JP2007159304A - Power supply - Google Patents

Abstract

Provided is a power supply device capable of dealing with fluctuations in an output end on a non-constant voltage control side while maintaining a voltage at an output end on a constant voltage control side.
A transformer 4 that inputs a DC voltage from a voltage supply circuit 3 to an input winding and outputs a predetermined rated voltage from each of first and second output windings S1 and S2, and an input winding of the transformer 4 The switching control circuit 5 that switches the current to S0, and the first and second outputs that are output from the first and second output windings S1 and S2 to the first output terminal OUT1 and the second output terminal OUT2 are smoothed and rectified. Two smoothing rectifier circuits 6 and 7, a voltage monitoring circuit 8 that monitors the DC voltage of the first output terminal OUT1 and instructs the switching control circuit 5 to change the switching pulse width and cycle; the first output terminal OUT1 and the first output terminal OUT1; A potential detection shunt circuit 9 is provided for shunting current from the first output terminal OUT1 to the second output terminal OUT2 when the difference in DC voltage from the second output terminal OUT2 is equal to or greater than a predetermined potential difference.
[Selection] Figure 1

Description

  The present invention relates to a power supply apparatus that converts an AC voltage into a DC voltage by a switching method and supplies the converted voltage to a load.

  There is a switching type power supply device that converts an AC voltage into a DC voltage and supplies a stable voltage to a load. In this switching method, a DC voltage is used as an AC power supply voltage, and a DC voltage from the voltage supply circuit is input to an input winding, and predetermined rated voltages are output from the first and second output windings, respectively. A transformer, a switching control circuit that switches a current to the input winding of the transformer, and a smoothing rectifier circuit that smoothes and rectifies outputs from the first and second output windings, respectively, and outputs them as first and second DC voltages And a voltage monitoring circuit serving as a feedback circuit for instructing the change of the switching pulse width and period of the switching control circuit so that the output of the smoothing rectifier circuit has a predetermined voltage value.

  In this power supply device, either the first or second DC voltage connected to the voltage monitoring circuit is used as a main output, and the voltage is monitored and constant voltage control is performed, so that the voltage of the other sub-output is also fixed. Voltage control can be performed.

A conventional power supply device of such a switching system is described in Patent Document 1. The stabilized power supply circuit described in Patent Document 1 suppresses the linkage spike voltage generated by the load fluctuation on the constant voltage control side from the output terminal on the non-constant voltage control side to the constant voltage control side. A potential detection and current shunt circuit for shunting a current due to a potential difference to the output terminal is provided.
JP-A-11-341805

  However, the stabilized power supply circuit described in Patent Document 1 is provided with a potential detection and current shunt circuit that shunts current due to a potential difference from the output terminal on the non-constant voltage control side to the output terminal on the constant voltage control side. Even if the current consumption of the load connected to the output terminal on the constant voltage control side increases and a voltage drop occurs, the voltage is not compensated. In addition, when the current consumption of the load connected to the output terminal on the constant voltage control side greatly increases in that state, the current is further supplied from the output terminal on the non-voltage control side to compensate for the non-constant voltage control side. The output terminal of this causes a voltage drop.

  Therefore, a load that consumes less current but requires a certain degree of accuracy cannot be connected to the output terminal on the non-constant voltage control side.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a power supply apparatus that can cope with fluctuations in the output terminal on the non-constant voltage control side while maintaining the voltage at the output terminal on the constant voltage control side.

A power supply apparatus according to the present invention includes a voltage supply circuit using an AC power supply voltage as a DC voltage, a DC voltage from the voltage supply circuit being input to an input winding, and a predetermined rated voltage from each of the first and second output windings. , A switching control circuit for switching the current to the input winding of the transformer, and smooth rectifying the outputs from the first and second output windings, respectively, and outputting them to the first and second output terminals In the power supply apparatus, the first and second smoothing rectifier circuits, and a voltage monitoring circuit that monitors the DC voltage of the first output terminal and instructs the switching control circuit to change the switching pulse width and cycle. A potential detection shunt circuit for shunting current from the first output terminal to the second output terminal when a difference in DC voltage between the first output terminal and the second output terminal is equal to or greater than a predetermined potential difference; Characterized in that was.

