JP2005020928A - Power supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a delay time for turning on a switch is different depending on the input voltage and the state of a load or the like, therefore, it is hard to obtain an optimum value of the delay time, and, as a result, a large rush current flows and a current limiting element is abnormally heated. <P>SOLUTION: A switching element is connected in parallel to the current limiting element for limiting the rush current. When a reset signal to be supplied to the load is asserted, the switching element is turned off. When the reset signal is negated, the switching element is turned on. The switching element maintains the off-state until an input capacitor completes the charging. Accordingly, a large secondary rush current does not flow. And, when the reset of the load is released, the switching element is turned on. As a result, it is possible to prevent the occurrence of abnormal heating and burnout of the current limiting element caused by the increase of a load current. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

BACKGROUND OF THE INVENTION
The present invention relates to a power supply device that limits inrush current at startup with a simple configuration.
[0001]
[Prior art]
FIG. 4 shows the configuration of the power supply device that limits the inrush current at the time of startup.
In the power supply device shown in FIG. 4, an input voltage is supplied to input voltage terminals Vin + and Vin− of the converter circuit 9, and this input voltage is converted to Vout and supplied to a load (not shown). C1 is a large-capacitance capacitor connected to the input side of the converter circuit 9.
[0002]
In such a power supply device, when the input voltage is applied, the capacitor C1 appears to be in a short-circuit state, and thus a very large inrush current may flow toward the capacitor C1.
[0003]
The inrush current is maximum E / Rin and may reach 50 to 100 A, where Rin is the impedance from the input voltage terminals Vin + and Vin− to the capacitor C1 and E is the voltage value of the input voltage.
[0004]
When such a large inrush current flows, elements inside the power supply device such as fuses and rectifier elements may be damaged. Also, external wiring and breakers must be able to withstand this large inrush current.
[0005]
In addition, the power supply voltage may drop temporarily, adversely affecting other devices connected to the same system, and the protection device of the device that supplies the power supply voltage may be activated, making it impossible to start up. is there.
[0006]
In order to prevent such a large inrush current from flowing, an input voltage is supplied to the converter circuit 9 via a resistor 6 which is a current limiting element having a switch 7 connected in parallel.
[0007]
When the input voltage is not supplied, the switch 7 is turned off, and the switch is turned on after the output voltage Vout becomes constant. An input voltage or an output voltage of an auxiliary winding wound around a switching transformer may be used instead of the output voltage Vout.
[0008]
However, if the switch 7 is turned on when the output voltage, the input voltage, and the auxiliary winding voltage reach predetermined values, the switch 7 is turned on before the capacitor C1 is completely charged. Cannot be prevented. Therefore, the delay circuit 8 delays these signals by a predetermined time so that the switch 7 is turned on.
[0009]
In Patent Document 1, in an AC / DC converter that converts alternating current to direct current, a resistor in which a triac is connected in parallel is inserted between an input terminal and a rectifying element that converts alternating current to direct current, and an auxiliary winding wound around a switching transformer. An invention of an inrush current limiting circuit is described in which the triac is turned on when a voltage obtained by rectifying and smoothing a voltage induced in a line exceeds a predetermined value. The present invention basically has the same function as the inrush current limiting circuit of FIG.
[0010]
In Patent Document 2, in a power supply device that converts alternating current into direct current and outputs, a triac is inserted between the input terminal and the rectifying element to rectify the voltage induced in the auxiliary winding wound around the switching transformer. An invention of an inrush current limiting circuit is described in which a voltage is smoothed by a smoothing circuit having a predetermined time constant, and the triac is turned on with the smoothed voltage. The basic operation of this invention is the same as that of the inrush current limiting circuit of FIG.
[Patent Document 1]
JP-A-5-292749 [Patent Document 2]
JP-A-8-191570 [Problems to be Solved by the Invention]
However, such an inrush current limiting circuit has the following problems.
[0011]
The delay time set in the delay circuit 8 must be longer than the time for completing the charging of the capacitor C1. However, the time for completing charging varies depending on the value of the input voltage, its rise time, or the state of the load.
[0012]
Further, a problem occurs even if the delay time set in the delay circuit 8 is too long. Therefore, the delay time has to be set assuming various conditions, and there is a problem that it is difficult to find an optimum value.
[0013]
On the other hand, if the delay time is too short, the switch 7 is turned on while the capacitor C1 is not sufficiently charged, so that a large secondary inrush current flows. The magnitude of the secondary inrush current is (Vin−Vc) / Ron, where Vin is the input voltage, Vc is the voltage across the capacitor C1 when the switch 7 is turned on, and Ron is the on-resistance of the switch 7.
[0014]
On the other hand, if the delay time is too long, the load rises before the switch 7 is turned on and the load current increases. As a result, excessive current flows through the resistor 6 to cause abnormal heat generation or burnout if it is severe. There is also.
[0015]
Furthermore, although it is rare, if the delay time is too long, the power supply may repeatedly turn on and off several times and start up. When the input voltage is turned on, the reset is released, the load is activated, and the current increases. As a result, the current flowing through the resistor 6 increases and the voltage drop increases, the voltage across the capacitor C1 decreases, and the output voltage decreases. For this reason, the reset of the load is again applied, the current flowing through the load is decreased, and the output voltage is increased again. This process is repeated until the switch 7 is turned on.
[0016]
Therefore, the object of the present invention is to control the switch that short-circuits the resistor that limits the inrush current by the reset signal supplied to the load, so that it can always start in the optimum state even if the input voltage or load state changes. An object of the present invention is to provide a power supply device including an inrush current limiting circuit that can be used.
[0017]
[Means for Solving the Problems]
In order to solve such a problem, the invention according to claim 1 of the present invention converts the input power into power to be supplied to the load and outputs the power, and the converter circuit inputs the power. A current limiting element that is installed in the middle of the line through which the current flows, limits the inrush current, and the output voltage of the converter circuit is input. After the power is supplied to the converter circuit, the output voltage is stabilized for a predetermined time. A reset signal output circuit for outputting a reset signal supplied to the load, which is maintained in an asserted state until a time elapses, and is connected in parallel to the current limiting element, and the reset signal is controlled to be off during the assertion, and the reset And a switch that is turned on when the signal is negated. Even if the input voltage or load state changes, the switch can be controlled at the optimum timing.
[0018]
According to a second aspect of the present invention, in the first aspect of the present invention, the switch is controlled by a photocoupler to which a signal related to the reset signal is input. It can be used even if the input and output of the converter circuit are insulated.
[0019]
According to a third aspect of the present invention, in the first or second aspect of the present invention, the reset signal output circuit is installed inside the converter circuit. Miniaturization is possible.
[0020]
According to a fourth aspect of the invention, in the invention according to any one of the first to third aspects, a P-channel MOSFET is used as the switch. Miniaturization is possible.
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a configuration diagram showing an embodiment of a power supply device including an inrush current limiting circuit according to the present invention.
[0021]
In addition, the same code | symbol is attached | subjected to the same element as FIG. 4, and description is abbreviate | omitted.
In FIG. 1, reference numeral 1 denotes a switch element having a drain D and a source S connected to both ends of an inrush current limiting resistor 6, which functions in the same manner as the switch 7 in FIG. In this embodiment, a P-channel MOSFET is used as the switch element 1.
[0022]
R1 and R2 are resistors for applying an appropriate voltage to the gate G of the switch element 1, the resistor R1 is between the input voltage terminal Vin + and the gate G of the switch element 1, and the resistor R2 is a gate G and a transistor 2 described later. Connected between collectors.
[0023]
The resistance values of the resistors R1 and R2 are set so that the gate-source voltage V _GS when the switch element 1 is turned on is, for example, −10V.
