JP2834337B2 - Constant voltage circuit and power supply circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant voltage circuit and a power supply circuit suitable for use in, for example, a power supply circuit of a cordless telephone.

[0002]

2. Description of the Related Art FIG. 2 shows an example of a power supply circuit used for a power supply for a cordless telephone handset. This power supply circuit is a circuit for setting an input power supply voltage to a constant output voltage Vo and supplying the output voltage to the next stage, and a battery or the like is used as the input power supply.

The circuit shown in FIG. 2 includes transistors Q11,
An output stage 1 constituted by Q12, a differential amplifier 2 for controlling an output current of the output stage 1, a bandgap circuit 3 for applying a reference voltage to the differential amplifier 2, and a bias for the bandgap circuit 3 It comprises a bias circuit 4 and a detection unit 5 which detects a voltage corresponding to the output voltage and supplies it to the differential amplification unit 2. The differential amplifier 2 includes transistors Q8 and Q9 and their peripheral resistors, and the bandgap circuit 3 includes a transistor Q5
To Q7 and resistors R4 to R6, and the bias circuit 4 includes transistors Q1 to Q3 and resistors R1 and R6.
2, and the detection unit 5 includes a transistor Q10 and resistors R10 and R11.

In FIG. 2, a current supplied to an input terminal Ti flows through a resistor R1 and diode-connected transistors Q1, Q2, Q3 to a ground point sequentially. Here, since the base-emitter voltage VBE of the transistor is substantially constant, a substantially constant voltage (3 · VBE) obtained at the collector of the transistor Q1 is supplied to the bandgap circuit 3. The bandgap circuit 3 is designed to obtain a stable voltage even with a change in temperature. The current gap circuit includes transistors Q5 and Q6, and a transistor Q7 in which the collector voltage of the transistor Q6 is applied to the base. And constitutes a constant voltage source as a whole. That is, the VBE of the transistor Q5 is used as a reference voltage, the emitter current i3 of the transistor Q6 and the current emitter i4 of the transistor Q7 are kept constant with respect to changes in the input voltage. The voltage is finally constant. Note that the VBE of the transistor Q5 is
R2 is relatively high (several KΩ)
As a constant current drive. This constant voltage is supplied to the base of the transistor Q8 as a reference voltage. The transistor Q9 and the transistor Q of the operation amplifier 2
Reference numeral 10 denotes a current mirror circuit. A diode-connected transistor Q10 divides an output voltage obtained at an output terminal To together with resistors R10 and R11 connected to an anode side and a cathode side, and obtains a voltage at a base thereof. The supplied voltage is supplied to the base of the transistor Q9 as a detection voltage. In this case, when the output voltage is a specified value, the resistance R1 is adjusted so that the detected voltage becomes equal to the reference voltage.
The values of 0 and R11 are set.

In the above-described configuration, when the output voltage obtained at the output terminal To becomes smaller than a specified value, the base potentials of the transistors Q10 and Q9 decrease, and the transistor Q10
The VBE of 8 rises and the emitter current increases. As a result, the transistor Q of the output stage 1 connected in Darlington
12, the base current of Q11 increases, and the transistor Q1
An attempt is made to flow a current of hFE × hFE times the base current of No. 2 to the load side via the transistor Q11. Then, the above operation is continued until the output voltage reaches the specified value, whereby the output voltage matches the specified value. On the other hand, when the output voltage exceeds the specified value, the circuit operates to decrease the output voltage, contrary to the above. As described above, the output voltage is maintained at the specified value.

[0006]

By the way, in the above-mentioned conventional circuit, a tentatively stabilized voltage of 3 VBE can be obtained from the connection point between the resistor R1 and the transistor Q1, but this is not enough. When the input voltage Vi increases, the bias current i1 increases and the transistor Q
VBE of 1 to Q3 slightly increases, and the supply voltage to the next band gap circuit 3 slightly increases. On the other hand, when the input voltage Vi decreases, the voltage supplied to the bandgap circuit 3 decreases slightly, contrary to the above. Therefore, there is a problem that the reference voltage changes and the output voltage Vo becomes unstable. That is, the conventional circuit has a disadvantage that the range of the input voltage Vi for obtaining a stable output voltage Vo is narrow.

