JPH09160661A - Dc stabilized power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely set temperature characteristics and to perform the low voltage operation of a circuit by connecting the emitter of a first transistor to a prescribed reference voltage and connecting the emitter of a second transistor between the transistor for driving and a driving current detection resistor in a driving current limiting circuit. SOLUTION: For the operation of the driving current limiting circuit ID, by comparing the voltage V2 of a base driving current detection resistor R1 with the voltage V3 between resistors R5 and R6, making a collector current flow to the transistor Q7 so as to equalize both voltages and controlling the base current of the transistor Q2, a driving limiting current Ido is decided. The temperature characteristics are turned to the function of ΔVBE=[VBE(Q 7)-VBE(Q8)] and the temperature characteristics of the driving limiting current Ido are changed by changing the ΔVBE. In order to change the ΔVBE, by changing the current ratio of the transistors Q7 and Q8, the temperature characteristics are adjusted by a fine value. As a result, the operation is stabilized even at the time of a high temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stabilized DC power supply, and more particularly to a stabilized DC power supply having an output transistor and a drive transistor for the output transistor, and having a current limiting circuit for limiting the base drive current of the drive transistor. Regarding the power source.

[0002]

2. Description of the Related Art In recent years, with the technical development of word processors, personal computers, etc., it has been required to lower the voltage of a DC stabilized power supply (hereinafter, simply referred to as a stabilized power supply), which serves as a power supply for these, and is 5 V or less. Especially, a stabilized power supply of 3.3V is required, and various circuit designs for this are made.

Here, a conventional stabilized power supply circuit will be described with reference to FIG.

As shown in FIG. 7, an output transistor Q
The collector of the base drive transistor Q2 is connected to the base of 1, and the emitter of the base drive transistor Q2 is grounded via the base drive current detection resistor R1. Further, the base of the base drive current limiting transistor Q3 is connected between the base drive transistor Q2 and the base drive current detection resistor R1, the emitter is connected to GND, and the collector is connected to the base of the base drive transistor Q2.

The emitter of the output transistor Q1 is connected to the input power supply terminal V _CC , and a constant current source I ₁ is inserted between this emitter and the base of the base drive transistor Q2.

[0006] The collector of the output transistor Q1 is connected to the output terminal V _O, Between the output terminals V _O and GND, resistors R2 and R3 of the voltage division is interposed in series, of the resistors connecting points Is input to the-terminal of the operational amplifier OP1 for comparison with the reference voltage Vref. The reference voltage Vref is input to the + terminal of the operational amplifier OP1.

The circuit operation of FIG. 7 will be briefly described. A change in the potential of V _{1 at} the connection point of the resistors R2 and R3 for voltage division is detected by the operational amplifier OP1 by comparison with the reference voltage Vref, and the output is predetermined. When it becomes larger than the value of, the base current of the base drive transistor Q2 is reduced, and when the output becomes smaller than a predetermined value, the base current is increased to stabilize the output voltage. ing.

The above operation is intended to stabilize the output voltage, but at the same time, the base current flowing through the base of the output transistor Q1 is also limited in the above circuit configuration. This is because if the base current flows too much, the current may flow too much to the output transistor Q1 and destroy the output transistor Q1.

Specifically, both ends of the base drive current detection resistor R1 have a base drive current limiting transistor Q.
Since it is connected between the base and the emitter of V3, V2 at the connection point of the resistor R1 and the base drive transistor Q2 does not exceed 0.7V. Therefore, R1 × I
A current (drive current limit) Ido flows only in a range where the relationship of do ≦ 0.7 V is satisfied, and R1 × Ido>
The current that reaches 0.7 V is limited so that it does not flow.

In the circuit of the above 76, the drive limit current Ido flowing through the base drive current detection resistor R1 is expressed by Ido = V _BE [Q3] / R1 (1) Here, when the temperature characteristic d {Ido} of the drive limit current Ido is obtained, d {Ido} = d {V _BE [Q3] / R1} (2)

That is, the temperature characteristic of the drive limiting current Ido is determined by the temperature characteristic of the base-emitter forward voltage V _BE [Q3] of the transistor Q3 and the temperature characteristic of the resistor R1.

FIG. 8 is a circuit diagram of a stabilized power supply circuit according to another conventional example. The difference from the circuit of FIG. 7 is that the reference voltage Vre
The point is that a transistor Q4 and a resistor R4 are added to form a differential circuit for comparing f with the terminal voltage V2 of the drive current detection resistor R1. Here, the transistor Q4
The base collector of is shorted.

In the case of the circuit of FIG. 7, the drive limit current Id
o is represented by Ido = Vref / R1 (3), and the temperature characteristic d (Id of the drive limit current Ido is represented by
o) is d (Ido) = Vref × d {1 / R1} (4)

Since the temperature characteristic of the reference voltage Vref is flat, the temperature characteristic of the drive limiting current Ido is determined by the temperature characteristic of the resistor R1.

In the circuit configuration of FIG. 7, the drive limit current Ido has a large negative temperature characteristic (-400).
The drive limit current Ido becomes small at a high temperature (about 0 ppm / ° C.), so it is necessary to set a large set value at room temperature.

On the other hand, also in the circuit configuration of FIG. 8, the drive limit current Ido has a relatively large negative temperature characteristic (-
2000 ppm / ° C.), which has the same problem as in FIG. 7.

By the way, the temperature characteristic of the circuit of FIG.
00 ppm / ° C) is calculated as follows.

At Tj = 25 ° C., V _BE = 0.7 V, V _BE and temperature characteristics of the resistor R1 are ΔV _BE = -2 mV / ° C., ΔR1 =
When it is set to +2000 ppm / ° C., (0.7 V + (− 2 mV / ° C.) × ΔT) / (R1 × (1
+2000 ppm / ° C. × ΔT)) = − 4000 ppm /
℃ Also, the temperature characteristics of the circuit in Fig. 8 (-2000ppm / ℃)
Is calculated as follows. That is, from the equation (4), Vref / (R1 × (1 + 2000 ppm / ° C. × Δ
T)) = − 2000 ppm ° C. Here, in order to change the temperature characteristic of the drive limiting current Ido, one having a different temperature characteristic is used as the resistor R1 for detecting the drive limiting current Ido, or a transistor is added as follows. There is a way to do. This content will be described with reference to FIGS. 9 and 10.

To increase the temperature characteristic, for example, as shown in FIG. 9, a PNP transistor Q5 and a constant current circuit I10 are added to the circuit configuration of FIG. As a result, the drive limit current Ido becomes Ido = (Vref + V _BE [Q5]) / R1 (5), so the temperature characteristic d (I of the drive limit current Ido
do) becomes d {Ido} = Vref × d {1 / R} + d {V _BE [Q5] / R1} (6).

The temperature characteristic of the drive limiting current Ido in the circuit configuration of FIG. 9 is about 700 ppm / ° C.

To reduce the temperature characteristic, as shown in FIG. 10, the NPN transistor Q6 is added to the circuit configuration of FIG.
Add. As a result, the drive limit current Ido becomes Ido = (Vref-V _BE [Q4]) / R1 (7), and the temperature characteristic d {Id of the drive limit current Ido is obtained.
o} is d {Ido} = Vref × d {1 / R} -d {V _BE [Q4] / R1} (8).

However, here, Vref> V _BE [Q4] +
It is V _BE [Q6] + V3.

As described above, in the conventional example shown in FIGS. 9 and 10, a transistor is added to adjust the temperature characteristic of the drive limit current Ido.

[0024]

However, even if an attempt is made to optimize the temperature characteristics of the drive limit current Ido by adopting resistors having different temperature characteristics and adding transistors as described above, the following problems still occur. there were.

That is, even if the temperature characteristic of the drive current detecting resistor R1 is changed, there are only a few types of drive current detecting resistor R1 having different temperature characteristics when the base drive circuit is integrated into an IC.

Further, since the temperature characteristic of the base-emitter voltage V _BE of the transistor is about −2 mV / ° C., it can be changed only by about −2 mV / ° C. by adding the transistor.

Due to the above reasons, the temperature characteristics of the drive limiting current Ido can be adjusted only by the discrete values regardless of which means is used or both are combined. That is, the drive limit current I
The temperature characteristic of do cannot be set to an arbitrary value according to the circuit configuration. If the temperature characteristic becomes a large negative characteristic, there is a problem that the output current decreases at a high temperature as described above. Conversely, if the temperature characteristic is a large positive characteristic, the output current may flow too much at a high temperature and thermal runaway may occur. There is a problem that there is.

Further, in the above-mentioned conventional circuit, the voltage drop across the resistor R1 for detecting the drive current is 0.
7V, 1.25V same as Vref in the configuration of FIG.
Vref + 0.7V = 2V in the configuration of FIG. 10, and Vref−0.7V = 1V in the configuration of FIG. 10 (where Vref ≧ 1.7.
Since it is necessary to be V and Vref = 1.25V is impossible), it has been an obstacle to lower voltage operation of the base drive current limiting circuit.

Therefore, an object of the present invention is to set the temperature characteristic of the base drive limit current Ido with a fine value, to stabilize the operation at high temperature, and to lower the voltage of the base drive current as compared with the conventional one. To realize the limiting circuit.

[0030]

In order to achieve the above object, the invention according to claim 1 includes an output transistor inserted between input and output terminals, and a drive transistor for driving the output transistor. A drive current detection resistor connected via the drive current detection resistor; and a drive current limiting circuit that controls the drive transistor according to the magnitude of the drive current flowing through the drive current detection resistor. The limiting circuit includes first and second bases that are commonly connected.
And the emitter of the first transistor is connected to a predetermined reference voltage, and the emitter of the second transistor is connected between the drive transistor and the drive current detection resistor. Characterize.

According to a second aspect of the present invention, an output transistor in which an emitter and a collector are inserted between the input and output terminals, and a drive current connected to the base of the output transistor via the drive transistor. In the stabilized DC power supply having a detection resistor and a drive current limiting circuit that controls the base current of the driving transistor according to the magnitude of the drive current flowing through the drive current detecting resistor, the drive current limiting circuit is The first and second transistors are connected in common, the emitter of the first transistor is connected to a predetermined reference voltage, and the emitter of the second transistor is between the drive transistor and the drive current detection resistor. Connected, the collector of the first transistor is connected to the driving transistor, and the collector of the first transistor is connected to the drive transistor. A first constant current source is connected between a connection point between the transistors for use and an input terminal, and a collector of the second transistor is connected to the input terminal via a second constant current source. To do.

According to a third aspect of the present invention, in the DC stabilized power supply according to any one of the first and second aspects, the reference voltage is obtained by dividing the voltage of the reference voltage source by a voltage dividing resistor. Is characterized by.

According to a fourth aspect of the present invention, in the DC stabilized power source according to the third aspect, a reference voltage adjusting transistor is inserted between the reference voltage source and the voltage dividing resistor. To do.

According to the structure of claim 1, the circuit operation is performed such that the voltage across the drive current detection resistor matches the reference voltage. As a result, the driving current flowing through the driving transistor is controlled so as not to flow too much. Here, the temperature characteristic of the drive current flowing through the drive current limiting resistor can be finely set by controlling the base-emitter temperature characteristic of the second transistor. Further, since the emitter of the second transistor is connected to the drive current detection resistor, the voltage drop can be suppressed to a low level as compared with the conventional configuration in which the base of the transistor is connected. The circuit can be operated at a low voltage.

According to the second aspect of the invention, the first and second constant current sources are provided. By changing the current value of the second constant current source, the temperature characteristic of the drive current detection resistor can be set arbitrarily and precisely. This is because the temperature characteristic of the drive current detection resistor changes by changing the base-emitter temperature characteristic of the second transistor,
Furthermore, the base-emitter temperature characteristic of the second transistor is proportional to the collector current of the second transistor, that is, the current value of the second constant current source in this circuit configuration.

According to the configuration of claim 3, the voltage of the reference voltage source can be easily set to an arbitrary reference voltage.

