JP2008011688A - Switching power supply apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply apparatus that can reduce a surge such as a rush current, and is inexpensive. <P>SOLUTION: A switching power supply apparatus has a series circuit which is connected to both ends of a power supply 3, and to which a choke coil 4 and a switching element 5 are connected in series, a series current which is connected in parallel to a switching element, and in which an output rectifying element 6, a surge suppressing element 7 and a smoothing capacitor 8 are connected in series, and a voltage-booster chopper circuit including a control circuit 10 that controls the turn-on/off of the switching element, The apparatus causes electric current to flow from a power supply to the choke coil to accumulate energy when the switching element is turned on, transfers energy accumulated in the power supply and the choke coil when the switching element is turned off to a smoothing capacitor via the output rectifying element, and supplies an output voltage of the smoothing capacitor to a load. The control circuit controls the turn-on/off of the switching element based on a voltage of a connection point between the output rectifying element and the surge suppressing element, to control the voltage at the connection point to a predetermined voltage. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a switching power supply device using a step-up chopper circuit, and mainly relates to a technique for reducing a current surge when power is turned on.

  Conventionally, a switching power supply device using a step-up chopper circuit is known (see, for example, Patent Document 1). FIG. 4 is a circuit diagram showing a configuration of a switching power supply device using a conventional step-up chopper circuit disclosed in Patent Document 1. In FIG.

  An input voltage 1 from an AC power source or a DC power source (hereinafter simply referred to as “power source”) (not shown) is rectified by a diode bridge 3 as an input rectifying element and applied to the boost chopper circuit 100. Between the input terminals of the boost chopper circuit 100 (between the output terminals of the diode bridge 3), a circuit in which a choke coil 4 and a MOSFET 5 operating as a switching element are connected in series is connected, and between the source and drain of the MOSFET 5 is connected. A circuit in which a diode 6 as an output rectifier, a surge suppression element 7 for reducing inrush current, and a smoothing capacitor 8 are connected in series is connected.

  Further, at the connection point between the smoothing capacitor 8 and the surge suppression element 7, the output voltage (voltage appearing at both ends of the smoothing capacitor 8) is detected and supplied to the gate of the MOSFET 5, thereby turning on / off the MOSFET 5. A control circuit 10 to be controlled is connected. The output of the step-up chopper circuit 100 is smoothed by the smoothing capacitor 8 and then supplied to the load 9.

  In the step-up chopper circuit 100 configured as described above, when the MOSFET 5 is turned on, a current flows from the diode bridge 3 to the choke coil 4, and energy is magnetically accumulated in the choke coil 4. When the MOSFET 5 is turned off, the energy from the power source and the energy stored in the choke coil 4 are transferred to the smoothing capacitor 8 via the diode 6 and the surge suppression element 7. The control circuit 10 controls the on / off of the MOSFET 5 to change the energy stored in the choke coil 4, thereby controlling the output voltage supplied to the load 9 to a constant voltage.

In this switching power supply device, an inrush current flows through the smoothing capacitor 8 when the power is turned on. The surge suppression element 7 is connected to the output stage of the boost chopper circuit 100, that is, between the diode 6 and the smoothing capacitor 8 in order to suppress the inrush current. For example, a power thermistor is used as the surge suppression element 7.
JP-A-11-69784

  However, the above-described conventional switching power supply device has the following problems. That is, the energy accumulated in the choke coil 4 when the MOSFET 5 is turned on is transferred to the smoothing capacitor 8 via the diode 6 and the surge suppression element 7 when the MOSFET 5 is turned off, so that a current surge such as an inrush current is suppressed. The voltage drop in the surge suppression element 7 provided as the surge suppression element is added to the output voltage and applied to the MOSFET 5.

  As a result, it is necessary to increase the rated voltage of the MOSFET 5, and the on-resistance is also increased. When the rated voltage of the MOSFET 5 is high and the on-resistance is the same, it is necessary to use a switching element having a large chip size, and there is a problem that the switching element and thus the switching power supply device becomes expensive.

  In particular, when a thermistor is used as the surge suppression element 7, if the load is shifted to the rated load during operation under light load conditions, the rated current will flow with the room temperature resistance value (high resistance value), suppressing surge. The voltage drop (surge voltage) due to the thermistor as an element increases.

  As a result, the voltage applied to the MOSFET 5 continues to be high until the temperature of the thermistor increases and the resistance value decreases. When such a situation occurs, there is a problem that the usage rate of the MOSFET 5 becomes high and the reliability deteriorates.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an inexpensive switching power supply device that can reduce surges such as inrush current.

  In order to solve the above-mentioned problem, the invention according to claim 1 is connected to both ends of an input power source, and is connected in parallel to the first series circuit in which a choke coil and a switching element are connected in series, and to the switching element. A step-up chopper circuit comprising: a second series circuit in which an output rectifying element, a surge suppression element, and a smoothing capacitor are connected in series; and a control circuit that controls on / off of the switching element; When the switching element is turned on, current is passed from the input power source to the choke coil to accumulate energy, and when the switching element is turned off, the energy accumulated in the input power source and the choke coil is passed through the output rectifier element. In a switching power supply that moves to a smoothing capacitor and supplies the output voltage of the smoothing capacitor to a load, The control circuit controls on / off of the switching element based on a voltage at a connection point between the output rectifying element and the surge suppression element to control the voltage at the connection point to a predetermined voltage. .

  According to a second aspect of the present invention, there is provided a first series circuit connected to both ends of an input power source, wherein a choke coil and a switching element are connected in series, an output rectifying element and a surge suppressing element connected in parallel to the switching element. And a step-up chopper circuit comprising a second series circuit in which a smoothing capacitor is connected in series and a control circuit for controlling on / off of the switching element, and the input power supply when the switching element is on Current is passed through the choke coil to accumulate energy, and when the switching element is turned off, the energy accumulated in the input power source and the choke coil is transferred to the smoothing capacitor via the output rectifying element, and the smoothing capacitor In the switching power supply device that supplies the output voltage of the capacitor to the load, the control circuit includes the output rectifier element. And controls the on / off of the switching element based on the output voltage the voltage at the connection point to appear at both ends of the smoothing capacitor of the surge suppression device and.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the switching element is turned on / off in parallel with a series circuit including the surge suppression element and the smoothing capacitor. A bypass capacitor for bypassing the generated high-frequency noise is connected.

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the surge suppression element is constituted by a thermistor.

  According to the first aspect of the present invention, since the control circuit controls the voltage at the connection point between the output rectifying element and the surge suppressing element to a predetermined voltage, a large surge voltage is not applied to the switching element or the output rectifying element. As a result, it is not necessary to use a large switching element with a low withstand voltage and low on-resistance, so that an increase in the price and size of the switching element can be prevented.

  According to the second aspect of the invention, the control circuit controls on / off of the switching element based on the voltage at the connection point between the output rectifying element and the surge suppression element and the output voltage appearing at both ends of the smoothing capacitor. Therefore, it is possible to reduce the surge voltage and reduce the fluctuation of the output voltage of the switching power supply device.

  According to the invention described in claim 3, since the bypass capacitor is connected in parallel to the series circuit including the surge suppression element and the smoothing capacitor, the surge voltage can be reduced and the EMI noise and the like can be reduced. .

  According to the invention described in claim 4, since the surge suppression element is constituted by the thermistor, the loss during steady operation can be reduced while reducing the inrush current.

  Hereinafter, a switching power supply according to an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a circuit diagram showing a configuration of a switching power supply apparatus according to Embodiment 1 of the present invention. This switching power supply device is a connection between the diode 6 and the surge suppression element 7 instead of inputting an output voltage to the input terminal of the control circuit 10 of the step-up chopper circuit 100 in the conventional switching power supply device shown in FIG. It is configured to input a point voltage.

  In the switching power supply according to the first embodiment configured as described above, the smoothing capacitor 8 provided in the output stage of the step-up chopper circuit 100 is not connected to the smoothing capacitor 8 when the input voltage 1 is applied to the diode bridge 3. Since no charge is accumulated, a charging inrush current tends to flow to the smoothing capacitor 8 via the choke coil 4 and the diode 6. However, since the surge suppression element 7 is inserted in this path, the inrush current for charging the smoothing capacitor 8 is suppressed by the surge suppression element 7.

  When charging of the smoothing capacitor 8 is completed after the power is turned on, the step-up chopper circuit 100 is operated by the on / off control of the MOSFET 5 by the control circuit 10, and the voltage at the connection point between the diode 6 and the surge suppression element 7 of the step-up chopper circuit 100. Is controlled to a predetermined voltage. As a result, the voltage applied to the MOSFET 5 becomes a predetermined voltage, and it is possible to solve the problem of the conventional switching power supply device in which the surge voltage is increased by inserting the surge suppression element 7.

  FIG. 2 is a circuit diagram showing a configuration of a switching power supply apparatus according to Embodiment 2 of the present invention. This switching power supply device is the same as the conventional switching power supply device shown in FIG. 4 except that the output voltage is input to the input terminal of the control circuit 10 of the step-up chopper circuit 100 and the connection point between the diode 6 and the surge suppression element 7. Is also input.

  In the switching power supply device according to the first embodiment configured as described above, the control circuit 10 includes two outputs such as the output voltage and the voltage at the connection point between the diode 6 and the surge suppression element 7, that is, the voltage applied to the MOSFET 5. On / off of the MOSFET 5 is controlled based on the voltage. Thereby, the output voltage can be stabilized while suppressing the voltage applied to the MOSFET 5.

