JP2011250584A - Power supply control apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the residual charge to be released rapidly when a power supply is turned off, in a DC-DC converter.SOLUTION: One end of a first switching part Q1 is connected to a DC power supply. One end of a second switching part Q2 is connected to the first switching part Q1 in series, and the other end thereof is connected to a common potential. A control part 1 carries out on-off switching of the first and second switching parts Q1 and Q2 in a high-frequency wave cycle alternatively to change the potential at a connection point P1 of the first and second switching parts Q1 and Q2. A smoothing circuit 5 has a smoothing capacitor C, and smooths the potential at the connection point P1 and supplies the DC power supply to a load side. A switch part SW turns on the second switching part Q2 based on a power supply off control signal S3.

Description

  The present invention relates to a power supply control apparatus, for example, a power supply control suitable for use in an image forming apparatus such as an electrophotographic copying machine, a facsimile machine, a printer, or a multi function peripheral (MFP) equipped with these functions. It relates to the improvement of the apparatus.

  In this type of image forming apparatus, printing (printing) is generally performed in which image data is optically read from image information on a document, a toner image is formed based on the image data, and is transferred and fixed onto a sheet. In addition to the functions, it has various image processing functions for image data, a facsimile function for transmitting and receiving image data by facsimile, and other various image data processing functions.

  In order to realize these various functions, the image forming apparatus has various components such as an electronic circuit and a motor. A DC-DC converter is used to generate DC power sources having different voltages and to them. Supply.

  However, in order to reliably start these components, as shown in FIG. 3A, various DC-DC converters are activated when the power is turned on to generate a DC power supply of a desired level, and when the power is turned off, the DCs are turned on. -It is required to quickly reduce the DC power source from the DC converter. The waveform in FIG. 3 is a DC power supply voltage from each DC-DC converter.

  In particular, in recent years, a configuration in which a CPU is mounted and controlled for each electronic circuit has been increased, and the on / off order of power supply tends to be determined.

  In such a situation, when the operation is stopped by turning off the power supply, if the output load becomes small, a residual voltage tends to remain due to the charge of the smoothing capacitor built in the DC-DC converter or externally connected.

  For this reason, there is a concern that an individual electronic circuit may malfunction due to a residual charge amount when the power is turned off. In an electronic circuit that generates and operates different power sources by a plurality of DC-DC converters, As shown in FIG. 3B, the amount of residual charge is different, and even if the power is turned off, the residual power supply voltage is reversed due to the influence of the residual voltage, and the operation sequence is disrupted. ing.

  Conventionally, a multi-output switching power supply device as disclosed in, for example, Japanese Patent Laid-Open No. 2000-102248 (Patent Document 1) has been proposed as a configuration for releasing residual charges.

  This Patent Document 1 has a primary DC voltage detection circuit, a switch circuit, and a discharge circuit, and rectifies and smoothes a negative voltage of power induced in a secondary winding by the primary DC voltage detection circuit. When the obtained comparison voltage is detected and the absolute value of the comparison voltage is less than or equal to the reference voltage, the switch circuit is forcibly opened to cut off the supply of the DC voltage, and the output terminal of the DC voltage is discharged by the discharge circuit. When the AC power input is cut off without causing an increase in cost and without affecting the load condition on the output side, multiple outputs can be generated. A sequence for dropping the voltages in a predetermined order can be surely executed.

JP 2000-102248 A

  However, in Patent Document 1 described above, with respect to a power-off sequence in the case of generating a plurality of power supplies from an AC input power supply, charges are discharged by discharge means such as a transistor using a detection voltage from a secondary winding of a transformer. Because of the configuration, in order to discharge the residual charge, it is necessary to newly add a device such as a transistor and add a circuit configuration, which increases the cost.

  Of course, there is a method of inserting a bleeder resistor in order to release the residual charge when the power is turned off, but since the current flows even during the normal operation, the power consumption efficiency is not good.

  The present invention has been made to solve such a problem. The power supply control capable of quickly discharging the residual charge when the power is turned off without reducing the power supply efficiency and reducing the number of additional components as much as possible. The purpose is to provide a device.

  In order to solve such a problem, a power supply control device according to claim 1 of the present invention includes a first switching unit having one end connected to a DC power supply, and one end connected in series to the first switching unit. The second switching unit whose end is connected to a common potential and the first and second switching units are alternately switched on and off at a high frequency cycle to vary the potential at the connection point of the first and second switching units. A control unit, a smoothing unit that has a smoothing capacitor and smoothes the potential at its connection point and supplies DC power to the load side, and a switch that turns on the second switching unit based on the power-off control signal, It has.

  The power supply control device according to claim 2 of the present invention includes a switch control unit that turns on the second switching unit based on the power-off control signal only when the first switching unit is off. is there.

