JPH0222725Y2 - - Google Patents

Description

[Detailed description of the invention] The invention relates to a simple constant voltage circuit that is suitable for semiconductor integrated circuits, and provides negative feedback to a transistor in the output stage of a current mirror circuit that outputs a constant current. The present invention relates to a constant voltage circuit that obtains a constant voltage based on a power supply voltage by forming a circuit.

Hereinafter, the constant voltage circuit of the present invention will be explained based on FIGS. 1 and 2.

FIG. 1 shows an embodiment of a constant voltage circuit according to the present invention, and numeral 1 indicates a constant current circuit equipped with a start-up circuit. Diode D ₁ and transistor Q ₁ are
It constitutes a current mirror circuit 2, in which the constant current _I0 from the constant current circuit 1 is connected to the bias stage of the current mirror circuit 2 (the base of _the transistor _Q1 is connected to the cathode of the diode D1). side)
The constant current circuit 1 is connected to the constant current circuit 1 so that the current is supplied to the constant current circuit 1.
The current mirror circuit 3 includes transistors Q ₂ and Q ₃ and resistors R ₁ and R ₂ connected between the emitters of these transistors Q ₂ and Q ₃ and the power supply voltage terminal 5, respectively. The cathode of the diode-connected transistor Q ₂ of the current mirror circuit 3 is connected to the collector of the transistor Q ₁ in the output stage of the current mirror circuit 2 . Also, the collector of transistor Q ₃ is connected to one end of resistor R ₃ and the base of transistor Q ₄ , the emitter of transistor Q ₃ is connected to one end of resistor R ₄ , and the other end is connected to the collector of transistor Q ₄ . It constitutes a negative feedback circuit. Resistors R ₅ and R ₆ are connected in series between the power supply voltage terminal 5 and the collector of the transistor Q ₄ , and a common connection point of these resistors R ₅ and R ₆ is connected to the output terminal 6 .

FIG. 2 shows another embodiment of the present invention, which differs from FIG. 1 only in the configuration of the current mirror circuit 4, and the other circuit configurations are the same. In the current mirror circuit 4 shown in FIG. 2, the base of the transistor Q ₂ in the bias stage is commonly connected to the base of the transistor Q ₃ in the output stage, and the transistor
The emitter of transistor _Q5 is connected to the emitter of transistor Q5, the base of transistor _Q5 is connected to the collector of transistor _Q2 , and the collector of transistor _Q5 is grounded. This current mirror circuit 4 is advantageous in flowing a more accurate mirror current compared to the current mirror circuit ₃ shown in FIG. This is an example in which a more stable constant voltage can be obtained from the voltage between terminals ₅ and _R6 .

Hereinafter, the operation of the constant voltage circuit according to the present invention will be explained based on the embodiment shown in FIG.

In the figure, the constant current obtained from constant current circuit 1
I ₀ is supplied to the bias stage of the current mirror circuit 2 , and a constant current I ₁ is drawn from the bias stage of the current mirror circuit 3 to the transistor Q ₁ at the output stage of the current mirror circuit 2 . The constant current I ₂ is supplied to the collector of the transistor Q ₃ in the output stage of the current mirror circuit 3 through the resistor R ₂ .
The collector current of transistor Q ₃ is supplied to resistor R ₃ so that transistor Q ₄ is biased by the voltage across its terminals, and at the same time, current I ₃ flows through resistor R ₄ .
Then, the current I ₄ is supplied as the collector current of the transistor Q ₄ via the resistors R ₅ and R ₆ , respectively.

Next, the feedback effect of the constant voltage circuit of the present invention will be explained.

When the collector current I _C of the transistor Q ₄ supplied via the resistors R ₄ to R ₆ attempts to increase due to some action, it is shunted from the constant current I ₂ flowing through the resistor R ₂ to the transistor Q The current supplied to transistor _{Q 3} tries to decrease, so the collector current of transistor Q ₃ decreases, so the resistor
The voltage across R ₃ drops and transistor Q ₄
Shallow biased. Therefore, the collector current I _C flowing into the transistor Q ₄ via the resistors R ₄ to R ₆
is reduced, so feedback is applied to stabilize it.