  The present invention restores the DC voltage of the second output terminal to the original predetermined voltage even when the consumption current increases in the load connected to the second output terminal and the voltage of the second output terminal drops. Since constant voltage control can be performed, it is possible to cope with fluctuations in the second output terminal on the non-constant voltage control side while maintaining the voltage at the first output terminal on the constant voltage control side.

  According to a first aspect of the present invention, a voltage supply circuit using an AC power supply voltage as a DC voltage, a DC voltage from the voltage supply circuit are input to an input winding, and a predetermined rated voltage is supplied from each of the first and second output windings. , A switching control circuit for switching the current to the input winding of the transformer, and a smoothing rectification of the outputs from the first and second output windings, respectively, to output to the first and second output terminals In the power supply apparatus having the first and second smoothing rectifier circuits and the voltage monitoring circuit that monitors the DC voltage of the first output terminal and instructs the switching control circuit to change the switching pulse width and cycle, A potential detection shunt circuit for shunting current from the first output end to the second output end when the difference in DC voltage from the second output end is equal to or greater than a predetermined potential difference is provided.

  The voltage supply circuit smoothes and rectifies the AC power supply voltage into a DC voltage. This voltage supply circuit is connected to the input winding of the transformer. The transformer outputs the rated voltage of the voltage input to the input winding according to the winding ratio of the first and second output windings. And the voltage output to a 1st output winding and a 2nd output winding is adjusted with the switching control circuit which switches the electric current to the input winding of a transformer. The first output winding and the second output winding are connected to first and second smoothing rectifier circuits that perform smooth rectification and output to the first and second output terminals. Then, the voltage monitoring circuit monitors the DC voltage output to the first output terminal by the first smoothing rectifier circuit and instructs to change the switching pulse width and cycle of the switching control circuit. As a result, even if the current connected to the load connected to the first output terminal increases and the DC voltage at the first output terminal decreases, the voltage monitoring circuit instructs the switching pulse width and cycle of the switching control circuit. Then, the switching control circuit controls the current to the input winding of the transformer, so that the constant voltage control for returning the DC voltage at the first output terminal to the original predetermined voltage value can be performed.

  The potential detection shunt circuit monitors the potential difference of the DC voltage between the first output terminal and the second output terminal when an increase in current consumption occurs in the load connected to the second output terminal, When the potential difference becomes equal to or greater than a predetermined potential, current is shunted from the first output end to the second output end. A constant voltage control for compensating the current from the first output terminal to the second output terminal by this shunting and returning the first output terminal to the original predetermined voltage value by the voltage drop of the first output terminal generated by this shunting. The DC voltage at the second output terminal as well as the first output terminal is increased. Therefore, even if an increase in current consumption occurs in the load connected to the second output terminal and the voltage at the second output terminal decreases, the constant voltage that restores the DC voltage at the second output terminal to the original predetermined voltage. Control can be performed.

  According to a second aspect of the present application, the potential detection shunt circuit is configured to output the first output when the divided resistor connected to the first output terminal and the second output terminal and the voltage divided by the divided resistor have a predetermined potential difference. And a shunt regulator that allows current to flow from the end to the second output end.

A dividing resistor is connected to the first output terminal and the second output terminal. A shunt regulator is connected to shunt current from the first output end to the second output end. Based on the voltage divided by the dividing resistor, the shunt regulator operates so as to shunt current from the first output terminal to the second output terminal. That is, the voltage at which the shunt regulator starts to shunt current from the first output terminal to the second output terminal needs to be compensated for because the current consumption of the load connected to the second output terminal increases and the DC voltage decreases. By setting the voltage value to be constant, the constant voltage control can be performed on the load connected to the second output terminal.

  According to a third invention of the present application, the potential detection shunt circuit has a first output when the divided resistor connected to the first output terminal and the second output terminal and the voltage divided by the divided resistor have a predetermined potential difference. And a transistor for shunting current from the end to the second output end.

  A transistor can be used instead of the shunt regulator. Since the transistor is less expensive than the shunt regulator, the power supply device can be reduced.

  In a fourth invention of the present application, a diode is provided in a forward direction between the first resistor and the second resistor of the divided resistor, and the transistor is divided by a voltage divided by the first resistor, the diode, and the second resistor. It is characterized by being diverted.

  Since the transistor has a characteristic change depending on the temperature, a diode is provided in the forward direction between the first resistor and the second resistor of the divided resistor, and the transistor is formed by the first resistor, the diode, and the second resistor. By shunting with the divided voltage, the temperature compensation of the transistor can be performed by the diode.

(Embodiment)
A power supply apparatus according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a circuit diagram illustrating a power supply device according to an embodiment of the present invention.

  As shown in FIG. 1, the power supply device 1 is used as a power supply for a facsimile machine. The power supply device 1 includes a voltage supply circuit 3 that smoothes and rectifies an AC power supply voltage supplied from an AC power supply 2 into a DC voltage. The voltage supply circuit 3 is subjected to smooth rectification by the diode bridge DB and the smoothing capacitor C0.

  In the voltage supply circuit 3, a DC voltage output from the voltage supply circuit 3 is input to the input winding S0, and a predetermined rated voltage is output from each of the first output winding S1 and the second output winding S2. 4 is connected.

  A switching control circuit 5 that switches current to the input winding S0 of the transformer 4 is connected to the input winding S0 of the transformer 4.

  The switching control circuit 5 includes an FET (Field Effect Transistor) Q1 that is connected to the transformer 4 and switches a path, and a pulse modulation control IC 51 that generates a pulse for switching. The pulse modulation control IC 51 changes a switching pulse width and cycle by receiving a notification from a power supply monitoring circuit, which will be described later, via the photocoupler PC1.

  A first smoothing rectifier circuit 6 is connected to the first output winding S <b> 1 of the transformer 4. A second smoothing rectifier circuit 7 is connected to the second output winding S <b> 2 of the transformer 4. In the first smoothing rectifier circuit 6 and the second smoothing rectifier circuit 7, diodes D1 and D2 are connected in series, and smoothing capacitors C1 and C2 are connected between the ground.

The first smoothing rectifier circuit 6 outputs a DC voltage as the main output voltage V1 to the first output terminal OUT1. In the present embodiment, 24V is output as the main output voltage V1, and a drive motor for carrying recording paper and originals, a print head for printing, and the like are connected and supplied as a load.

The second smoothing rectifier circuit 7 outputs a DC voltage as the sub output voltage V2 to the second output terminal OUT2. In this embodiment, 6V is output as the sub output voltage V2, and a circuit element mounted on a printed wiring board as a load, an LED (Light Emitting Diode) used as illumination, or an LCD (LCD) provided as a display unit ( Liquid Crystal
Display) etc. are connected and supplied.

  Connected to the first output terminal OUT1 is a voltage monitoring circuit 8 that monitors the DC voltage and instructs the switching control circuit 5 to change the switching pulse width or cycle.

  The voltage monitoring circuit 8 includes a first output terminal OUT1, divided resistors R4 and R5 connected between the ground, and a transistor Q2 that is turned off based on the voltage divided by the divided resistors R4 and R5. Yes. The transistor Q2 turns off the path connected from the first output terminal OUT1 to the ground. In this path, a zener diode ZD1 that limits the voltage so that it does not exceed a predetermined voltage when the transistor Q2 is turned on, a photocoupler PC1 that emits light when current flows and notifies the pulse modulation control IC 51, And a resistor R3 for limiting current. The primary side and the secondary side of the transformer 4 are electrically separated by the photocoupler PC1.

  When the difference in DC voltage between the first output terminal OUT1 and the second output terminal OUT2 is equal to or greater than a predetermined potential difference between the first output terminal OUT1 and the second output terminal OUT2, the first output terminal OUT1. To a second output terminal OUT2 is provided with a potential detection shunt circuit 9.

