JP2012005317A - Dc power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC power supply circuit that can stop detecting a transient overcurrent if the transient overcurrent flows through a voltage conversion circuit during a rush current limitation period.SOLUTION: The DC power supply circuit provides a DC power supply input voltage which is applied to an input terminal to a load connected to an output terminal through a voltage conversion circuit. The DC power supply circuit comprises: a rush current limiting circuit for limiting a rush current, which flows into a voltage holding capacitor that is connected between the input terminals when the input voltage is applied, by a control signal from a rush current control circuit for a predetermined period; and an overcurrent detection circuit that makes switch means which connects an output of the voltage conversion circuit to the load open, when a current flowing into the voltage conversion circuit is equal to or greater than a specified value. The DC power supply circuit provides an overcurrent detection ignoring means for stopping the switch means operation by the overcurrent detection circuit during the predetermined period of limiting the rush current.

Description

  The present invention is a DC power supply circuit that applies an input voltage of a DC power supply applied to an input terminal to a load connected to an output terminal via a voltage conversion circuit, and is connected between the input terminals when the input voltage is applied. An inrush current limiting circuit for limiting the inrush current flowing into the voltage holding capacitor, which is limited to a predetermined time by a control signal from the inrush current control circuit, and when the current flowing into the voltage conversion circuit is a predetermined value or more, The present invention relates to a DC power supply circuit comprising an overcurrent detection circuit that opens a switch means for connecting an output of a voltage conversion circuit and the load.

  FIG. 5 is a functional block diagram showing a configuration example of a conventional DC power supply circuit. The basic configuration of the DC power supply circuit is such that the input voltage Vin of the DC power supply 1 applied to the input terminals T1 and T2 is converted into the voltage Vout via the voltage conversion circuit 6, and the load 2 connected to the output terminals T3 and T4. To give.

  The inrush current limiting circuit 3 limits the inrush current Ir1 flowing into the voltage holding capacitor 4 connected between the input terminals T1 and T2 for a predetermined time when the input voltage Vin is applied. The inrush current limiting circuit 3 includes an inrush current limiting resistor 31 (R1), a short-circuit switch 32 (SW1) connected in parallel to the inrush current limiting resistor 31, and an inrush current control for opening and closing the short-circuit switch 32 with an operation signal P. A circuit 33 is provided.

  The inrush current control circuit 33 opens the short-circuit switch 32 (SW1) when the input voltage Vin is applied by the operation signal P, and is output when the input voltage of the voltage conversion circuit 6 reaches a predetermined operating voltage. The restriction release signal S is acquired and the short-circuit switch 32 (SW1) is operated to close.

  When the current Ir2 flowing into the voltage conversion circuit 6 is greater than or equal to a predetermined value, the overcurrent detection circuit 5 opens the switch means 62 (SW2) that connects the output of the voltage conversion circuit 6 described later and the load 2. The output voltage supply to the load 2 is cut off.

  The overcurrent detection circuit 5 includes a current detection resistor 51 (R2) for the current Ir2, a current / voltage conversion circuit 52 that converts a voltage generated in the current detection resistor 51 into a detection voltage Vir2 of a predetermined span, and a detection voltage Vir2. The comparator 53 is configured to compare the overcurrent detection set voltage Vocd1 and output an overcurrent detection signal C1 when Vir2> Vocd1.

  The main component of the voltage conversion circuit 6 is a DC / DC converter 61 composed of a switching regulator or the like. The DC / DC converter 61 receives the inter-terminal voltage Vcap of the capacitor 4 and applies the output voltage Vout converted into a predetermined constant voltage to the load 2 connected to the output terminals T3 and T4 via the switch means 62 (SW2). give.

  The voltage conversion circuit 6 compares the input voltage Vcap of the DC / DC converter 61 with the operation start setting voltage Vreg, and inputs the operation start signal C2 with a comparator 63 that outputs an operation start signal C2 in a state of Vcap> Vreg. And a logic circuit 64 for operating the switch means 62 to open when Vcap ≦ Vreg, and operating the switch means 62 (SW2) to close when Vcap> Vreg.

  The logic circuit 64 also receives the overcurrent detection signal C1, and in the state of Vir2> Vocd1, forcibly operates the switch means 62 (SW2) to cut off the supply of the output voltage Vout to the load 2, Prevent current.

  FIG. 6 is a waveform diagram for explaining the operation of FIG. FIG. 6A shows the DC voltage Vin applied stepwise between the input terminals T1 and T2 at time t1. FIG. 6B shows the inter-terminal voltage Vcap of the capacitor 4 that rises at a predetermined time constant due to the resistance value R1 of the inrush current limiting resistor 31 and its own capacitance from time t1.

  Here, Vcap is an input voltage of the DC / DC converter 61. The level Vreg set for Vcap in FIG. 6B is the operation start voltage of the DC / DC converter 61, and Vrated is the rated output voltage of the DC / DC converter 61, which is the output voltage Vout for the load 2. .

  FIG. 6C shows the operation of the short-circuit switch 32 (SW1) connected in parallel to the inrush current limiting resistor 31 (R1). The short-circuit switch 32 (SW1) is operated to open when Vin is applied at time t1 and is in an inrush current limiting mode, but is output when the DC / DC converter 61 reaches the rated output voltage Vrated at time t3. From the restriction release signal S, the operation signal P from the inrush current control circuit 33 is operated from open to close. Thereby, the power loss of Ir1 × R1 is eliminated.

  FIG. 6D shows a waveform of the inrush current Ir1 flowing through the inrush current limiting circuit 3. It falls after reaching a predetermined peak value by the function of the inrush current limiting circuit 3 operating from time t1. After Vcap reaches Vreg at time t2, the switch means 62 (SW2) is operated to close and the operation of the DC / DC converter 61 is started, so that Ir1 rises again.

  6E shows a waveform of the input current Ir2 of the DC / DC converter 61. FIG. Although the flow of Ir2 starts at time t2, the DC / DC converter 61 operates at a constant power, so that the input current Ir2 increases when the input voltage Vcap is lower than the rated voltage Vrated. This is a transient overcurrent.

  Ir2 rises, a transient overcurrent flows in the middle of the period T during which the inrush current is restricted at times t1 to t3, and the overcurrent detection voltage Vir2 exceeds the overcurrent detection setting voltage Vocd1 during the predetermined period τ Will occur.

  FIG. 6F shows the waveform of the output C1 of the comparator 53 of the overcurrent detection circuit 5. That is, the output C1 of the comparator 53 transitions to the H state in a predetermined period τ in the middle of the period T during which the inrush current is limited.

  Since the logic circuit 64 to which the comparator output C1 is input forcibly operates the switch means 62 (SW2) to open by the transition of C1, the supply of the output voltage of the DC / DC converter 61 to the load 2 is cut off.

  FIG. 6G shows the waveform of the output voltage Vout of the DC / DC converter 61 applied to the load 2. The voltage rising from the operation start time of the DC / DC converter 61 at time t2 toward the rated voltage Vrated at time t3 is forced to open the switch means 62 (SW2) for overcurrent detection during a predetermined period τ. To be operated. As a result, the current supply to the load 2 is interrupted, so that the output voltage Vout decreases according to the time constant of the load 2.

  When the operation of the overcurrent detection circuit 5 stops after the elapse of the period τ and the output C1 of the comparator 53 transitions to L, the switch means 62 returns to the closed state, so that the output voltage Vout rises again, and at time t3, DC / The rated output voltage Vrated of the DC converter 61 is reached, and this voltage is maintained thereafter.

JP-A-5-219733

  In general, since the power supplied to the DC / DC converter 61 is constant, a transient overcurrent Ir2 flows in the period of the input voltage Vcap during the inrush current limiting period and Vrated> Vcap> Vreg. When the transient overcurrent Ir2 is detected by the overcurrent detection circuit 5, the supply of the output voltage of the voltage conversion circuit 6 to the load 2 is stopped for a certain period (τ). Therefore, as shown in FIG. 6G, distortion occurs in the rising waveform of the output voltage Vout.

  An object of the present invention is to realize a DC power supply circuit capable of stopping the detection of this overcurrent even if a transient overcurrent flows through the voltage conversion circuit during the inrush current limiting period.

