JP2017139900A - Rush current regulation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rush current regulation circuit that can bring forward supply of power through an output terminal when a power supply is actuated from a stop state while a switch is in an ON state.SOLUTION: A charging circuit 110 changes a potential difference between an input terminal and a control terminal of a first switch element 101 by being charged with a voltage applied to an input terminal. A second switch element 102 discharges the charging circuit 110 by being conductive, and that can charge the charging circuit 110 by being disconnected. A switch 103 is arranged between a DC power supply 11 and the input terminal. An actuation circuit 120 switches conduction and disconnection of the second switch element 102 depending on a potential difference between the front and the rear of the switch 103.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an inrush current regulating circuit that regulates an inrush current when a switch is turned on.

  2. Description of the Related Art A power supply device that supplies a power supply voltage to a load through an output terminal of a switch element that changes continuity according to a potential difference between an input terminal and a control terminal is widely used. In the power supply device, a large transient current (inrush current) may be output from the output terminal of the switch element in the process of increasing the voltage applied to the input terminal of the switch element.

  For this reason, the power supply device is provided with an inrush current regulation circuit that gradually increases the continuity of the switch element at the start of conduction of the switch element, and regulates the rush current taken from the output terminal at the start of conduction of the switch element.

  Patent Document 1 discloses an inrush current prevention circuit in which a MOSFET is used as a switch element and the continuity of the switch element is controlled by a charging circuit.

JP 2006-238655 A

  A switch (for example, an OFF / ON operation in conjunction with opening / closing of the cover) is provided between the power supply of the power supply device and the switch element, and the switch is turned on / off while the power supply itself is kept in an operating state. There is a case where power supply to the load through the element is started.

  At this time, if the power supply is operated from the stop state with the switch kept in the ON state (with the cover closed), as will be described later, the output is the same as when the switch is turned on from the OFF state in the power supply operation state. Power supply to the load through the terminal will be delayed.

  The present invention reliably regulates the inrush current when the switch is turned from OFF to ON while the power is in operation, and supplies power through the output terminal when the power is operated from the stop state while the switch is ON. An object of the present invention is to provide an inrush current regulation circuit that can be advanced.

  The inrush current regulating circuit of the present invention is applied to the input terminal and the first switch element that changes the continuity between the input terminal and the output terminal according to the potential difference between the input terminal and the control terminal. A charging circuit that changes the potential difference by being charged with a voltage; a second switching element that discharges the charging circuit by its conduction and enables charging of the charging circuit by its interruption; and a power source and an input terminal And a switching circuit that switches between conduction and interruption of the second switch element according to a potential difference before and after the switch.

  According to the present invention, the power supply through the output terminal when the power supply is operated from the stop state while the switch is in the ON state is reliably regulated while the inrush current when the switch is turned from OFF to ON in the operation state of the power supply. It is possible to provide an inrush current regulation circuit that can speed up the process.

2 is an explanatory diagram of a power supply system of the image forming apparatus. FIG. FIG. 3 is a circuit diagram of an inrush current prevention circuit according to the first embodiment. It is explanatory drawing of arrangement | positioning of a housing | casing switch. FIG. 3 is a detailed circuit diagram of the inrush current prevention circuit according to the first embodiment. 3 is a time chart of the operation of the inrush current prevention circuit according to the first embodiment. It is a circuit diagram of the inrush current prevention circuit of a comparative example. It is a time chart of operation | movement of the inrush current prevention circuit of a comparative example.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<Embodiment 1>
(Image forming device)
FIG. 1 is an explanatory diagram of a power supply system of the image forming apparatus. As shown in FIG. 1, the image forming apparatus 10 is an example of a load connected to a load terminal 15 using a power supply voltage (DC voltage) generated by a DC power supply 11 upon receiving power supply from a commercial power supply (AC100V) 16. This is supplied to a certain motor 12 and control unit 13.

  A section from the output side of the DC power supply 11 to the smoothing capacitor 106 is called a “power supply line”. The smoothing capacitor 106 is connected in parallel to the power supply line, smoothes the voltage of the power supply line, and stabilizes the voltage of the load terminal 15. The smoothing capacitor 106 stabilizes the DC voltage against load fluctuations of the loads (12, 13) connected to the load terminal 15. The motor 12 operates with a voltage smoothed by the smoothing capacitor 106.

  When the switch 103 is turned on, a steady-state DC voltage is immediately applied from the DC power supply 11 while the continuity of the switch element 101 is high. At this time, a “rush current” that is a transient current flows through the power supply line before the smoothing capacitor 106 completes charging. The inrush current is larger than the steady current taken out to the load (12, 13) and is unfavorable because it affects the operation of the DC power supply 11.

  Therefore, the image forming apparatus 10 is provided with an inrush current preventing circuit 20 which is an example of an inrush current regulating circuit for the purpose of preventing an inrush current from flowing through the power supply line.

(Inrush current prevention circuit)
FIG. 2 is a circuit diagram of the inrush current prevention circuit according to the first embodiment. As shown in FIG. 2, the smoothing capacitor 106 is connected to the output terminal (D) of the first switch element 101 and smoothes the voltage supplied to the load terminal 15. The inrush current prevention circuit 20 has a first switch element 101 disposed between the DC power supply 11 and the load terminal 15 (power supply line).

  The first switch element 101 is a conductive FET element that bypasses the DC power supply 11 to the load terminal 15. The first switch element 101 uses a conductive FET element that is a power control semiconductor element. The conductive FET element is, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The conduction FET element has a source (input terminal) S connected to the DC power supply 11, a drain (output terminal) D connected to the load terminal 15, and a gate (control terminal) G. The conduction FET element conducts between the source / drain with conductivity (resistance value) according to the gate-source voltage. The conduction FET element starts conduction between the source / drain when the gate / source voltage exceeds the threshold value Vth. The gate / source voltage of the first switch element 101 is determined by the voltage division ratio between the voltage dividing resistor 105 and the resistor 112.

  The inrush current prevention circuit 20 causes the charging circuit 110 to gently change the gate / source voltage at the start of conduction between the source / drain of the first switch element 101. As a result, the continuity between the source and drain of the first switch element 101 is lowered (resistance is increased), and the inrush current is reduced.

  That is, the first switch element 101 which is an example of the switch element or the first switch element has an input terminal (S) and an output terminal (in accordance with a potential difference between the input terminal (S) and the control terminal (G). D) is changed in continuity. And the charging circuit 110 which is an example of a charging circuit is charged with the voltage applied to the input terminal (S), thereby changing the potential difference between the input terminal (S) and the control terminal (G).

(Charging circuit)
The charging circuit 110 includes a capacitor 111 and a resistor 105 connected between the gate / source of the first switch element 101, and a resistor 112 connected between the gate / ground potential. The charging circuit 110 gently changes the potential difference between the gate and the source of the first switch element 101 according to the time constant τ1 when a DC voltage is applied from the DC power supply 11 through the power supply line. The charging circuit 110 charges the capacitor 111 with the voltage of the power supply line according to the time constant τ1. The time constant τ1 is determined by the resistance component of the gate-source resistor 105 and the capacitance component of the capacitor 111.

  A DC voltage applied from the DC power supply 11 between the source S of the first switch element 101 and the ground potential GND is applied to the resistor 105 and the resistor 112 connected in series. At this time, if the capacitor 111 is not provided, a voltage obtained by dividing the DC voltage by the resistor 105 and the resistor 112 is immediately applied between the gate / source of the first switch element 101.

  However, since the capacitor 111 is connected in parallel to the resistor 105, a voltage (charging voltage) corresponding to charging of the capacitor 111 is applied to both ends of the resistor 105. The capacitor 111 gradually accumulates electric charge according to the time constant τ1 to increase the charging voltage. As the charging voltage increases, the potential difference between both ends of the resistor 105 gradually increases and converges to a voltage obtained by dividing the DC voltage according to the voltage dividing ratio between the resistor 105 and the resistor 112. Since the resistor 105 is connected between the gate and the source of the first switch element 101, the voltage between the gate and source of the first switch element 101 gradually increases as the potential difference across the resistor 105 gradually increases. To rise.

  When the gate / source voltage of the first switch element 101 gradually increases and exceeds the threshold value of the first switch element 101, conduction between the drain / source of the first switch element 101 starts. In the first switch element 101, the conductivity of the first switch element 101 gradually increases as the gate / source voltage gradually increases after the drain / source conduction starts. In other words, the internal resistance between the drain / source gradually decreases. As the continuity of the first switch element 101 is gradually increased, the voltage applied from the drain D to the smoothing capacitor 106 gradually increases toward the power supply voltage of the DC power supply 11.

  Thereafter, as the gate-source voltage increases, the conductivity of the first switch element 101 further increases, and when the capacitor 111 is fully charged, the internal resistance between the source and drain becomes approximately 0Ω.

  Thus, the charging circuit 110 gradually increases the voltage applied to the smoothing capacitor 106 from the output terminal (D) when a DC voltage is applied to the input terminal (S) of the first switch element 101. The inrush current increases as the voltage applied across the smoothing capacitor 106 increases. As a result, charging of the smoothing capacitor 106 is gradually performed, and the inrush current flowing through the first switch element 101 is regulated.

(switch)
FIG. 3 is an explanatory diagram of the arrangement of the housing switches. As shown in FIG. 2, the inrush current prevention circuit 20 of the power supply device 10 </ b> D includes a switch 103 between the DC power supply 11 and the first switch element 101. The switch 103 is a mechanical switch that mechanically conducts / cuts off a current between the DC power supply 11 and the first switch element 101.

  As shown in FIG. 3, the image forming apparatus 10 has a power supply device 10 </ b> D disposed inside a cover 10 </ b> C that opens and closes from the housing 10 </ b> B. The switch 103 is a cover switch that performs an OFF / ON operation in conjunction with opening / closing of the cover 10 </ b> C of the image forming apparatus 10. The switch 103 opens the cover 10C to cut off the connection between the DC power supply 11 and the input terminal (S) shown in FIG. 2, and closes the cover 10C to connect the DC power supply 11 and the input terminal (S). Conduct.

  As shown in FIG. 2, since the inrush current prevention circuit 20 is provided with the switch 103, the load through the first switch element 101 is turned off by turning off the switch 103 while keeping the DC power supply 11 in the ON state. The power supply to the terminal 15 can be stopped. The switch 103, which is an example of a switch, is disposed between a DC power source 11 which is an example of a power source and an input terminal (S).

  The inrush current prevention circuit 20 controls the inrush current when the switch 103 is quickly turned OFF / ON while the DC power supply 11 is ON and the DC voltage on the input side of the switch 103 is maintained. The switch element 102 and the operation circuit 120 are provided.

  That is, when the capacitor 103 is fully charged and a potential difference exceeding the threshold value is generated between the source and gate of the first switch element 101, the switch 103 is quickly turned OFF / ON, and the first switch element 101 enters. Current flows. This is because a current difference flows between the source / gate and the smoothing capacitor 106 through the first switch element 101 in which the internal resistance is maintained in a conductive state of approximately 0Ω due to a potential difference exceeding the threshold value.

  That is, after the switch 103 is turned off, the first switch element 101 is maintained in a conductive state between the source and the drain until the charging voltage charged in the capacitor 111 is sufficiently discharged through the resistor 112. For this reason, at the moment when the switch 103 is turned ON, the power supply voltage of the DC power supply 11 is directly conducted from the source S to the drain D. As a result, the power supply voltage of the DC power supply 11 is applied to the smoothing capacitor 106 from the beginning, and an inrush current flows through the first switch element 101.

  Therefore, the inrush current prevention circuit 20 is provided with a second switch element 102 and an operation circuit 120 which are examples of a discharge circuit, and when the switch 103 is turned off, the charging voltage remaining in the capacitor 111 is forcibly discharged. ing. The second switch element 102, which is an example of the second switch element, discharges the charging circuit 110 by the conduction and enables the charging circuit 110 to be charged by the interruption.

(Discharge circuit)
As shown in FIG. 2, the operating circuit 120 is connected to both ends of the switch 103 and the second switch element 102. The second switch element 102 is a semiconductor element for discharging the charge accumulated in the capacitor 111 of the charging circuit 110.

  When the voltage applied to the source S of the first switch element decreases, the operating circuit 120 causes the second switch element 102 to conduct and quickly discharge the charge accumulated in the capacitor 111 of the charging circuit 110. The second switch element 102 is turned on in accordance with the output of the operating circuit 120, and discharges the capacitor 111 via the resistor 104 at a time with a time constant τ2 smaller than the time constant τ1.

  By discharging the electric charge of the capacitor 111, the source / gate voltage of the first switch element 101 becomes 0V, and the source / drain of the first switch element 101 is cut off. Therefore, immediately after the switch 3 is turned on and the DC voltage of the DC power supply 11 is suddenly applied to the source S of the first switch element 101, no current flows from the drain D to the smoothing capacitor 106.

  If the charging voltage of the capacitor 111 is discharged, the internal resistance between the gate and the source of the first switch element 101 is high when the DC voltage of the DC power supply 11 is turned on again by turning on the switch 103, and smoothing is performed. The current flowing into the capacitor 106 can be cut off. For this reason, the DC voltage applied to the smoothing capacitor 106 does not rise at a stretch and causes an inrush current.

  If there is no charge remaining in the capacitor 111, charging of the capacitor 111 starts after the switch 103 is turned on, and the gate-source voltage of the first switch element 101 is gradually increased by the time constant τ1. Then, as the charging voltage of the capacitor 111 increases, the source / gate resistance of the first switch element 101 can be gradually decreased, and the voltage applied to the smoothing capacitor 106 can be gradually increased.

(Comparative example)
FIG. 6 is a circuit diagram of an inrush current prevention circuit of a comparative example. FIG. 7 is a time chart of the operation of the inrush current prevention circuit of the comparative example. 7, (a) is the ON / OFF state of the switch, (b) is the DC voltage of the DC power supply, (c) is the state of the first switch element, (d) is the state of the second switch element, (e ) Is the charging voltage.

  As shown in FIG. 6, the inrush current prevention circuit 20H of the comparative example has the same configuration as that of the first embodiment except that the operation circuit (120: FIG. 2) is replaced with a voltage detection unit 203. For this reason, in FIG. 6, the same code | symbol as FIG. 2 is attached | subjected to the structure which is common in Embodiment 1, and the overlapping description is abbreviate | omitted.

  In the inrush current prevention circuit 20H of the comparative example, the voltage detection unit 203 operates the second switch element 102 so that the inrush current can be regulated even when the switch 103 is quickly turned OFF / ON. The voltage detection unit 203 monitors the voltage applied to the source S of the first switch element.

  The voltage detection unit 203 conducts the second switch element 102 and discharges the capacitor 111 of the charging circuit 110 in the process in which the switch 103 is turned OFF and the voltage of the source S of the first switch element decreases. By discharging the electric charge of the capacitor 111, the voltage between the source and gate of the first switch element 101 is made lower than the threshold voltage of the first switch element 101, and the voltage between the source and drain of the first switch element 101 is reduced. Cut off.

  As shown in FIG. 7A, when the switch 103 is turned off, as shown in FIG. 7B, the DC voltage applied to the source S of the first switch element decreases. When the DC voltage becomes lower than a specific voltage in the lowering process, as shown in FIG. 7D, the second switch element 102 is released from interruption (discharge release) and switched to conduction (discharging). .

  When the second switch element 102 is turned on, the charging voltage of the capacitor 111 is discharged as shown in FIG. As shown in FIG. 7 (a), the conduction state of the second switch element 102 is activated when the switch 103 is turned ON and the source S of the first switch element is pulled as shown in FIG. 7 (b). This is maintained until the applied DC voltage exceeds a specific voltage.

(Problems when starting up DC power supply)
The inrush current prevention circuit 20H of the comparative example has a case where the switch 103 is switched from OFF to ON in the operating state of the DC power supply 11 even when the DC power supply 11 is operated from the stopped state while the switch 103 is ON. Operates similarly.

  As shown in FIG. 1, when the power switch 18 of the image forming apparatus 10 is turned off while the switch 103 is turned on, the DC power source 11 is stopped and the voltage applied to the source S of the first switch element is The voltage drops from 24V to 0V. Even in the lowering process, as shown in FIG. 7A, when the voltage becomes lower than a specific voltage, the second switch element 102 is released from the cutoff state and switched to the conductive state.

  Thereafter, when the power switch 18 is turned on, the DC power supply 11 starts to operate and the output voltage rises from 0V to 24V. At this time, the rise of the DC voltage applied to the output side of the switch 103 (the source of the first switch element 101) is more gradual than when the switch 103 is turned OFF / ON. For this reason, the start of increasing the charging voltage of the capacitor 111 is delayed as compared with the case where the switch 103 is turned OFF / ON, and the timing at which the potential difference between the source / gate of the first switch element reaches the threshold is also delayed.

  As shown in FIG. 7A, the supply of power to the DC power supply 11 is started to raise the DC voltage. When the DC voltage exceeds a predetermined voltage, the conduction of the second switch element 102 is released and the circuit is switched to cutoff, and the capacitor 111 can be charged with the DC voltage.

  As shown in FIG. 7D, after the second switch element 102 is cut off, the charging voltage is slowly charged in the capacitor 111 with a time constant τ1 corresponding to the resistance of the resistor 105 and the capacitance of the capacitor 111. . As the charging of the capacitor 111 progresses, the potential difference between the source / gate of the first switch element 101 gradually increases, and when the threshold voltage of the first switch element 101 is reached, the source / drain of the first switch element 101 is increased. Conduction in between starts.

  As shown in FIG. 7B, after the start of conduction between the source and drain of the first switch element 101, the voltage between the source and gate of the first switch element 101 gradually rises and the first switch The internal resistance between the source / drain of the element 101 gradually decreases. Along with this, the voltage applied to the smoothing capacitor 106 gradually increases and converges to the output voltage of the DC power supply 11.

  As shown in FIG. 6, in the comparative example, the voltage detection unit 203 determines whether the increase in the voltage applied to the source S of the first switch element 101 is due to the rise in the output voltage accompanying the turning on of the DC power supply 11. Whether the switch 103 is ON cannot be determined.

  For this reason, in the comparative example, if the output voltage does not rise to a specific voltage when the output voltage rises when the DC power supply 11 is activated, the second switch element 102 is turned on (initialization of the charging circuit 110). Cannot be released. For this reason, the start of power supply to the load connected to the load terminal 15 of the inrush current prevention circuit 20H until the output voltage reaches a specific voltage as shown in FIGS. 7B and 7E. Delayed by the time DL delays the activation of the image forming apparatus (10).

  Therefore, in the first embodiment, whether the increase in the voltage applied to the source S of the first switch element 101 in the operating circuit 120 is caused by turning on the DC power supply 11 or by turning on the switch 103. , Is determined. In the case where the voltage rises due to the DC power supply 11 being turned on, the timing at which charging of the capacitor 111 is started is made earlier than in the case where the voltage rises due to the switch 103 being turned on.

(Operating circuit)
FIG. 4 is a detailed circuit diagram of the inrush current preventing circuit according to the first embodiment. As illustrated in FIG. 4, the operation circuit 120, which is an example of a switching circuit, switches between conduction and interruption of the second switch element 102 according to a potential difference before and after the switch 103. The operation circuit 120 switches between conduction and interruption of the second switch element 102 according to the operation / stop state of the DC power supply 11 and the conduction / interruption state of the switch 103.

  The operation circuit 120 changes the start timing of the conduction of the first switch element 101 according to the potential difference before and after the switch 103. When there is no potential difference before and after the switch 103, the operating circuit 120 starts to charge the capacitor 111 more than when there is a potential difference before and after the switch 103 because the DC voltage rises by turning on the DC power supply 11. Speed up the timing.

  The actuation circuit 120 blocks the second switch element 102 when there is no potential difference before and after the switch 103. That is, when the DC power supply 11 is stopped and the switch 103 is conductive, the second switch element 102 is cut off.

  The operation circuit 120 makes the second switch element 102 conductive when there is a potential difference before and after the switch 103. That is, when the DC power supply 11 is operating and the switch 103 is cut off, the second switch element 102 is turned on.

  The operation circuit 120 compares the potential difference between the input side and the output side of the switch 103 with the comparator 121. The comparator 121, which is an example of a comparison circuit, operates by a potential difference before and after the switch 103 to switch between conduction and interruption of the second switch element 102. The comparator 121 operates between the power supply voltage and the ground potential, and operates when the power supply voltage is 2V or more.

  The + terminal of the comparator 121 is connected to an intermediate point between the resistor 125 and the resistor 126 in the series circuit of the resistor 125 and the resistor 126 connected to the output side of the switch 103. The negative terminal of the comparator 121 is connected to an intermediate point between the resistor 123 and the resistor 124 in the series circuit of the Zener diode 122, the resistor 123, and the resistor 124 connected to the input side of the switch 103. The Zener voltage of the Zener diode 122 corresponds to a threshold voltage that switches between conduction and interruption of the second switch element 102.

  When the switch 103 is cut off while the DC power supply 11 maintains the DC voltage, the potential difference between the input side and the output side of the switch 103 is 24 V, which exceeds the Zener voltage of the Zener diode 122. When the potential difference between the input side and the output side of the switch 103 exceeds the Zener voltage of the Zener diode 122, a current flows through the series circuit of the resistor 123 and the resistor 124, and the potential of the negative terminal of the comparator 121 is greater than the potential of the positive terminal. Also gets higher. As a result, the comparator 121 outputs a low level (ground potential) to make the second switch element 102 conductive.

  When the DC power supply 11 starts up in a state where the switch 103 is conductive, the potential difference between the input side and the output side of the switch 103 is 0 V, which is equal to or less than the Zener voltage of the Zener diode 122. If the potential difference between the input side and the output side of the switch 103 is equal to or less than the Zener voltage of the Zener diode 122, no current flows through the series circuit of the resistor 123 and the resistor 124, and the potential of the negative terminal of the comparator 121 becomes the ground potential. , Lower than the potential of the + terminal. As a result, the comparator 121 outputs a high level to shut off the second switch element 102.

  The charging circuit 110, the second switch element 102, and the operation circuit 120, which are an example of the switch element operation circuit, are connected to the first switch element 101 when the DC power supply 11 is started and when the switch 103 is turned OFF / ON. Different conduction timing. In the state where the DC power supply 11 is stopped and the switch 103 is turned on, the source / gate is increased in the process of increasing the voltage applied to the input terminal (S) than in the state where the DC power supply 11 is activated and the switch 103 is cut off. The voltage at which the potential difference between them begins to increase is lowered.

(Operation when starting DC power supply)
FIG. 5 is a time chart of the operation of the inrush current prevention circuit of the first embodiment. In FIG. 5, (a) is the ON / OFF of the switch, (b) is the DC voltage of the DC power supply, (c) is the voltage on the output side of the switch, (d) is the on / off state of the first switch, ) Is the conduction / cutoff of the second switch element, and (f) is the charging voltage.

  As shown in FIG. 5A, when the power supply to the DC power supply 11 is started, the DC voltage rises gently.

  As shown in FIG. 5E, the second switch element 102 is cut off (opened) at the start of rising of the DC voltage. Therefore, as shown in FIG. 5 (f), charging of the capacitor 111 starts from the start of rising of the DC voltage. When the charging voltage of the capacitor 111 reaches the threshold voltage of the first switch element 101, the conduction of the first switch element 101 starts.

  As shown in FIG. 5D, the continuity of the first switch element 101 is gradually increased, and the voltage applied to the smoothing capacitor 106 from the drain D of the first switch element 101 is gradually increased to increase the inrush current. Is prevented.

(Operation when the switch is OFF / ON)
As shown in FIG. 5B, when the switch 103 is turned off, the source potential of the first switch element 101 decreases. Thereafter, when the switch 103 is turned on, the source potential of the first switch element 101 rises.

  As shown in FIG. 5C, after the switch 103 is turned OFF, the potential difference between the input side (DC voltage) and the output side (source potential) of the switch 103 is increased, and the output of the comparator 121 is inverted, and the second The switch element 102 becomes conductive.

  As shown in FIG. 5 (e), when the second switch element 102 changes from cutoff (open) to conduction (short), the charging voltage of the capacitor 111 is rapidly discharged, and the first switch element 101 becomes Turns off rapidly.

  As shown in FIG. 5C, after the switch 103 is turned on, the potential difference between the input side (DC voltage) and the output side (source potential) of the switch 103 is decreased, and the output of the comparator 121 is inverted to cause the second output. The switch element 102 is cut off.

  As shown in FIG. 5E, when the second switch element 102 changes from conduction (short) to cutoff (open), charging of the capacitor 111 by the source voltage is started and the charge voltage gradually increases. When the charging voltage of the capacitor 111 reaches the threshold voltage of the first switch element 101, the conduction of the first switch element 101 starts.

  As shown in FIG. 5D, the continuity of the first switch element 101 is gradually increased, and the voltage applied to the smoothing capacitor 106 from the drain D of the first switch element 101 is gradually increased to increase the inrush current. Is prevented.

