JPH0124646Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a constant voltage power supply circuit, a so-called shunt regulator circuit, used in electronic circuits and the like.

This type of circuit consists of Darlington connected transistors Q ₁ and Q ₂ , resistor R ₁ and
R ₂ consists of a constant voltage diode ZD. The load is indicated by R _L. If the load R _L changes and the load current I _L decreases by △I _L , the voltage Vcc will rise by R ₀ × △I _L , and the base potential of transistor Q ₂ will follow this and rise accordingly. Then, the collector currents of transistors _Q1 and _Q2 increase (current I increases), and the voltage Vcc
will begin to lower. If the load current I _L increases by ΔI _L , the opposite operation occurs. In this way, when the load current I increases (decreases), the current I of the constant voltage power supply circuit decreases (increases) by a corresponding amount, and the voltage Vcc is kept constant.

Also, the Darlington connected transistor _Q1 and
If the common emitter current amplification factor of Q ₂ is hfe (>>1), then the voltage Vcc is Vcc=R ₂ /h _fe・I+(R ₂ /R ₁ +1)・2V _BE +V _Z …(1) . However, V _BE is the base-emitter voltage of transistors Q ₁ and Q ₂ , and V _Z is the voltage regulator diode ZD.
voltage. The first term on the right side of equation (1) indicates the internal impedance of the constant voltage circuit, and in order to lower this internal impedance, transistors Q ₁ and Q ₂ are connected in Darlington as shown in FIG. In this case, if you ignore the internal impedance, the voltage
Vcc is almost constant regardless of the current I, and is expressed as Vcc=(R ₂ /R ₁ +1)·2V _BE +V _Z (2). Further, a power supply circuit is generally required that its output voltage does not change with temperature, that is, that the temperature coefficient ∂/∂TVcc of the voltage Vcc is constant. In the case of FIG. 1, ∂/∂TVcc=2(R ₂ /R ₁ +1)·∂/∂TV _BE +∂/∂TV _Z (3). As is generally well known, ∂/∂TV _BE has a value of about -2 mv/℃, and ∂/∂TV _Z is positive, and as shown in Figure 2, the voltage V _Z (i.e., P・It changes almost in proportion to the impurity concentration of the N junction). Therefore, as can be seen from equation (3), when ∂/∂TV _Z <+4mv/°C (4), it is impossible to set ∂/∂TVcc=0. In particular, when trying to convert this circuit into an IC, it is necessary to satisfy ∂/∂TV _Z ≧+4mv/℃ (5), and the IC manufacturing method (impurity concentration) must be satisfied.
is limited, and other properties of the IC are adversely affected.

The present invention was developed in consideration of the above points.
The purpose of the present invention is to provide a constant voltage power supply circuit that is suitable for various applications and has little voltage fluctuation with respect to temperature.

An embodiment of the present invention will be described below with reference to FIG. In FIG. 3, the base bias of the latter transistor Q 2 of the transistors Q ₁ and Q ₂ connected to Darlington is obtained by the transistor Q ₃ and the resistors R ₂ and R 1, and the base bias of the transistor Q ₃ is obtained by the transistor Q ₃ and the resistors R 2 and _{R 1} . Resistors R ₃ , R ₄ , n diodes
A constant voltage diode ZD is connected in parallel to _{the resistor R 4 and} the n diodes D ₁ to _{D o .}

In other words, the potential accumulated on the anode potential of the constant voltage diode ZD by n diodes D ₁ to D _o is applied to the base of the transistor Q ₃ , thereby providing positive feedback to the base of the transistor Q ₂ . be.

The basic operation of this circuit is the same as the circuit shown in FIG. Further, in this circuit, if internal impedance is ignored, Vcc=(2R ₂ /R ₁ +3−n)V _BE +V _Z (6). Therefore, even if ∂/∂TV _Z = +3mv/℃ (< 4mv/℃), if constants are chosen as n=2 and R ₂ /R ₁ = 1/4, ∂/∂TVcc=0 It can be done.

From the above, according to the present invention, even if the temperature coefficient of the internal voltage regulator diode is +4mv/℃ or less when integrated into an IC, it is possible to design the output voltage so that the fluctuation due to temperature changes is zero. become able to.

[Brief explanation of the drawing]

FIG. 1 is a diagram of a conventional constant voltage circuit, FIG. 2 is a temperature characteristic diagram of a constant voltage diode, and FIG. 3 is a diagram of a constant voltage circuit according to an embodiment of the present invention. Q...transistor, ZD...constant voltage diode, D...diode.

Claims (1)

[Scope of utility model registration request] A Darlington-connected transistor circuit provided between a voltage source and a reference potential point, a transistor for driving the base of a previous stage transistor in this transistor circuit, and a constant voltage diode and a resistor connected in series between the voltage source and the reference potential point. The voltage setting circuit includes a voltage setting circuit connected in series, a resistor connected in parallel to the voltage regulator diode, and a predetermined number of diodes connected in series, and means for applying the voltage accumulated by the diodes to the base of the base drive transistor. Constant voltage power supply circuit.