JPH04245313A - Constatn voltage cirucit - Google Patents

Abstract

PURPOSE:To realize the constant voltage circuit which is stable against variation in temperature and freely settable in output voltage by using a relatively simple circuit. CONSTITUTION:This circuit consists of a transistor(TR) Q2 which controls a current Ic flowing in from a power source 1, a bias circuit 3 which applies a bias voltage to the TR Q2, and a P-N junction element Q1 connected to the TR Q2 in series, and the output voltage is obtained at the connection point between the P-N junction element Q1 and TR Q2. Assuming that the P-N junction element Q1 and TR Q2 have nearly the same temperature coefficients, the output voltage corresponds to the difference voltage between the inter- junction voltage of the P-N junction element Q1 and the inter-junction voltage of the TR Q2, so the output voltage which is stable against temperature is obtained. Further, the output voltage is varied by varying the bias value.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a constant voltage circuit, which can obtain a stable constant voltage at a voltage lower than the bandgap voltage of semiconductors such as silicon (Si) or gallium arsenide (GaAs). Regarding.

0002

2. Description of the Related Art A bandgap Zener circuit as shown in FIG. 5 has generally been used as a reference voltage circuit for generating an internal reference voltage for an IC (integrated circuit) or the like. The bandgap Zener circuit consists of constant voltage source 4 and resistors R8 to R10.
, NPN transistors Q5 to Q7, and the output terminals T5 and T6 are configured to provide a stable output voltage against temperature fluctuations.

[0003] Also, the present applicant is
In the publication, we proposed a low voltage reference power supply circuit (the principle circuit diagram is shown in Fig. 6). In the figure, 5 is a differential amplifier circuit consisting of transistors Q8 and Q9, transistors Q10 to Q12, and a resistor R11, which have different current densities from each other, and its output is supplied to the base of a control PNP transistor Q13, and between output terminals T6 and T7. The voltage is controlled to be constant. Also, the voltage across the resistor R12 is the same as that of the differential amplifier circuit 5.
are supplied to the two inputs of .

In the circuit of FIG. 6, by making the voltage Vref between the terminals T6 and T7 equal to the voltage Vgo corresponding to the energy bandgap of silicon constituting the transistor Q14, Vref can have a temperature characteristic having a zero temperature coefficient. and V even when the temperature fluctuates.
The structure was designed to keep ref stable.

[0005]

[Problems to be Solved by the Invention] However, in conventional constant voltage circuits, the output voltage Vref is stable against temperature fluctuations and serves as a good constant voltage power supply, but Vref is approximately 1.2
Must be set to V. Therefore, it is not compatible with the variety of devices that operate at low voltages of 1.2 V or less, which have been increasing in recent years, and the circuits must be complicated to operate at low voltages of 1.2 V or less. There were problems such as the

The present invention has been made in view of the above points, and it is an object of the present invention to provide a constant voltage circuit that is a relatively simple circuit, has a zero temperature coefficient, and can freely set the output voltage. .

[0007]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a transistor for controlling the current flowing from a power supply, a bias circuit for applying a bias voltage to the transistor, and a transistor connected in series with the transistor. A connected PN junction element is provided, and a connection point between the PN junction element and the transistor serves as an output terminal.

[0008]

[Operation] The output voltage is taken out from the connection point between the PN junction element and the transistor. Therefore, the output voltage corresponds to the difference between the junction voltage of the PN junction element and the junction voltage of the transistor. If both the PN junction element and the transistor have substantially the same temperature coefficient, the difference voltage between the junction voltage of the PN junction element and the junction voltage of the transistor will not change due to a temperature change. Therefore, it is possible to obtain an output voltage that is stable with respect to temperature.

Furthermore, the output voltage can be varied by changing the voltage across the transistor junction by changing the bias value of the bias circuit.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a circuit diagram of a first embodiment of the present invention. In the figure, 1 indicates a constant current circuit. As shown in FIG. 2, the constant current circuit 1 includes a PNP transistor Q3, resistors R3, R
4 is applied to the base of a PNP transistor Q4 to which a resistor R5 is connected in series, and a constant current I
I got a C.

One end of the constant current circuit 1 is connected to the input terminal T1, and the other end is connected to the resistor circuit 3 and the NP junction element.
Connected to N transistor Q1. The resistor circuit 3 includes resistors R1 and R2 connected in series, and is connected between the constant current circuit 1 and the input terminal T2 and output terminal T4 to generate a bias voltage. The base and collector of the NPN transistor Q1 are short-circuited, and the PN transistor Q1 is connected between the base and emitter.
forming a junction. The collector and base of the NPN transistor Q1 are connected to the constant current circuit 1, and the emitter is connected to the NPN transistor Q2, which serves as a current control transistor.
connected to the collector of

The base of the NPN transistor Q2 is connected to the connection point between the resistor R1 and the resistor R2 constituting the resistor circuit 3, and a constant bias voltage is applied thereto, and the emitter is connected to the input terminal T2 and the output terminal T4. NP
The connection point between the N transistor Q1 and the NPN transistor Q2 is connected to the output terminal T3, and the output terminals T3,
Obtain constant output voltage VS from between T4. Further, a DC power supply 2 is connected between input terminals T1 and T2.

In the circuit of FIG. 1, the base-emitter voltages of NPN transistors Q1 and Q2 are set to VBE, respectively.
1, VBE2, and the emitter junction area ratio is n:1.
and the base current i of the NPN transistor Q2
The relationship between B2 and the current I1 flowing through the resistor circuit 3 is iB2
≪If I1, then

[0014]

[Math 1]

[0015] Here, VBE2 - VBE1 = △VB
If E,

[0016]

[Math 2]

[0017] Also, here, △VBE is generally

001
8]

[Math 3]

It is expressed as: Furthermore, VBE2 is

0
020]

[Math 4]

It is expressed as: Here, Vgo is the voltage (approximately 1.2 V) corresponding to the energy bandgap of silicon constituting transistor Q1, T is temperature, and T0 is
is the reference operating temperature, and VBE0 is the base-emitter voltage of the transistor Q1 when T=T0.

Next, by substituting equations (3) and (4) into equation (2), we get

[0023]

[Math 5]

[0024] Here, in order to make the temperature change of VS zero, the value obtained by partially differentiating equation (5) with respect to the temperature T needs to become zero. Therefore, if we partially differentiate equation (5) with respect to temperature T, we get

[0025]

[Math 6]

[0026] therefore,

[0027]

[Math 7]

If the values of the resistors R1 and R2 are set so that the temperature change in VS can be made zero.

With such a configuration, the temperature change in VS can be made zero, and by changing the values of the resistors R1 and R2 and further changing the bias voltage of the NPN transistor Q2, the voltage between the base and emitter of the NPN transistor Q2 can be reduced to zero. The output constant voltage VS can be freely set by changing the voltage VBE2.

Therefore, even if the energy bandgap voltage of silicon is approximately 1.1 V or less, a stable output voltage that does not fluctuate due to temperature changes can be obtained. Furthermore, the circuit configuration becomes extremely simple.

FIG. 3 shows a circuit diagram of a second embodiment of the invention. In the figure, the same components as in the first embodiment are denoted by the same reference numerals, and the explanation thereof will be omitted.

In this embodiment, a resistor R6 is connected to the base of an NPN transistor Q1 which becomes a PN junction element in the circuit of the first embodiment.
The configuration consists of connecting the . hFE of NPN transistor Q1 by setting resistor R6 to an appropriate value.
It is possible to correct variations in the base current due to variations in the base current.

FIG. 4 shows a circuit diagram of a third embodiment of the invention. In the figure, the same components as those in the first and second embodiments are denoted by the same reference numerals, and their explanations will be omitted.

In this embodiment, in the circuit of the second embodiment, P
A resistor R7 is connected to the emitter of an NPN transistor Q1 constituting an N-junction element. Resistor R7
This corrects variations in the output constant current Icc of the constant current circuit 1.

[0035] In the first, second and third embodiments, NPN
Although transistors Q1 and Q2 are used, they are PNP with opposite polarity.
It is also possible to implement the circuit with transistors.

[0036]

As described above, according to the present invention, a transistor is connected in series to a PN junction element, and the output voltage is taken out from the connection point between the PN junction element and the current control transistor. is a voltage that corresponds to the voltage difference between the PN junction element and the transistor, so if the PN junction element and the transistor have the same temperature coefficient, a stable output voltage can be obtained against temperature changes, and the bias voltage of the transistor By changing the voltage difference between the PN junction element and the transistor, the output voltage can be freely set.

[Brief explanation of the drawing]

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

FIG. 2 is a circuit diagram of main parts of the first embodiment of the present invention.

FIG. 3 is a circuit diagram of a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a third embodiment of the present invention.

FIG. 5 is a circuit diagram of a conventional example.

FIG. 6 is a circuit diagram of another conventional example.

[Explanation of symbols]

1 Constant current source 2 DC power supply 3 Resistance circuit

Claims (1)

[Claims] 1. A transistor that controls current flowing from a power source, a bias circuit that applies a bias voltage to the transistor, and a PN junction element connected in series to the transistor, the PN junction element and the A constant voltage circuit characterized by using a connection point with a transistor as an output terminal.