  The potential detection shunt circuit 9 is configured such that the divided resistors R1 and R2 connected to the first output terminal OUT1 and the second output terminal OUT2 and the voltage divided by the divided resistors R1 and R2 have a predetermined potential difference. A shunt regulator IC2 that flows current from the first output terminal OUT1 to the second output terminal OUT2 and a resistor Rb that limits the current are provided. In the present embodiment, the dividing resistor R1 is 94 KΩ, and the dividing resistor R2 is 15K. Therefore, when the main output voltage V1 is output at 24V and the sub output voltage V2 is 6V, the divided voltage is about 2.5V, and if the reference voltage of the shunt regulator IC2 is 2.5V, When the sub output voltage V2 becomes 6V or less, the diversion starts.

  The operation of the power supply device 1 according to the embodiment of the present invention configured as described above will be described with reference to FIGS. FIG. 2A is a graph showing the voltage-current characteristic of the second output terminal of the power supply device 1, and FIG. 2B is a graph showing the current-diverted current Ib characteristic of the second output terminal.

  As a load (for example, a drive motor) connected to the first output terminal OUT1 operates, the main output voltage V1 gradually decreases according to the consumption current Is1. However, since the switching monitoring circuit 5 is instructed to change the switching pulse width and cycle by monitoring the voltage monitoring circuit 8, constant voltage control is performed on the main output voltage V1, and the main output voltage V1 increases. At the same time, the sub output voltage V2 also rises.

As shown in FIG. 2A, when the current consumption of the load connected to the first output terminal OUT1 is large, the output current Is1 of the first smoothing rectifier circuit 6 increases. When the output current Is1 increases, the main output voltage V1 is increased by constant voltage control and the sub output voltage V2 is also increased so as not to decrease the main output voltage V1, so that the output current Is2 of the second smoothing rectifier circuit 7 is increased. Even if it increases, it is maintained at a high voltage state as indicated by a one-dot chain line, and does not fall below the operating limit voltage V2min (6 V in the present embodiment) of the load connected to the second output terminal OUT2.

  However, when the current consumption of the load connected to the first output terminal OUT1 is minimum (in this case, I1min), the main output voltage V1 does not decrease, so the voltage monitoring circuit 8 detects a voltage decrease. Without constant voltage control in the direction of increasing the main output voltage V1. Accordingly, when the current consumption of the load connected to the second output terminal OUT2 increases in this state, the sub output voltage V2 gradually decreases, and the load connected to the second output terminal OUT2 exceeds the current consumption I2pass. As shown by the dotted line, the voltage is lower than the operable voltage V2min.

  However, when the voltage at the second output terminal OUT2 is less than 6V, the potential difference between the first output terminal OUT1 and the second output terminal OUT2 increases. Therefore, when the voltage divided by the dividing resistors R1 and R2 of the potential detection shunt circuit 9 exceeds 2.5 V, it exceeds the reference voltage of the shunt regulator IC2, and the shunt regulator IC2 starts to shunt through the resistor Rb. .

  Therefore, as shown in FIG. 2A and FIG. 2B, the shunt current Ib passing through the shunt regulator IC2 with respect to the load connected to the second output terminal OUT2 supplements the current I2. Since the output current Is1 of the rectifier circuit 6 increases by the amount corresponding to the shunt current Ib, the main output voltage V1 decreases. As the main output voltage V1 decreases, the switching monitor circuit 5 is notified of the switching pulse width and cycle by monitoring the voltage monitoring circuit 8, so that constant voltage control is performed on the main output voltage V1. As the main output voltage V1 rises, the sub output voltage V2 also rises.

  Further, even if the current increases to the second output terminal OUT2, the main output voltage V1 further decreases according to the increased amount, so that the shunt current Ib can be increased according to the voltage decrease. The current can be supplied up to the maximum supply current I2max that can be output to the end OUT2.

  In this way, it is possible to cope with fluctuations in the second output terminal OUT2 that is the output terminal on the non-constant voltage control side while maintaining the voltage of the first output terminal OUT1 that is the output terminal on the constant voltage control side.

  Next, a power supply device according to another embodiment of the present invention will be described with reference to FIG. FIG. 3 is a diagram showing a potential detection shunt circuit of a power supply device according to another embodiment of the present invention. In FIG. 3, only the potential detection shunt circuit of FIG. 1 is shown.

  As shown in FIG. 3, a potential detection shunt circuit 20 of a power supply device according to another embodiment of the present invention is provided with a diode D3 in the forward direction between divided resistors R6 and R7. The transistor Q3 is connected to the base terminal so as to be shunted by the voltage divided by the dividing resistor (first resistor) R6 and the diode D3 and the dividing resistor (second resistor) R7.

  The dividing resistors R6 and R7 determine their resistance values in consideration of the voltage drop of the diode D3.

  In this way, the element that passes the shunt current Ib that shunts Is1 from the first output terminal OUT1 to the second output terminal OUT2 is the transistor Q3 instead of the shunt regulator IC2, so that the area occupied by the substrate and the like can be reduced. Can be reduced.

When the temperature of the transistor Q2 rises, the base current I _B increases even if the base-emitter voltage V _BE is constant. In the present embodiment, a diode D3 is provided in the forward direction between the dividing resistors R6 and R7, and the transistor Q3 is divided by the voltage divided by the dividing resistor R6, the diode D3, and the dividing resistor R7. The cathode of the diode D3 is connected to the base terminal. Therefore, even if the increase in the base current I _B in the transistor Q2 is increased temperatures, the diode D3 also can increase the base current I _B in the reduction of the forward voltage based on the same temperature increase, characteristics of the transistor Q2 Can compensate for change. Therefore, the accuracy can be improved.

  Since the present invention can cope with fluctuations in the output terminal on the non-constant voltage control side while maintaining the voltage at the output terminal on the constant voltage control side, the AC voltage is converted into a DC voltage by a switching method and supplied to the load. It is suitable for a power supply device.

The circuit diagram explaining the power supply device which concerns on embodiment of this invention (A) The graph which shows the voltage-current characteristic of the 2nd output terminal of a power supply device, (B) The graph which shows the current- shunt current characteristic of the 2nd output terminal The figure which shows the electric potential detection shunt circuit of the power supply device which concerns on other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power supply device 2 AC power supply 3 Voltage supply circuit 4 Transformer 5 Switching control circuit 6 1st smoothing rectification circuit 7 2nd smoothing rectification circuit 8 Voltage monitoring circuit 9 Potential detection shunt circuit 20 Potential detection shunt circuit 51 Pulse modulation control IC
C0, C1, C2 Smoothing capacitor D1, D2, D3 Diode DB Diode bridge IC2 Shunt regulator OUT1 First output terminal OUT2 Second output terminal PC1 Photocoupler Q1 FET
Q2, Q3 Transistor R1, R2 Split resistor R3 Resistor R4, R5 Split resistor R6, R7 Split resistor Rb Resistor S0 Input winding S1 First output winding S2 Second output winding V1 Main output voltage V2 Sub output voltage ZD1 Zener diode

Claims (4)

A voltage supply circuit using the AC power supply voltage as a DC voltage;
A transformer that inputs a DC voltage from the voltage supply circuit to an input winding and outputs a predetermined rated voltage from each of the first and second output windings;
A switching control circuit for switching a current to an input winding of the transformer;
First and second smoothing rectifier circuits for smoothing and rectifying the outputs from the first and second output windings, respectively, to the first and second output terminals;
In the power supply apparatus having a voltage monitoring circuit that monitors the DC voltage of the first output terminal and instructs the switching pulse width or cycle of the switching control circuit,
A potential detection shunt circuit that shunts current from the first output end to the second output end when a difference in DC voltage between the first output end and the second output end is equal to or greater than a predetermined potential difference; A power supply characterized by. The potential detection shunt circuit starts from the first output terminal when the divided resistor connected to the first output terminal and the second output terminal and the voltage divided by the divided resistor have a predetermined potential difference. The power supply apparatus according to claim 1, further comprising a shunt regulator that allows current to flow to the second output terminal. The potential detection shunt circuit starts from the first output terminal when the divided resistor connected to the first output terminal and the second output terminal and the voltage divided by the divided resistor have a predetermined potential difference. The power supply device according to claim 1, further comprising a transistor that shunts current to the second output terminal. A diode is provided in a forward direction between the first resistor and the second resistor of the divided resistor,
4. The power supply device according to claim 3, wherein the transistor is shunted by a voltage divided by the first resistor and the diode and the second resistor.

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