JPH04328613A - Power unit circuit - Google Patents

Abstract

PURPOSE:To prevent the deterioration in the ripple rejection caused with the reduction of the electric power. CONSTITUTION:A power circuit is provided with a stabilizing circuit 2 which receives the reference voltage Vref and takes out the stabilized output (output voltage) Vout and an output saturation preventing circuit 4 which prevents the saturation of the output circuit of the circuit 2. A capacitor 6 is connected to the voltage dividing resistors 44, 45 and 46 added to the feedback circuit 47 of a 2nd amplifier 47 of the circuit 4. So that the fluctuation of the voltage Vref is smoothed. Thus the ripple ejection is prevented to the reduction of the electric power and the stabilized output is secured.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a power supply circuit for amplifying and extracting a reference voltage using an amplifying means,
This invention relates to a power supply circuit suitable for C and the like.

0002

2. Description of the Related Art Generally, power supplies with extremely small voltage fluctuations are used in various control circuits that perform control that requires high precision, such as the tracking servo and focus servo of the pickup of a CD player. For power supplies, a power supply circuit that stabilizes the voltage output is essential. By the way, when a battery or the like is used as the input power source for this power supply circuit, when the voltage decreases due to its consumption, the output transistor of the regulator circuit becomes saturated, and the saturated current flows to the IC board on which the regulator circuit is formed, causing damage to the board. Causes fever. In particular, the saturation current is a reactive current, which not only increases power consumption, but also causes the substrate potential to fluctuate due to the rush current, which is a factor that inhibits the normal operation of other circuits on the attached substrate.

In order to prevent such saturation of the output circuit of a power supply circuit, for example, Japanese Patent Application No. 63-288225 ``Regulator Circuit'' has been proposed. In this regulator circuit, as shown in FIG. 5, an output saturation prevention circuit 4 is installed before the stabilization circuit 2. In the stabilizing circuit 2, a differential amplifier 21 serving as a voltage comparator is installed as a first amplifier receiving a reference voltage Vref on the positive phase input side.
A first output circuit 22 for taking out the ut is installed. This output circuit 22 is provided with an output transistor 23 . A PNP transistor is used as the output transistor 23, and a load resistor is connected between the collector side and the ground point to convert the current flowing through the output transistor 23 into a voltage, and the output is connected to the negative phase input of the differential amplifier 21. Resistors 25 and 26 forming a voltage dividing circuit for forming a feedback voltage to be fed back through a feedback circuit 24 are connected in series on the side.

According to the stabilizing circuit 2, the current flowing through the output transistor 23 causes a voltage drop across the resistors 25 and 26, and the voltage Vn generated at the intermediate connection point between the resistors 25 and 26 is applied to the differential amplifier 21. It is fed back to the negative phase input (-) side of. Therefore, in the stabilizing circuit 2, the positive phase input (
The reference voltage Vref applied to +) and the voltage Vn of the resistors 23 and 24 are compared and amplified by the differential amplifier 21, and the base current of the output transistor 23 is adjusted according to the output of the differential amplifier 21, that is, its linear output. is drawn into the differential amplifier 21 side, and the collector current of the output transistor 23 is controlled so that the reference voltage Vref and the voltage Vn become equal. As a result, an output voltage Vout corresponding to the reference voltage Vref applied to the positive phase input side of the differential amplifier 21 is taken out at the output terminal 27.

However, in a power supply circuit consisting only of such a stabilizing circuit 2, when the power supply voltage Vcc decreases,
That is, when the power decreases, the emitter voltage of the output transistor 23 decreases, and when the value approaches the output voltage Vout, the output transistor 23 enters a saturated state. The output transistor 23 is formed as a part of an IC constituting a regulator circuit, for example, as shown in FIG. That is, a buried layer 29 made of an N-type high concentration region is formed on the substrate 28, and this buried layer 29
An N-type base region 30 is formed over the. This base region 30 is separated from other regions by an isolation region 31, and a base electrode 32 is formed on its surface layer by a highly doped N-type region, and an emitter made of a highly doped P-type conductive region. A region 33 is formed, and a collector region 34 made of a highly doped P-type conductive region is formed surrounding the emitter region 33. Therefore, during normal operation, the output transistor 23 performs an amplification operation using the base region 30, emitter region 33, and collector region 34.

However, when the potential on the emitter region 33 side decreases due to a decrease in the power supply voltage Vcc, and the potential difference between that potential and the potential on the collector region 34 side becomes smaller, the emitter region 33 becomes an emitter, the base region 30 becomes a base, A parasitic transistor 35 is generated whose collector is the isolation region 31, that is, the substrate 28, and this parasitic transistor 35
Through this, a rush current flows from the emitter region 33 to the substrate 28 side. The magnitude of this rush current depends on the scale of the parasitic transistor 35, that is, the scale of the output transistor 23. In this case, output transistor 2
Since transistor No. 3 is expected to have a large output current, its emitter area is large, and the rush current flowing through the parasitic transistor 35 having this emitter area is proportionally extremely large.

In this way, when the output transistor 23 is in a saturated state, in addition to the saturation current, a rush current due to the parasitic transistor 35 flows to the substrate 28 side, causing overheating of the substrate 28 and making the substrate potential unstable. In order to prevent this, an output saturation prevention circuit 4 is installed before the differential amplifier 21. In this output saturation prevention circuit 4, a differential amplifier 41 is installed as a second amplifier corresponding to the differential amplifier 21, and a second output circuit 42 is installed on the output side of this differential amplifier 41. . This output circuit 42 is provided with a transistor 43 having an emitter area approximately 1/n of that of the output transistor 23, and resistors 44, 45, 4 are connected between the collector of this transistor 43 and the ground point.
6 series circuits are connected. A reference voltage Vref is applied to the positive phase input (+) side of the differential amplifier 41 from a reference voltage source such as a bandgap circuit, and a reference voltage Vref is applied to the negative phase input (-) side of the differential amplifier 41 at the intermediate connection point P between the resistors 45 and 46. The generated voltage Vp is fed back via a feedback circuit 47. Since this voltage Vp becomes equal to the reference voltage Vref on the positive-phase input (+) side by the control operation by the differential amplifier 41, the positive-phase input (+) of the differential amplifier 21 of the stabilizing circuit 2 has the reference voltage Vref. will be added. Therefore, in this power supply circuit, the output saturation prevention circuit 4, which constitutes a positive feedback amplifier equivalent to the stabilization circuit 2, is installed before the stabilization circuit 2, so that the output transistor 23 can be prevented from entering the saturation state. By forcing the transistor 43 of the output saturation prevention circuit 4 to enter the saturated state, it is possible to prevent the output transistor 23 from entering the saturated state.

To explain this saturation prevention, the transistor 43 corresponds to the output transistor 23, and the resistance values of the resistors 45, 46, 25, 26 are set as Ra, Rb,
If Rc and Rd, each resistance value Ra=k・Rc, Rb=
If it is set to k・Rd (k is an arbitrary number) and consistency is maintained on the IC, the output voltage Vout is

[0009]

[Math 1]

[0010] However, when the power is reduced, current flows through the transistor 43 to the resistors 44, 45, and 46, and the voltage Vp at the connection point P between the resistors 45 and 46 decreases by the voltage drop across the resistor 44, and this voltage Vp is applied to the differential amplifier 41. is added to the negative phase input (-) of Therefore, if the resistance value of the resistor 44 is Rα, the voltage Vα generated across the resistor 44 is

[
0011

[Math 2]

[0012] Therefore, during power reduction, the voltage Vα generated across the resistor 44 selectively saturates only the transistor 43 and prevents the output transistor 23 from becoming saturated. This is equivalent to increasing the voltage, and as a result,
The transition of the output transistor 23 to the saturated state is alleviated.

[0013]

By the way, the idea of preventing output saturation in the output saturation prevention circuit 4 in this power supply circuit is to install a transistor 43, which has a smaller capacitance than the output transistor 23 and is less affected by parasitic transistors, in the preceding stage. However, the purpose is to prevent saturation of the output transistor 23 by quickly saturating the transistor 43 under adverse conditions that would cause the output transistor 23 to become saturated.Moreover, the transistor 43 has a small capacity, and even if it becomes saturated, the saturation current is small. Therefore, the influence of saturation can be suppressed compared to saturation of the output transistor 23.