On the other hand, if the collector current I _C of transistor Q ₄ tries to decrease for some reason, the current supplied to transistor Q ₃ tries to increase, and the voltage across the terminals of resistor R ₃ increases, causing the transistor Deeply bias Q ₄ . Therefore, the resistance R ₄
The current I ₃ flowing through the transistor Q 3 and the current flowing through the resistors R ₅ and R ₆ increase and become stable as feedback is applied to increase the collector current I _c of the transistor Q ₃ . In this way, negative feedback is applied to the transistors Q ₃ and Q ₄ , and the collector current I _C of the transistor Q ₄ is controlled to always be constant. Therefore, the power supply voltage terminal 5
A constant voltage is obtained between the terminals of the resistors R ₅ and R ₆ connected between the collector of the transistor Q ₄ and the collector of the transistor Q 4 .

That is, the collector current I _C of the transistor Q ₄ is determined by the current I ₃ flowing through the resistor R ₄ and the current I ₄ flowing through the resistors R ₅ and R ₆ as follows: I _C = I ₃ + I ₄ (1) If this relationship holds true and the voltage at the collector electrode of transistor Q ₄ is V _C , then the following relationship holds true between the power supply voltage V _CC and the voltage V _C at the collector electrode of transistor Q ₄ .

V _CC −V _C = I ₂ R ₂ + I ₃ R ₄ …(2) V _CC −V _C = I ₄ (R ₅ + R ₆ ) …(3) Also, the collector current I _C of transistor Q ₄ is calculated by the following formula. It is expressed as follows.

I _C = I _S exp (V _BE /V _T ) ...(4) = I _S exp (I _M R ₃ /V _T (where I _S is the saturation current, I _M is the collector current of transistor Q ₃ , V _T is the thermal voltage) From equations (2) and (3), I ₂ R ₂ + I ₃ + R ₄ = I ₄ (R ₅ + R ₆ ) ...(5), and substituting equation (1) into equation (5), When the current I ₃ is erased, the current I ₄ flowing through the resistors R ₅ and R ₆ connected between the power supply voltage V _CC and the collector of the transistor Q ₄ is expressed as follows.

I ₃ = I ₂・R ₂ + (I _C − I ₄ ) R ₄ / R ₅ + R ₆ I ₄ = I ₂・R ₂ + I _C・R ₄ / (R ₄ + R ₅ + R ₆ ) …(6) ( In equation 6), the collector current I _C of transistor Q ₄ is a constant current, as is clear from equation (4),
Also, the current _{I 2 flowing} through the resistor R 2 of the current mirror circuit 3
Since the current I 4 is made constant by the constant current circuit 1, the current I ₄ can be regarded as a constant current. Therefore, the voltage between the terminals of the resistor _R5 is made constant. Of course, the voltages between the respective terminals of the resistors R ₅ and R ₆ connected between the power supply voltage terminal 5 and the collector of the transistor Q ₄ are made constant with reference to the reference voltage V _CC .

In addition, in the above embodiment, the constant current circuit 1 is
Although a start-up circuit is provided, it goes without saying that the present invention is not limited to this embodiment and that various known constant current circuits can be used. Furthermore, various well-known circuits can be used as the current mirror circuit.

As described above, the constant voltage circuit according to the present invention supplies a constant current to the current mirror circuit, connects the collector of the transistor Q ₃ in the output stage of the current mirror circuit to the resistor R ₃ and the base of the transistor Q 4, and connects the collector of the transistor Q 3 to the base of the transistor Q ₄ . By configuring a feedback circuit with the resistor _R4 connected between the emitter of _Q3 and the collector of the transistor _Q4 , the terminal of the resistor connected between the power supply voltage terminal 5 and the collector of the transistor _Q4 It is possible to easily obtain a constant voltage whose voltage is based on the power supply voltage V _CC .

[Brief explanation of the drawing]

1 and 2 are drawings showing an embodiment of a constant voltage circuit according to the present invention. 1: constant current circuit, 2, 3, 4: current mirror circuit.

Claims (1)

[Scope of utility model registration request] a constant current circuit, a first current mirror circuit to which a constant current is supplied from the constant current circuit to a bias stage, and a second current mirror circuit to which a constant current is supplied from an output stage of the first current mirror circuit. and first and second resistors connected between the respective emitters of the first transistor in the bias stage and the second transistor in the output stage of the second current mirror circuit and the power supply voltage terminal;
a third resistor connected to the collector of the second transistor; a third transistor whose base is connected to a connection point between the collector of the second transistor and the third resistor; a fourth resistor connected between the emitter of the transistor and the collector of the third transistor, the voltage between the terminals of the resistor connected between the collector of the third transistor and the power supply voltage terminal is made constant; A constant voltage circuit characterized by: