JPH0888968A - Step-up converter - Google Patents

Abstract

PURPOSE: To stop the output from an output terminal, too, so as to prevent the malfunction of load connected to the output terminal, when a step-up converter is turned off, by connecting the second switching means to the output end of a smoothing means, and also, turning on the switching means in response to the output of an AC coupling means. CONSTITUTION: When a controller COT is turning on and off a switching element Q1 periodically, an inductance element L outputs boosted pulse voltage, and it is coupled with AC in a capacitor C2, and it turns on a transistor Tr through a rectifying circuit. Therefore, a switching circuit Q2 becomes conductive, and the voltage smoothed with a smoothing circuit is outputted from an output terminal OUT. On the other hand, when the ON/OFF control of the switching element Q1 by the controller COT is suspended, the output of the inductance element L becomes DC voltage inputted from an input terminal IN, so the switching element Q2 is turned off, and the outputs does not occur.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a step-up converter.

[0002]

2. Description of the Related Art In portable electronic devices that are widely used at present, it is required to use not only commercial alternating current but also direct current obtained from a DC socket in a vehicle as a drive source. However, the voltage itself output from this type of DC power supply does not necessarily match the voltage value required by the utilizing device. For this reason, a step-up converter is used in the power supply circuit of this kind of equipment (see "Linear / Switch Mode Voltage Regulator Handbook" issued on June 10, 1988 by Language Communication).

FIG. 2 is a circuit diagram for explaining the principle of this type of converter. In this converter, DC voltage energy supplied from an input terminal IN to an inductance element L formed of a coil or the like is applied to, for example, an N-type channel FET.
The switching element Q1 consisting of is turned on and off under the control of the controller COT to repeatedly accumulate and release to boost (step up), and the boosted pulse voltage is smoothed by a smoothing circuit consisting of a diode D1 and a capacitor C1. And output it.

The controller COT specifically detects the value of the smoothed output voltage by using the voltage dividing resistors R1 and R2, and outputs the predetermined smoothed output voltage value based on the detected value. The ON / OFF duty ratio of the switching element Q1 is controlled, and the switching element Q1 is completely turned off when an abnormality such as a short circuit on the load side is detected by the detection value or the like. Such a controller C
Examples of OT include Texas Instruments (TI)
An integrated circuit TL5001 manufactured by the company can be used.

[0005]

In the conventional step-up converter shown in FIG. 2, even when the controller COT detects an abnormality and turns off the switching element Q1 to make it non-conductive, the DC voltage supplied from the input terminal IN is set. Energy is inductance element L and diode D1
Since it is output without being boosted via the output terminal O
There is a problem that it causes a malfunction of the load connected to the UT.

[0006]

The present invention has been made in view of the above problems, and is characterized by an inductance element, a first switching means connected to the output terminal of the element, and the inductance element. Smoothing means connected to the output end of the first switching means
A step-up converter for stepping up a DC current supplied from an input end of the inductance element by switching OFF and smoothing the output by the smoothing means, and outputting the smoothed current, further connected to an output end of the inductance element. It is provided with a means for AC coupling with the output and a second switching means which is connected to the output end of the smoothing means and becomes conductive in response to the output of the AC coupling means.

[0007]

In the structure of the present invention, the second switching means is rendered conductive only when the output of the inductance element is in a pulse form.

[0008]

1 is a circuit diagram showing an embodiment of the present invention.
The difference from the basic step-up converter shown in FIG. 2 is that a capacitor C2 as an AC coupling means connected to the output terminal of the inductance element L and this capacitor C
2 is a half-wave rectification circuit for rectifying the output of D2, D3 and a capacitor C3, a switching transistor Tr whose ON / OFF is controlled by the output from the rectification circuit, and an ON / OFF of the transistor Tr
In response to the operation, the output terminal O of the output voltage of the diode D1
The second switching element Q2, which is a P-type channel FET that controls the supply to the UT, is added.

In this circuit, when the controller COT periodically turns ON / OFF the switching element Q1, the boosted pulse voltage is output from the inductance element L as in the circuit of FIG. This pulse voltage is AC-coupled by the capacitor C2, and the voltage turns on the transistor Tr via the rectifier circuit. As a result, the switching element Q2 becomes conductive,
The voltage generated by the inductance element L and smoothed by the smoothing circuit including the diode D1 and the capacitor C1 is output from the output terminal OUT.

On the other hand, if the ON / OFF control of the switching element Q1 by the controller COT is interrupted,
Since the output of the inductance element L is the DC voltage itself input from the input terminal IN, AC coupling does not occur in the capacitor C2, and as a result, the transistor Tr becomes O.
It becomes FF, and the switching element Q2 also becomes non-conducting. As a result, no output is generated from the output terminal OUT.

[0011]

According to the present invention, when the operation of the step-up converter is stopped, the output from the output terminal can also be stopped, so that the malfunction of the load connected to the output terminal can be prevented.

Since the output from the output terminal is stopped based on the presence or absence of AC coupling with the output of the inductance element L, the immediacy is excellent, and as a result, the malfunction prevention is further effective. Further, the control by the AC coupling can be performed with a simple structure of a capacitor, a rectifying circuit and a switching means, which is advantageous in cost.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing a basic form of a step-up converter.

[Explanation of symbols]

 L inductance element Q1 switching element Q2 switching element D1 diode D2 〃 D3 〃 C1 capacitor C2 〃 C3 〃 Tr switching transistor IN input terminal OUT output terminal

Claims (1)

[Claims] 1. An ON / OFF switch of the first switching means, comprising an inductance element, a first switching means connected to an output terminal of the element, and a smoothing means connected to an output terminal of the inductance element. A step-up converter that steps up the direct current supplied from the input terminal of the inductance element and then smoothes it by the smoothing means to output, and further connects to the output terminal of the inductance element A step-up converter comprising: means for AC coupling; and second switching means connected to the output end of the smoothing means and being in a conductive state in response to the output of the AC coupling means.