JPH0487561A - Voltage stabilization circuit - Google Patents

Abstract

PURPOSE:To obtain stable output voltage by making a feedback circuit including a shunt regulator. CONSTITUTION:A shunt regulator 13 composing a feed-back circuit 9 controls an anode-cathode current with the voltage at a reference voltage input terminal 14. That is, when the induction voltage of the secondary coil 4 of a switching transistor 3 increases, voltage divided by voltage division resistors 7 and 8 increases, the anode-cathode current of the shunt regulator 13 increases, and potential at point (a) lowers. As a result, the turn-on time of the switching transistor 3 shortens and the induction voltage of the secondary coil 4 decreases. When decreasing, the induction voltage of the secondary coil 4 can be controlled so as to be constant by reverse action. Thereby stable output voltage can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a voltage stabilizing circuit using a switching power supply that turns on and off the voltage applied to the primary coil of a switching transformer using a switching transistor.

BACKGROUND OF THE INVENTION In recent years, with the spread of office automation equipment, voltage stabilization circuits using switching power supplies that use switching transistors to turn on and off the voltage applied to the primary coil of a switching transformer have come into wide use. ing.

Conventionally, this type of voltage stabilizing circuit has generally had a configuration as shown in FIG. The configuration will be explained below.

As shown in the figure, a switching transformer 1 has a primary coil 2 connected in series to a switching transistor 3, to which a DC voltage of 10 B is applied. Secondary coil 4 is diode 5
It is connected to the output terminal 6 via. The voltage dividing resistors 7 and 8 divide the voltage at the output terminal 6 and input it to an operational amplifier 10 forming a feedback circuit 9. The output of the operational amplifier 1o is input to the switching transistor 3 via the tertiary coil 11. A constant voltage source 12 provides a reference voltage to the operational amplifier 10.

To explain the operation of the above configuration, the switching transistor 3 turns on and off the current flowing through the primary coil 2 of the switching transformer 1, and induces a voltage in the secondary coil 4. Here, when the induced voltage of the secondary coil 4 increases, the voltage divided by the voltage dividing resistors 7 and 8 increases,
The output of the operational amplifier 10 becomes low. As a result, the DC voltage applied to the base of the switching transistor 3 is low, the ON time of the switching transistor 3 is short, and the induced voltage in the secondary coil 4 is reduced. Secondary coil 4
When the induced voltage in the secondary coil 4 becomes low, the secondary coil 4 operates in the opposite manner to the above operation to control the induced voltage in the secondary coil 4 to be constant.

Problems to be Solved by the Invention Such a conventional voltage stabilizing circuit requires an operational amplifier 10 and a constant voltage source 12 as a feedback circuit 9, resulting in a complicated circuit configuration and high cost. .

The present invention solves the above problems, and aims to simplify the circuit configuration and reduce the circuit cost.

Means for Solving the Problems In order to achieve the above object, the present invention provides a means for solving the problems by configuring the feedback circuit with a shunt regulator.

Effect of the present invention By using the above-mentioned problem solving means, the DC voltage at the base of the switching transistor can be controlled by controlling the current of the shunt regulator by the voltage divided by the voltage dividing resistor, and the secondary The induced voltage in the coil can be controlled to a constant level. Moreover, the circuit configuration of the feedback circuit can be simplified.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to FIG. Note that components having the same configuration as those of the conventional example are given the same reference numerals, and description thereof will be omitted.

As shown in the figure, the shunt regulator 13 constitutes the feedback circuit 9 and can control the current between the anode and the cathode by the voltage of the reference voltage input terminal 14.
The reference voltage input terminal 14 is connected to the voltage dividing resistor 8, and the anode and cathode are connected to GND and the negative power supply (-V
), and one end of the tertiary coil 11 is connected to the connection point between the cathode and the resistor 16.

To explain the operation in the above configuration, when the induced voltage of the secondary coil 4 increases, the voltage divided by the voltage dividing resistors 7 and 8 increases 9, the current between the 7 node of the shunt regulator 13 and the cathode increases, The potential at point a decreases. As a result, the on-time of the switching transistor 3 is shortened, and the induced voltage in the secondary coil 4 is reduced. When the induced voltage of the secondary coil 4 becomes low, the operation is reversed to that described above, so that the induced voltage of the secondary coil 4 can be controlled to be constant, and a stable output voltage can be obtained.

Effects of the Invention As is clear from the above embodiments, according to the present invention, since the feedback circuit is configured with multiple shunt regulators, a stable output voltage can be obtained, and the number of circuit components can be reduced, resulting in cost reduction.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a voltage stabilizing circuit according to an embodiment of the present invention,
FIG. 2 is a circuit diagram of a conventional voltage stabilizing circuit. 1...Switching transformer, 2.Old...-secondary coil, 3...Switching transistor, 4
...Secondary coil, 7, 8...Voltage dividing resistor (voltage dividing circuit), 9...RtR times Wl&, 1s.
...Shunt regulator.

Claims (1)

[Claims] a switching transformer having a primary coil to which a DC voltage is input and a switching transistor connected in series; a voltage dividing circuit that divides a voltage induced in a secondary coil of the switching transformer by on/off operations of the switching transistor; and a feedback circuit that controls the on-time of the switching transistor using the output of the voltage circuit to keep the secondary coil voltage substantially constant, the feedback circuit comprising a shunt regulator.