JPH09149631A - Power supply apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To constitute a stepup type power supply circuit having a circuit protective function with a simple circuit construction and make the power supply circuit easy to be built in an apparatus such as a display. SOLUTION: A power supply apparatus is composed of an inductance element 1, a diode 2, an output voltage detector 3 for detection of an output voltage, a transistor 5 which is a switching device, a driver 4 which has an oscillator and switching on/off transistor 5 periodically, a capacitor 6 and an output circuit 7 which controls the supply of the output voltage to a load. Further, the output circuit 7 has a transistor 7a whose emitter is connected to the cathode side of the diode 2 and whose collector is connected to a voltage output terminal T2 side and so operates as to cut off the transistor 7a when the charging voltage of the capacitor 6 is lower than a voltage which is obtained by deducting the forward voltage of the diode from the input voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device called a step-up DC-DC converter used as a power supply circuit for a liquid crystal display device or the like, and more particularly to a circuit configuration thereof.

[0002]

2. Description of the Related Art Conventionally, in a device which requires a voltage higher than a supply voltage in a part of a circuit, a high voltage is supplied by using a power supply device called a step-up DC-DC converter as shown in FIG. It is common to obtain. The power supply device of FIG. 4 has an inductance element 1 for generating a counter electromotive force.
A diode 2 for preventing the boosted voltage from decreasing, an output voltage detection circuit 3a for detecting the output voltage, a transistor 5 for connecting one end of the inductance element 1 to a reference potential, and an oscillation. A drive circuit 4 having a circuit for periodically switching the transistor 5, a capacitor 6 for reducing the output impedance and stabilizing the output voltage, and an output circuit for controlling the supply of the output voltage to the load. 12, an output abnormality detection circuit 13 for detecting that the power supply device has an operation abnormality, and an output drive circuit 14 for controlling the operation of the output circuit 12 according to the output of the output abnormality detection circuit 13. A battery 11 having a voltage V1 (V) is connected to the voltage input terminal T1 and a load circuit requiring a high voltage is connected to the voltage output terminal T2 for use.

With such a configuration, during normal operation, conduction and interruption of the transistor 5 are periodically controlled according to the clock signal generated in the drive circuit 4, and when the transistor 5 is in the conducting state, the inductance element 1 is controlled. When the flowing current gradually increases and the transistor 5 is turned off, the current due to the counter electromotive force generated in the inductance element 1 flows in the diode 2. The current due to this back electromotive force becomes a charging current for charging the capacitor 6, but since the back electromotive force of the inductance element 1 gradually decreases and the charging current also decreases, the transistor 5 is turned on again. It is necessary to increase the charging current. While repeating such switching operation, the capacitor 6
Is charged to a constant potential, the charging voltage V2 of the capacitor 6 becomes higher than the input voltage V1, and the boosted charging voltage V2 is connected to the voltage output terminal T2 via the transistor of the output circuit 12. It becomes possible to supply it to the load as an output voltage.

It should be noted that the output voltage detection circuit 3a uses the charging voltage V2
Charging voltage V2 so that the voltage does not rise above the required voltage value.
In accordance with the above, the output abnormality detection circuit 1 operates by controlling the switching operation of the transistor 5 via the drive circuit 4.
The circuit 3 operates by rectifying and smoothing the clock signal of the drive circuit 4 and comparing it with the output voltage using the generated voltage as a reference voltage to monitor whether there is any abnormality in the circuit operation of the power supply device.

That is, in normal operation, the output abnormality detection circuit 1
By setting the output voltage of 3 to a high level, the drive circuit 4
The transistor 5 performs a switching operation in response to the clock signal and the transistor of the output circuit 12 is turned on via the output drive circuit 14. Further, in an abnormal state in which the voltage output terminal T2 is short-circuited to the reference potential, the clock signal input to the output abnormality detection circuit 13 is stopped and the voltage generated in the output abnormality detection circuit 13 is reduced to cause an abnormal state. The output voltage of the output abnormality detection circuit 13 is detected to a low level to stop the switching operation of the transistor 5 in the cutoff state, and the output of the output circuit 12 is cut off via the output drive circuit 14. By this operation, the voltage input terminal T
Since the short-circuit current does not flow from 1 to the voltage output terminal T2, the circuit of the power supply device is protected.

[0006]

However, in the conventional power supply device whose circuit diagram is shown in FIG. 4, in order to protect the power supply circuit from an abnormal state such as a short circuit of the voltage output terminal T2, the output abnormality detection as described above is performed. Since the circuit 13 is used, a circuit for rectifying and smoothing the clock signal, a circuit for comparing the output voltage with the voltage, and the like are required, and the number of components used increases and the circuit scale of the power supply device increases. At the same time, there is a problem that the area of the circuit board increases. In addition, due to the above-mentioned problems, it becomes difficult to purchase and manage parts and the like, and the external size of the power supply device and the external size of the device using the power supply device become large, which makes it difficult to reduce the size. There is also a problem that the power supply device and the equipment become large in size and expensive.

Therefore, the present invention solves these problems and makes it possible to form a step-up power supply circuit having a circuit protection function with a simple circuit structure so that it can be easily incorporated in a device such as a display device. To aim.

[0008]

In order to solve the above-mentioned problems, a power supply device according to a first aspect of the present invention provides an inductance element, a diode and an output connected in series between a voltage input terminal and a voltage output terminal. A circuit, a switching transistor connected between the connection point of the inductance element and the anode of the diode and the reference potential, and a capacitor connected between the cathode of the diode and the reference potential, the conduction of the switching transistor or In a power supply device called a step-up DC-DC converter that outputs a voltage higher than an input voltage by repeating cutoff, in an output circuit, an emitter is connected to a cathode side of a diode and a collector is connected to a voltage output terminal side. It has an output transistor, and the output transistor has the same voltage as the charging voltage of the capacitor. Characterized in that it operates to cut off the voltage input from the power terminal when lower than the voltage obtained by subtracting the forward voltage of the diode.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to FIGS. In this specification, the same or similar circuit elements are denoted by the same reference symbols throughout the drawings, and redundant description will be omitted. FIG.
Shows a circuit configuration of a power supply device (also referred to as a "step-up converter") called a step-up type chopper type DC-DC converter using the present invention, in which an inductance element 1 for generating a counter electromotive force and a boosted voltage are used. A diode 2 for preventing a voltage drop, an output voltage detection circuit 3 for detecting an output voltage, an NPN type transistor 5 for connecting one end of an inductance element 1 to a reference potential, and an internal A drive circuit 4 having an oscillation circuit for periodically switching the transistor 5;
It is composed of an electrolytic capacitor 6 for reducing the output impedance and stabilizing the output voltage, and an output circuit 7 for controlling the supply of the output voltage to the load. still,
The inductance element 4 is composed of a coil wound with ferrite or amorphous metal as a core.

The connection relationship will be described. The terminal T1 (hereinafter referred to as “voltage input terminal T1”) is connected to the terminal T2 (hereinafter referred to as “voltage output terminal T2”) via the inductance element 1, the diode 2 and the output circuit 7 which are connected in series. The connection point between the cathode of the diode 2 and the output circuit 7 is connected to the reference potential (GND) via the capacitor 6, and is also connected to the output voltage detection circuit 3, and the output of the output voltage detection circuit 3 is connected to the drive circuit 4. It is connected to the base of the transistor 5 via. The collector of the transistor 5 is connected to the connection point between the inductance element 1 and the anode of the diode 2, and the emitter is connected to the reference potential. When using, the voltage is V at the voltage input terminal T1.
A DC power supply 11 such as a 1 (V) battery is connected, and a load circuit such as a display device or a storage device requiring a high voltage is connected to the voltage output terminal T2.

The output circuit 7 will be further described. The output circuit 7 is a PNP having an emitter connected to the cathode side of the diode 2 and a collector connected to the voltage output terminal T2 side.
Type output transistor 7a, and resistors 7b and N connected in series between the base of transistor 7a and the reference potential.
A PN transistor 7c, a Zener diode 7d and a resistor 7e connected in series between the emitter of the transistor 7a and a reference potential, and a resistor 7f connected between the anode side of the Zener diode 7d and the base of the transistor 7c. It consists of Furthermore, the constants such as the resistance values and the Zener voltage of the Zener diode are set such that when the charging voltage V2 of the capacitor is lower than the voltage obtained by subtracting the forward voltage (VF) of the diode 2 from the input voltage V1.
It is set to block a.

Next, the operation of the circuit of the present invention will be described. In a normal operation state, switching of conduction and interruption (non-conduction) of the transistor 5 is periodically controlled according to a clock signal generated by the drive circuit 4. When the transistor 5 is in the conducting state, the current flowing through the inductance element 1 gradually increases until it reaches a constant current value, and when the transistor 5 is in the shut-off state, the counter current generated in the inductance element 1 in an attempt to hold the immediately preceding current value. Electric current causes a current to flow in the diode 2. The current flowing due to this counter electromotive force becomes the charging current for charging the capacitor 6, but since the counter electromotive force of the inductance element 1 gradually decreases and the charging current decreases, the transistor 5 is made conductive again. It is necessary to increase the current that flows (see FIG. 2 described later). By charging the capacitor 6 to a constant voltage while repeating such operations, the charging voltage V2 of the capacitor 6 becomes a voltage higher than the input voltage V1, and the boosted charging voltage V2 charges the transistor of the output circuit 12. The load connected to the voltage output terminal T2 can be supplied as an output voltage. The output voltage detection circuit 3 performs a control operation such that the switching speed of the transistor 5 is changed via the drive circuit 4 according to the charging voltage V2 so that the charging voltage V2 does not rise above a required voltage value. There is.

Here, the output voltage of the voltage output terminal T2 is V
o (V), the zener voltage of the zener diode 7d is Vz
(V) and the voltage between the base and emitter of the transistor 7c is VBE (V), V1 <(Vz
Since + VBE) <V2≈Vo, the transistor 7c becomes conductive and the base voltage of the transistor 7a decreases, so that the transistor 7a becomes conductive. On the other hand, in an abnormal state where the voltage output terminal T2 is short-circuited to the reference potential, the relationship of (Vz + VBE)> V2 is established, so that the base voltage of the transistor 7c is lowered and the transistor 7c is cut off.
Also shut off. Further, the output voltage detection circuit 3 detects that the charging voltage V2 has dropped to about the input voltage V1, thereby stopping the switching operation of the switching transistor 5 via the drive circuit 4, and the output voltage detection circuit 3
The switching operation is not restored until the output voltage detection circuit 3 is reset by the supply of power supply voltage to the output voltage to the output voltage or by a reset input (not shown) from the outside. By such a circuit operation, even when an abnormal state occurs, the transistor 7a is quickly shut off, and a large current does not continue to flow from the capacitor 6 toward the voltage output terminal T2, so that the circuit and load of the power supply device are protected. Will be done.

The constant values in this embodiment may be set according to the current required for the connected load. For example, the switching cycle may be several μs to several tens μs, and the inductance value of the inductance element 1 may be set. Is several mH to several tens mH, and the capacitance value of the capacitor 6 is several tens μF to several thousands μF.
If it is set to about, it becomes possible to supply a current of about several tens of mA to the load.

