JPH0576050B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field to Which the Invention Pertains] The present invention is directed to adjusting the voltage drop in the main circuit from the power supply terminal to the output terminal by using a pass transistor whose current is controlled based on the actual value of the output voltage. The present invention relates to a constant voltage circuit that maintains a voltage at a constant value and compensates for the temperature dependence of an output terminal voltage using a band gap voltage, and in particular relates to a constant voltage circuit that is advantageous for being incorporated into a bipolar integrated circuit.

[Prior art and its problems]

The above-mentioned type of constant voltage circuit is known for its excellent constant voltage characteristics and low temperature dependence of the output voltage, and is often used as an independent voltage constant device or incorporated into an electronic circuit device. However, this type of constant voltage circuit has the disadvantage of relatively high power consumption, and even though there is no way to avoid power consumption due to the voltage drop in the pass transistor of the main circuit due to the circuit's construction principle, the power consumption in the control circuit is Power consumption also often reaches a level that cannot be ignored.

FIG. 1 shows an example of this type of constant voltage circuit. As shown in the figure, a power supply S whose voltage can fluctuate is provided between a pair of power supply terminals B and E, and output terminals that supply a constant voltage to a load L are indicated by C and E. Load current IL
The main circuit through which the current flows has a path from power supply terminal B to output terminal C via pass transistor Tp, and the voltage fluctuation of power supply S is controlled by the voltage drop between the collector and emitter of pass transistor Tp, which is shown enclosed by a chain line. This is compensated by so-called current control by circuit A, and a constant voltage is always output to the output terminal. In this example, the base current of the pass transistor Tp is given by the Darlington-connected current control transistor 6, and the control current Ic for current control of this constant voltage circuit, that is, the base current of the pass transistor Tp, is provided by the pass transistor. The current flows through a path from the base of Tp to the ground E via the collector and emitter of the second stage transistor 6b of the current control transistor 6.

A control signal to be applied to the base of the first-stage transistor 6a of the current control transistor 6 in order to generate this control current Ic is generated by a pair of transistors 1 and 2 and a resistor 5. A substantially constant current is supplied to the output terminal of the pass transistor Tp via the high resistances 3 and 4. Transistors 1 and 2 provide the well-known so-called bandgap reference, and the emitters of these transistors 1 and 2 are given different current densities, so that the collector of transistor 2 has a theoretically zero current density. An extrapolated and therefore temperature-independent bandgap reference signal is produced and the result of the comparison with the actual value signal representative of the output voltage produced by the resistor 5 is applied to the base of the first stage 6a of the transistor 6. Note that the field effect transistor 7 shown in the upper left of the figure is a constant current source transistor that receives a reference signal 7a and supplies a base current to the pass transistor Tp.

An example of the current consumption of the control circuit section A in the conventional constant voltage circuit configured as described above is as follows. That is, the output voltage at output terminal C is set to 3V, the emitter area ratio of transistors 1 and 2 is selected to be large at 1:3 in order to obtain the bandgap reference effect, and resistor 3 is set to 1kΩ.
Then, the current flowing through transistor 1 is 300μA
It is. On the other hand, if the resistor 4 is 27 kΩ and the base-emitter voltage of the two stages of the Darlington-connected transistor 6 is 1.2V, the current flowing through the transistor 2 will be about 70 μA. Therefore, even if the current of the constant current source 7 is about 50 μA, the total current consumption is 420 μA. Although the value of this current consumption may seem small as it is, it is a value that cannot be ignored compared to the current consumption of recently advanced electronic circuit devices. For example, the load current of a constant voltage circuit incorporated in an integrated circuit is often only about 1 mA, and therefore a current equivalent to 40% of the load current is consumed in the control circuit. Of course, in order to reduce this current consumption, it is sufficient to increase the resistance values of resistors 3 and 4, but if a diffused resistor with a normal sheet resistance of 100 to 200 Ω is used when integrating the circuit, the resistance value of resistor 3 , 4 will occupy a large area on the semiconductor chip, and it will be difficult to manufacture the resistance value ratio of both resistors with high accuracy.
If this resistance value ratio deviates from a predetermined value, the temperature dependence of the constant voltage circuit will of course worsen. As described above, the conventional technology has the drawback that it is practically difficult to reduce power consumption for control while maintaining circuit performance.

