JPS61207170A - Multiple output switching regulator - Google Patents

Abstract

PURPOSE:To prevent a device from generating error movement, by arranging a rectification smoothing circuit for one kind of output among multiple output, to be of a condenser input type, and by providing a stabilizing circuit between the rectification smoothing circuit and the output. CONSTITUTION:DC output rectifying and smoothing AC input 1 with a diode bridge DB1 and a condenser C1 is ON/OFF-controlled via the primary winding of a transformer T1 and a switching transistor Q1, and voltage induced to the secondary winding is rectified and smoothed, and desired much DC output is obtained. Then, the rectification smoothing circuit of one kind of output among multiple output, for example, of output 4 is arranged to be of condenser input type, and between this and the output, a stabilizing circuit IC2 is provided. As the result, the rectification smoothing circuit of condenser input type for constant-voltage protection against excess current can be easily organized, and the output 3 of hard output current fluctuation can be directed to a controlling section 2 for feedback.

Description

Detailed Description of the Invention (Technical Field) The present invention turns on and off a current flowing through a primary winding of a transformer having a plurality of secondary windings using a switching element, and when the switching element is on. , supplies energy to the secondary side, rectifies and smoothes the plurality of secondary winding outputs, obtains a plurality of DC outputs, and controls the on/off ratio of the switching element by one of the plurality of DC outputs. The present invention relates to a multi-output switching regulator that obtains a plurality of desired outputs.

(Prior Art) FIG. 2 shows a circuit diagram of a multi-output switching regulator according to a conventional example.

In the figure, AC human power 1 is diode bridge DB,
, the DC output rectified and smoothed by the capacitor CI is connected to one end of the primary winding of the converter transformer T1.

The other end of the primary winding of TI is a switching transistor Q,
The other end of the DC power supply is connected to the other end of the DC power supply. QI
A signal from a control section, which will be described later, is turned on and off at an appropriate on/off ratio to generate an induced voltage in the secondary winding of Tt, and by rectifying and smoothing this, a desired DC output is obtained.

This example has four secondary windings to obtain four independent outputs. Each @ line has a rectifier diode D.
s, D5. D? ,D? , commutation diode D4. Di
, Ds, D+. , smoothing choke coil L+, Lx
, Ls, La, smoothing capacitor Cm, (,
&, C? , Cs are provided.

Also, dummy resistors R%, R, for output 1 to output 3.

R, Output short circuit protection fuse FU2. FU3゜FU4
It is equipped with Further, the output 4 is provided with a variable resistor VR1 for detecting an output voltage and a resistor R1 for detecting an output current, which also serves as a dummy resistor.

These voltage and current information are fed back to the control section 2.

The control unit 2 mainly includes a switching regulator IC.
(494 manufactured by TI). The voltage and current information from the output 4 is compared with a reference value built into the IC, and based on the difference, the on/off ratio of the switching transistor Q is approximately stabilized by the sleggregation effect so that the output of the output 4 is constant.

Note that since overcurrent detection is performed only at output 4, outputs 1 to 3 are provided with protective fuses. A power supply configured in this manner is low cost and capable of multiple outputs, and is therefore often used in copying machines and the like.

When applied to a copying machine, output 4 is a control circuit (consisting of μCOM, etc.) that has a relatively small capacity and requires precision, output 3 is a photoreceptor drum, optical system scanning motor, and output 2 is a timing control circuit. The output 1 is used as a high-voltage power source for charging transfer, etc. In a copying machine, the current of output 4 is almost constant, but outputs 1 to 3 vary drastically according to the process of the copying machine. In particular, output 3 for the motor rotates the motor with high precision.
Since it has to be stopped, the fluctuation is significant and a large current flows transiently.

In order to prevent voltage drop due to this wraparound, it is desirable that each output be in a floating state.
However, if this is done, overcurrent protection of the output 3 by detecting the current of the output 3 and controlling the switching transistor Q becomes impossible. Furthermore, if a photocoupler or the like is used for the float, the circuit becomes complicated and very expensive. Furthermore, when the output voltage and output current of output 3 are detected and returned to the control section,
The output voltage accuracy of output 4 is insufficient and is not possible, and if the fuse is used as shown in the figure, the current fluctuates rapidly, so the life of the fuse is short and troubles occur such that the fuse breaks even under normal conditions. When the power switch is turned on, the rise of each output is almost the same, and the control system output 4
A certain amount of voltage is supplied to outputs 1 to 3 while the controllable voltage is not yet reached, and there is also a drawback that the electromagnetic counter for counting the number of copies may malfunction and the motor may operate unnecessarily.

(Objective) The purpose of the present invention is to eliminate the drawbacks of the conventional example, provide a multi-output switching regulator with a simple configuration and a difference in output rise and fall, and furthermore, provide a multi-output switching regulator with a difference in output rise and fall. The object of the present invention is to provide a multi-output switching regulator that provides overcurrent protection without using fuses.

(Structure) To achieve this, the present invention uses at least one output rectifying and smoothing circuit as a capacitor input type, and the other as a choke input type, and also provides an output stabilizing circuit between the capacitor input rectifying and smoothing circuit and the output. The present invention is characterized in that the on/off ratio of the switching element is controlled by the output voltage and output current of the output provided with the input rectifying and smoothing circuit.

Hereinafter, one embodiment of the present invention will be described based on the circuit diagram shown in FIG. Note that the same parts as in the conventional example are given the same reference numerals.

As mentioned above, the present invention has the following advantages in comparison with the conventional example shown in FIG.
The rectifying and smoothing circuit with two outputs (output 4 in this example) is of a capacitor input type, and a stabilizing circuit is provided between the rectifying and smoothing circuit and the output. In this embodiment, a series regulator is used as the stabilizing circuit. A three-terminal regulator (7805 manufactured by FC) ICz is used. If the rectifier and smoothing circuit is a capacitor input type, its output voltage will have little relationship with the switching on/off ratio.
A three-terminal regulator, etc. is required for the output, but since the output current is small, constant voltage protection and overcurrent protection can be easily configured (a three-terminal regulator, etc. as mentioned above is sufficient), but on the other hand, output current fluctuations Since it is possible to feed back the intense output (output 3 in this example) to the control section 2, there is no need to use a fuse for such output, and the troubles caused by fuses seen in the conventional example can be solved. Also, the rise of output 4, where there is no inductance component in the rectifying and smoothing circuit, is L+.
Compared to outputs 1 to 3, which have ~L, the fall is much faster and does not require a dummy resistor, so outputs 1 to 3 have
Since it is gentle compared to output 3, the voltage to the control system rises faster and falls slower than others, so when the power is turned on,
When shutting off, it is possible to prevent copying machines, etc. from malfunctioning.

(Effects) The present invention is as described above, and according to the multi-output switching regulator according to the present invention, a difference can be provided between the rise and fall of the output of the multi-output power supply, so that the equipment Malfunctions can be prevented, and overcurrent protection can be performed without using fuses for outputs with significant load fluctuations, so there are effects such as no fuses being erroneously disconnected.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a multi-output switching regulator according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional switching regulator. T...Transformer, Q...Switching element, IC,...Stabilized three-terminal regulator.

Claims (1)

[Claims] A switching element turns on and off the current flowing through the primary winding of a transformer having a plurality of secondary windings, and when the switching element is on, it supplies energy to the secondary side and connects the plurality of secondary windings. A multi-output switching regulator that rectifies and smoothes an output to obtain a plurality of DC outputs, and controls the on/off ratio of the switching element by one of the plurality of DC outputs to obtain a plurality of desired outputs.
One of the output rectifying and smoothing circuits is a capacitor input type, and the other one is a choke input type, and an output stabilizing circuit is provided between the capacitor input rectifying and smoothing circuit and the output. A multi-output switching regulator characterized in that the on/off ratio of a switching element is controlled by the output current.