JPH03226809A - Constant-voltage circuit - Google Patents

Abstract

PURPOSE:To obtain a stable output voltage by providing a correcting circuit for correcting a current flowing to a series circuit in accordance with fluctuation of the applied voltage of a P-N junction element. CONSTITUTION:An input voltage is applied between terminals 1, 3, an output constant-voltage Vc is taken out from terminals 2, 3, and the terminal 1 is connected to the terminal 2 through a constant-current source 4. Between the terminal 2 and the terminal 3, a series circuit 5, a differential amplifier 6, a control circuit 7 being a correcting circuit, and a PNP transistor Q2 are con nected in parallel to each other. In such a case, the control circuit 7 can execute a correction at the part of a DC current amplification factor hFE is higher in level than the level of correction by a conventional resistance R4 being not sufficient, therefore, even if the voltage of an NPN transistor Q1 for constituting a P-N junction element which comes to a reference is fluctuated, a supply current to the series circuit 5 is corrected in proportion to the fluctuation. In such a way, a stable output voltage is obtained in a wide range.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a constant voltage circuit, and more particularly to a constant voltage circuit that uses a PN junction element to maintain a low output voltage at a constant level.

2. Description of the Related Art A bandgap Zener using a PN junction is known as a constant voltage circuit that obtains an output voltage that can be used as a stable reference voltage at a low voltage.

A conventional constant voltage circuit using a bandgap Zener has a configuration as shown in FIG.

A power source l is disconnected between input terminal 1 and terminal 3, and input terminal 1 is connected to output terminal f2 via constant current source 4. Resistor R+ at the gate between output terminal 4 and terminal 3.

R2, R3, NPN transistor Q forming the PN junction
A series circuit consisting of 15. Differential amplifier6. NPN1 to transistor Q2, which are control elements, are connected.

The connection point between the resistors R1 and R2 of the series circuit 5 is the differential amplifier 6.
The connection point between the resistors R2 and R3 of the series circuit 5 is connected to the base of the transistor Q4 which becomes the other input of the differential amplifier 6 via the resistor R4. Ru. The output of the differential amplifier 6 is connected to the base of a transistor Q2, which is a control element.
The output voltage Vc is controlled to be constant according to the output of the differential amplifier 6.

At this time, the base-emitter voltage VBE of the transistor Q1 exhibits a variation as shown in FIG. 7 with respect to the DC current amplification factor hFE of the transistor.

Therefore, normally, the output voltage Vc would also have characteristics as shown by the broken line in FIG. 6 accordingly.

In the sizing circuit shown in Fig. 5, by inserting a correction resistor R4, the change in VBE due to hFE is corrected, and the characteristics of the output voltage Vc are changed to the characteristics shown by the dashed line in Fig. 6. If the current flowing through the ICQ series circuit 5 is 1+ and the voltage across the resistor R2 is ΔVBE by reducing the fluctuation of the voltage Vc, then Vc = (R1+R2+R3> ・ΔVBE/R20VBE Here, the transistor Q3 of the differential amplifier 6 , If the voltage between the emitter of Q4 is △■BEO, and the current flowing into the base of transistor Q4 is TB4, then △VBE, = (△
VBE〇-R4i4B), therefore, Vc, = (△VB EO-R4i4B > (R1+R2
+R3)/R2+Vs E Here, the sum of the emitter currents of transistors Q4 and Qs is 2. Let the DC current amplification factor of transistor Q4 be hFE<
Then, B 4 = I2 /2hFE4.

Therefore, Vc'=(△VBEO-R4I2/2, hr
: E 4 ) (R1+R2+R3) /R2→-
It can be expressed as BE.

VBE varies depending on hFE as shown in FIG. Looking at the above equation, hFE4 is included in the first term. Here h
Since FE4 is a term with an opposite positive/negative relationship to VBE and is included in the numerator, it can be seen that a small portion of hFE4 is effective in correcting Vc.

Problems to be Solved by the Invention However, in the conventional constant voltage circuit, the voltage V of the PN junction element
When BE fluctuates, it is corrected by the resistor R4 installed at the input of the differential amplifier 6, and the characteristics of the correction are as shown by the dashed line in Fig. 5 in the region where the DC current amplification factor hFE is small. is effective, but becomes ineffective in areas where hFE is large, and conversely, if correction is applied effectively in areas where hFE is large, it becomes ineffective in areas where hFE is small, so P
There have been problems such as correction of voltage fluctuations of the N-junction element can only be made within a narrow range.