The present invention has been made in view of the above circumstances, and provides a constant voltage circuit capable of supplying a stable voltage in a wide input voltage range. It is an object of the present invention to provide a power supply circuit capable of obtaining a stable output voltage.

[0008]

According to a first aspect of the present invention, there is provided one or more diode means for generating a constant voltage from an input DC power supply by a forward voltage drop. A transistor constituting a current mirror circuit with the diode means; and a resistor means interposed between an output terminal of the transistor and a first anode terminal of the diode means.

Further, in the invention according to claim 2,
An output stage for increasing and decreasing the current supplied from the input DC power supply by the current flowing to the control terminal, and a detection unit for detecting a value corresponding to the output voltage of the output stage; and a reference voltage based on the supplied voltage. A differential amplifier that controls the current flowing through the control terminal so that the reference voltage and the detection voltage of the detection unit are equal, and a constant voltage from the input DC power supply due to a forward voltage drop. One or more diode means for generating a current mirror circuit, a transistor constituting a current mirror circuit with the diode means, and a resistance means interposed between an output terminal of the transistor and a first anode terminal of the diode means, A bias circuit for supplying power to the band gap circuit from an output terminal of the transistor.

[0010]

According to the first aspect of the present invention, the voltage at the output terminal of the transistor is double stabilized because the current mirror circuit and the resistor have a constant voltage effect in addition to the constant voltage effect by the diode means. You.

According to the second aspect of the present invention, the doubly stabilized voltage is supplied to the bandgap circuit, whereby the reference voltage is highly stabilized.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a configuration of one embodiment of the present invention. In the figure, parts corresponding to the respective parts in FIG. 2 described above are denoted by the same reference numerals, and description thereof is omitted.

The embodiment shown in this figure differs from the conventional circuit shown in FIG. 2 in that a resistor R3 is interposed between the resistors R2 and R4, and a transistor Q4 is provided. The transistor Q4 has a collector connected to a connection point between the resistors R2 and R3, and an emitter and a base connected to an emitter and a base of the transistor Q3, respectively.

In the configuration described above, the transistor Q
3, Q4 and the resistors R1, R2, R3 constitute a current mirror circuit.

In the circuit shown in FIG. 1, as the input voltage Vi increases, the current i1 increases. At this time, since the transistor Q3 and the transistor Q4 form a current mirror circuit, the emitter current i2 of the transistor Q4 also increases, and the relationship of i1 = i2 is always maintained. As a result, the voltage drop across the resistor R2 also increases, and the voltage supplied to the bandgap circuit 3 does not change. Even when the input voltage Vi decreases, the supply voltage to the bandgap circuit 3 does not change by the same operation. As described above, according to this embodiment, the supply voltage to the bandgap circuit 3 is double stabilized by the stabilization by the VBE of the diode-connected transistor and the stabilization by the current mirror circuit.

[0017]

As described above, according to the present invention, a stable voltage can be supplied in a wide input voltage range. Further, the output voltage of the power supply circuit can be extremely stabilized.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram showing a configuration of a conventional power supply circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Output stage, 2 Differential amplification part 3 Band gap circuit 4 'Bias circuit 5 Detection part Q1-Q3 Transistor (died means) Q4 Transistor R2 Resistance (resistance means)

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G05F 1/00

Claims (2)

(57) [Claims] 1. A diode which generates a constant voltage from an input DC power supply by a forward voltage drop, a transistor which forms a current mirror circuit with the diode, an output terminal of the transistor and an output terminal of the diode. A resistance means interposed between the first anode terminal and the first anode terminal. 2. An output stage for increasing and decreasing a current supplied from an input DC power supply by a current flowing to a control terminal, and
A detection unit that detects a value corresponding to the output voltage of the output stage, a band gap circuit that generates a reference voltage based on the supplied voltage, and an output voltage of the band gap circuit and a detection voltage of the detection unit. A differential amplifier for controlling a current flowing through the control terminal so as to be equal, one or more diode means for generating a constant voltage from an input DC power supply by a forward voltage drop, and a current mirror circuit with the diode means A constant voltage circuit having a transistor and a resistance means interposed between an output terminal of the transistor and a first anode terminal of the diode means, and supplying power to the band gap circuit from an output terminal of the transistor. A power supply circuit, characterized in that: