JP2001275354A - Switching power supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problems where the load of a control tap 2 is low, where a primary power circuit includes the control tap 2 of which the voltage is fed back and output taps 3, 4 of which voltage is not fed back, and that the voltage of the output tap lowers where at least one of the output taps 3, 4 has high load. SOLUTION: This switching power supply unit is added with a dummy resistor 7 as a load for the control tap 2 by having a transistor 71 turned on.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply for keeping an output voltage constant.

[0002]

2. Description of the Related Art For example, a power supply device incorporated in a water heater has a control tap for supplying power to a remote controller and a CPU. The voltage of the control tap is fed back to the primary-side power supply circuit, and is configured as a switching power supply that is always stabilized at, for example, 12 volts even if the load state changes. Further, the power supply device is provided with an output tap for outputting a voltage of, for example, 40 volts for driving a fan and a proportional valve, and an output tap for outputting a voltage of, for example, 24 volts to various terminal units. The voltages of these two output taps are not fed back, and the voltage may change to some extent when the load state changes.

[0003]

When the load state of the control tap is large, sufficient power is supplied from the primary side power supply circuit to the control tap, and at the same time, sufficient power is supplied to both output taps. Therefore, even if the load state of the output tap changes, the voltage of the output tap does not change so much and is stable. However, when the load state of the output tap is increased while the load state of the control tap is small, sufficient power is not supplied from the primary side power supply circuit, so that the voltage of the output tap greatly decreases as the load state increases. Occurs.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a switching power supply device in which the voltage of an output tap does not decrease even when the load state of an output tap increases while the load state of a control tap is small. And

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a control tap which is fed back to a primary side power supply circuit and controlled so that an output voltage becomes constant, and a control tap from the primary side power supply device. A switching power supply having at least one output tap receiving power supply and outputting a predetermined voltage, wherein a load state of the control tap is smaller than a first predetermined value, and a load state of the output tap is a second predetermined value. A load increasing means for increasing a load state of the control tap when the control tap is larger than the predetermined value is provided.

When the load state of the output tap increases while the load state of the control tap is small, the voltage of the output tap becomes unstable as described above. Therefore, in such a case, sufficient power is supplied from the primary power supply circuit to the output tap by increasing the load state of the control tap.

By the way, a load such as a dummy resistor may be interposed between the control tap and the ground via a transistor in order to increase the load. What is necessary is just to operate the water amount servo which is a kind of the electric on-off valve having the function as a load. However, if the water volume servo is rotated in one direction, a desired hot water supply amount cannot be obtained. Therefore, by alternately supplying the electric power from the control tap and supplying the electric power to the water amount servo, the load state is increased, but the actual tapping amount is not changed.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference numeral 1 denotes a switching power supply which converts power supplied from an AC power supply 11 into a desired voltage by a transformer 12 and outputs it. The output is made from the control tap 2 and the two output taps 3,4. The voltage of the control tap 2 is monitored by the control circuit 21, and the transistor 22 is pulse-driven so that the tap voltage becomes 12 volts. Therefore, when the voltage of the control tap 2 decreases, the ON duty width of the pulse drive increases, and the operation is performed so as to keep the voltage constant. As the ON duty width increases, the power supplied to the output taps 3 and 4 also increases. The output tap 3 is set to 40 volts, and is used as a power supply for driving a load 31 such as a fan for supplying combustion air to a gas burner 61a described later and a proportional valve for controlling a gas supply amount. The output tap 4 is set at 24 volts, and is used as a drive power source for a load 41 such as various units built in the water heater except for the control unit 5 described later. The control tap 2 supplies power to a control unit 5 having a CPU. The control unit 5 detects the driving state of each of the loads 31 and 41 and communicates with the remote controller 51. Gas burner 6
The drive circuit 52 of the water amount servo 6 for controlling the amount of water flowing to the heat exchanger 61 heated in 1a is connected. The water amount servo 6 has a valve attached to a valve shaft that moves forward and backward by a geared motor. The valve is moved by rotating the geared motor to increase or decrease the flow area of water to the heat exchanger 61. Further, in the present embodiment, the control tap 2 is grounded via a series circuit of the transistor 71 and the dummy resistor 7. The transistor 71 is turned on / off by the control unit 5.

When the water volume servo 6 is operated, a large current flows through the geared motor, so that the load on the control tap 2 increases. Then, since the voltage of the control tap 2 decreases, the ON duty width increases as described above, and the power supplied to the output taps 3 and 4 increases. In this state, even if the other loads 31 and 41 increase, sufficient power is supplied, so that the voltage of the output taps 3 and 4 does not decrease. However, once the water position servo 6 adjusts the position of the valve, the position of the valve is maintained even when the geared motor is not energized, so that the load on the control tap 2 is reduced. Then, the ON duty width becomes smaller, and the power supplied to the output taps 3, 4 decreases. However, when the loads 31 and 41 are still high, the voltages of the output taps 3 and 4 decrease. Therefore, the control unit 5 constantly monitors the load state of the control tap 2 and the output taps 3 and 4, and when the load state of the control tap 2 is smaller than the predetermined load state, When either of them is larger than the predetermined load state, the load state of the control tap 2 is increased, the ON duty width is increased, and the supplied power is increased. Specifically, the transistor 71
Is turned on, and a dummy resistor 7 is loaded on the control tap 2. As a result, the load state of the control tap 2 increases, so that the supplied power increases, and the voltages of the output taps 3 and 4 are stabilized. When it is necessary to operate the water volume servo 6 with the transistor 71 turned on, or when the load state of the output taps 3 and 4 becomes small, the transistor 71 is turned off to consume power. I tried not to get more.

In the above-described embodiment, the dummy resistor 7 is used to increase the load on the control tap 2.
And the transistor 71 are added, but the load state may be increased by using the water volume servo 6 instead of the dummy resistor 7. However, when the water amount servo 6 is operated, the position of a certain built-in portion moves and the amount of water flowing to the heat exchanger 61 changes. Therefore, when using the water amount servo 6 to increase the addition of the control tap 2,
The drive power supplied to the water volume servo 6 is alternated in a short cycle. As described above, when the driving power is alternated, the geared motor rotates forward and backward at the alternating cycle. If the alternating cycle is short, the position of the valve does not substantially change. Therefore, the amount of water to the heat exchanger 61 does not change, and the pulsation of the water flow can be ignored.

[0011]

As is apparent from the above description, according to the present invention, when the load state of the control tap is small, even if the load state of the output tap becomes large, it is possible to suppress the voltage drop of the output tap. it can.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

[Explanation of symbols]

 1 DC power supply 2 Control tap 3 Output tap 4 Output tap 5 Control unit 6 Water volume servo

Claims (2)

[Claims] 1. A control tap which is fed back to a primary side power supply circuit and controlled so that an output voltage is constant, and at least one output tap which receives power supply from the primary side power supply and outputs a predetermined voltage. In the switching power supply device having the above, when the load state of the control tap is smaller than a first predetermined value and the load state of the output tap is larger than a second predetermined value, the load increase for increasing the load state of the control tap. A switching power supply device comprising means. 2. The switching power supply device is incorporated in a water heater provided with a water amount servo, and the load increasing means alternately supplies power from the control tap to the water amount servo to increase the load state of the control tap. The switching power supply according to claim 1, wherein