[0024]
Reference numeral 2 denotes a transistor having a collector connected to one end of the resistor R2 and an emitter connected to the input voltage terminal Vin−. Further, a reset signal XRESET described later is input to the base via a resistor R3. Further, a resistor R4 is connected between the base and the input voltage terminal Vin−. The resistor R3 is a base resistor, and R4 is a bleeder resistor.
[0025]
Reference numeral 3 denotes a converter circuit, which receives an input voltage applied to input voltage terminals Vin + and Vin− through a resistor 6 and converts the input voltage into an output voltage Vout for output. The capacitor C1 is a large capacity capacitor connected to the input side of the converter circuit 3.
[0026]
31 is a reset signal output circuit built in the converter circuit 3, and maintains a low level for a predetermined period after the output voltage Vout of the converter circuit 3 is stabilized after the input voltage is applied to the input terminals Vin + and Vin−. The reset signal XRESET to be output is output. This reset signal XRESET is input to the base of the transistor 2 via the resistor R3.
[0027]
Generally, in a power supply used for a logic circuit such as a microprocessor, a power supply voltage supplied to the logic circuit or the like for several tens of milliseconds until the clock frequency is stabilized when the power is turned on or when the power is cut off. When it drops and the operation becomes indeterminate, the operation must be stopped.
[0028]
The power supply device outputs a reset signal for this purpose. While the reset signal is at a low level (asserted), the logic circuit or the like is in a reset state, and its current consumption becomes a low value. When the reset signal becomes high level (negate), the logic circuit starts to operate, and the current consumption increases.
[0029]
Reference numeral 4 denotes a load device to which the output voltage Vout of the converter circuit 3 is input. That is, power is supplied from the converter circuit 3. Further, a reset signal XRESET, which is an output of the reset signal output circuit 31, is input, and the reset signal XRESET is reset.
[0030]
Next, the operation of this embodiment will be described.
As described above, after the input voltage is applied to the converter circuit 3 and the output voltage of the converter circuit 3 is stabilized, the reset signal XRESET is maintained at a low level for a predetermined period.
[0031]
Therefore, the transistor 2 is turned off, and the gate G of the switch element 1 becomes the voltage of the input voltage terminal Vin +. As a result, the switch element 1 is turned off, the charging current of the capacitor C1 is limited by the resistor 6, and a large inrush current does not flow. Further, since the reset signal XRESET resets the load device 4, the current consumption of the load device 4 becomes a small value.
[0032]
When a predetermined time (generally several tens of milliseconds) elapses after the output voltage Vout of the converter circuit 3 is stabilized, the reset signal XRESET becomes a high level and the transistor 2 is turned on.
[0033]
As a result, the gate-source voltage V _GS of the switch element 1 becomes a negative value, and the switch element 1 is also turned on. Therefore, although the resistor 6 is short-circuited, the charging of the capacitor C1 is completed, so that the secondary inrush current is suppressed to a small value.
[0034]
In addition, the load device 4 is released from the reset state and shifts to normal operation, and a large load current flows.
[0035]
Specific values when this embodiment is applied to a DC-DC converter in which the input voltage is 12 VDC and the inrush current must be suppressed to 6 A or less are shown below.
-Voltage applied between input terminals Vin + and Vin-: 12 VDC
-Resistance value of resistor 6: 2.2Ω
-Resistance value of resistor R1: 10 kΩ
-Resistance value of resistor R2: 2.2 kΩ
-Resistance value of the resistor R3 and the resistor R4: 100 kΩ
・ Capacitor C1 capacitance value: 680 μF
・ High level voltage of reset signal XRESET: 3.3V
[0036]
FIG. 2 shows another embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the same element as FIG. 1, and description is abbreviate | omitted.
[0037]
In FIG. 2, 5 is a photocoupler, 51 is an LED built in the photocoupler 5, and 52 is a phototransistor. R5 is a resistor connected between the output terminal of the reset signal output circuit 31 and the anode of the LED 51. The phototransistor 52 is connected between the side of the resistor R2 not connected to the gate G and the input voltage terminal Vin− terminal.