  In such a power supply control device according to the first aspect of the present invention, the first and second switching units are alternately switched on and off at a high frequency cycle to vary the potential at the connection point of the first and second switching units. In the situation, when the power-off control signal is input, the second switching unit is turned on. Therefore, when the power is turned off, the residual charge is discharged through the second switching unit, and the residual charge is quickly discharged. It is possible to reduce the number of additional parts as much as possible without reducing the power supply efficiency.

  The power supply control device according to claim 2 of the present invention includes a switch control unit that turns on the second switching unit based on the power-off control signal only when the first switching unit is off. The second switching unit is prevented from being turned on at the same time.

1 is a schematic circuit diagram showing an embodiment of a power supply control device according to the present invention. It is a wave form diagram explaining operation | movement of the power supply control apparatus which concerns on this invention. It is a figure explaining the operation | movement used as the reference in the conventional power supply control apparatus.

  Embodiments of a power supply control device according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic circuit diagram showing an embodiment of a power supply control device according to the present invention.

  In FIG. 1, for example, a first switching unit Q1 and a second switching unit Q2 are connected in series between a DC power source of 5V and a ground that is a common potential, and the first switching unit Q1 is on the high potential side. On the (H side), the second switching portion Q2 is located on the low potential side (L side).

  The first switching unit Q1 is, for example, an N-type FET (field effect transistor) having a drain connected to a DC power supply of 5V, and the second switching unit Q2 has a drain connected to the source of the first switching unit Q1, The same N-type FET with the source connected to ground.

  An on / off control signal S1 from the control unit 1 is connected to the gate of the first switching unit Q1.

  An output signal S4 from the switch SW is connected to the gate of the second switching unit Q2, and an ON / OFF control signal S2 from the control unit 1 and a 5V DC power source are connected to the input of the switch SW.

  A control signal S5 from the switch control unit 3 is connected to the switching signal input unit a of the switch SW. The switch SW has a function of selectively outputting either the on / off control signal S2 of the control unit 1 or the 5V DC power supply (that is, the “H” state) as the output signal S4 based on the control signal S5.

  The control unit 1 is operated by a predetermined DC power source, for example, the above-described 5V DC power source, and the first and second switching units Q1 and Q2 are alternately switched on and off at a high frequency cycle, and the first and second switching units It has a function of varying the potential at the connection point P1 between Q1 and Q2.

  That is, the control unit 1 applies a 5 V DC power source, for example, 1 MHz high frequency on / off control signals S1 and S2 to the gates of the first and second switching units Q1 and Q2, and the first and second switching units Q1 and Q2. Q2 is alternately switched on at 1 MHz.

  As shown in FIG. 2, the on / off control signals S1 and S2 applied to the gates of the first and second switching units Q1 and Q2 have the “H” state and the “L” state in opposite phases. .

  The control unit 1 receives all of the on / off control signals S1 and S2 applied to the gates of the first and second switching units Q1 and Q2 in response to the input of the power off control signal S3 that detects the power off state (not shown). It has a function to make a state.

  Reference numeral 3 in FIG. 1 denotes a switch control unit, which receives an on / off control signal S1 and a power-off control signal S3 applied from the control unit 1 to the gate of the first switching unit Q1 (see FIG. 2). Is an “L” state, a logic circuit (AND circuit) that outputs the “H” state to the switching signal input unit a of the switch SW as the control signal S5, and operates with the same power supply as the control unit 1.

  The switch SW selects the 5V DC power supply (that is, the “H” state) when the control signal S5 of the switching signal input unit a is in the “H” state, and selects the on / off control signal S2 of the control unit 1 in the “L” state. It has a function.

  1 is a resistor, which is for preventing the capacitance of the switch control unit 3 from affecting the operation of the first switching unit Q1.

  One end of the smoothing capacitor C is connected to the connection point P1 between the source of the first switching unit Q1 and the drain of the second switching unit Q2 via the smoothing coil CH, and the other end of the smoothing capacitor C is grounded. And a smoothing circuit 5 is formed.

  A load circuit (not shown) is connected to a connection point P2 between the smoothing coil CH and the smoothing capacitor C. The above circuit as a whole constitutes a DC-DC converter.

  Next, the operation of the power supply control apparatus according to the present invention will be briefly described with reference to FIG.

  When the power is on and the power-on control signal S3 is in the “H” state, the control unit 1 is operated by a DC power source of 5V, and 1 MHz with respect to the gates of the first and second switching units Q1 and Q2. Are applied to the gates of the first and second switching units Q1 and Q2, respectively.

  Here, the on / off control signal S2 is applied to the input part of the switch SW, but the power-on control signal S3 is in the “H” state, the control signal S5 of the switch control part 3 becomes “L”, and the switch SW Since the on / off control signal S2 of the control unit 1 is selected, the on / off control signal S2 is directly applied to the gate of the second switching unit Q2 as the output signal S4.

  As a result, the first and second switching units Q1 and Q2 are alternately switched on at 1 MHz, and the potential at the connection point P1 of the first and second switching units Q1 and Q2, as shown in FIG. Together, it changes into a sawtooth shape.

  That is, during a period in which the first switching unit Q1 is on and the second switching unit Q2 is off, a current flows from the connection point P1 through the smoothing coil to the smoothing capacitor C and is charged and the voltage at the connection point P1. During the period in which the first switching unit Q1 is off and the second switching unit Q2 is on, the charge flows from the smoothing capacitor C to the ground via the smoothing coil CH and the second switching unit Q2. As C is discharged, the voltage at the connection point P1 drops.

  On the other hand, in these processes, the voltage at the connection point P2 is smoothed by the smoothing circuit 3, and DC power is supplied to the load circuit.

  When the power is turned off and the power-off control signal S3 is in the “L” state, the on / off control signals S1 and S2 applied from the control unit 1 to the gates of the first and second switching units Q1 and Q2 are in the “L” state. Thus, both inputs of the switch control unit 3 are in the “L” state, and the control signal S5 of the switch control unit 3 is in the “H” state. As a result, the switch SW selects the 5V DC power supply (that is, the “H” state), the output signal S4 of the switch SW becomes the “H” state, and only the second switching unit Q2 is turned on, while the first The switching unit Q1 is kept off.

  Therefore, the electric charge charged in the smoothing capacitor C flows to the ground via the second switching unit Q2, and is discharged. The remaining electric charge of the smoothing capacitor C is rapidly reduced, and the potential at the connection point P2 is rapidly reduced. The power supply to the load circuit is stopped.

  Here, the switch control unit 3 is not necessarily required, and the power-off control signal S3 may be directly input as the control signal S5 of the switch SW by inverting the signal level.

  The operation of the control unit 1 and the first and second switching units Q1 and Q2 when the power is turned off is performed by the residual voltage of the DC power source of 5V.

  Thus, the power supply control device of the present invention has the first switching unit Q1 having one end connected to the DC power source, one end connected in series to the first switching unit Q1, and the other end connected to a common potential. The second switching unit Q2 and the first and second switching units Q1 and Q2 are alternately switched on and off at a high frequency cycle to vary the potential at the connection point P1 of the first and second switching units Q1 and Q2. The control unit 1, the smoothing circuit 5 having the smoothing capacitor C and smoothing the potential at the connection point P1 to supply DC power to the load side, and the second switching unit Q2 being turned on based on the power-off control signal And a switch SW.

  Therefore, when the power is turned off, the charge charged in the smoothing capacitor C flows to the ground via the second switching unit Q2 and is discharged, and the residual charge obtained from the smoothing capacitor C is rapidly reduced, and the residual charge to the load circuit is reduced. It is possible to avoid the influence.

  Moreover, since the switch SW controls the operation only when the power is turned on / off, it does not affect the power consumption efficiency during normal operation, and can be configured by using the second switching unit Q2 as it is and adding one switch SW. The number of additional parts is small, and it can be realized at low cost. Since the switch SW does not operate during normal operation, power consumption efficiency is good and power supply efficiency can be maintained high.

  In addition, since the switch control unit 3 is provided to turn on the second switching unit Q2 based on the power-off control signal S3 only when the first switching unit Q1 is off, the first and second switching units Q1, Q2 is not turned on at the same time, and it is possible to prevent malfunction.

  In particular, the power supply control device of the present invention rarely varies the drop time of the power supply due to the difference in load capacity when the power is turned off, suppresses an increase in the number of parts and increases the cost, consumes residual charges, and turns off the power. This is useful in a configuration in which a plurality of DC power sources are generated from a DC power source and an on / off sequence needs to be taken for each power source because the time sequence can be observed.

  In the present invention, the power-off control is a control signal for detecting the power-off of the entire device on which the power control device is mounted, or the power supply for each circuit board on which the power control device arranged in the device is mounted. It detects off and includes a control signal.

  By the way, the power supply control apparatus according to the present invention is not limited to an image forming apparatus such as a copying machine, a facsimile machine, and a multifunction machine, and can be implemented in various electronic devices.

1 Control unit 3 Switch control unit (logic circuit)
5 smoothing circuit C smoothing capacitor CH smoothing coil Q1 first switching unit Q2 second switching unit P1, P2 connection point SW switch S1, S2 on / off control signal S3 power off control signal S4 output signal S5 control signal

Claims (2)

A first switching unit having one end connected to a DC power source;
A second switching unit having one end connected in series to the first switching unit and the other end connected to a common potential;
A control unit configured to alternately switch on and off the first and second switching units at a high frequency period to vary a potential at a connection point of the first and second switching units;
A smoothing unit having a smoothing capacitor and smoothing the potential at the connection point and supplying a DC power to the load side;
A switch for turning on the second switching unit based on a power-off control signal;
A power supply control device comprising:   The power supply control apparatus according to claim 1, further comprising a switch control unit that turns on the second switching unit based on the power-off control signal only when the first switching unit is off.

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