JPH06311748A - Power supply apparatus - Google Patents

Abstract

PURPOSE:To obtain a power supply apparatus which eliminates a waste power consumption and the abnormal rise of an output voltage. CONSTITUTION:A power supply apparatus has a forward type DC-DC converter. The output of the secondary side of a transformer T is rectified and smoothed by rectifiers D1 and D2, an inductance L and a capacitor C1 and supplied to a load 1. A secondary 36 V circuit is composed of a dummy resistor 5 which shunts and grounds the output, a switching device 4 which turns on and off the dummy resistor 5 and a current detector 3 which detects a current applied to the load 1. When the load 1 is disconnected, the dummy resistor 5 is connected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a forward type DC-D provided in an image recording device such as a copying machine or a printer.
The present invention relates to a power supply device having a C converter.

[0002]

2. Description of the Related Art An outline of the circuit configuration of a conventional power supply device is shown in FIG.
And shown in FIG.

The power supply device shown in FIG. 6 is a forward type DC-DC converter type power supply device having a power supply transformer T, and a 24V circuit rectified and smoothed by a diode D and a capacitor C on the secondary side and a diode D1. , D2
A 36V circuit rectified and smoothed by the capacitor C1 and the inductance L1 and various output circuits for developing, transferring, discharging, etc. are provided.

Then, the output voltage of the 24V circuit is compared with the reference voltage by the comparator 11, and the result is input to the central processing unit (hereinafter referred to as CPU) of the control unit 12, and the control unit 12 outputs the input 24V circuit. Based on the output voltage information, the switching device 13 on the primary side is turned on / off to perform feedback control so that the output of the 24V circuit on the secondary side becomes a constant voltage.

The output of the 36V circuit is 3 as shown in FIG.
Feedback control is performed within a small loop of the 6V circuit, and the accuracy of the output voltage of the 36V output is about ± 5% when such a circuit is used.

[0006]

However, in the above-mentioned conventional power supply device, the output of 36V system is mainly used for motor control, and the voltage accuracy required for motor control is ± 2.
About 0% is sufficient, and the above-mentioned conventional circuit becomes over-specified and leads to cost increase.

Therefore, the chopper circuit 14 controlling the output voltage is removed from the 36V system circuit of the circuit shown in FIG. Then, when the load current of the 30V system is 0A, the maximum output voltage will be about 70V, so if the load is a DC brushless motor, the maximum applied voltage of the motor control semiconductor is about 50V, so the semiconductor element will have a dielectric breakdown. Will cause.

In order to prevent the above phenomenon, as shown in FIG.
A resistor (hereinafter referred to as a dummy resistor) 5 is inserted and connected between the output terminal of 36V and the ground, and a dummy current (load current) is passed to make the output of the 36V system to a voltage that does not damage the semiconductor element for motor control. You can hold it down. With such a configuration, a current will always flow through the dummy resistor 5 which enables control with a voltage accuracy of about ± 20%, resulting in a large loss.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and it is an object of the present invention to provide a power supply device which suppresses cost, prevents wasteful power consumption, and prevents abnormal rise in output voltage. It is intended.

[0010]

Therefore, a power supply device according to the present invention is a power supply device including a forward type DC-DC converter, and is not used in a secondary side circuit for smoothing and outputting with an inductance and a capacitor. A dummy circuit for branching an output and a switch circuit for turning on / off the connection of the dummy resistor and a power supply control means for controlling the connection of the dummy resistor are provided to achieve the above object. is there.

In the above structure, the connection control of the dummy resistor by the power supply control means is provided with the load current detection means and the load current detection means is provided so that the load current is equal to or less than a predetermined value. When the output voltage is equal to or higher than a predetermined value, or when the load operation sequence information is input, the load is turned on. Alternatively, the above object is achieved by providing a plurality of dummy resistance circuits and selectively connecting the dummy resistance circuits corresponding to the current amount from the secondary side circuit to the load.

[0012]

With the above structure, the secondary side circuit that smoothes and outputs the inductance and the capacitor has a dummy resistor for branching and flowing the output, and the power supply control means turns on the dummy resistor connection by the switch circuit. By causing the output current to flow through the dummy resistor, it is possible to suppress the output voltage and prevent the output voltage from rising above a predetermined value without the chopper means.

The dummy resistor is turned on when the load is in a no-load state, when the load current is below a predetermined value, when the output voltage is above a predetermined value, or when the load becomes light. As a result, the output voltage rise can be suppressed only when the output voltage rises abnormally. Also, by providing a plurality of dummy resistance circuits and selectively connecting the dummy resistance circuits corresponding to the amount of current from the secondary side circuit to the load, the output voltage of the output voltage can be adjusted to an appropriate value when the output voltage rises abnormally. The rise can be suppressed and controlled.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A power supply device according to the present invention will be described below with reference to embodiments.

(First Embodiment) FIG. 1 is a circuit diagram showing a main structure of a first embodiment of the present invention. The same or corresponding parts as those of the conventional power supply device are designated by the same reference numerals, and the duplicated description will be omitted.

In this embodiment, the current flowing in the load 1 (mainly the motor) of the 36V circuit is detected by the current detection circuit 3 of the control unit 2, and the transistor 4 is activated by the transistor 4 when the motor 1 is stopped and the load current becomes 0A. The configured switching circuit is turned on to pass a dummy current through the dummy resistor 5.

The dummy resistor 5 has such a resistance value that the output voltage can be suppressed to a voltage at which the control semiconductor element (not shown) of the load motor 1 does not cause dielectric breakdown.

With the above-described structure, it is possible to prevent wasteful consumption of electric power by preventing current from flowing unnecessarily because a current flows through the dummy resistor 5 only when necessary, and to prevent an abnormal increase in output voltage.

(Second Embodiment) FIG. 2 is a circuit diagram of an essential part of the second embodiment, in which the same or corresponding parts as in the first embodiment are designated by the same reference numerals.

In this embodiment, a voltage that does not cause dielectric breakdown of the control semiconductor element of the motor 1 is set as the reference voltage of the comparator 6, and the output voltage of the 36 V output circuit is input to the other input of the comparator 6. When the voltage exceeds the reference voltage, the switching element 4 is turned on and a dummy current is passed through the dummy resistor 5 to suppress the increase in the output voltage of the 36V circuit.

(Third Embodiment) FIG. 3 is a circuit diagram of an essential part of the third embodiment.

The present embodiment is provided with a control section 7 for system-controlling the entire power supply by using a CPU, and has a configuration in which the CPU is operating at which timing and which circuit is operating. The switching element 4 is turned on only when the load state or a state close to the load state is made to flow a current through the dummy resistor 5 to prevent the output voltage of the 36V circuit from increasing.

(Fourth Embodiment) FIG. 4 is a circuit diagram of an essential part of the fourth embodiment.

In the present embodiment, the CPU of the control unit 8 determines whether the amount of current detected by the current detection circuit 3 is below a certain set value, and if the amount of current is less than the set value, the switching element 4 is operated. It is configured so that it is turned on and a current is passed through the dummy resistor 5 to prevent an increase in the output voltage of the 36V circuit.

(Fifth Embodiment) FIG. 5 is a circuit diagram of an essential part of the fifth embodiment.

In this embodiment, a plurality of dummy resistors 5a, 5a
Switching elements 4a, 4b and 4c are connected to b and 5c, respectively.
4b and 4c can be selected and turned on / off.

Then, the current load of the 36V system is set to a certain constant value, and the CPU of the control unit 9 judges how much the current amount detected by the current detection circuit 3 is smaller than the set value. The dummy resistors 5a, 5b, 5c for passing dummy currents are selected according to the difference. With such a configuration, the amount of change in the output voltage of the 36V circuit can be suppressed to a small amount.

[0028]

As described above, according to the present invention, the secondary side circuit for smoothing and outputting by the inductance and the capacitor has the dummy resistor for branching and flowing the output, and the power supply control means is the switching element. By turning on the connection of the dummy resistor by and flowing the output current to the dummy resistor,
It is possible to provide a power supply device that can suppress the output voltage and prevent the output voltage from rising above a predetermined value without using a chopper means, reduce the cost, prevent wasteful power consumption, and prevent an abnormal increase in the output voltage.

The dummy resistor is turned on when the load is in a no-load state, when the load current is below a predetermined value, when the output voltage is above a predetermined value, or when the load becomes light. As a result, the output voltage rise can be suppressed only when the output voltage rises abnormally. Further, by providing a plurality of dummy resistance circuits and selectively connecting the dummy resistance circuits according to the amount of current from the secondary side circuit to the load, the output voltage is adjusted to an appropriate voltage value when the output voltage rises abnormally. The rise can be suppressed and controlled.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a main part of a first embodiment.

FIG. 2 is a circuit diagram of a main part of a second embodiment.

FIG. 3 is a circuit diagram of a main part of a third embodiment.

FIG. 4 is a circuit diagram of a main part of a fourth embodiment.

FIG. 5 is a circuit diagram of a main part of a fifth embodiment.

FIG. 6 is a circuit portion of a conventional power supply device.

FIG. 7 is a circuit diagram of a main part of a conventional power supply device.

[Explanation of symbols]

 C, C1 capacitors D, D1, D2 rectifying element L1 inductance T1 transformer 1 load (motor) 2 controller 3 current detection circuit 4 switching circuit 5 dummy resistor 6 comparator 7, 8, 9 controller with CPU

Claims (6)

[Claims] 1. A power supply device comprising a forward type DC-DC converter, wherein a dummy resistor and a dummy resistor are connected to a secondary resistor for smoothing and outputting with an inductance and a capacitor and turning on / off the connection of the dummy resistor. A power supply device comprising power supply control means for controlling the connection between the switch circuit and the dummy resistor. 2. The power supply control means is provided with a load current detection means for detecting the amount of current from the secondary side circuit to the load, and a dummy resistor is connected when the load is in an unloaded state. 1. The power supply device according to 1. 3. The power supply control means comprises a load current detection means for detecting the amount of current from the secondary side circuit to the load, and a dummy resistor is connected when the load current falls below a predetermined value. The power supply device according to item 1. 4. The power supply device according to claim 1, wherein the power supply control means detects an output voltage of the secondary side smoothing circuit and connects a dummy resistor when the output voltage is a predetermined value or more. 5. The power supply device according to claim 1, wherein the power supply control means inputs the operation sequence information of the load and connects the dummy resistor at the timing when the load becomes light. 6. A plurality of dummy resistance circuits each comprising a dummy resistance and a switch circuit for turning on / off the connection of the dummy resistance, wherein the power supply control means selectively connects the dummy resistance circuit corresponding to the amount of current from the secondary side circuit to the load. The power supply device according to claim 1, wherein: