JPH06348355A - Reference voltage generating circuit - Google Patents

Abstract

PURPOSE:To suppress the fluctuation of the reference voltage against the fluctuation of the power voltage for a reference voltage generating circuit consisting of the diode groups. CONSTITUTION:A bypass circuit including a transistor TR Q7 is placed in parallel to the diode groups D11-D15 which generate the reference voltage Vref. When the power voltage Vcc increases, the collector current I4 flowing to the TR Q7 increases. As a result, the increase of the collector current (I3-I4) of a TR Q6 is absorbed so that the fluctuation of the current I3 flowing to the groups D11-D15 can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reference voltage generating circuit provided with a diode group, and more particularly to a circuit technique for keeping a reference voltage which fluctuates according to a fluctuation of a power supply voltage stable.

[0002]

2. Description of the Related Art Conventionally, as a reference voltage generating circuit of this kind, there is a circuit which includes a diode group and generates a reference voltage by supplying a current from a power supply voltage to the diode group. Examples of this circuit configuration include those shown in FIGS. 2 and 3. FIG. 2 shows a circuit including diode groups D1 to D5, a resistor R1 connected in series to the diode group D1, and a transistor Q1. Power supply voltage Vcc to resistance R1
The current I1 is supplied to the diode groups D1 to D5 through the diode group D1 to D5, and the reference voltage Vref is obtained at the emitter of the transistor Q1. The current I1 at this time is expressed as follows when the generated voltage of each diode is Vbe1.

## EQU1 ## I1 = (Vcc-5Vbe1) / R1

In the circuit shown in FIG. 2, the current I1 is supplied from the resistor R1 to the diode groups D1 to D5.
Shows a circuit in which the current I2 is supplied from the transistors Q2 and Q3 forming the mirror circuit to the diode groups D6 to D10. The reference voltage Vref is obtained at the emitter of the transistor Q4. If the generated voltage between the emitter and the base of the transistor Q2 is Vbe2, the resistance R2
The current flowing through is equal to the current I2 flowing through the diode groups D6 to D10 because the transistors Q2 and Q3 are mirror circuits, and is expressed as follows.

## EQU00002 ## I2 = (Vcc-Vbe2) / R2

[0004]

However, in such a conventional circuit configuration, the supplied power supply voltage V
When cc fluctuates, the current flowing through the diode group fluctuates, so that the voltages of Va (FIG. 2) and Vb (FIG. 3) fluctuate, and as a result, the reference voltage Vref, which should be a stable voltage, fluctuates. is there. Furthermore, this reference voltage Vr
A device using ef may malfunction. For example, in FIG. 2, the variation of the power supply voltage Vcc (ΔVc
c) the current change amount of the diode groups D1 to D5 (Δ
I1) is ΔI1 = ΔVcc / R1. Also, FIG.
In, the current change amount (ΔI2) of the diode groups D6 to D10 with respect to the power supply voltage Vcc change amount (ΔVcc) is
ΔI2 = ΔVcc / R2.

The present invention solves the above-mentioned problems. When the power supply voltage fluctuates, a bypass current is caused to flow so as to suppress the resulting fluctuation in the current flowing through the diode group. It is an object of the present invention to provide a reference voltage generation circuit capable of keeping the voltage stable.

[0006]

In order to achieve the above object, the present invention provides a reference voltage generating circuit that includes a diode group and generates a reference voltage by supplying a current from a power supply voltage to the diode group. In parallel with this, a bypass circuit in which a current flows so as to absorb a variation in the current flowing in the diode group caused by the variation in the power supply voltage is provided.

[0007]

According to the above structure, when the power supply voltage fluctuates, the amount of current flowing through the bypass circuit is adjusted according to the fluctuation. As a result, the current flowing through the diode group does not fluctuate, and a stable reference voltage can be obtained.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment embodying the present invention will be described below with reference to FIG. The reference voltage generating circuit includes diode groups D11 to D15 in which respective diodes are connected in series.
A transistor Q7 and a resistor R5 which are bypass circuits connected in parallel with the diode groups D11 to D15, and transistors Q5 and Q6 which form a mirror circuit for supplying a current to the diode groups D11 to D15 and the bypass circuit.
And a resistor R through which the collector current of the transistor Q5 flows
3, R4 and a transistor Q8 that generates a reference voltage Vref. The power sources (voltage Vcc) are applied to the emitters of the transistors Q5 and Q6 and the collector of the transistor Q8.
On the other hand, one ends of the resistors R4 and R5 and the cathode of the diode D15 are connected to GND. The reference voltage Vref is obtained at the emitter of the transistor Q8.

Next, the case where the power supply voltage Vcc rises will be described. At this time, the voltage applied to the resistors R3 and R4 rises, and the current I5 flowing through the resistors R3 and R4 increases.
Accordingly, since the transistors Q5 and Q6 are mirror circuits, the collector current of the transistor Q6 (I3 +
I4) increases. This point is the same as the conventional example shown in FIG. However, in this embodiment, the diode group D
A bypass circuit formed by a series circuit of a transistor Q7 and a resistor R5 is provided in parallel with 11 to D15. Power supply voltage V
As cc rises, the base voltage V of the transistor Q7
Since c and the emitter voltage Vd also rise and the voltage applied to the resistor R5 rises, the collector current I4 flowing through the transistor Q7 increases. Therefore, the increase in the collector current (I3 + I4) of the transistor Q6 is absorbed by the increase in the collector current I4 of the transistor Q7, so that the current I3 flowing through the diode groups D11 to D15 does not change. As a result, even if the power supply voltage Vcc rises, a stable reference voltage Vref can be obtained at the emitter of the transistor Q8. Similarly, when the power supply voltage Vcc drops, a stable reference voltage Vref can be obtained. From the above, even if the power supply voltage Vcc fluctuates, a stable reference voltage Vref can always be obtained by the action of the bypass circuit.

Describing the above description with mathematical expressions, the current I3 flowing through the diode groups D11 to D15 is the emitter-base generated voltage of the transistors Q5 to Q7 being Vb.
If we say e3,

[0011]

[Equation 3]

[0012] The fluctuation amount of the power supply voltage Vcc (Δ
The current change (ΔI3) of the diode groups D11 to D15 with respect to Vcc) is

[0013]

[Equation 4]

[0014] In this formula, if the resistance values of the resistors R5 and R4 are equal, the current I3 flowing through the diode groups D11 to D15 does not change, no matter how much the power supply voltage Vcc changes. That is, the fluctuation of the current I4 flowing through the bypass circuit corresponding to the fluctuation of the power supply voltage Vcc can absorb the fluctuation of the current I3 flowing through the diode groups D11 to D15.

[0015]

As described above, according to the present invention, by adjusting the current flowing through the bypass circuit, the fluctuation of the current flowing through the diode group can be suppressed even if the power supply voltage fluctuates. A voltage can be generated. Further, since the reliability of the reference voltage is improved, it is possible to guarantee that the device using the reference voltage operates normally without being affected by the fluctuation of the power supply voltage.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a reference voltage generating circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a reference voltage generation circuit according to a conventional example.

FIG. 3 is a circuit diagram of a reference voltage generating circuit according to another conventional example.

[Explanation of symbols]

D1 to D5, D6 to D10, D11 to D15 Diode group Vcc Power supply voltage Q1 to Q8 Transistors R1 to R5 Resistances I1 to I3 Current flowing in each diode group

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H03K 19/00 A 8941-5J

Claims (1)

[Claims] 1. A reference voltage generation circuit comprising a diode group, wherein a current is supplied from a power supply voltage to the diode group to generate a reference voltage, wherein the diode group is provided in parallel with the diode group, the diode group being generated by fluctuations in the power supply voltage. A reference voltage generation circuit comprising a bypass circuit through which a current flows so as to absorb a variation in the flowing current.