In order to achieve such a subject, the present invention has the following configuration.
(1) A DC power supply circuit that applies an input voltage of a DC power supply applied to an input terminal to a load connected to an output terminal via a voltage conversion circuit, and is connected between the input terminals when the input voltage is applied. An inrush current limiting circuit that limits the inrush current flowing into the voltage holding capacitor by a control signal from the inrush current control circuit for a predetermined time, and when the current flowing into the voltage conversion circuit is a predetermined value or more, the voltage In a DC power supply circuit comprising: an overcurrent detection circuit that opens a switch means that connects an output of a conversion circuit and the load;
A DC power supply circuit comprising: overcurrent detection invalidating means for stopping operation of the switch means by the overcurrent detection circuit during the predetermined time during which the inrush current is limited.

(2) The DC power supply according to (1), wherein the overcurrent detection invalidating means stops an output of a comparator forming the overcurrent detection circuit according to a control signal from the inrush current control circuit. circuit.

(3) The overcurrent detection invalidating means changes a set value of overcurrent detection for a comparator forming the overcurrent detection circuit according to a control signal from the inrush current control circuit (1) DC power supply circuit described in 1.

(4) The inrush current control circuit outputs the control signal based on an operation signal given from the voltage conversion circuit during a period in which the input voltage of the voltage conversion circuit reaches a rated output value after exceeding a predetermined value. The DC power supply circuit according to any one of (1) to (3).

(5) The voltage conversion circuit includes switch operation means for opening the switch means during a period from when the DC power supply is applied until the input voltage of the voltage conversion circuit exceeds a predetermined value. The DC power supply circuit according to any one of (1) to (4).

(6) The DC power supply circuit according to any one of (1) to (5), wherein the voltage conversion circuit is a DC / DC converter that controls an applied voltage to the load to a constant value.

  According to the present invention, it is possible to stop overcurrent detection of the overcurrent detection circuit with respect to a transient overcurrent that occurs during a period during which the inrush current is limited, and the rising waveform of the output voltage Vout Can be prevented from occurring.

It is a functional block diagram which shows one Example of the DC power supply circuit to which this invention is applied. It is a wave form diagram explaining the operation | movement of FIG. It is a functional block diagram which shows the other Example of the DC power supply circuit to which this invention is applied. It is a wave form diagram explaining the operation | movement of FIG. It is a functional block diagram which shows the structural example of the conventional DC power supply circuit. FIG. 6 is a waveform diagram for explaining the operation of FIG. 5.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a functional block diagram showing an embodiment of a DC power supply circuit to which the present invention is applied. The same elements as those of the conventional circuit described with reference to FIG.

  The basic configuration of the DC power supply circuit to which the present invention is applied is the same as the conventional configuration described with reference to FIG. 5 and the operation described with reference to FIG. The feature of the present invention added to the conventional configuration is that an operation signal P of the inrush current control circuit 33 that operates opening and closing of the short circuit switch 32 is led to an OE (Output Enable) terminal of the comparator 53 of the overcurrent detection circuit 5. The current detection invalidating means 100 is provided.

  Since the operation signal P is held at the L level from the time when the DC voltage Vin is applied until the inrush current limit release command S indicating the start of operation of the DC / DC converter is generated, the inrush current limit is utilized using this signal P. The function of the comparator 53 is stopped in synchronization with the period, and the generation of the output C1 is prevented.

  By preventing the output C1 of the comparator 53 from occurring, even if a transient overcurrent Ir2 flows through the DC / DC converter 61 during the inrush current limit period, it is possible to prevent this from being detected. Thus, there is no possibility of distortion occurring in the rising waveform of the output voltage Vout.

  FIG. 2 is a waveform diagram for explaining the operation of FIG. 2A to 2G correspond to FIGS. 6A to 6G. 2A to 2E show the same waveforms as those in FIGS. 6A to 6E, and redundant description is omitted.

  FIG. 2F shows the waveform of the output C1 of the comparator 53 of the overcurrent detection circuit 5. Since the overcurrent detection function is stopped during the inrush current limiting period, the transition of the output C1 of the comparator 53 does not occur even if the transient overcurrent Ir2 flows through the DC / DC converter 61, and the switch Means 62 remains closed. Accordingly, as shown in FIG. 2G, the output voltage Vout does not fluctuate during the inrush current limiting period, and a smooth rise characteristic can be realized.