However, in this power supply circuit, P
Fluctuations in the point voltage Vp become a problem. That is, transistor 4
If the saturation voltage of 3 is Vsat and the power supply voltage is Vcc, then
The P point voltage Vp is

[0015]

[Math 3]

[0016] Therefore, if a ripple is added to the power supply voltage Vcc, the voltage at the P point will also fluctuate due to the ripple. FIG. 7 shows the power supply voltage V in this power supply circuit.
The characteristics of the cc-output voltage Vout are shown, and Vr represents the reference line when the input/output voltage difference=0. Each differential amplifier 21
, 41 are equal, the power supply voltage Vcc
This fluctuation will directly appear in the output voltage Vout, and when the power supply voltage Vcc is reduced, ripple rejection will suddenly deteriorate. Output voltage Vo with such fluctuations
When ut is used as a power source for an audio system, the output voltage Vo
The shaking of the UT causes noise.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a power supply circuit that prevents deterioration of ripple rejection during power reduction.

[0018]

[Means for Solving the Problems] The power supply circuit of the present invention includes:
The reference voltage (Vref) is applied to the first amplifier (differential amplifier 21
) and takes out the output through a first output circuit (22) and returns it to the input side of the amplifier to take out a stabilized output (output voltage Vout) according to the reference voltage. , a second amplifier (41) installed before the first amplifier and receiving the reference voltage;
) and a second output circuit (42) on its output side, the reference voltage is applied to the first amplifier through the second amplifier and the second output circuit, and when the power is reduced,
output saturation prevention, which inputs the reduced reference voltage by saturating the second output circuit before the saturation of the first output circuit to the first amplifier to prevent saturation of the first output circuit; A power supply circuit comprising a circuit (4), wherein the reference voltage is applied to a voltage dividing resistor (resistors 44, 45, 46) added to a feedback circuit (47) of the second amplifier of the output saturation prevention circuit. The feature is that a capacitor (6) is connected to smooth the fluctuations.

[0019]

[Operation] The reference voltage is input to the first amplifier of the stabilizing circuit via the output saturation prevention circuit. In the stabilization circuit, the first
When a reference voltage is applied to the first amplifier, an output corresponding to the reference voltage is applied to the first output circuit, and the output is fed back to the first amplifier, so that the first output circuit A stabilized output is obtained through the When the power is reduced, in the output saturation prevention circuit, the second output circuit to which the reference voltage should be applied to the first amplifier enters the saturated state before the first output circuit, and the reference voltage to be applied to the first amplifier The voltage is reduced in accordance with the power reduction. A reduced level reference voltage is applied to the first amplifier to prevent saturation of the first output circuit in the stabilization circuit.

When the power is reduced, a capacitor is added to the feedback circuit of the output saturation prevention circuit, and this capacitor smoothes fluctuations due to ripples on the power supply side. As a result, fluctuations in the output voltage taken out through the first output circuit are suppressed. Therefore, a stabilized output without ripples can be obtained even when the power is reduced.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a power supply circuit according to the present invention, and the same parts as those of the power supply circuit shown in FIG. 5, which is the premise of the present invention, are given the same reference numerals. This power supply circuit is equipped with a stabilizing circuit 2 that outputs a stabilized output according to the reference voltage Vref, and at the previous stage, the reference voltage Vref is input to the stabilizing circuit 2, and the output of the stabilizing circuit 2 is An output saturation prevention circuit 4 is installed to prevent saturation.

In the stabilizing circuit 2, a differential amplifier 21 serving as a voltage comparator is installed as a first amplifier receiving a reference voltage Vref on the positive phase input side. A first output circuit 22 that takes out the output voltage Vout is installed, and this output circuit 22 has, for example, P
An output transistor 23 made of an NP type transistor is installed. Between the collector side of the output transistor 23 and the ground point, there is a load resistor that converts the current flowing through the output transistor 23 into a voltage, and a feedback circuit 24 that sends the output back to the negative phase input side of the differential amplifier 21. Resistors 25 and 26 forming a voltage dividing circuit for forming a voltage
are connected in series. Therefore, according to this stabilizing circuit 2, the current flowing through the output transistor 23 causes a voltage drop across the resistors 25 and 26, and the voltage Vn generated at the intermediate connection point is applied to the negative phase input (-) of the differential amplifier 21. returned to the side. As a result, the reference voltage Vref applied to the positive phase input (+) and the voltage Vn of the resistors 25 and 26 are compared and amplified by the differential amplifier 21, and the output of the differential amplifier 21, that is, the linear output is output transistor 23
The base current of the output transistor 23 is drawn into the differential amplifier 21 side, the collector current of the output transistor 23 is controlled so that the reference voltage Vref and the voltage Vn are equal, and the output terminal 27 is connected to the positive phase input side of the differential amplifier 21. Applied reference voltage V
An output voltage Vout corresponding to ref is obtained.

Further, in the preceding stage of the stabilizing circuit 2, in order to prevent the output transistor 23 from entering the saturated state,
An output saturation prevention circuit 4 is installed. A differential amplifier 41 is installed in this output saturation prevention circuit 4 as a second amplifier corresponding to the differential amplifier 21.
A second output circuit 42 is installed on the output side of. This output circuit 42 is provided with a transistor 43 having an emitter area approximately 1/n of that of the output transistor 23.
A series circuit of resistors 44, 45, and 46 is connected between the collector of this transistor 43 and the ground point. A reference voltage Vref is applied from a reference voltage source such as a band gap circuit to the positive phase input (+) side of the differential amplifier 41, and a voltage Vp generated at the intermediate connection point P is applied to the negative phase input (-) side. It is fed back via a feedback circuit 47. Since this voltage Vp becomes equal to the reference voltage Vref on the positive-phase input (+) side by the control operation by the differential amplifier 41, the positive-phase input (+) of the differential amplifier 21 of the stabilizing circuit 2 has the reference voltage Vref will be added. Therefore, in this power supply circuit, by installing the output saturation prevention circuit 4 which forms a positive feedback amplifier equivalent to the stabilization circuit 2 before the stabilization circuit 2, the output saturation prevention circuit 4 is installed before the stabilization circuit 2. By forcing the transistor 43 of the saturation prevention circuit 4 to enter the saturated state, it is possible to prevent the output transistor 23 from entering the saturated state.

The voltage dividing resistor installed in the feedback circuit 47 in the output saturation prevention circuit 4, that is, the differential amplifier 41
A capacitor 6 is connected to the resistor 46 of the series circuit of resistors 44, 45, and 46 for setting the amplification gain of the ripple smoothing means.
are connected in parallel.

The operation of the above configuration will be explained. In this power supply circuit, since the smoothing capacitor 6 is connected in parallel to the resistor circuit that generates the feedback voltage of the feedback circuit 47, the fluctuation of the feedback voltage Vp due to the ripple superimposed on the power supply voltage Vcc during power reduction is suppressed by the capacitor. The reference voltage Vref to be smoothed by 6 and applied to the stabilizing circuit 2
The deterioration of ripple rejection is prevented.

Here, it is assumed that the input impedance of the differential amplifier 21 is sufficiently high during power reduction, and the resistors 44 and 4
The additional resistance value of resistor 5 is R1, and the resistance value of resistor 46 is R2 (
=Rb), and the capacitance of the capacitor 6 is C, the voltage Vp at point P is,

[0027]

[Math 4]

[0028] As a result, the output voltage Vout is

[0029]

[Math 5]

Then, the ripple rejection of the output voltage Vout is:

[0031]

[Math 6]

It can be seen that the ripple rejection in the output during power reduction is improved.

FIG. 2 shows the characteristics of the output voltage Vout with respect to the power supply voltage Vcc in this power supply circuit,
The resistance value Rα of the resistor 44 is set to set the gain of the differential amplifier 41 in order to obtain an output voltage Vout that is not affected by the ripple, that is, fluctuation, of the power supply voltage Vcc.
is determined, and the value of the voltage Vα is determined based on the value. In other words, the value of the voltage Vα can be arbitrarily set by the resistance value Rα. That is, the ripple voltage is the voltage V
If it is larger than α, the power supply voltage Vcc fluctuates even though the input to the differential amplifier 21 is smoothed, so the transistor 23 becomes saturated, the rush current increases, and ripple rejection deteriorates. Therefore, the resistance R
By adjusting the value of α, it is possible to set the optimum voltage Vα for erasing the ripple according to the amplitude of the ripple to be eliminated.