The present invention has been made in view of the above points, and an object of the present invention is to provide a constant voltage circuit that can obtain a stable output voltage over a wide range.

Means for Solving the Problems The present invention applies all or part of the output voltage to both ends of a series circuit consisting of a PN junction element and at least two resistors,
In a constant voltage circuit in which a voltage across one of two resistors is applied between two input terminals of a differential amplifier, and the output voltage is controlled to be constant by the differential output of the differential amplifier, the PN junction element A correction circuit is provided for correcting the voltage applied to the series circuit in accordance with voltage fluctuations so that the output voltage becomes constant.

Even if the voltage of the PN junction element, which serves as a reference for operation, fluctuates, the correction circuit corrects the current supplied to the series circuit in accordance with the fluctuation, and the output voltage is held constant.

Embodiment FIG. 1 shows a circuit diagram of a first embodiment of the present invention. An input voltage is applied between 1° terminals 1 and 3, and an output constant voltage Vc is taken out from terminals 2° and 3. Terminal 1 is connected to terminal 2 via constant current source 4 .

A series circuit 5 is connected between terminal 2 and terminal 3. Differential amplifier6.
Control circuit 7. PNP1 to transistor Q2 as control elements
are connected in parallel with each other. The series circuit 5 includes NPNI to transistor Q+, resistor R+, and R, which constitute a PN junction element.
2, R3, R5, and R6, the emitters of NPN1 to transistor Q+ are connected to terminal 3, and resistors R+, R2, and R are connected between the [rector of NPN transistor Q1 and terminal 2].
3. Rs.

Connect R6 from the terminal 2 side with resistors Rs, R+, R2R3,
They are connected in series in the order of R6. NPN transistor Q
The base of the resistor 1 is connected to the connection point between the resistor R3 and the resistor R6, and a PN junction is formed between the base and emitter.

One end of the resistor R2 on the terminal 2 side is connected to the base of the NPNI transistor Q3 which becomes the input terminal of the differential amplifier 6, and one end of the resistor R2 on the PN junction element side is connected to the base of the NPNI transistor Q3 which becomes the input terminal of the differential amplifier 6. It is connected to the base of Q4 via a characteristic correction resistor R4.

A PNPI helanistor Q2, which is a control element, has its collector connected to terminal 2, its emitter connected to terminal 3, and the output of the differential amplifier 6 inputted to its base, thereby controlling the voltage between terminals 2 and 3.

The control circuit 7 is a detection NPN+- transistor Qs.

Current mirror circuit8. NPN transistor Q6 for
It becomes more. The base of the detection NPN transistor Q5 is connected to the collector of the transistor Q1, which is a PN junction element of the series circuit 5, and the collectors of the transistors Q1 to Q5 are connected to the current circuits 8. Control N P N
The base of the l-transistor Q6 is connected to the current mirror circuit 8, and the collector is connected to the resistor R5 and the resistor R1 of the series circuit 5.
connected to the connection point.

Here, the output voltage between terminals 2 and 3 is Vc, and the resistance R+1
．． R2, R3, Rs, the current flowing through the transistor Q1 is 1+, the base-emitter voltage of the transistor Q1 is Ve E, and the sum of the emitter currents of the transistors Q3 and Q4 forming the differential amplifier 6 is I2. The base current of transistor Q4 is changed to IB4°transistor Q3. The voltage difference between the emitters of Q4 is ΔVe E O, and the voltage across resistor R2 is ΔVBE.

The current ratio between transistor Q1 and transistor Q5 is n+
, when the input-output current ratio of the current mirror circuit 8 is replaced by n2, Vc = (R1+R2+R3+R5) It +Rs
11'-1-VB E
(1) ρ ■1-△VBE/R2 (2) Mano[, △VBE -△V[3EO-R41B4
(3), so 11-(△Vs EO-R4
184)/R2(4) Furthermore, It' = 1+'hFE6/n+n
26) hFE6 is the DC current amplification factor of transistor Q6.

