JPH01307811A - Constant voltage circuit - Google Patents

Abstract

PURPOSE:To flow a current to a load without reducing the output voltage of a power source by providing a rush current by-pass circuit, which consists of a transistor TR for shunt circuit and a load current measuring resistance, and a power supply part. CONSTITUTION:When a large current like a rush current does not flow, the voltage drop of a load current measuring resistance 23 is set to a value lower than the voltage between the base and the emitter of a TR 22 for shunt circuit, and therefore, the base current does not flow. Consequently, the circuit between the emitter and the collector is turned off, and a rush current by-pass circuit 24 consisting of the TR 22 and the resistance 23 has not an influence on a power supply part 21 at all. However, when the load current is increased and the voltage drop of the resistance 23 exceeds a prescribed voltage, the base current flows by its excess voltage, and the current amplified approximately in proportion to this current flows through the emitter and the collector to form the circuit 24. That is, the current exceeding the prescribed value does not pass the power supply part 21 at all but passes the circuit 24, and thus, the current flows to the load without reducing the output voltage of the power source.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a constant voltage circuit for controlling the on/off of an additional circuit using the same power source as the control unit.

[Conventional technology]

FIG. 4 is a circuit diagram showing an example of a constant voltage circuit used in a conventional DC constant voltage power supply. In the figure, 1 is a transistor for output voltage control, 2 is an error amplifier circuit, and 3 is a Zener diode 3a. This is a reference circuit that outputs a reference voltage.

Next, the operation will be explained. When a load (not shown) is connected to the output terminal VB, the load current flows from the input terminal V through transistor 1, and the power supply output voltage 2 is equal to the input voltage 1 minus the voltage drop across transistor 1. will be the value. The error amplification circuit 2 compares and amplifies the output voltage of the reference circuit 3 and the power supply output voltage 2, and
The base current is controlled to set an appropriate value to obtain a predetermined power supply output voltage V2 corresponding to the load current.

[Problem to be solved by the invention]

Since the conventional constant voltage circuit is configured as described above,
If the initial inrush current when a load is connected or an unexpected abnormal overcurrent flows and exceeds the voltage control capability of transistor 1,
There was a problem that the power supply output voltage (2) instantaneously dropped below the specified value.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to obtain a constant voltage circuit that can allow current to flow through a load without reducing the power supply output voltage.

[Means to solve the problem]

The constant voltage circuit according to the present invention includes a power supply section that controls the output voltage within a predetermined range in response to the load current, and an inrush current bypass circuit that shunts the load current flowing from the input side to the output side to the power supply section. It is equipped with the following.

[Effect]

In the constant voltage circuit according to the present invention, inrush current or unexpected abnormal overcurrent when a load is connected flows to the inrush current bypass circuit and does not flow to the output voltage control transistor.
Predetermined circuit characteristics can always be maintained.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is a circuit diagram showing an embodiment of the present invention. In the figure, 21 is a transistor 1 for controlling the output voltage shown in FIG.
, a power supply section consisting of an error amplifying circuit 2 and a reference circuit 3, 22 a transistor for a shunt circuit, and 23 a resistor for measuring a load current to control the base current of the transistor 22 for a shunt circuit. The shunt circuit transistor 22 is controlled by the voltage drop caused by the load current flowing through the resistor 23. The shunt circuit transistor 22 and the load current measuring resistor 23 constitute an inrush current bypass circuit 24.

Next, the operation will be explained. When a large current such as an inrush current does not flow, the voltage drop across the load current measuring resistor 23 is set to be lower than the voltage between the base and emitter of the shunt circuit transistor 22, so no base current flows. So the emitter.

The collector-to-collector circuit is in an off state, and the rush current bypass circuit 24 has no effect on the power supply section 21. However, when the load current increases and the voltage drop across the load current measuring resistor 23 exceeds a predetermined voltage, the excess voltage causes a base current to flow, and an amplified current approximately proportional to this flows through the emitter and collector. Inrush current bypass circuit 24
is formed. That is, all current exceeding a predetermined value does not pass through the power supply section 21 but passes through the inrush current bypass circuit 24.

Note that this bypass function is always formed in real time with almost no delay and shunts a predetermined current value, regardless of whether the inrush current is instantaneous or continuous.

FIG. 2 is a configuration diagram showing another embodiment of the present invention, in which a positive characteristic thermistor 2 is used instead of the load current measuring resistor in the above embodiment.
5 was used. This positive temperature coefficient thermistor 25 is a nonlinear resistor that is almost the same as a normal resistance material when its temperature is below a certain value, but when the temperature exceeds a predetermined temperature, its resistance value increases rapidly. It is element. Therefore, in this case, as the temperature of the positive temperature coefficient thermistor 25 increases, the potential difference between its both ends increases, causing the shunt circuit transistor 22 to conduct.

Therefore, if this positive temperature coefficient thermistor 25 is installed on the input side of the power supply section 21, it can be installed to sense overheating at the point.
The load current can be shunted to the inrush current bypass circuit 24.

FIG. 3 is a configuration diagram showing yet another embodiment of the present invention, in which a relay 2 having a coil 26L and a contact point 26° is used instead of the load current measuring resistor and positive temperature coefficient thermistor of the above embodiment.
6. Coil 26L of this relay 26
is connected in series with the power supply unit 21, and a contact 26c is connected to the base resistor 27 of the shunt circuit transistor 22. In this case, when the load current increases and exceeds a certain predetermined value, the contact 26c closes and the base current flows, forming a predetermined inrush current bypass circuit 24.

〔Effect of the invention〕

As described above, according to the present invention, since the structure includes an inrush current bypass circuit that functionally shunts inrush current and unexpected overcurrent to the power supply unit when the power is turned on or when a load is connected, the inrush current bypass circuit is provided. This has the effect of preventing a drop in output voltage.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment according to the present invention. Second
The figure is a configuration diagram showing another embodiment of the present invention using a nonlinear resistance element. FIG. 3 is a block diagram showing another embodiment of the present invention using a relay. FIG. 4 is a circuit diagram showing a conventional constant voltage circuit. In the figure, 21 is a power supply section, 22 is a shunt circuit transistor, and 24 is an inrush current bypass circuit. Note that the same reference numerals in each figure indicate the same or corresponding parts. 24: Rush 1rtno (Monk V, tO*,, 24.2

Claims (1)

[Claims] A constant voltage circuit comprising a power supply section that controls an output voltage within a predetermined range in response to a load current, and an inrush current bypass circuit that shunts a load current flowing from an input side to an output side to the power supply section.