Next, FIG. 3 shows a specific example of the circuit configuration of the power supply circuit of the present invention, and the same parts as those of the circuit of the previous embodiment are given the same reference numerals. This power supply circuit is configured as an audio power supply inside the multi-power supply IC. That is, the differential amplifier 21 installed in the stabilization circuit 2
A differential pair consisting of transistors 203 and 204 whose emitters are shared by resistors 201 and 202 is installed, and transistors 205 and 206 are installed on the base input side of each transistor 203 and 204. A voltage Vp corresponding to the reference voltage Vref is applied to the base of the transistor 205, and a voltage Vn is applied to the base of the transistor 206 from the output circuit 22 via the feedback circuit 24. On the collector side of the transistors 203 and 204, a transistor 207 is connected as an active load.
A current mirror circuit 209 consisting of 208 is installed.

This differential amplifier 21 includes a transistor 2
A constant current source 210 that generates a constant current to drive the transistors 203, 204, 205, 206, etc. is installed. 206. The current mirror circuit 211 includes transistors 212, 213, 214, 215 and a resistor 216.
, 217, 218, and as a result of a constant current being drawn from the transistor 212 to the constant current source 210, a corresponding constant current flows to each transistor 213, 214, 215,
A differential pair of transistors 203 and 204 through 216;
That is, it is supplied to the emitter sides of transistors 205 and 206.

The output of this differential amplifier 21 is taken out from the collector side of the transistor 208 and applied to the output circuit 22. In this output circuit 22, Darlington-connected transistors 221 and 222 are installed at the input part, and the output of the differential amplifier 21 is connected to the transistor 22.
It is added to the base of 1. A phase adjustment capacitor 223 is connected between the base and collector of the transistor 221, and a resistor 224 is connected between the emitter of the transistor 221, the base of the transistor 222, and a ground point.

Resistors 225 and 226 are connected in series between the collector of the transistor 222 and the power supply line 36, and the transistor 2 is connected at the intermediate connection point between the resistors 225 and 226.
27 and the base of the output transistor 23 are connected. A resistor 228 is connected between the collector of the transistor 227 and the ground line 37, and the current flowing through the transistor 227 is converted into a voltage by the resistor 228. Further, the transistor 22 is connected to the collector side of the transistor 227.
The base of a transistor 229 inserted between the base of the transistor 228 and the ground line 37 is connected to the base of the transistor 229, and the voltage generated in the resistor 228 is fed back to the base of the transistor 229, and the current flowing through the transistor 227 is fed back to the base of the transistor 229. has been done. That is, the transistor 229 constitutes a feedback circuit with respect to the transistor 221, and the output of the output circuit 22 is fed back to the base input side of the transistor 221 for level adjustment.

The output transistor 23 is connected to the power supply line 3 through a series circuit of resistors 25 and 26 on the collector side.
6 and a ground line 37, an output terminal 27 is formed at its collector and output voltage Vout is taken out, and a transistor 206 is connected to the connection point between the resistors 25 and 26 via a feedback circuit 24. The voltage Vn to be fed back to the base is generated by the voltage drop across the resistor 26 due to the output current flowing through the output transistor 23.

Furthermore, the differential amplifier 4 of the output saturation prevention circuit 4
1, a differential pair consisting of transistors 413 and 414 whose emitters are shared by resistors 411 and 412 is installed, and the base input side of the transistor 413 receives a reference voltage Vref from a reference voltage source, and the base input side of the transistor 414 receives a reference voltage Vref from a reference voltage source. A voltage Vp is applied from an output circuit 42 to . A resistor 4 is connected to the emitter side of the transistors 413 and 414.
A constant current source 415 is connected through 11 and 412, and an operating current for the differential pair flows through this constant current source 415. A current mirror circuit 416 is connected between the collectors of the transistors 413 and 414 and the power supply line 36 as an active load of a differential pair. The current mirror circuit 416 includes a transistor 417 having a common base and collector on the collector side of the transistor 414, and a transistor 418 having a common base and collector with the base of the transistor 417 on the collector side of the transistor 413. There is. The output taken out from the collector side of the transistor 418 is applied to the base of the transistor 43 of the output circuit 42. A phase adjustment capacitor 48 is connected between the base and collector of the transistor 43. The emitter area of the transistor 43 is set to about 1/N (for example, 1/70) of the output transistor 23.