[Purpose of the invention]

The present invention solves the above-mentioned drawbacks of the prior art, and provides a constant voltage circuit that does not have the risk of performance deterioration even if the power consumption of the control circuit is reduced, and is easy to manufacture when integrated. There is a particular thing.

[Key points of the invention]

According to the invention, the above object is achieved in a constant voltage circuit of the type mentioned in the opening paragraph, in which an actual value voltage signal representative of the actual value of the output terminal voltage is applied to the bases of the first and second transistors for generating the bandgap voltage; first and second resistors are provided for receiving emitter currents of the first and second transistors, the resistance values of the resistors are selected to compensate for the temperature dependence of the output terminal voltage; Second
This is achieved by having one of the transistors control a current control transistor which controls the base current of the pass transistor.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 2 shows a circuit according to an embodiment of the present invention, in which the same parts as in FIG. The corresponding control circuit section B is likewise shown surrounded by a chain line.

In FIG. 2, the first and second transistors for obtaining the bandgap reference effect are indicated by T1 and T2, and in this embodiment, the emitter area of transistor T1 is smaller than the emitter area of transistor T2. , for example, about 1/2. These transistors T1 and T2 include two transistors 11 and 11, which constitute a current mirror circuit shown in the upper part of the figure.
Constant currents I having the same value from each of the 12
1, I2 is supplied. The emitters of the pnp transistors 11 and 12 that constitute these current mirror circuits are connected to the output terminal C via current balancing resistors 13 and 14, and these resistors 1
3 and 14 are current mirror transistors 11,
Together with the large equivalent resistance inherent in transistors 12 and 12, this creates a high equivalent resistance during constant current supply to the first and second transistors T1 and T2. In addition,
The resistors 13 and 14 and the transistors 11 and 12 are
Resistors 13 and 14 need to have the same resistance value or characteristics, but since they need only have a resistance value of several kΩ, which is necessary to maintain current balance, high accuracy can be achieved and the car Difficulties in manufacturing are eliminated along with the current mirror transistors 11 and 12. In order to further ensure a good current balance, a transistor 15 is attached to this current mirror circuit in a known manner as shown.

The aforementioned first and second transistors T1, T
As shown in the figure, first and second resistors R1 and R2 are inserted between the emitter circuit of No. 2 and ground E, and in this embodiment, the first resistor R1 is connected to the first and second transistors T1. , T2, and the second resistor R2 is connected so that the emitter current of the second transistor T2 flows therethrough. The functions of these resistors R1 and R2 will be explained in detail later.

Now, at the bases of these first and second transistors, there are two resistors 17 and 1 inserted in series between the output terminals C and E shown on the right side in the figure.
Actual values representing the output terminal voltages as divided voltages of a voltage divider circuit consisting of 8 are given as shown. However, the circuit elements of this voltage dividing circuit are not limited to resistors, but may also be diodes. Further, the collector of the first transistor T1 is connected to the base of the current control transistor TC, so that the control current Ic flowing from the base of the pass transistor Tp to the ground terminal E via the emitter and collector of the current control transistor TC is the first and the actual values applied to the bases of the second transistors T1, T2. Note that although a diode 18 is inserted as a level shift element in this control current path, this need not be taken into account in terms of control principle. Further, a field effect transistor 7 is connected as shown in the figure in a known manner as a constant current source that provides a basic base current to the pass transistor Tp, and in this embodiment, the ground potential is applied to its gate as a reference potential. There is. The supply current from this constant current source is the load current flowing to output terminal C.
When IL is zero, it flows to the ground via the above-mentioned control current path, but when there is a load current, the current according to the load condition flows through the pass transistor Tp.
flows to earth E via the base emitter of , load L.

The operation of the control loop as described above is as follows. Assuming that the voltage at output terminal C has risen slightly above the specified value, the resistors 17 and 18 will respond accordingly.
, the interconnection point of the first transistor T1 rises and the first transistor T1
As more of the collector current I1 of the current control transistor is sucked into its base, more base current is sucked from the emitter of the current control transistor so that its emitter current becomes constant, so the current control transistor TC becomes constant. More current from the current source 7 is allowed to flow, and therefore the base current of the pass transistor Tp decreases by that amount, increasing the voltage drop between its collector and emitter, and reducing the output voltage at the output terminal C. When the voltage at the output terminal C falls slightly below the specified value, the control circuit operates in such a way that the above-mentioned operating direction is reversed and the output terminal voltage is increased. Looking at the above operation in conclusion, the interconnection point potential of the resistors 17 and 18 of the voltage divider circuit is the same as that of the first and second transistors T1 and T2 and the first and second resistor R1
The control system operates so that it is equal to the bandgap reference voltage produced by R2, and accordingly the voltage at the output terminal C is maintained at a constant value.

Next, the roles of the first and second resistors R1 and R2 will be explained with reference to FIG. The same figure is the second
Only the main parts have been extracted from the example circuit in order to make it easier to understand.
4 first and second transistors T1,
The constant current supply circuit of T2 is depicted as a simplified equivalent high resistance 3, 4, and the configuration of the current control loop is also omitted, and the bases of the first and second transistors T1 and T2 are connected to the first transistor. transistor T
It is shown as being at a collector potential of 1. First, in such an equivalent circuit, it can be seen from known equations that the following equation holds true.

I1=I2=V _T /R2・lnS1/S2 (1) However, S1 and S2 are the first and second
The emitter area of transistors T1 and T2 (S2
>S1), R2 is the resistance value of the second resistor R2,
V _T is Boltzmann constant k and absolute temperature T
It is a quantity given by V _T =k·T. In equation (1), V _T can be regarded as a constant determined by the operating temperature T, so the current to be supplied from the constant current sources 3 and 4 to the first and second transistors T1 and T2, that is, the current consumption of the control circuit I1 + I2 is , first and second
Emitter area ratio S of transistors T1 and T2
It is determined by 1/S2 and the resistance value of the second resistor R2. Now, as explained above, if we choose the emitter area ratio as S1/S2=1/2,
Assuming that the resistance value of the second resistor R2 is a relatively low resistance value of R2=1.8kΩ, I1=I2=
10μA, that is, the constant current consumption of the control circuit is
It can be seen that the current is 20 μA, which is one order of magnitude smaller than that of the conventional example described above.

Next, consider conditions for compensating for the temperature dependence of this circuit. In this circuit, if EB is the base potential of the first transistor with respect to the ground E which determines the voltage of the output terminal C mentioned above, this is the result of the voltage drop in the first resistor R1 through which the current I1+I2 flows and the voltage drop in the first transistor T1. Since it is nothing but the sum of the base-emitter voltage V _BE , it is expressed as EB = V _BE + (I1 + I2) · R1 (2) Considering the previous equation (1), EB = V _BE + 2・R1/R2・k・T・lnS2/S1. Therefore, its temperature dependence is obtained by differentiating the above equation with respect to T and becomes d/dT (EB) = d/dT (V _BE ) +2・R1/R2・k・T・lnS2/S1. The conditions for completely _compensating for the
/S1(3). Now, the base-emitter voltage of this type of transistor is about V _BE = 0.7 V at room temperature, and its temperature dependence is about d/dT (V _BE ) = -2 mV/〓, so the previous S2/ S1=2, R2=
The resistance value of the first resistor R1 that satisfies equation (3) under the condition of 1.8 kΩ is R1=30 kΩ, which is just within the resistance value that can be built into the integrated circuit.

Next, a preferred embodiment of the current control transistor TC will be explained. Returning to FIG. 2, since the base current of the current control transistor TC flows into the first transistor T1, if this base current value is too large, it is necessary to add this base current to I1 in equation (2) above. , the condition of equation (3) will change, and this condition will be influenced by the magnitude of the load current IL flowing through the output terminal.
Therefore, the base current of the current control transistor is small,
In other words, it can be seen that it is desirable that the amplification factor be large. To be more precise, the constant current source 7 also has a finite resistance value, although it is highly resistive, so when the voltage at the power supply terminal B becomes extremely high, it is inevitable that the constant current value will increase. Accordingly, the base current of the current control transistor also increases slightly in accordance with the amplification factor, so the condition of the previous equation (3) will be slightly deviated. In order to reduce dependence on the power supply voltage in this way, it is desirable that the amplification factor of the current control transistor TC be large.
Figure 4 shows an example in which the current control transistor TC is configured in a Darlington type two-stage composite configuration to increase the amplification factor, and Figure a shows an example in which the collectors of the two-stage transistors TC1 and TC2 are commonly connected. , Figure b shows an example in which two stages of transistors TC3 and TC4 are completely connected in cascade. When integrating this composite transistor into an integrated circuit, in the example shown in Figure 4a, TC1 is a horizontal pnp transistor, and TC2 is a horizontal pnp transistor.
It is preferable to use npn transistors, and in the example shown in FIG. 4b, it is preferable to use both TC3 and TC4 as vertical pnp transistors.

The effects of the composite transistor are explained numerically as follows. If we assume that the constant current value supplied by the constant current source 7 is 50 μA and the load current IL does not flow to the output terminal C, all of this constant current value flows through the current control transistor TC, so let's say that the amplification factor is set to about 10. Assuming that it is low, its base current will be about 4.5μA, which is the above-mentioned I1=
It is added to 10μA and increased to 14.5μA, which greatly upsets the condition of equation (3). Of course, the circuit constants can be selected so that equation (3) holds true at this time, but in this case, when a large load current flows to the output terminal C, the constant current of 50 μA supplied from the constant current source 7 will mostly pass. Since it will flow as the base current of the transistor Tp, the condition of equation (3) will be deviated again. The same applies to the dependence on the power supply voltage. Assuming that the constant current source 7 has an equivalent high impedance of about 1MΩ, when the voltage at the power supply terminal B is 5V, the base current of the power supply control transistor TC is
Even if the current is around 4μA, if for some reason the power supply voltage rises to 20V, the base current will become around 7μA, and the voltage drop across the first resistor R1 will increase accordingly. Therefore, the deviation from equation (3) becomes large. However, if the amplification factor of the current control transistor is 100, the aforementioned base current will be about 0.4 μA, and the condition of equation (3) will be hardly affected. When connected with a high amplification factor as shown in Figure 4b, each stage of this type of vertical PNP transistor is
Since it has an amplification factor of about 50, the total amplification factor increases to about 2500, and the current supplied from constant current source 7 increases.
Even if it is 50 μA, the base current of the current control transistor TC is only 20 nA, and there is no worry that the condition of equation (3) will be disturbed.

Next, diode 1 as a level shift element
The role of number 8 will be explained. This is to set the base potential of the current control transistor TC to a value necessary for circuit operation, and this potential is set to EC.
As can be easily seen, it is necessary that the base potential EB of the first transistor described above is higher than the base current of the current mirror transistors 11 and 12, but lower than the base current of the current mirror transistors 11 and 12. Expressing this in the formula, EB＜EC＜VO−R13・I13. However, VO is the voltage at output terminal C, R1
3 is the resistance value of the balance resistor 13, I13 is the emitter current of the current mirror transistor 11 (≒
I1). Due to its forward voltage drop, the diode 18 determines the base potential of the current control transistor TC to satisfy the above equation with respect to the base potential of the pass transistor Tp (approximately equal to VO in practice). Of course, as a means to determine the base potential of this transistor TC, the diode 1
8 in series in the control current path, various known means can be taken. Incidentally, when a composite transistor structure as shown in FIG. 4B is used, there is actually no need to use this level shift element. In other words, in this type of connected transistor, unlike the example shown in FIG.
There are two stages of base-emitter voltage between the emitter of This is because the base potential of the first stage transistor TC3 is determined within the conditions. Looking at this from another perspective, the second stage transistor
The area between the base and emitter of TC4 plays the role of the level shift diode 18, and in this sense, the second stage transistor TC4 plays the dual role of increasing the current amplification factor and as a level shift element. That's why.

As mentioned above, it is desirable to increase the amplification factor of the current control transistor TC, but on the other hand, if its base current becomes small, the operational stability of the circuit will decrease and it will be more susceptible to the effects of noise and the like. However, this point is solved by the current control transistor as shown in Figure 2.
This can be improved relatively easily by attaching a small capacitance capacitor 16 to the base of the TC. This stabilizing capacitor 16 is of course intended to improve the dynamic characteristics of the circuit, and does not have any adverse effect on the static control performance of the circuit as described above.

In the circuit of the present invention as described above, the current consumption of the band gear preference circuit is essentially lower than that in the prior art. As can be seen from the numerical values listed in the above embodiment, the current consumption required for this circuit portion is only about 20 μA. In comparison, the current supplied by constant current source 7 is about 50 μA, which may seem quite large, but this supplied constant current becomes pure current consumption only when the load current is zero. Under normal load current conditions, most of this is effectively used as part of the current supplied to the load. Further, in order to reduce the current consumption in this no-load state, it is possible to reduce it to substantially zero by using an appropriate known switching means. Furthermore, the voltage divider circuit for detecting the actual value of the power supply voltage requires some current consumption, but this can be reduced by choosing a high resistance value, or by using a diode divider or a combination of a diode and a resistor. This can be further reduced by adopting a dividing method. In an example of an integrated constant voltage circuit for 3V power supply using the circuit of the present invention, even when a diffused resistor using an easy-to-manufacture sheet resistor is used for voltage division and the load is zero, even under the worst condition, Current consumption is approximately 100μA.

〔Effect of the invention〕

As can be seen from the above explanation, the present invention maintains the advantages of the current control method, which has a small voltage fluctuation rate at the output terminal, and the advantage of the bandgap reference method, which can theoretically make the temperature dependence of the output voltage zero. However, the current consumption required by the control circuit can be reduced to a fraction of that of the conventional circuit. In addition, when integrating the circuit of the present invention, functional circuit elements such as transistors and resistors can be easily manufactured. In particular, since it is not necessary to use a resistor with a high resistance value in principle, it is possible to use a diffused resistor that has a sheet resistance with good reproducibility in manufacturing, and can reduce variations in resistance value and occupy a high resistance value in the chip. There is no need to take up a large area. A resistor pair whose resistance value ratio should be strictly controlled in manufacturing, for example, the first and second
resistor, vs. the resistor attached to the current mirror circuit,
Furthermore, when resistor division is used, the voltage division resistor pairs can all be placed close to each other on the chip, as can be easily seen from the circuit diagram, so they can be manufactured with high resistance ratio accuracy. This provides significant benefits in terms of production control. Furthermore, since the circuit performance is not affected even if these resistor pairs having different functions are placed apart from each other, there is the advantage that a large degree of freedom is allowed in the arrangement of circuit elements within the chip.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an example of a constant voltage circuit according to the prior art, Fig. 2 is a circuit diagram showing an example of a constant voltage circuit according to the present invention, and Fig. 3 explains the roles of the first and second resistors. FIG. 4 is a circuit diagram showing a preferred embodiment of the current control transistor in the circuit of the present invention. In the figure,
17, 18...dividing resistance of the voltage dividing circuit that creates the actual value of the output terminal voltage, B...power supply terminal, C...output terminal, E...earth terminal, R1...first resistor, R2...first 2 resistor, T1...first transistor, T2...second transistor, TC...
Current control transistors TC1 to TC2...transistors in each stage forming a composite current control transistor, Tp...pass transistors.

Claims (1)

[Claims] 1 a pass transistor whose collector is connected to a power supply terminal and whose emitter is connected to an output terminal; a constant current source connected to the base of the pass transistor;
a voltage divider circuit that is provided between the output terminal and the ground terminal and divides and outputs the output voltage therebetween; first and second transistors whose bases receive the output of the voltage divider circuit; first and second resistors are connected in series between the emitter of the transistor and the ground terminal, and the emitter of the first transistor is connected to the connection point thereof; is connected to the output terminal and the collector is connected to the first and second terminals.
a current mirror circuit having a pair of current mirror transistors each connected to the collector of the first transistor, a base connected to the collector of the first transistor, a collector connected to the ground terminal, and an emitter connected to the first transistor through a level shift element. A constant voltage circuit comprising current control transistors connected to bases of the pass transistors.