[0038]
When the reset signal XRESET is at a low level, no current flows through the LED 51, so that the phototransistor 52 is turned off and the switch element 1 is also turned off.
[0039]
When the reset signal XRESET is at a high level, a current flows through the LED 51 and the phototransistor 52 is turned on. Therefore, the switch element 1 is also turned on. If the input side and the output side of the converter circuit 3 are insulated, the switch element 1 cannot be directly controlled by the reset signal XRESET as in the embodiment of FIG.
[0040]
FIG. 3 shows the effect of the embodiment of FIG.
FIG. 3A shows measured values of the inrush current when the input voltage of the converter circuit 3 is 12.0 V, and represents changes in the input voltage, the reset signal, and the inrush current from above. The horizontal axis is 20 ms / div in time, and the vertical axis is the current value.
[0041]
FIG. 5B is an enlarged view of the primary inrush current portion of FIG. When the input voltage rises, the primary inrush current with a peak current of 4.5 A flows for about 10 ms, and the secondary inrush current with a peak current of 2.5 A flows only for a short time after 100 ms after the reset signal is negated, It can be seen that the inrush current is suppressed to a small value.
[0042]
In these embodiments, the P-channel MOSFET is used as the switch element, but another switch element or a mechanical switch may be used. In short, any switch may be used as long as the resistance value when turned on is sufficiently smaller than the resistance value of the resistor 6. Further, although the reset signal output circuit 31 is built in the converter circuit 3, it may be provided outside.
【The invention's effect】
As is clear from the above description, the following effects can be expected according to the present invention. The switch connected in parallel with the current limiting element that limits the inrush current is controlled to be turned off while the reset signal supplied to the load is asserted, so the input voltage to the converter circuit, the state of the load, or the supply source Even if characteristics such as the power supply rise, the switch can always be turned on at the optimum timing. As a result, a sufficient charging time for the input capacitor can be ensured, and the secondary inrush current when the switch is turned on can be minimized.
[0043]
In addition, since the reset signal supplied to the load is used as the switch control signal, the reset of the load is not released when the switch is off. Therefore, there is an effect that an abnormal temperature rise or burning of the current limiting element due to an increase in the load current or a phenomenon that the power supply device starts up normally after repeated operation / stop several times when the power is turned on does not occur.
[0044]
Furthermore, the reset signal is insulated by a photocoupler, and the switch is controlled by this signal. There is an effect that even a converter circuit in which the input side and the output side are insulated can be used.
[0045]
Furthermore, a reset signal output circuit is built in the converter circuit, and a P-channel MOSFET is used as a switch. There is an effect that downsizing becomes possible.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an embodiment of the present invention.
FIG. 2 is a block diagram showing another embodiment of the present invention.
FIG. 3 is a characteristic diagram showing the effect of an embodiment of the present invention.
FIG. 4 is a configuration diagram of a power supply device incorporating a conventional inrush current limiting circuit.
[Explanation of symbols]
1 P-channel MOSFET
2 Transistor 3 Converter circuit 31 Reset signal output circuit 4 Load device 5 Photocoupler 6, R1 to R5 Resistor C1 Capacitor

Claims (4)

A converter circuit that converts the input power into power to be supplied to the load and outputs the power; and
A current limiting element that is installed in the middle of the line through which the current that is input to the converter circuit flows, and that limits the inrush current;
A reset signal output circuit that asserts a reset signal supplied to the load until a predetermined time elapses after the output voltage is stabilized after power is supplied to the converter circuit;
A switch connected in parallel to the current limiting element and controlled to be off while the reset signal is asserted and turned on when the reset signal is negated;
A power supply device characterized by comprising: 2. The power supply device according to claim 1, further comprising a photocoupler to which a signal related to the reset signal is input, wherein the switch is controlled by the photocoupler. The power supply apparatus according to claim 1, wherein the reset signal output circuit is installed inside the converter circuit. The power supply device according to claim 1, wherein the switch is a P-channel MOSFET.

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