The resistor 46 in the feedback circuit 47 is connected to a capacitor 6 to prevent fluctuations due to ripples.
are connected in parallel.

The power supply circuit of this embodiment is composed of a monolithic IC, and the resistors 45 and 25, and the resistors 46 and 26 are set to have the same resistance value.

According to this configuration, when the power is reduced, fluctuations in the voltage Vp due to ripples in the power supply voltage Vcc are smoothed by the capacitor 6 and applied to the stabilizing circuit 2.
In addition to stabilizing the output voltage Vout, saturation of the output transistor 23 can be prevented as described in the previous embodiment. Therefore, when an audio circuit is driven by such a power supply circuit, it is possible to suppress the deterioration of ripple rejection, that is, the generation of noise, etc., due to a drop in input voltage due to a high load when the power is reduced.

In this regulator circuit, the resistors 44 and 45 and the resistor 25, and the resistor 46 and the resistor 26 are set to the same resistance value, respectively, so that the regulator circuit is stable regardless of temperature changes or variations in the manufacturing process. Output can be extracted.

In the embodiment, the reference voltage Vref input to the stabilizing circuit 2 due to the ripple of the power supply voltage Vcc is
The capacitor 6 is connected in parallel to the resistor 46 in the feedback circuit 47 of the output saturation prevention circuit 4, but it may be connected anywhere in the feedback circuit 47, for example, in FIG.
As shown in FIG. 2, it may be connected between the connection point of the resistors 44 and 45 and the ground point.

[0045]

[Effects of the Invention] As explained above, according to the present invention, the following effects can be obtained. a. By smoothing the fluctuation of the reference voltage input to the stabilization circuit during power reduction using a capacitor, the sudden ripple rejection within the input/output differential voltage is set to prevent saturation of the output circuit of the stabilization circuit. It is possible to prevent such deterioration, and it is possible to obtain stable output even when the power is reduced. b. Since ripple rejection during power reduction is determined by the resistor and capacitor in the output prevention circuit, it is possible to prevent deterioration of ripple rejection by using a small capacitor, and it is possible to reduce manufacturing costs.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a power supply circuit of the present invention.

FIG. 2 is a diagram showing operating characteristics of the power supply circuit shown in FIG. 1;

FIG. 3 is a circuit diagram showing a specific example of the circuit configuration of the power supply circuit of the present invention.

FIG. 4 is a circuit diagram showing another embodiment of the power supply circuit of the present invention.

FIG. 5 is a circuit diagram showing a power supply circuit that is a premise of the present invention.

FIG. 6 is a circuit diagram showing parasitic transistor effects in a conventional power supply circuit.

7 is a diagram showing operating characteristics of the power supply circuit shown in FIG. 5. FIG.

[Explanation of symbols]

2 Stabilization circuit 4 Output saturation prevention circuit 6 Capacitor 21 Differential amplifier (first amplifier) 22 First output circuit 24 Feedback circuit 41 Differential amplifier (second amplifier) 42 Second output circuit 44, 45, 46 resistance 47 Feedback circuit

Claims (1)

[Claims] 1. A stabilizer that receives a reference voltage in a first amplifier, takes out its output through a first output circuit, and feeds it back to the input side of the first amplifier to take out a stabilized output according to the reference voltage. A second output circuit is provided on the output side of the second amplifier, which is installed on the front stage side of the first amplifier and receives the reference voltage, and a second output circuit is provided on the output side thereof, The reference voltage is applied to the first amplifier through the output circuit of an output saturation prevention circuit that prevents saturation of the first output circuit;
A power supply circuit comprising: a capacitor for smoothing fluctuations in the reference voltage is connected to a voltage dividing resistor added to a feedback circuit of the second amplifier of the output saturation prevention circuit. .