Therefore, Vc= (△Ve E 0−R4Is 4 >, (R1+R2
@-R3+ R5) / R2+ R5・I] ・hF
E6/n+n2+VsE'
(5) Here, if the DC current amplification factor of 1 to transistor Q4 is hFE4, then Is 4 = 12 /2hF R4 (7) Therefore, Vc = (△Ve E O-'R4・12 /2hFE4 ) (
R1+R2+R3+R5)/R2+R5I+ 0hr
Es /n+ n2 +Vs E (8)VB
It is known that E changes as shown in Figure 7 in response to changes in the DC current amplification factor hFE, and as shown in equation (8), hFE6 appears in the first term and hFE6 appears in the second term. Therefore, even if hFE fluctuates and VBE fluctuates, hFE4° hFE6 fluctuate accordingly, and the output voltage Vc is held constant by compensating for the fluctuation in VBE.

The control circuit 7 is related to the second term and is variable, so the conventional resistance R
4 (FIG. 6 - dot-dashed line) can correct the portions where hFE is high. Therefore, the characteristics of the output voltage Vc with respect to changes in hFE are as shown by the solid line in FIG. 6, and a constant output voltage can always be obtained regardless of changes in hFE.

FIG. 2 shows a circuit diagram of a second embodiment of the invention.

Components that are the same as those in FIG. 1 are designated by the same reference numerals, and their explanations will be omitted. This example is the resistor R5 in the first example.
, Rs are shared by the resistors R+ and R3, and the number of parts can be reduced compared to the first embodiment.

FIG. 3 shows a circuit diagram of a third embodiment of the invention.

The same numbers as those in FIGS. 1 and 2 are used for the same parts, and the explanation thereof will be omitted. In this embodiment, the correction circuit 7 is composed of a 1-transistor transistor Q7, which is a control element, and a detection circuit 9. The collectors of the transistors 1 to Q7 are connected to resistors R+,'
The detection circuit 9 detects the voltage between the terminals 2 and 3, controls the transistor Q7, and controls the current supplied to the DC circuit 5.

FIG. 4 is a circuit diagram of a third embodiment of the present invention.

In the drawings, the same components as in FIGS. 1, 2, and 3 are designated by the same reference numerals, and their explanations will be omitted.

In this embodiment, the connection point between the terminal 3 and the emitter of the transistor Q2 is connected to the emitter of the transistor Q1 via a resistor R7. Is the correction circuit 7 a constant current? l! The emitter of the transistor Q8 is connected to the connection point between the emitter of the transistor Q1 and the resistor R7, and the constant current source 10 is connected to the base of the transistor Q8.

Transistor Q8 remains 1- even if the voltage of series circuit 5 fluctuates.
A constant current is supplied to one connection point between the emitter of the transistor Q1 and the resistor R7, and the output voltage Vc is held constant.

Note that the circuit is not limited to the above embodiment, and a structure in which the polarity of the transistors is changed may also be considered.

Effects of the Invention As described above, according to the present invention, by providing a correction circuit that corrects the current flowing through the series circuit in accordance with changes in the voltage applied to the PN junction element, fluctuations in the output voltage due to changes in the voltage applied to the PN junction element f can be suppressed. Since the output voltage can be corrected, fluctuations in the output voltage can be reduced and a stable output voltage can be obtained.

[Brief explanation of drawings]

1 is a circuit diagram of a first embodiment of the present invention, FIG. 2 is a circuit diagram of a second embodiment of the present invention, FIG. 3 is a circuit diagram of a third embodiment of the present invention, and FIG. FIG. 5 is a circuit diagram of a fourth embodiment of the present invention, FIG. 5 is a circuit diagram of a conventional example, FIG. 6 is an output voltage characteristic diagram, and FIG. 7 is a PN junction element voltage characteristic diagram. 5...Series circuit, 6...Differential amplifier, 7...Correction circuit. 2

Claims (1)

[Claims] All or part of the output voltage is applied to both ends of a series circuit consisting of a PN junction element and at least two resistors, and the voltage across one of the two resistors is applied to a differential amplifier. in a constant voltage circuit that controls the output voltage to be constant by the differential output of the differential amplifier, the current flowing through the series circuit depending on the voltage fluctuation of the PN junction element is applied between the two input terminals of the differential amplifier. A constant voltage circuit characterized by comprising a correction circuit that corrects the output voltage to be constant.