JPH0836435A - Constant voltage circuit - Google Patents

Abstract

PURPOSE:To generate a temperature compensated constant voltage equal to or lower than a band gap voltage. CONSTITUTION:Emitters of transistors TRs 1, 4, 6, 7, and 9 are connected to a power source 14, and their bases are connected in common, and respective collectors are grounded through the series connection body of TRs 2, 3, and 5 and a resistance 10, a TR 8, and a resistance 11. TRs 1, 5, and 8 are diode- connected, and bases of TRs 3 and 5 are connected, and the series connection body or resistances 12 and 13 is inserted between collectors of TRs 7 and 9, and a constant voltage is obtained from the connection point between resistances 12 and 13. In this circuit, the area ratio of TRs 2 and 3, a resistance 10, and resistance temperature coefficients of resistances 10 to 13 are set to 3, 3kOMEGA, and 1000ppm/ deg.C respectively to obtain 0.75V constant voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant voltage generating circuit.

[0002]

2. Description of the Related Art Conventionally, a bandgap circuit has been widely used as a constant voltage generating circuit having a small temperature characteristic. The operation of the conventional constant voltage generating circuit will be described below. FIG. 2 shows a conventional constant voltage generating circuit, 1, 2, 3 are transistors, 4,
Reference numerals 5 and 6 are resistors, 7 is a constant current source, and 8 is a constant voltage output.

A difference in VBE between the transistor 1 and the transistor 2 occurs across the resistor 6. Resistor 6 at both ends of resistor 5
A voltage proportional to the voltage across both ends of is generated. The voltage of the constant voltage output 8 is the voltage VBE3 of the base and emitter of the transistor 3.
And the voltage VR5 across the resistor 5 are expressed by the following equation.

VREF = VBE3 + VR5 = VBE3 × (R5 / R6) × VT × ln (J1 / J2) where J1 and J2 are current densities of the transistors 1 and 2, respectively. VT = kT / q, k is Boltzmann's constant, q is unit charge, and T is absolute temperature. A constant voltage can be obtained by differentiating both sides with the temperature T to generate a voltage stable with respect to the temperature and selecting a constant of resistance so that the left side becomes zero.

[0005]

However, in the above-mentioned structure, the constant voltage value is usually about 1.25 V (bandgap voltage), and it is impossible to generate a temperature-compensated constant voltage value equal to or lower than the bandgap voltage. There was a problem. The present invention solves the above-mentioned conventional problems, and an object thereof is to generate a temperature-compensated constant voltage equal to or lower than the bandgap voltage.

[0006]

To achieve this object, in a constant voltage generating circuit of the present invention, an emitter of a first transistor is connected to a power source, a base and a collector are diode-connected, and a collector of a second transistor is The base of the second transistor is connected to the collector of the first transistor, the base of the second transistor is connected to the collector of the third transistor, and the base of the third transistor is connected to the base of the third transistor.
Is connected to the base and collector of the transistor and the collector of the sixth transistor, the emitter of the fifth transistor is grounded through the first resistor, and the collector of the seventh transistor is the base and collector of the eighth transistor and the second transistor. The collector of the ninth transistor is connected to the third and fourth resistors, the other end of the fourth resistor is grounded, and the bases of the first, fourth, sixth, seventh, and ninth transistors are The emitters of the commonly connected first, fourth, sixth, seventh and ninth transistors are commonly connected to the power source, the emitters of the second, third and eighth transistors are grounded, and the other end of the second resistor and the third resistor are connected. The other end of the resistor is connected.

[0007]

With this structure, a temperature-compensated constant voltage equal to or lower than the bandgap voltage can be generated.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. 1 is the first PNP transistor Q1, 2 is the second NPN transistor Q2, 3 is the third NPN transistor Q3, 4 is the fourth PNP transistor Q4, 5
Is a fifth NPN transistor Q5, 6 is a sixth PNP transistor Q6, 7 is a seventh PNP transistor Q7,
8 is an eighth NPN transistor Q8, 9 is a ninth PNP
Transistors Q9, 10 have a first resistor R1, 11 a second resistor
The resistors R2 and 12 are third resistors R3, 13 is the fourth resistor R4, 14 is a power source, and 15 is a constant voltage VREF.

The operation of this embodiment configured as described above will be described below. First, Q1, Q4, Q6, Q7, Q9
A current represented by the following formula flows through the mirror circuit of.

Ic = {VT × ln (N)} / R1 (1) where N is the area ratio of Q2 and Q3.

The voltage at the point A is VA = VBE8 (2) The voltage at the point B is VB = Ic × R4 (3) If the resistors 2 and 3 are equal to each other, the constant voltage VREF is VREF = (VA + VB) / 2. Therefore, it is sufficient if the equations (2) and (3) are differentiated with respect to the temperature T. Since VA is usually the base-emitter voltage of the transistor, the temperature coefficient is -2 mV / ° C. That is, dVB / dT = R4 × (dIc / dT) + Ic × (dR4 / dT) (4) Substituting equation (2) into equation (4), the left side of equation (4) is -2 m.
A constant may be set with V / ° C.

An example of constant setting will be shown. N = 3, R1 = 3
K, temperature coefficient of resistance 2000ppm / ℃, VT = 26
If mV, R4 = 56K. At this time, VREF = 0.
It becomes 78V.

As described above, according to this embodiment, a temperature-compensated constant voltage equal to or lower than the bandgap voltage can be generated.

[0014]

According to the structure of the present invention, a temperature-compensated constant voltage equal to or lower than the bandgap voltage can be generated.

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining a conventional bandgap circuit.

[Explanation of symbols]

 1 1st PNP transistor Q1 2 2nd NPN transistor Q2 3 3rd NPN transistor Q3 4 4th PNP transistor Q4 5 5th NPN transistor Q5 6 6th PNP transistor Q6 7 7th PNP transistor Q7 8 Eighth NPN transistor Q8 9 Ninth PNP transistor Q9 10 First resistor R1 11 Second resistor R2 12 Third resistor R3 13 Fourth resistor R4 14 Power supply 15 Constant voltage

Claims (1)

[Claims] 1. An emitter of a first transistor is connected to a power supply, a base and a collector of which are diode-connected, a collector of a second transistor is connected to a collector of a first transistor, and a base of a second transistor is a third transistor. Is connected to the collector of the fourth transistor and the base of the third transistor is connected to the base and collector of the fifth transistor and the collector of the sixth transistor, and the emitter of the fifth transistor is connected through the first resistor. Grounded, the collector of the seventh transistor is connected to the base and collector of the eighth transistor and the second resistor, and the collector of the ninth transistor is connected to the third and fourth
The other end of the fourth resistor is grounded, the bases of the first, fourth, sixth, seventh and ninth transistors are commonly connected, and the emitters of the first, fourth, sixth, seventh and ninth transistors are connected. Is commonly connected to a power source, the emitters of the second, third and eighth transistors are grounded, and a constant voltage is generated at the point where the other end of the second resistor and the other end of the third resistor are connected. circuit.