JPS6231371B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a constant voltage circuit, and particularly to a two-terminal constant voltage circuit composed of a transistor and a resistor.

In general, a constant voltage circuit or a constant voltage element is essential for keeping the power supply voltage of an electronic circuit constant or for obtaining a reference voltage for a comparator or DAC. Among these, the simplest ones use a single element such as a Zener element or a forward voltage of a diode, but it is not possible to obtain an arbitrary constant voltage with these devices.

On the other hand, a circuit as shown in FIG. 1 is well known as a simple constant voltage circuit that has two terminals like a single element and can arbitrarily set the output voltage. In the figure, a resistor _R1 is connected between the collector and base terminals of the transistor _Q1 , and a resistor _R2 is connected between the base and emitter terminals of the transistor Q1. Now, if the voltage between the base and emitter of Q ₁ is V _BE1 , the voltage V ₀ generated in this constant voltage circuit is V ₀ = (1+R ₁ /R ₂ )V _BE1 (1), and R ₁ /R ₂ can be set appropriately. By choosing V ₀ > V _B
It can be set arbitrarily within the range of _E1 . On the other hand, the circuit current I ₀
is I ₀ =I _E1 +V _BE1 /R ₂ (2). However, I _E1 is the emitter current of Q ₁ , h _F
Assume that _E is sufficiently large.

From equations (1) and (2), the AC operating resistance γ of this circuit is
If you ask for becomes. However, γ _e1 is the emitter operating resistance of Q ₁ , and γ _e1 = △V _BE1 / △I _E1 ≪R ₂ .

As is clear from equation (3), the operating resistance γ of this circuit is _{approximately} ( ₁₊
R ₁ /R ₂ ) times, and in order to make the operating resistance sufficiently small, it is necessary to flow a large emitter current I _E1 .

The present invention eliminates these drawbacks and provides a constant voltage that has two terminals like a single unit, allows the output voltage to be arbitrarily set with a very simple circuit configuration, and can sufficiently reduce the operating resistance from the small current range. It is intended to provide a circuit.

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 shows an embodiment of a two-terminal constant voltage circuit according to the present invention. In the figure, resistor R ₁ is connected between terminal 1 and the base terminal of transistor Q ₁ , resistor R ₂ is connected between the base and emitter terminal of transistor Q ₁ , and resistor R ₃ is connected between terminal 1 and the collector terminal of transistor Q ₁ . , the transistor Q ₂ having the opposite polarity to the transistor Q ₁ has its emitter terminal connected to the terminal 1, its base terminal connected to the collector terminal of the transistor Q ₁ , and its collector terminal connected to the emitter terminal of the transistor Q ₁ .

In FIG. 2, the output voltage V ₀ is the same as equation (1), and can be set to any value by appropriately selecting R ₁ /R ₂ .

On the other hand, the circuit current I ₀ is caused by the transistor Q ₁ and
Let the emitter currents of Q ₂ be I _E1 and I _E2 , respectively, and the voltage between the base and emitter terminals be V _BE respectively.
₁ and V _BE2 , then I ₀ =I _E2 +V _BE2 /R ₃ +V _BE1 /R ₂ (4) From equations (1) and (4), the operating resistance γ is becomes. Here, the emitter operating resistance γ _e of Q ₁ and Q _2
1 , γ _e2 is γ _e1 = △V _BE1 / △I _E1 , γ _e2 = △V _B
E2 /△I _E2 , and △V _BE1 /△V _BE2 = △I _E1・γ _e1 /△I _E
Since ₁・R ₃ = γ _e1 /R ₃ , formula (5) is becomes. Here, considering γ _e1 ≪R ₂ and γ _e2 ≪R ₃ , equation (6) becomes γ≒(1+R ₁ /R ₂ )・γ _e1・γ _e2 /R ₃ (7).

As is clear from comparing equations (3) and (6), in the circuit according to the invention the operating resistance is ₃ times the conventional γ _e1 /R, which is the reciprocal of the voltage gain of Q ₁ Therefore, it can be seen that this is significantly reduced compared to the conventional circuit.

As explained above, in the conventional simple two-terminal constant voltage circuit, it was impossible to reduce its operating resistance to less than the operating resistance of the emitter, but according to the circuit configuration of the present invention, it is extremely simple. A two-terminal constant voltage circuit can be realized in which the operating resistance can be made lower than the operating resistance of the emitter, and the output voltage can be set to any desired value. Furthermore, less current consumption is required to obtain a stabilized output voltage.

These advantages make the present invention highly suitable as a stabilized voltage source for various electronic circuits.

[Brief explanation of the drawing]

FIG. 1 shows an example of a conventional two-terminal constant voltage circuit.
FIG. 2 shows an example of a two-terminal constant voltage circuit according to the present invention. _Q1 , _Q2 ...Transistor, _R1 , _R2 , _R3 ...Resistor,
1, 2...External terminal.

Claims (1)

[Claims] 1 The first terminal is connected to the first external terminal.
a first transistor having a base terminal connected to a second terminal of the first resistor and an emitter terminal connected to a second external terminal; the first terminal being connected to the base terminal of the first transistor; , the second terminal is
a second resistor connected to the second external terminal;
A first terminal is connected to a collector terminal of the first transistor, a second terminal is connected to a third resistor connected to the first external terminal, and a base terminal is connected to the collector terminal of the first transistor. A constant voltage circuit comprising: a second transistor having an emitter connected to a first external terminal, a collector connected to the second external terminal, and having a polarity opposite to that of the first transistor. .