  FIG. 3 is a functional block diagram showing another embodiment of the DC power supply circuit to which the present invention is applied. The difference from the embodiment shown in FIG. 1 is that the function of the comparator 53 of the overcurrent detection circuit 5 is not stopped during the inrush current limit period, and the overcurrent detection set voltage during the inrush current limit period is changed from the steady value Vocd1. In this configuration, the transient current is not detected and the setting voltage Vocd2 is higher than that of Vocd1.

  The changeover switch 54 for switching the overvoltage detection set voltage Vocd1 and the set voltage Vocd2 to be supplied to the set terminal of the comparator 53 is changed over by an operation signal P from the inrush current control circuit 33.

  FIG. 4 is a waveform diagram for explaining the operation of FIG. The waveforms in FIGS. 4A to 4G are the same as the waveforms in FIGS. 2A to 2G, and redundant description is omitted. 4H added between FIG. 4D and FIG. 4E shows changes in the setting voltage Vocd1 and the setting voltage Vocd2 of the setting terminal of the comparator 53 switched by the changeover switch 54. FIG.

  The set voltage of the comparator 53 is maintained at a high set voltage Vocd2 that does not detect the transient overcurrent Ir2 during the inrush current limiting period from time t1 to time t3, and is a steady set voltage after the inrush current limiting period after t3 ends. It is switched to Vocd1.

  By such switching, the overcurrent detection circuit 5 does not detect the transient overcurrent Ir2 even during the inrush current limit period. Therefore, the output C1 of the comparator 53 does not change, and the switch means 62 (SW2) is not operated to be opened. As a result, as in the embodiment of FIG. 1, as shown in FIG. 4G, the output voltage Vout does not fluctuate during the inrush current limiting period, and a smooth rise characteristic can be realized.

DESCRIPTION OF SYMBOLS 1 DC power supply 2 Load 3 Inrush current limiting circuit 31 Inrush current limiting resistance 32 Short-circuit switch 33 Inrush current control circuit 4 Capacitor 5 Overcurrent detection circuit 51 Current detection resistance 52 Current / voltage conversion circuit 53 Comparator 6 Voltage conversion circuit 61 DC / DC Converter 62 Switch means 63 Comparator 64 Logic circuit

Claims (6)

A DC power supply circuit for applying an input voltage of a DC power supply applied to an input terminal to a load connected to an output terminal via a voltage conversion circuit, and holding the voltage connected between the input terminals when the input voltage is applied An inrush current limiting circuit for limiting the inrush current flowing into the capacitor for a predetermined time by a control signal from the inrush current control circuit, and when the current flowing into the voltage conversion circuit is a predetermined value or more, the voltage conversion circuit In a DC power supply circuit comprising: an overcurrent detection circuit that opens a switch means for connecting an output and the load;
A DC power supply circuit comprising: overcurrent detection invalidating means for stopping operation of the switch means by the overcurrent detection circuit during the predetermined time during which the inrush current is limited.   2. The DC power supply circuit according to claim 1, wherein the overcurrent detection invalidating unit stops an output of a comparator forming the overcurrent detection circuit according to a control signal from the inrush current control circuit.   The overcurrent detection invalidating means changes a set value of overcurrent detection for a comparator forming the overcurrent detection circuit according to a control signal from the inrush current control circuit. DC power supply circuit.   The inrush current control circuit outputs the control signal based on an operation signal given from the voltage conversion circuit during a period when the input voltage of the voltage conversion circuit reaches a rated output value after exceeding a predetermined value. The DC power supply circuit according to any one of claims 1 to 3.   The voltage conversion circuit includes switch operation means for opening the switch means during a period from when the DC power supply is applied until the input voltage of the voltage conversion circuit exceeds a predetermined value. Item 5. The DC power supply circuit according to any one of Items 1 to 4.   6. The DC power supply circuit according to claim 1, wherein the voltage conversion circuit is a DC / DC converter that controls a voltage applied to the load to a constant value.

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