FIG. 2 illustrates the normal operation of the circuit of FIG.
The operation waveforms of the main part when sufficient boosting is performed and the operation is stable are shown. FIG. 2A shows the timing waveform of the collector voltage of the transistor 5, and FIG. 2B shows the voltage input terminal T1 and The timing waveform of the current flowing through the inductance element 1, t1 (s), indicates the cycle of the operation cycle of the transistor 5. When the operation is stable, the collector of the transistor 5 has (V2 + VF) ≈Vo (> V)
The high voltage of 1) and the reference potential are generated periodically. For the sake of clarity, the voltage ripple, the saturation voltage (Vsat (V)) of the transistor 5 and the like are omitted in FIG.

FIG. 3 shows another example of the output circuit of the present invention. The output circuit 7'of FIG. 3 (a) has a structure in which a resistor 7g is connected instead of the Zener diode 7d of the output circuit of FIG. And V1 <((7g + 7e) VF / 7e)
Each resistance value is set so as to satisfy the relationship of <Vo.
As a result, as in the case of FIG. 1, the transistor 7a conducts during normal operation, and the transistor 7a operates in an abnormal state.

The output circuit 7 "of FIG. 3B has a transistor 7a, a comparator circuit 7h, and a voltage of VREF.
(V) voltage source 7i, the inverting input of the comparator circuit 7h is connected to the emitter of the transistor 7a, the non-inverting input is connected to the voltage source 7i, and the output of the comparator circuit 7h is connected to the base of the transistor 7a. It is connected. Also in this circuit, by setting VREF so that V1 <VREF <Vo, the transistor 7a conducts during normal operation, and the transistor 7a shuts off during an abnormal state.

The present invention is not limited to the above-described embodiment. For example, the circuit configuration of the output circuit 7 is not limited to that shown in FIGS. Input voltage V1 to diode forward voltage V
The circuit configuration may be such that it operates so as to cut off the transistor 7a when the voltage is lower than the voltage obtained by subtracting F 2. The resistors 7b and 7f of the output circuit 7 may be omitted, MOS transistors may be used instead of the bipolar transistors, and the clock signal of the drive circuit 4 may be supplied from the outside. Furthermore, the power supply device of the present invention may be formed as a hybrid integrated circuit by using only a single electronic component, or may be formed by using a semiconductor device in which only a circuit portion including a transistor, a diode and a resistor is integrated. You may.

[0019]

According to the present invention as described above, claim 1
Since the power supply device according to the above description can be formed with a simple circuit configuration even though it is a booster type power supply circuit having a circuit protection function, the number of parts constituting the power supply device is reduced and the management of the parts is facilitated. In addition, the circuit board can be made small, and the power supply device and the equipment using the same can be easily incorporated, and the power supply device and the equipment using the same can be formed in a small size and at low cost. . There is also an effect that a semiconductor device in which these are integrated can be easily formed.

[Brief description of the drawings]

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

FIG. 2 is a timing diagram showing operation waveforms of a main part of the embodiment of the present invention,

FIG. 3 is a circuit diagram showing another circuit example of the output circuit of the present invention,

FIG. 4 is a circuit diagram showing a conventional embodiment.

[Explanation of symbols]

 1: Inductance element 3: Output voltage detection circuit 4: Drive circuit 5: Switching transistor 7: Output circuit 7a: Output transistor 11: Voltage source (battery) T1: Voltage input terminal T2: Voltage output terminal

Claims (1)

[Claims] 1. An inductance element, a diode and an output circuit connected in series between a voltage input terminal and a voltage output terminal, and a connection point between the inductance element and the anode of the diode and a reference potential. A step-up DC that has a switching transistor and a capacitor connected between the cathode of the diode and a reference potential, and outputs a voltage higher than the input voltage by repeating conduction or interruption of the switching transistor.
In a power supply device called a DC converter, the output circuit has an output transistor having an emitter connected to the cathode side of the diode and a collector connected to the voltage output terminal side, and the output transistor has a charging voltage of the capacitor. Is operated so as to cut off when the voltage is lower than a voltage obtained by subtracting the forward voltage of the diode from the voltage input from the voltage input terminal.