JP2000155619A - Constant voltage power supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify constitution and to reduce terminals for connection in a power supply unit provided with the circuits of two systems for supplying different voltages in accordance with the on/off states of a switch. SOLUTION: When an ignition switch IG is turned off, an operand amplifier OP2 drives a control transistor Tr4 and controls the base current of an output transistor Tr2 so that power voltage VOS supplied to ECU becomes second voltage V2 for standby. When the ignition switch IG is turned on, an operand amplifier OP 1 drives a control transistor Tr3 and the base current of a control transistor Tr1 is controlled so that power voltage VOS supplied to ECU becomes first voltage V1 for operation (V1>V2). Since the control transistors Tr3 and Tr4 selectively operate, the base current route of the transistors Tr3 and Tr4 is made to be common and one capacitor for phase compensation CO connected to the route is given. Consequently, circuit constitution can be simplified and terminals installed in power IC 10 can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant voltage power supply for receiving a power supply from a DC power supply and supplying a DC constant voltage to an electric load.

[0002]

2. Description of the Related Art Conventionally, a constant-voltage power supply for supplying power to an electronic circuit including a CPU or the like has been required to minimize power consumption in a standby state (standby state) of the electronic circuit, and to reduce the power consumption of the electronic circuit. In order to secure the current supply capability during the transition from the standby state to the normal operation and during the normal operation, the power supply circuit that supplies power to the electronic circuit when the electronic circuit is in the standby state and operates the electronic circuit with low power consumption. When letting
There is known a power supply circuit having two power supply circuits, and a power supply circuit capable of supplying a sufficient current necessary for the operation.

[0003] Such a constant voltage power supply device is configured, for example, as shown in FIG. The constant voltage power supply device shown in FIG. 4 is for supplying power to an electronic control device for a vehicle (hereinafter, referred to as an ECU) including a CPU and the like, and includes a battery BT via an ignition switch IG.
The first output transistor Tr1 provided in the first power supply path L1 connected to the positive terminal of the battery BT and the second output transistor L1 provided in the second power supply path L2 directly connected to the positive terminal of the battery BT via the diode D1. And a two-output transistor Tr2.

The first output transistor Tr1 is for supplying a constant voltage for operation (first voltage V1; for example, 5 V) to the ECU when the ignition switch IG is in an on state. Tr2 is
When the ignition switch IG is in the off state,
A constant voltage for standby (standby) lower than the first voltage V1 for operation (second voltage V2;
75 V).

Then, each output transistor Tr1, Tr
Numerals 2 each consist of a PNP type bipolar transistor, the emitter is on the battery BT side, and the collector is EC
It is provided on each of the power supply paths L1 and L2 so as to be on the U side. Also, the base of the first output transistor Tr1
A resistor R1 for preventing current leakage is connected between the collectors, and a resistor R2 for preventing current leakage is also connected between the base and the emitter of the second output transistor Tr2.

The diode D1 provided in the second power supply path L2 is a diode for preventing a current from flowing backward.
The power supply path L2 is connected via the diode D1 regardless of the on / off state of the ignition switch IG.
Battery voltage is always applied. Also, battery B
The negative terminal of T is grounded to a ground line (specifically, the body of an automobile).

Next, the output transistors Tr1, T
By controlling the base current, r2 can control the current flowing to the ECU side, that is, the power supply voltage VOS output to the ECU side. For this reason, each output transistor Tr
Control transistors Tr3 and Tr4 for controlling the base current are connected to the bases of the transistors Tr1 and Tr2, respectively. By controlling the current flowing through the control transistors Tr3 and Tr4, the power supply voltage VOS output to the ECU can be controlled. It has been like that.

That is, the control transistors Tr3 and Tr4
Consists of an NPN-type bipolar transistor, the collector of which is connected to the base of each of the output transistors Tr1 and Tr2, and the emitter of which is connected via a series circuit of resistors R11 and R12 and a series circuit of resistors R21 and R22, respectively. To the ground line, and the base is connected to the operational amplifier OP
1 and OP2, respectively.

An operational amplifier (first operational amplifier) OP1 having an output terminal connected to the base of the first control transistor Tr3 controls the base current of the first output transistor Tr1 by controlling the driving of the first control transistor Tr3. And the first output transistor Tr1 to EC
The power supply voltage VOS output to U is controlled to the first voltage V1, and operates by receiving power supply from the first power supply path L1.

Further, the output terminal is the second control transistor T
An operational amplifier (second operational amplifier) OP2 connected to the base of r4 controls the base current of the second output transistor Tr2 by controlling the drive of the second control transistor Tr4, and controls the current from the second output transistor Tr2 to the EC.
This is for controlling the power supply voltage VOS output to U to the second voltage V2, and operates by receiving power supply from the second power supply path L2.

Next, these operational amplifiers OP1 and OP2
A reference voltage Vref (for example, 1 V) is applied to a non-inverting input terminal (+) of the power supply, and a power supply voltage VOS supplied to the ECU via the output transistors Tr1 and Tr2 is applied to an inverting input terminal (-). Voltage dividing resistors R3, R4, R for dividing the voltage
5, a divided voltage corresponding to the power supply voltage VOS is applied.

That is, the voltage dividing resistors R3, R4 and R5 are connected to the collectors of the output transistors Tr1 and Tr2 by the ECU.
Are connected in series between the power supply path LOS for power supply voltage output and the ground line, with the resistor R3 on the power supply path LOS side and the resistor R5 on the ground line side. Then, a voltage VO1 (= VOS × R) between the resistors R4 and R5
5 / (R3 + R4 + R5)) is applied to the inverting input terminal (-) of the first operational amplifier OP1 for driving and controlling the first control transistor Tr3, and the voltage VO2 (= VOS × (R4 + R5)) between the resistors R3 and R4. / (R3 + R4 + R
5)) is applied to the inverting input terminal (-) of the second operational amplifier OP2 that drives and controls the second control transistor Tr4.

A grounding resistor R1 provided between the emitter of the first control transistor Tr3 and the ground line.
A capacitor C1 for phase compensation with respect to the first operational amplifier OP1 is provided between the connection point of the R1 and R12 and the ECU-side power supply path LOS, and a ground provided between the emitter of the second control transistor Tr4 and the ground line. Resistor R for
A capacitor C2 for phase compensation with respect to the second operational amplifier OP2 is provided between the connection point between the terminals 21 and R22 and the power supply path LOS on the ECU side.

In the conventional constant-voltage power supply device configured as described above, when the ignition switch IG is off, the second operational amplifier OP2 operates, and the voltage obtained through the voltage dividing resistors R3 to R5 is used. The second control transistor Tr4 is set so that the voltage VO2 becomes the reference voltage Vref.
Is controlled to drive the second output transistor Tr.
2 to control the base current of the second output transistor Tr2.
The power supply voltage VOS supplied to the ECU side via the controller is controlled to the second voltage V2 for standby. At this time, the ECU
Is in a standby state (standby state), the current consumption is very small, and the base current of the second output transistor Tr2 is also small.

Next, when the ignition switch IG is turned on in this state, the first operational amplifier OP1 operates. Then, at this time, the divided voltage VO1 inputted via the voltage dividing resistors R3 to R5 is always lower than the reference voltage Vref, so that the output of the first operational amplifier OP1 becomes High level and the first control transistor Tr3 is turned on. Let it.
Then, a base current flows through the first output transistor Tr1, and the first voltage V1 for operation is supplied to the ECU via the first output transistor Tr1.

Further, as described above, the first output transistor T
When the first voltage V1 is supplied from r1 to the ECU, the divided voltage VO2 input to the second operational amplifier OP2 becomes higher than the reference voltage Vref, so that the output of the second operational amplifier OP2 becomes low level, Control transistor Tr4
Turns off. As a result, the second output transistor Tr2 is also turned off, and the ECU outputs the first output transistor T2.
The first voltage V1 for operation is supplied only by r1.

[0017]

As described above, immediately after the power switch such as the ignition switch IG is switched from the off state to the on state, the power switch is turned off in order to quickly start the electric load such as the ECU. A conventional constant-voltage power supply that supplies a standby power supply voltage to an electric load when the power supply is in a standby state and puts the electric load in a standby state includes a power supply circuit that supplies power for standby and a power supply for operation. And a power supply circuit to be used.

Conventionally, these two power supply circuits are configured as independent power supply circuits, respectively, so that the same components are required for each of the two power supply circuits, and the configuration cannot be simplified. There was such a problem. On the other hand, when such a conventional constant voltage power supply is actually used, it is desirable to integrate the IC into a single semiconductor integrated circuit so that wiring work and the like at the time of assembly can be easily performed. Incorporation into a circuit cannot be realized due to problems such as chip size and cost. In particular, the first output transistor that supplies a power supply voltage for operation when the power switch is turned on generates a large amount of heat, so that the semiconductor integrated circuit It was impossible to build in.

Therefore, when the above-mentioned conventional power supply circuit is formed into an IC, as shown by dotted lines in FIG. 4, operational amplifiers OP1 and OP2, control transistors Tr3 and Tr4, voltage dividing resistors R3 to R5, a grounding resistor R11, R12, R21, R
22 are incorporated in one semiconductor integrated circuit (IC) as the power supply IC 20, and the output transistors Tr1,
Tr2 and phase compensating capacitors C1 and C2 are externally attached to the power supply IC 20 to constitute a constant voltage power supply.

As a result, the power supply IC 20 includes the battery B
In addition to a battery terminal TBT, an ignition terminal TIG, and a ground terminal TGD for receiving power supply from the T-side power supply paths L1 and L2, the ECU-side power supply path LOS to EC
A voltage feedback terminal TFB for taking in an output voltage (power supply voltage VOS) to U, each output transistor Tr1,
There is a problem that a large number of terminals must be provided, such as control terminals TC1 and TC2 for controlling the base current of Tr2, and capacitor connection terminals TS1 and TS2 for connecting phase compensation capacitors C1 and C2. In addition, there is also a problem that the wiring during use is troublesome due to the large number of terminals.

The present invention has been made in view of such a problem, and as described above, a constant voltage circuit having two power supply circuits for supplying different power supply voltages to an electric load when a power switch is turned on and off. In the power supply device, by sharing a part of each circuit, the configuration is simplified, and
It is an object of the present invention to reduce the number of terminals when an IC is used and to easily perform wiring during use.

[0022]

According to a first aspect of the present invention, a first output transistor is provided in a first power supply path connected to a DC power supply via a switch. The second output transistor is provided in the second power supply path provided directly connected to the DC power supply. Further, a first control transistor and a second control transistor for controlling the base current are respectively connected to these output transistors, and the base current is controlled via each of the control transistors, so that each output transistor is The power supply voltage output to the electric load is detected by a voltage detection circuit.

When the switch is off and the power is supplied from the DC power supply to only the second power supply path of the two power supply paths, the second operational amplifier operates and the voltage detection circuit operates. The second control transistor is driven so that the detected power supply voltage becomes the second voltage. As a result, when the switch is in the off state, the second voltage is supplied to the electric load.

When the switch is turned on and power is also supplied to the first power supply path, the first operational amplifier operates, and the power supply voltage detected by the voltage detection circuit is higher than the second voltage. The second control transistor is driven to have one voltage. As a result, when the switch is in the off state, the second voltage is supplied to the electric load. In this state, since the power supply voltage detected by the voltage detection circuit is higher than the second voltage, the second operational amplifier stops driving the second control transistor, and
The control transistor, and thus the second output transistor, is turned off.

As described above, the constant voltage power supply of the present invention has two power supply circuits including an output transistor, a control transistor, and an operational amplifier, similarly to the conventional constant voltage power supply shown in FIG. The operation of the circuit is
Switching is performed according to the on / off state of the switch.
Therefore, a base current for controlling output voltages from the first output transistor and the second output transistor does not flow through the first control transistor and the second control transistor at the same time.

Therefore, in the present invention, as in the conventional constant voltage power supply device shown in FIG. 4, a path (base current path) through which the base current of each output transistor flows through the first control transistor and the second control transistor. Are not formed independently of each other, but a base current path on the opposite side to each output transistor of the first control transistor and the second control transistor is made common, and further, the common base current path and each output transistor A common phase compensation capacitor is provided between the operational amplifier and a common power supply path to an electric load.

That is, in the present invention, attention is paid to the fact that the first control transistor and the second control transistor are not driven at the same time, and the base current paths of the output transistors formed by these control transistors are shared. Thus, each control transistor has a differential pair configuration (OR configuration), and the number of resistors provided in the base current path and the number of phase compensation capacitors connected thereto are reduced to one power supply circuit. Therefore, according to the constant voltage power supply of the present invention, compared with the conventional constant voltage power supply as shown in FIG. 4, the number of components can be reduced, and the size and cost of the device can be reduced.

When the constant voltage power supply device of the present invention is integrated into an IC, the first control transistor, the second control transistor, the voltage detection circuit, the first operational amplifier, and the second The operational amplifier may be incorporated in one semiconductor integrated circuit as a power supply IC, and the first output transistor, the second output transistor, and the phase compensation capacitor may be externally attached to the semiconductor integrated circuit.

In this case, the power supply IC only needs to be provided with one terminal for connecting a phase compensating capacitor.
The number of terminals formed in C can be reduced by one, and wiring can be easily performed when used.

[0030]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an electric circuit diagram illustrating a configuration of the constant voltage power supply device according to the present embodiment. Similar to the conventional device shown in FIG. 4, the constant voltage power supply device of the present embodiment is configured such that when an ignition switch IG serving as a power switch is in an on state, a vehicle electronic control unit (ECU) as an electric load is turned on. When the first voltage V1 for operation (for example, 5 V) is supplied and the ignition switch IG is in the off state, the second voltage V2 for standby (for example, 4.75) is supplied.
V).