  FIG. 3 is a circuit diagram showing a configuration of a switching power supply apparatus according to Embodiment 3 of the present invention. This switching power supply apparatus is configured by adding a bypass capacitor 12 in parallel to the series circuit including the surge suppression element 7 and the smoothing capacitor 8 in the switching power supply apparatus according to the first embodiment. The bypass capacitor 12 has a capacitance (for example, 1000 pF to several μF) so as to bypass the high-frequency component current flowing through the smoothing capacitor 8 in accordance with the switching period (for example, 20 kHz to 200 kHz) of the MOSFET 5.

  Providing the bypass capacitor 12 provides the following advantages.

(1) When the MOSFET 5 operating as an inverter shifts from on to off, a surge-like peak current is generated. The peak value is suppressed by the high-frequency component of the peak current flowing through the bypass capacitor 12. As a result, the voltage depending on the peak current generated in the surge suppression element 7 is suppressed to suppress an increase in the inverter voltage, and as a result, a suppression operation like a DCR snubber composed of a diode, a capacitor, and a resistor can be obtained.

(2) When the high-frequency component of this peak current flows through the bypass capacitor 12, noise generated from the switching power supply device is suppressed, and noise characteristics such as EMI are improved.

  The switching power supply device according to the third embodiment described above is configured to add the bypass capacitor 12 to the switching power supply device according to the first embodiment. However, the bypass capacitor 12 is added to the switching power supply device according to the second embodiment. It can also be configured as follows.

  In the switching power supply according to the first to third embodiments described above, the MOSFET 5 is used as the switching element for the inverter of the step-up chopper circuit 100. However, other devices such as a bipolar transistor and an IGBT (Insulated Gate Bipolar Transistor) are used. These switching elements can also be used. As the surge suppression element 7, a thermistor (power thermistor), a resistor, a resistance element using a semiconductor, a reactor, a ferrite bead, or the like can be used. This is not limited to simply suppressing the inrush current, but the switching element withstand voltage rises similarly for a surge caused by a ferrite bead inserted as an EMI countermeasure between the output rectifying element and the smoothing capacitor, This is because it is considered effective against these.

It is a circuit diagram which shows the structure of the switching power supply device which concerns on Example 1 of this invention. It is a circuit diagram which shows the structure of the switching power supply device which concerns on Example 2 of this invention. It is a circuit diagram which shows the structure of the switching power supply device which concerns on Example 3 of this invention. It is a figure which shows the structure of the conventional switching power supply device.

Explanation of symbols

1 Input voltage 3 Diode bridge 4 Choke coil 5 MOSFET
6 Diode 7 Surge suppressor (Thermistor, etc.)
8 Smoothing capacitor 9 Load 10 Control circuit 12 Bypass capacitor 100 Boost chopper circuit

Claims (4)

A first series circuit that is connected to both ends of the input power source and in which a choke coil and a switching element are connected in series, and is connected in parallel to the switching element, and an output rectifying element, a surge suppression element, and a smoothing capacitor are connected in series. A step-up chopper circuit comprising: a second series circuit connected to the control circuit; and a control circuit for controlling on / off of the switching element,
When the switching element is turned on, current is passed from the input power source to the choke coil to store energy, and when the switching element is turned off, energy stored in the input power source and the choke coil is passed through the output rectifier element. In a switching power supply that moves to a smoothing capacitor and supplies the output voltage of the smoothing capacitor to a load,
The control circuit controls on / off of the switching element based on a voltage at a connection point between the output rectifying element and the surge suppression element to control the voltage at the connection point to a predetermined voltage. Switching power supply. A first series circuit that is connected to both ends of the input power source and in which a choke coil and a switching element are connected in series, and is connected in parallel to the switching element, and an output rectifying element, a surge suppression element, and a smoothing capacitor are connected in series. A step-up chopper circuit comprising: a second series circuit connected to the control circuit; and a control circuit for controlling on / off of the switching element,
When the switching element is turned on, current is passed from the input power source to the choke coil to accumulate energy, and when the switching element is turned off, the energy accumulated in the input power source and the choke coil is passed through the output rectifier element. In a switching power supply that moves to a smoothing capacitor and supplies the output voltage of the smoothing capacitor to a load,
The control circuit controls on / off of the switching element based on a voltage at a connection point between the output rectifying element and the surge suppression element and an output voltage appearing at both ends of the smoothing capacitor. Power supply.   2. A bypass capacitor for bypassing high-frequency noise generated due to on / off of the switching element is connected in parallel to a series circuit including the surge suppression element and the smoothing capacitor. The switching power supply device according to claim 2. The switching power supply according to any one of claims 1 to 3, wherein the surge suppression element is a thermistor.

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