  As shown in FIG. 5C, the source voltage at which the potential difference between the source and the gate starts increasing when the DC power supply 11 is stopped and the switch 103 is conductive is Vi. On the other hand, the source voltage at which the potential difference between the source and the gate starts increasing in the state where the DC power supply 11 is operating and the switch 103 is cut off is Vj. Vi is lower than Vj.

  In the first embodiment, as shown in FIG. 5 (f), the conduction of the second switch element 102 (initialization of the charging circuit 110) is released from the beginning of the rise of the DC power supply 11. As shown in FIG. 7A, charging of the capacitor 111 is started without waiting for the DC voltage to rise to a specific voltage, so that the start of conduction of the first switch element 101 is accelerated.

(Effect of Embodiment 1)
In the first embodiment, charging of the charging circuit 110 can be started immediately after the DC power supply 11 is turned on. For this reason, when the DC power supply 11 is turned on, there is no need to provide a time lag until the DC voltage on the load terminal 15 rises, and the supply of the DC voltage to the loads (12, 13) can be started quickly.

  In Embodiment 1, since the potential difference before and after the switch 103 is detected and the charging circuit 110 is initialized, the charging circuit 110 can be initialized without waiting for the output voltage of the DC power supply 11 to rise. Therefore, charging of the charging circuit 110 can be started simultaneously with the rise of the DC power supply 11.

  In the first embodiment, when the DC power supply 11 is started up, the inrush current is effectively regulated, the delay in power supply from the DC power supply 11 is eliminated, and the load (12, 12) connected to the inrush current prevention circuit 20 is eliminated. 13) The delay of the power supply to 13) can be reduced.

  In the first embodiment, it is possible to shorten the time until the power supply to the load (12, 13) through the inrush current prevention circuit 20 is started. The start-up of the image forming apparatus 10 when the power is turned on is quickened, and the start of the image forming operation can be accelerated.

  In the first embodiment, the second switch element 102 is switched between conduction and cutoff according to the potential difference before and after the switch 103. The second switch element 102 is switched between conduction and interruption according to the operation / stop state of the DC power supply 11 and the conduction / interruption state of the switch 103. For this reason, when the DC power supply 11 is activated and when the switch 103 is turned on, the timing when the first switch element 101 is turned on after the start of the increase of the source voltage can be varied without impairing the inrush current regulation performance. .

  In the first embodiment, when there is no potential difference before and after the switch 103, the second switch element 102 is cut off. When the DC power supply 11 is stopped and the switch 103 is conductive, the second switch element 102 is cut off. For this reason, charging of the charging circuit 110 can be started immediately when the DC power supply 11 is started.

  In Embodiment 1, when there is a potential difference before and after the switch 103, the second switch element 102 is made conductive. When the DC power supply 11 is operating and the switch 103 is cut off, the second switch element 102 is made conductive. Therefore, when the switch 103 is turned off, the charging circuit 110 is quickly discharged to cut off the first switch element 101, and the inrush current when the switch 103 is turned on next time is reliably regulated. be able to.

  In the first embodiment, since the analog element comparator 121 is used, the operating circuit 120 can function reliably even under a low power supply voltage due to the DC power supply 11 being stopped or the like.

  In the first embodiment, since the Zener diode 122 having the Zener voltage corresponding to the threshold voltage for switching between conduction and interruption of the second switch element 102 is provided, the circuit output is sharply changed by the threshold voltage and the second switch element is changed. 102 can be reliably turned on / off.

  In the first embodiment, when the DC power supply 11 is stopped and the switch 103 is conductive, the voltage applied to the input terminal (S) is higher than when the DC power supply 11 is operating and the switch 103 is cut off. The voltage at which the potential difference starts to change during the rising process is lowered. For this reason, charging of the charging circuit 110 can be started immediately when the DC power supply 11 is started.

<Other embodiments>
The inrush current regulating circuit of the present invention is not limited to the specific configuration of each part, combination of electronic components, voltage type, voltage positive / negative, and semiconductor element characteristics in the first embodiment. Another embodiment in which a part or all of the configuration of the first embodiment is replaced with an equivalent member is also possible.

  The MOSFET used for the first switch element 101 is not limited to the enhancement type that conducts due to the potential difference between the source and the gate. A blocking depletion type may be employed depending on the potential difference between the source and the gate. Either an N-type channel junction type or a P-channel junction type may be used. The first switch element 101 is not limited to a MOSFET but may be a normal transistor element. However, the peripheral circuit needs to be changed according to the type (characteristic) of the transistor element.

  The switch 103 is not limited to a cover switch that conducts / cuts off according to the opening / closing of the cover 10C. It may be a manually operated power switch, or may be replaced with a reed switch, a bimetal contact, a relay contact or the like.

  The image forming apparatus 10 is not limited to an apparatus that performs an electrophotographic image forming process. You may replace with an inkjet printer, an offset printing apparatus, etc.

  The power supply apparatus 10D can also be mounted in a general apparatus other than the image forming apparatus provided with a DC power supply.

DESCRIPTION OF SYMBOLS 10: Image forming apparatus, 10B: Housing | casing, 10C: Cover, 12: Motor, 13: Control part, 101: 1st switch element (switch element, 1st switch element), 102: 2nd switch element (1st 2 switch element), 103: switch, 104, 105, 112, 123, 124, 125, 126, 127, 128: resistor, 106: smoothing capacitor, 110: charging circuit, 111: capacitor, 120: operating circuit, 121: Comparator (comparison circuit), 122: Zener diode, D: Drain (output terminal), G: Gate (control terminal), S: Source (input terminal)

Claims (12)

A first switch element that changes conductivity between the input terminal and the output terminal according to a potential difference between the input terminal and the control terminal;
A charging circuit that changes the potential difference by being charged with a voltage applied to the input terminal;
A second switch element that discharges the charging circuit by the conduction and enables the charging circuit to be charged by the interruption;
A switch disposed between a power source and the input terminal;
And a switching circuit that switches between conduction and interruption of the second switch element in accordance with a potential difference before and after the switch.   2. The inrush current regulating circuit according to claim 1, wherein the switching circuit blocks the second switch element when there is no potential difference before and after the switch.   3. The inrush current regulating circuit according to claim 2, wherein the switching circuit conducts the second switch element when there is a potential difference before and after the switch. 4.   4. The rush according to claim 1, wherein the switching circuit includes a comparison circuit that operates by a potential difference before and after the switch to switch between conduction and interruption of the second switch element. 5. Current regulation circuit.   5. The inrush current regulating circuit according to claim 4, wherein the comparison circuit includes a Zener diode having a Zener voltage corresponding to a threshold voltage for switching between conduction and interruption of the second switch element. A first switch element that changes conductivity between the input terminal and the output terminal according to a potential difference between the input terminal and the control terminal;
A charging circuit that changes the potential difference by being charged with a voltage applied to the input terminal;
A second switch element that discharges the charging circuit by the conduction and enables the charging circuit to be charged by the interruption;
A switch disposed between a power source and the input terminal;
An inrush current regulation circuit comprising: a switching circuit that switches between conduction and interruption of the second switch element according to the state of the power source and the state of the switch.   The inrush current regulating circuit according to claim 6, wherein the switching circuit cuts off the second switch element when the power supply is stopped and the switch is turned on.   8. The inrush current regulating circuit according to claim 7, wherein the switching circuit conducts the second switch element in a state where the power source is operated and the switch is cut off. A switch element that changes electrical conductivity between the input terminal and the output terminal according to a potential difference between the input terminal and the control terminal;
A switch disposed between a power source and the input terminal;
In the state where the power supply is stopped and the switch is turned on, the voltage at which the potential difference starts to change in the process of increasing the voltage applied to the input terminal is higher than in the state where the power supply is activated and the switch is cut off. An inrush current regulating circuit, comprising: a switch element operating circuit that operates the switch element so as to be low. Inrush current regulation circuit according to any one of claims 1 to 9,
The power source;
A power supply device comprising: a smoothing capacitor connected to the output terminal for smoothing a voltage supplied to a load. Inrush current regulation circuit according to any one of claims 1 to 9,
The power source;
A smoothing capacitor connected to the output terminal;
An image forming apparatus comprising: a motor that operates with a voltage smoothed by the smoothing capacitor. The image forming apparatus has a cover on a housing,
The switch is a cover switch that shuts off the power supply and the input terminal by opening the cover and closes the cover to connect the power supply and the input terminal. The image forming apparatus according to claim 11.

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