuit. Even if an overcurrent is detected within the predetermined time τ, the overcurrent detection signal from the first overcurrent detection circuit is ignored, the output signal of the overcurrent protection circuit is not output, and the output current is the first overcurrent. It is not suppressed by the level value. Thereafter, when this predetermined time τ elapses, the mask is released.

  If the overcurrent exceeding the first overcurrent level continues to flow when the mask is released, the output of the first overcurrent detection circuit continues to be in the low level state. A low-level overcurrent protection signal is output as an output signal of the protection circuit, and a current flows through the photodiode of the feedback signal photocoupler. When a current flows through the photodiode of the feedback signal photocoupler due to the output signal of the overcurrent protection circuit, the overcurrent protection signal is transmitted to the primary side control circuit of the DC stabilized power supply device via the phototransistor of the feedback signal photocoupler. The primary side control circuit operates to suppress the overcurrent to the first overcurrent level. Even if the mask is released, the time constant of the time constant circuit is not affected by the time constant as in the prior art 1, as will be described in detail below.

Embodiments according to the present invention will be specifically described below with reference to the drawings.
FIG. 1 shows a configuration of a stabilized DC power supply device 1 according to this embodiment. The stabilized DC power supply device 1 is configured as a flyback converter.

  Reference numeral 3 denotes a filter provided at the input terminal of the stabilized DC power supply 1. When the stabilized DC power supply 1 is connected to an AC power supply 2 such as a commercial power supply, switching from the stabilized DC power supply 1 to the AC power supply 2 side is performed. The transmission of noise is suppressed, and noise entering the stabilized DC power supply 1 from the AC power supply 2 side is suppressed.

  DB is a rectifier that performs full-wave rectification of the AC voltage of the AC power supply 2 input through the filter 3 and converts it to a DC voltage. C1 is a smoothing capacitor connected to the output terminal of the rectifier, and smoothes the pulsation contained in the DC voltage rectified by the rectifier DB to obtain a smooth DC voltage.

T is a transformer and includes primary windings P1 and P2 and a secondary winding S1. Q1 is a switching element. In this embodiment, an N-channel MOSFET (Metal) is used as the switching element Q1.
Oxide Semiconductor FET) is used. However, the switching element Q1 is not limited to the N-channel MOSFET. R2 is a resistor for detecting the current flowing through the switching element Q1. A primary winding P1, a switching element Q1, and a resistor R2 of the transformer T are connected in series between a positive electrode and a negative electrode of a DC power source constituted by a rectifier DB and a smoothing capacitor C1.

  Reference numeral 6 denotes a primary side control circuit (DC / DC control) of the DC stabilized power supply device 1 configured as a flyback converter, between the positive electrode and the negative electrode of the DC power source to which the rectifier DB and the smoothing capacitor C1 are connected. It is connected to the. The control circuit power supply of the primary side control circuit 6 is obtained by converting the AC voltage obtained from the primary winding P2 of the transformer T into a DC voltage using the diode D1 and the smoothing capacitor C2. The resistor R1 is a starting resistor.

  The primary side control circuit 6 has an input terminal oc for a current detection signal. A current detection signal is input to the input terminal oc from the connection point where the source terminal of the switching element Q1 and the resistor R2 are connected, and the current flowing through the primary winding P1 of the transformer T and the switching element Q1 is detected by the resistor R2. The

  Further, the primary side control circuit 6 has an input terminal fb for inputting a feedback signal from the feedback signal photocoupler PC-2. The feedback signal photocoupler PC-2 is a photocoupler including a phototransistor and paired with a feedback signal photocoupler PC-1 including a photodiode on the secondary side of the transformer T. The feedback signal photocoupler PC-1 is connected to the feedback signal photocoupler PC-1. The optical signal is received by the phototransistor of the feedback signal photocoupler PC-2 and output as a feedback signal to the input terminal fb. The feedback signal photocoupler PC-2 is fed back in common to the output voltage feedback signal output from the output voltage detection circuit 5 and the overcurrent protection signal output from the overcurrent protection circuit 4.

  The primary side control circuit 6 has a gate signal output terminal g for supplying a gate signal to the switching element Q1. The primary side control circuit 6 outputs a gate signal from the gate signal output terminal g based on the current detection signal input from the input terminal oc and the feedback signal input from the input terminal fb, and the on / off state of the switching element Q1 To control. When the output current becomes an overcurrent exceeding the second overcurrent level that is larger than the first overcurrent level, the gate signal is controlled so as to limit the power to the secondary side. This has the same effect as the second comparator function in the prior art 1.

  S1 is a secondary winding of the transformer T, D2 is a diode, and C3 is a smoothing capacitor. One terminal of the secondary winding S1 is connected to the anode of the diode D2, and the cathode of the diode D2 is connected to the output terminal Vo. The smoothing capacitor C3 is connected between the cathode terminal of the diode D2 and the other terminal of the secondary winding S1. The other terminal of the secondary winding S1 is connected to one terminal of the overcurrent protection circuit 4, and the other terminal of the overcurrent protection circuit 4 is connected to the ground terminal GND. The output of the overcurrent protection circuit 4 is connected to the cathode terminal of the photodiode of the feedback signal photocoupler PC-1. An output voltage detection circuit 5 is connected in parallel with the smoothing capacitor C3, and its output terminal is connected to the cathode terminal of the photodiode of the feedback signal photocoupler PC-1. The anode terminal of the photodiode of the feedback signal photocoupler PC-1 is connected to a control circuit power supply Vs (not shown).

  The output voltage of the secondary winding S1 is rectified by the diode D2 and then smoothed by the smoothing capacitor C3 to become a DC voltage. This DC voltage is output from the output voltage terminal Vo and the ground terminal GND of the DC stabilized power supply device 1. .

  The overcurrent protection circuit 4 inserted in the line of the ground terminal GND detects this overcurrent when the output current exceeds the first overcurrent level, and outputs the output signal of the overcurrent protection circuit as a feedback signal after a predetermined time τ. To the photocoupler PC-1. The output signal of the overcurrent protection circuit output to the feedback signal photocoupler PC-1 is fed back via the feedback signal photocoupler PC-1 to the feedback signal photocoupler PC-2 and to the input terminal fb of the primary side control circuit 6. Feedback.

  As will be described later, an overcurrent detection signal that is an output signal from the overcurrent protection circuit 4 is masked for an overcurrent detection signal for a predetermined time τ from the occurrence of the overcurrent. Thereafter, when the overcurrent continues to flow, the mask is released and output as a low level overcurrent protection signal. The low-level overcurrent protection signal is fed back to the primary side control circuit 6 via the feedback signal photocoupler PC-2 so that the current flows through the photodiode of the feedback signal photocoupler PC-1 and the overcurrent is suppressed. .

  The output voltage detection circuit 5 detects the output voltage terminal Vo, and supplies a current to the feedback signal photocoupler PC-1 so that the output voltage Vo becomes a predetermined target voltage. The feedback signal photocoupler PC-1 is a photocoupler paired with the feedback signal photocoupler PC-2 provided in the primary side circuit of the transformer T, and outputs the output signals of the overcurrent protection circuit 4 and the output voltage detection circuit 5, The signal is commonly output to the phototransistor of the feedback signal photocoupler PC-2 via the feedback signal photocoupler PC-1. The feedback signal received by the phototransistor of the feedback signal photocoupler PC-2 is output to the input terminal fb of the primary side control circuit 6.

  FIG. 2 shows a detailed configuration of the overcurrent protection circuit 4. In FIG. 2, the same reference numerals as those in FIG. 1 denote the same components.

  In FIG. 2, a dotted frame indicated by reference numeral 4 indicates an overcurrent protection circuit. In addition, a dotted line frame indicated by reference numeral 42 in the overcurrent protection circuit 4 is a first overcurrent detection circuit that detects an overcurrent of the first overcurrent level or higher, and a dotted line frame indicated by reference numeral 41 is the first overcurrent detection circuit. A masking circuit that masks the output of the overcurrent detection circuit for a predetermined time τ is shown. A dotted frame indicated by reference numeral 43 in the masking circuit 41 indicates a time constant circuit for generating a masking time of a predetermined time τ. Vs represents a control circuit power supply (not shown). Further, GND is a ground terminal GND as an output terminal of the direct current stabilized power supply device 1.

  The first overcurrent detection circuit 42 includes an operational amplifier OP1, a phase compensation resistor Rf, a phase compensation capacitor Cf, an overcurrent detection reference voltage Vsc, and resistors R3 and R4.

  The non-inverting input terminal of the operational amplifier OP1 is connected to the positive terminal of the overcurrent detection reference voltage Vsc, and the negative terminal of the overcurrent detection reference voltage Vsc is one terminal of the resistor R3 and the other terminal of the secondary winding S1 of the transformer T. It is connected to the connection point to which the terminal (the negative side of the capacitor C3) is connected. The other terminal of the resistor R3 is connected to the ground terminal GND, and is connected to the inverting input terminal of the operational amplifier OP1 through the resistor R4. A phase compensation resistor Rf and a phase compensation capacitor Cf are connected in series between the inverting input terminal and the output terminal of the operational amplifier OP1.

  An output current Io flows from the other terminal side (ground terminal GND side) to one terminal side (negative electrode side of the smoothing capacitor C3) in the resistor R3, and a voltage drop of R3 * Io occurs in the resistor R3. At this time, the voltage of the other terminal of the resistor R3 is input to the inverting input terminal of the operational amplifier OP1 via the resistor R4.

  The non-inverting input terminal of the operational amplifier OP1 is connected to the positive terminal of the overcurrent detection reference voltage Vsc having one terminal of the resistor R3 connected to the negative terminal, so that the voltage drop R3 * Io is the overcurrent detection reference voltage Vsc. The output of the operational amplifier OP1 outputs a low level signal. On the other hand, when the voltage drop R3 * Io falls below the overcurrent detection reference voltage Vsc, the output of the operational amplifier OP1 outputs a high level signal. The phase compensation resistor Rf and the phase compensation capacitor Cf are connected to compensate for the phase of the operational amplifier OP1 and prevent oscillation.

  Here, the voltage of the overcurrent detection reference voltage Vsc is a reference voltage for setting the first overcurrent level of the secondary side overcurrent protection. It is set lower than the second overcurrent level for current detection. Therefore, when an output current larger than the first overcurrent level of the secondary side overcurrent protection and smaller than the second overcurrent level of the overcurrent detection by the primary side control circuit 6 flows, the output of the operational amplifier OP1 Outputs a low level signal.

  If an output current smaller than the first overcurrent level of the secondary side overcurrent protection flows, the output of the operational amplifier OP1 outputs a high level signal, and the secondary side overcurrent protection does not operate. Further, when an output current larger than the second overcurrent level of the overcurrent detection by the primary side control circuit 6 flows, the output of the operational amplifier OP1 outputs a low level signal. At this time, the primary side control circuit 6 The overcurrent prevention control based on the current detection value at the resistor R2 input to the input terminal oc of the input terminal enters the current limiting operation before the secondary overcurrent protection. Therefore, in this case, the output current is first limited at the second overcurrent level, and then limited at the first overcurrent level after the masking time has elapsed.

  The masking circuit 41 includes a transistor Q2, resistors R10, R11, R12, a capacitor C10, and diodes D3, D4. Here, a P-channel bipolar transistor is used as the transistor Q2, but the present invention is not limited to this, and other switching elements such as MOSFETs can also be used.

  The emitter terminal of the transistor Q2 is connected to the control circuit power supply Vs, and the collector terminal is connected to one terminal of the resistor R10. This connection point is shown as point E. The cathode terminal of the diode D3 and the cathode terminal of the diode D4 are also connected to the point E. One terminal of the resistor R11 is connected to the control circuit power supply Vs, and the other terminal of the resistor R11 is connected to one terminal of the resistor R12. The other terminal of the resistor R12 is connected to one terminal of the capacitor C10. The anode terminal of the diode D4 is connected to a connection point between the other terminal of the resistor R12 and one terminal of the capacitor C10. The other terminal of the capacitor C10 is connected to the other terminal of the resistor R10. The connection point between the other terminal of the capacitor C10 and the other terminal of the resistor R10 is connected to the output terminal of the operational amplifier OP1. The connection point between the other terminal of the resistor R11 and one terminal of the resistor R12 is connected to the base terminal of the transistor Q2. The anode terminal of the diode D3 is connected to the cathode terminal of the photodiode of the photocoupler PC-1, and the anode terminal of the photodiode of the photocoupler PC-1 is connected to the control circuit power supply Vs. The output terminal of the output voltage detection circuit 5 is connected to the connection point between the anode terminal of the diode D3 and the cathode terminal of the photodiode of the photocoupler PC-1.

When the operational amplifier OP1 detects an output current larger than the first overcurrent level of the secondary side overcurrent protection and smaller than the second overcurrent level of the overcurrent detection by the primary side control circuit 6, The output of the operational amplifier OP1 outputs a low level signal, and an electric current is attempted to flow through the photodiode of the photocoupler PC-1. However, the current flowing through the photodiode of the photocoupler PC-1 is blocked for a predetermined time τ by the masking circuit 41 connected in series between the output of the operational amplifier OP1 and the photocoupler PC-1.
Hereinafter, the operation of the masking circuit 41 will be described.

  When the output of the operational amplifier OP1 outputs a low level signal, the base terminal voltage of the transistor Q2 is lowered to the low voltage side via the capacitor C10 and the resistor R12 of the masking circuit 41 connected in series with the output of the operational amplifier OP1. As a result, the base current of the transistor Q2 flows and the transistor Q2 is turned on.

  Here, the collector terminal of the transistor Q2 is connected to the connection point between the cathode terminal of the diode D3 and the resistor R10, and the current that should flow through the photodiode of the photocoupler PC-1 is supplied from the collector terminal of the transistor Q2, Block current flowing through the photodiode of PC-1.

  At this time, since the output of the operational amplifier OP1 maintains a low-level signal state, the power supply voltage of the control circuit power supply Vs is between the emitter terminal of the transistor Q2 and the output terminal of the operational amplifier OP1 (both ends of the time constant circuit 43). Is applied. Therefore, the capacitor C10 is charged with a time constant determined by the resistors R11 and R12 and the capacitor C10. The time constant determined by the resistors R11 and R12 and the capacitor C10 determines the time for blocking the output signal of the operational amplifier OP1, that is, the masking time τ for masking the secondary overcurrent protection function.

This masking time τ can be obtained as follows.
3 and 4 are explanatory diagrams of the masking time τ, FIG. 3 shows the voltage relationship of each part of the time constant circuit 43, and FIG. 4 is a diagram showing the relationship between the charged state of the capacitor C10 and the masking time τ. .
C and R for determining the time constant of the time constant circuit 43 are C is a capacitor C10, and R is a series resistance value (R11 + R12) of a resistor R11 and a resistor R12.

When the output of the operational amplifier OP1 (point C in FIG. 3) becomes a low level (approximately 0V) signal, the capacitor C10 is charged from approximately 0V toward the power supply voltage of the control circuit power supply Vs according to the equation (1). (FIG. 4).
Vc = Vs * (1-exp (-t / CR)) (1)
Where Vc: voltage of capacitor C10
Vs: power supply voltage of the control circuit power supply Vs on the secondary side
C; C = C10
R; R = R11 + R12
t; time

At this time, the voltage Vx applied to the series resistance value (R11 + R12) is expressed by equation (2).
Vx = Vs-Vc (2)

When the capacitor C10 is charged and the voltage applied to the resistor R11 becomes the Min base voltage of the transistor Q2 (defined as the minimum base voltage at which the transistor can be turned on), the transistor Q2 is turned off. The voltage Vxmin applied to the series resistance value (R11 + R12) when the voltage applied to the resistor R11 at this time becomes the Min base voltage is the voltage applied to the resistor R11 obtained by dividing the voltage Vx by the resistors R11 and R12. Therefore, equation (3) holds.
Vxmin = Vbemin * (R11 + R12) / R11 (3)
Here, Vbemin is a Min base voltage.

The time when the voltage applied to the resistor R11 becomes the Min base voltage Vbemin of the transistor Q2 after the power supply voltage Vs of the control circuit power supply Vs is applied to the time constant circuit 43 becomes the masking time τ.
From the above equations (1) to (3), equation (4) is established.
Vbemin * (R11 + R12) / R11 = Vs * (exp (-τ / CR)) (4)

Therefore, the masking time τ to be obtained is obtained by equation (5).
τ = -C10 * (R11 + R12) * ln ((Vbemin / Vs) * (R11 + R12) / R11) (5)
Here, the low level state of the output voltage of the operational amplifier OP1 is treated as almost 0V.

(A)-(g) in FIG. 5 is the time sequence which showed operation | movement of the overcurrent protection circuit of this embodiment.
In FIG. 5, the waveform of (a) indicates the output voltage Vo of the DC stabilized power supply device 1. Moreover, the waveform of (b) has shown the output current Io of the direct current | flow stabilized power supply device 1. FIG. The waveform (c) shows the input voltage to the inverting input terminal of the operational amplifier OP1 shown as “point A” in FIG. Further, the waveform of (d) shows the voltage at the output terminal of the operational amplifier OP1 shown as “C point” in FIG. The waveform (e) shows the on / off state of the transistor Q2. The waveform (f) shows the collector terminal voltage of the transistor Q2 (= the voltage at the connection point between the cathode of the diode D3 and the resistor R10), which is shown as “point E” in FIG. The waveform (g) indicates the current Ipc flowing through the photodiode of the photocoupler OP1. The waveform of (h) shows the voltage at point E of the prior art 1 for comparison.

  FIG. 5 shows that when the overcurrent prevention control is not performed, an average current that is equal to or higher than the first overcurrent level and equal to or lower than the second overcurrent level immediately after startup flows for the masking time τ or more. An example of a load in which the average current drops below the first overcurrent level is taken.

(Period-t1)
First, it is assumed that the output current Io is 0 A before the time t1, and the load is connected to the output of the DC stabilized power supply 1 and the output current Io starts to flow at the time t1.

(Period t1-t2)
The output current Io increases from time t1 as shown in the waveform of (b), and the voltage at point A (the voltage at the inverting input terminal of the operational amplifier OP1) is overcurrent at time t2 as shown in the waveform of (c). When the voltage exceeds the detection reference voltage Vsc, the voltage at point C (the voltage at the output terminal of the operational amplifier OP1) changes from the high level to the low level as shown in the waveform of (d). When the voltage at the point C becomes low level, as described above, the on-voltage is input to the base voltage of the transistor Q2. Therefore, as shown in the waveform of (f), the voltage at the point E remains at a high level.

(Period t2-t3)
At time t2 to t3, the transistor Q2 is in the on state, the voltage at the point E is kept at the high level, and the photodiode of the photocoupler PC1 is in spite of the overcurrent state as shown in the waveform of (g). There is no current flowing through. Accordingly, the overcurrent protection signal is not output during this period. That is, this period is the masking time τ.

(Period t3-t4)
When a predetermined time τ set as the masking time in the time constant circuit 43 of the masking circuit 41 elapses at time t3, the transistor Q2 is turned off as shown in the waveform (e) due to a decrease in the base voltage of the transistor Q2. At this time, since the overcurrent state continues, the output of the operational amplifier OP1 maintains the low level state as shown in the waveform of (d). Therefore, the voltage at the point E is in a low level state slightly lowered from the high level as shown in the waveform of (f) (specifically, the voltage drop Vf of the photodiode of the photocoupler PC-1 and the voltage drop Vf of the diode D3 are combined). The voltage level is reduced by a corresponding amount), and a current flows through the resistor R10 to the photodiode of the photocoupler PC1 as shown in the waveform of (g), and the overcurrent protection for limiting the overcurrent to the primary side control circuit. The signal is fed back.

  As a result, the output of the operational amplifier OP1 is output so that the voltage drop of the resistor R3, which is the input voltage to the inverting terminal (point A) of the operational amplifier OP1, becomes the same voltage as the overcurrent detection reference voltage Vsc ((c)). The primary side control circuit 6 controls the output voltage Vo via the photocouplers PC-1 and PC-2. As a result, the output voltage Vo is suppressed to be lower than the rated voltage so as to suppress overcurrent, as shown in the waveform of (a), and as a result, the output current is the first as shown in the waveform of (b). Controlled to an overcurrent level.

  At this time, the masking by the masking circuit 41 is released, and the current flowing through the photodiode of the photocoupler PC-1 is directly controlled by the output of the operational amplifier OP1 without going through the time constant circuit as in the prior art 1. Therefore, the operation of the overcurrent prevention control becomes faster, and the problem that the output voltage does not quickly return to the normal state due to the influence of the time constant circuit as in the prior art is eliminated.

(Period t4 ~)
Next, when the overcurrent state is released at time t4, the voltage drop of the resistor R3 is decreased, the input voltage to the inverting input terminal of the operational amplifier OP1 is decreased, and is lower than the overcurrent detection reference voltage Vsc. The output of the operational amplifier OP1 changes from the low level state to the high level state, and the current flow from the photodiode of the photocoupler PC1 to the operational amplifier OP1 is stopped.

  Further, when the output of the operational amplifier OP1 changes from the low level state to the high level state, the charge of the capacitor C10 is discharged through the diode D4 and the resistor R10 to prepare for the next overcurrent. At this time, as shown in the waveform (d) and the waveform (f), the output of the operational amplifier OP1 is at a high level, and the overcurrent protection signal is not fed back. Therefore, it is possible to set the repetitive masking time, and it is possible to stably operate the electronic component mounted on the DC stabilized power supply device 1. Further, the charging / discharging time of the time constant circuit can be arbitrarily set by adjusting the resistance values of the resistors R11, R12, and R10.

Here, the control of the prior art 1 will be described for comparison. As shown in the waveform (h), the voltage at the point E in the prior art 1 can cause a peak current to flow until a predetermined time τ elapses due to a response delay of the time constant circuit. However, overcurrent prevention control is performed through the time constant circuit during the period from time t3 to t4 when the predetermined time τ has elapsed. In addition, the time for returning to the normal state is delayed from time t4 to t5 due to the influence of the time constant circuit. Therefore, there is a problem that the output voltage cannot be controlled at high speed due to the influence of the time constant circuit.
On the other hand, according to the present embodiment of the present invention, since the masking circuit does not affect the response of the overcurrent protection signal after the time t3 when the predetermined time τ has elapsed, the output voltage can be controlled at high speed. it can.

  Note that when the overcurrent prevention control is operating in the period t3 to t4, the output signal of the operational amplifier OP1 (the waveform of (c)) is simplified to be a continuous low level as shown in FIG. Since the output current is controlled to be at the first overcurrent level, the input voltage to the inverting terminal (point A) of the operational amplifier OP1 operates so as to be close to the overcurrent detection reference voltage Vsc. The output signal (waveform (c)) of the operational amplifier OP1 does not always become a continuous low level as shown in FIG.

  While the present invention has been described with reference to specific embodiments, it is needless to say that the present invention is not limited to the above-described embodiments and can be modified and implemented within the scope of the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 ... DC stabilized power supply device 2 ... AC power supply 3 ... Filter 4 ... Overcurrent protection circuit 5 ... Output voltage detection circuit 6 ... Primary side control circuit 41 ... Masking Circuit 42 ... first overcurrent detection circuit 43 ... time constant circuit DB ... rectifiers C1 to C3 ... smoothing capacitors C10 ... capacitors D1 to D4 ... diodes R1 to R4, R10 R12 ... Resistance T ... Transformer P1, P2 ... Transformer primary winding S1 ... Transformer secondary winding PC-1, PC-2 ... Feedback signal photocoupler Vo ... Output voltage Vs ... Control circuit power supply Q1 ... Switching element Q2 ... Transistor

Claims (6)

In the overcurrent protection circuit configured to perform overcurrent prevention control by determining the overcurrent by comparing the output current with a predetermined set value,
A first overcurrent detection circuit for detecting an overcurrent exceeding a first overcurrent level and outputting an overcurrent detection signal;
A masking circuit that masks the overcurrent detection signal from the first overcurrent detection circuit for a predetermined time;
The overcurrent protection circuit, wherein the masking circuit is configured to release the mask after the predetermined time has elapsed. A feedback signal photocoupler connected to the output side of the first overcurrent detection circuit and feeding back the overcurrent detection signal;
2. The overcurrent protection circuit according to claim 1, wherein the feedback signal photocoupler is configured to feed back the overcurrent detection signal that has been unmasked from the masking circuit. 3. The masking circuit is
A time constant circuit composed of a resistor and a capacitor, and a transistor, and by turning on the transistor for the predetermined time based on a charging voltage of the capacitor of the time constant circuit, an output signal of the overcurrent detection circuit By passing a corresponding current to the output of the overcurrent detection circuit, the current flowing through the photodiode of the feedback signal photocoupler is cut off, and the overcurrent detection signal is masked for the predetermined time. The overcurrent protection circuit according to claim 2. The masking circuit is
A time constant circuit composed of a resistor and a capacitor, and a transistor, and based on a charging voltage of the capacitor of the time constant circuit, after the predetermined time has elapsed, the transistor is released by turning off the transistor, 4. The overcurrent protection circuit according to claim 2, wherein a current is passed through a photodiode of a feedback signal photocoupler.   The overcurrent protection circuit according to any one of claims 1 to 4, further comprising control means for performing overcurrent prevention control for suppressing overcurrent after the output signal of the masking circuit is stopped.   A direct-current stabilized power supply device comprising the overcurrent protection circuit according to any one of claims 1 to 5.

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