As described in claim 4, by inserting the transistor for adjusting the reference voltage, the relationship between the current value of the second constant current source and the temperature characteristic of the drive current obtained by the configuration of claim 1 or 2. Can be arbitrarily shifted in the vertical direction (that is, in the direction of high and low temperature characteristics). As a result, it is possible to cover the change range of the temperature characteristic very greatly.

[0038]

1 is a block diagram of an embodiment of the present invention.
This will be described with reference to FIG. FIG. 1 is a circuit diagram of a stabilized DC power supply circuit according to this embodiment. The same functional parts as those of the conventional example shown in FIGS. 7 to 10 are designated by the same symbols.

As shown in FIG. 1, the output transistor Q
The collector of the base drive transistor Q2 is connected to the base of 1. The emitter of this base drive transistor Q2 is a base drive current detection resistor R.
The base is connected to an input power supply terminal V _CC (hereinafter, referred to as power supply V _CC ) via a constant power supply I ₁ . The emitter of the output transistor Q1 is connected to the power supply V _CC ,
The collector is connected to GND via resistors R2 and R3 for voltage division connected in series. Resistors R2 and R3 for voltage division
The connection point of is + of the operational amplifier OP1 for comparison with the reference voltage.
The reference voltage Vref is input to the negative terminal of the operational amplifier OP1. The output of the operational amplifier OP1 is connected to the base of the base drive transistor Q2.

The collector of the transistor Q7, which is the first transistor, is the base drive transistor Q.
The base 2 and the emitter are connected to the connection point of the voltage dividing resistors R5 and R6 connected in series.

The emitter of a transistor Q8, which is a second transistor whose base is commonly connected to the transistor Q7, is connected to the connection point between the base drive transistor Q2 and the base drive current detection resistor R1.
The collector is connected to the power supply V _CC via the constant current source I ₂ . The other end of the resistor R5 is connected to the-terminal of the operational amplifier OP1.
The other end of the resistor R6 is grounded. In the figure, I _D is a drive current limiting circuit which is a feature of this embodiment.

In the circuit shown in FIG. 1, the error amplifier OP
The reference voltage Vref (here, 1.25
V) is input, and the resistance R2 of the output voltage dividing resistor,
The error amplifier OP1 operates so that the voltage V1 at the connection point between R3 and the reference voltage is 1.25V.

For example, when the output voltage V _O drops, the voltage V1 between the resistors R2 and R3 for dividing the output voltage also drops, is amplified by the operational amplifier OP1 serving as an error amplifier, drives the transistor Q2, and drives the output transistor Q1. Subtract the base current, let the output flow, and set the voltage V1 to 1.2.
I try to keep it at 5V.

When the output voltage rises, the voltage V1 between the resistors R2 and R3 for dividing the output voltage also rises, so that the base current of the transistor Q2 amplified by the error amplifier is reduced and the voltage to the output transistor Q1 is reduced. The base current is reduced to reduce the output current, and the voltage V1 between the resistors R2 and R3 for dividing the output voltage is kept at 1.25V.

The operation of the drive current limiting circuit ID is performed by the voltage V2 of the base drive current detection resistor R1 and the resistors R5 and R5.
The voltage V3 across 6 is compared, the collector current flows through the transistor Q7 so that both voltages become equal, and the drive limit current Ido is determined by controlling the base current of the transistor Q2.

A more specific description will be given below. First, assuming that the base drive current is limited when the drive limit current becomes Ido, first, when there is no load, Id
<Ido, and at this time, the collector current of the output transistor Q1 only flows through the resistors R2 and R3. Assuming that the current at this time is i1, the base current Id of the output transistor Q1 is Id = i1 / hFE because the current of 1 / hFE of the output transistor Q1 flows. Therefore, the current flowing from the operational amplifier OP1 is 1 / hFE of Id.

Since the potential V2 of the drive current detection resistor R1 is set lower than the potential V3, the transistor Q7 does not operate.

Then, when the load current is gradually subtracted, the voltages of the resistors R2 and R3 in the output stage drop, and the potential V1 of the resistor R3 amplified by the operational amplifier OP1 operates so as to become the same potential as Vref. The potential V2 of the base drive current detection resistor R1 is Id × R1 of the output current 1 / hFE. At this time, the transistor Q7 does not operate because the emitter potential of the transistor Q7 is still higher than the emitter potential of the transistor Q8. When further flowing the output current,
By the same operation, Id becomes large and the resistances R1 and R6
Potentials become equal, transistor Q7 starts to operate,
The collector current of the transistor Q7 draws the same current as the collector current of the transistor Q8.

When the output current further increases, the transistor Q
Since the emitter potential of 8 becomes higher than the emitter potential of the transistor Q7, the transistor Q8 does not operate and all the current i2 of the constant current circuit flows through the transistor Q7. As a result, the collector current of the transistor Q7 is I
1 × hFE, I1 × from the current of the operational amplifier OP1
IFE is hFE times the remaining current after subtracting hFE.
That is, Ido is limited by this value.

At this time, the drive limiting current Ido is Ido = (Vref × (R6 / (R5 + R6)) + ΔV _BE ) / R1 (9) The temperature characteristic d (Ido) of the drive limiting current Ido is d {Ido}. = Vref × R6 / (R5 + R6) × d {1 / R1} -d {(ΔV _BE ) / R1} (10) ΔV _BE = V _BE [Q7] -V _BE [Q8] (11) The temperature characteristic of the drive limit current Ido can be changed by changing ΔV _BE .

The temperature characteristic of V _BE of the transistor is as in Figure 2, the temperature characteristics of the collector current and V _BE is proportional, by varying the current ratio of the transistors Q7, Q8 to change the [Delta] V _BE, temperature The characteristics can be adjusted with fine values.

Specifically, as shown in FIG. 3, by changing the value of the current i2 of the constant current source I2, it is possible to set an arbitrary temperature characteristic on the line A. Here, i1 = 100 μA.

Lines B and C in FIG. 3 are characteristics corresponding to the other circuits of this embodiment, and FIGS. 4 and 5, respectively. 4 shows a configuration in which a transistor Q9 is added to the circuit of FIG. 1, and FIG. 5 shows a configuration in which a transistor Q10 and a constant current source I3 are added to the circuit of FIG.

The characteristics of the lines A, B and C shown in FIG.
It can be shifted further up and down by changing the emitter area ratio of the transistors Q7 and Q8.
Specifically, taking the case of FIG. 1, for example, if the emitter area of the transistor Q8 is made larger than the emitter area of the transistor Q7, the line of FIG. 3 shifts upward. Conversely, if the emitter area of the transistor Q7 is increased, the line shifts downward.

Actually changing the emitter ratio can be realized by using two transistors (parallel connection).

As described above, according to the stabilized power supply circuit having the current limiting circuit as shown in FIG. 1, the temperature is improved by adding the transistor and changing the emitter ratio of the transistor as in the embodiments of FIGS. The characteristics can be set arbitrarily.

By the way, how much the temperature characteristic of the drive limiting current Ido is set to be an appropriate value for the entire circuit depends on the circuit configuration, and the temperature of the drive limiting current Ido is simply changed. It is not enough to set the characteristic to zero. For example, in the circuit of FIG. 1, there is a temperature characteristic of the hFE of the output transistor Q1, and it is necessary to design the circuit in consideration of these characteristics. Moreover, as shown in FIG. 6, the temperature characteristic of the hFE of the transistor changes greatly even if the type of transistor is changed, and various temperature characteristics are required for each circuit design.

Although these temperature characteristics have been taken into consideration in the prior art, as described in (Problems to be solved by the invention), it was not possible to provide fine temperature characteristics, so that the output at high temperature There was no choice but to design a circuit that lacks reliability, leaving the possibility that the voltage will drop.

Further, in the conventional circuits shown in FIGS. 7 to 10, since the base drive current detection resistor R1 is connected to the base of the base drive current limiting transistor Q3, the base drive transistor Q2 and the base drive current detection are detected. The potential V2 at the connection point with the resistor R1 needs to be at least a voltage for turning on the base drive current limiting transistor Q3, that is, 1 V _BE or more, but in the present embodiment, the base drive current detection resistor R1 is the base drive current. Since it is connected to the emitter of the limiting transistor Q3, it operates even when set to 0.1V.

Specifically, as described above, 1 VBE (about 0.7 V) is used in the conventional circuit of FIG.
ref (mainly 1.25V), Vref + VBE in FIG.
(About 1.95V when Vref = 1.25V), FIG.
In contrast, Vref-VBE (Vref> 1.7V is required) in the present embodiment, whereas in the present embodiment, Ido × R1 and therefore R
By reducing the value of 1, the voltage can be lowered. For example, when I1 = 100 mA and R1 is 3.3Ω, it is 0.33 V, which is lower than the conventional value. That is, the voltage drop in the base drive current detection resistor R1 can be reduced, and low voltage operation can be realized.

In recent years, the stabilized power supply has been lowered in voltage, especially 3.3.
The voltage of V is required, and the present invention is extremely effective in this respect as well.

[0062]

As described in detail above, according to the present invention, the temperature characteristic of the drive current of the output transistor in the stabilized power supply circuit can be set arbitrarily and finely, and as a result, the temperature characteristic is high. Even if the operation is stable, a highly reliable stabilized power supply circuit can be realized.

Further, since the resistance value of the drive current detection resistor of the output transistor can be made small, the voltage drop in this resistor can be reduced and low voltage operation can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a stabilized power supply circuit according to an embodiment of the present invention.

FIG. 2 is a relationship diagram between a collector current and a temperature characteristic of a transistor.

FIG. 3 is a temperature characteristic diagram showing the effect of the present invention.

FIG. 4 is a circuit diagram of a stabilized power supply circuit according to another embodiment of the present invention.

FIG. 5 is a circuit diagram of a stabilized power supply circuit according to still another embodiment of the present invention.

FIG. 6 is a temperature-hFE characteristic diagram of a transistor.

FIG. 7 is a circuit diagram of a stabilized power supply circuit according to a conventional example.

FIG. 8 is a circuit diagram of a stabilized power supply circuit according to another conventional example.

FIG. 9 is a circuit diagram of a stabilized power supply circuit according to still another conventional example.

FIG. 10 is a circuit diagram of a stabilized power supply circuit according to still another conventional example.

[Explanation of symbols]

V _CC input terminal _VO output terminal Q1 output transistor Q2 driving transistor Q7 first transistor Q8 second transistor R1 driving current detection resistor _ID driving current limiting circuit

Claims (4)

[Claims] 1. An output transistor inserted between input / output terminals, a drive current detection resistor connected via a drive transistor for driving the output transistor, and a drive current flowing through the drive current detection resistor. And a drive current limiting circuit for controlling the drive transistor according to the size of the drive current limiting circuit, wherein the drive current limiting circuit has a first base connected in common.
And a second transistor, the emitter of the first transistor is connected to a predetermined reference voltage, and the emitter of the second transistor is connected between the driving transistor and the drive current detection resistor. DC stabilized power supply characterized in that 2. An output transistor having an emitter and a collector interposed between input and output terminals, a drive current detection resistor connected to the base of the output transistor via a drive transistor, and the drive current detection resistor. In a stabilized direct current power supply having a drive current limiting circuit for controlling a base current of the driving transistor according to the magnitude of a drive current flowing through the drive current limiting circuit, the drive current limiting circuit has a first base commonly connected.
And a second transistor, the emitter of the first transistor is connected to a predetermined reference voltage, the emitter of the second transistor is connected between the drive transistor and the drive current detection resistor, and A collector of the transistor is connected to the driving transistor, a first constant current source is connected between a connection point between the first transistor and the driving transistor and an input terminal, and a collector of the second transistor is A stabilized direct current power supply, characterized in that it is connected to the input terminal via a second constant current source. 3. The stabilized DC power supply according to claim 1, wherein the reference voltage is a voltage of a reference voltage source divided by a voltage dividing resistor. Power supply. 4. The stabilized DC power supply according to claim 3, wherein a transistor for adjusting the reference voltage is inserted between the reference voltage source and the voltage dividing resistor. .