Therefore, in the constant voltage power supply of the present embodiment, the ignition switch IG
And a first output transistor Tr1 provided in the first power supply path L1 connected to the positive terminal of the battery BT (in other words, a DC power supply) via the DC terminal, and directly connected to the positive terminal of the battery BT via the diode D1. The second power supply path L
2 provided with the second output transistor Tr2. The output transistors Tr1 and Tr2 are respectively
A PNP-type bipolar transistor is provided on each of the power supply paths L1 and L2 such that the emitter is on the battery BT side and the collector is on the ECU side. A resistor R1 for preventing current leakage is connected between the base and the collector of the first output transistor Tr1.
A resistor R2 for preventing current leakage is also connected between the base and the emitter of the output transistor Tr2.

On the other hand, each output transistor Tr1, Tr2
In order to control the base current, N
The collectors of the control transistors Tr3 and Tr4 formed of PN-type bipolar transistors are connected. The output terminals of the operational amplifiers OP1 and OP2 are connected to the bases of the control transistors Tr3 and Tr4, respectively.
It is grounded to a ground line via a series circuit of four resistors R01 and R02 serving as a common current path. The ground line is connected to the negative terminal of the battery BT.

The operational amplifiers OP1 and OP2 receive power from the first power supply path L1 and the second power supply path L2, respectively, and operate in the same manner as in the conventional device, and operate on the first control transistor Tr3 side. Operational amplifier) OP1
Controls the power supply voltage VOS output from the first output transistor Tr1 to the ECU to the first voltage V1 by controlling the driving of the first control transistor Tr3, and the operational amplifier (second operational amplifier) on the second control transistor Tr4 side O
P2 controls the power supply voltage VOS output from the second output transistor Tr2 to the ECU to the second voltage V2 by controlling the drive of the second control transistor Tr4.

That is, the reference voltage Vref (for example, 1 V) is applied to the non-inverting input terminals (+) of the operational amplifiers OP1 and OP2.
Is applied to the inverting input terminal (−), and the power supply voltage V provided between the ground line and the power supply path LOS from the collectors of the output transistors Tr1 and Tr2 to the ECU.
The power supply voltage V is supplied via the OS voltage dividing resistors R3, R4 and R5.
Voltage VO1 (= VOS × R5 / (R3 + R4 +
R5)), VO2 (= VOS × (R4 + R5) / (R3 + R
4 + R5)) is applied to each of the operational amplifiers OP
1 and OP2 control the driving of the control transistor Tr3 or Tr4 such that the voltage VO1 or VO2 applied to the inverting input terminal (-) becomes the reference voltage Vref, respectively, thereby controlling the base of the output transistor Tr1 or Tr2. By controlling the current, the output transistors Tr1 and Tr2
The power supply voltage VOS output to the CU is controlled to the first voltage V1 or the second voltage V2. Note that the power supply voltage VOS is divided and
Voltage dividing resistors R3 to R5 for applying the voltages VO1 and VO2 to the inverting input terminals (-) of the operational amplifiers OP1 and OP2 are:
This corresponds to a voltage detection circuit according to claim 1.

The control transistors Tr3, Tr3
A phase compensation capacitor C0 common to the operational amplifiers OP1 and OP2 is provided between a connection point of the resistors R01 and R02 provided between the emitter and the ground line of the Tr4 and the power supply path LOS on the ECU side.

In the constant voltage power supply of this embodiment, the operational amplifiers OP1 and OP2 and the control transistor Tr
3, Tr4, voltage dividing resistors R3 to R5, grounding resistor R01,
A power supply voltage control circuit composed of R02 and the like is incorporated in one semiconductor integrated circuit (IC) as a power supply IC 10 as shown by a dotted line in FIG.
1, Tr2 and the capacitor C0 for phase compensation
Is externally attached.

Therefore, the power supply IC 10 includes the battery BT.
Terminals TBT, an ignition terminal TIG, and a ground terminal TGD for receiving power supply from each of the power supply paths L1 and L2, and an output voltage (power supply voltage VOS) from the power supply path LOS on the ECU side to the ECU. The voltage feedback terminal TFB and each output transistor Tr1, T
Control terminals TC1 and TC2 connected to the base of r2 for controlling the base current and a capacitor connection terminal TS for connecting the phase compensation capacitor C0 are provided.

In the constant voltage power supply device of the present embodiment thus configured, the ignition switch IG is turned off and the battery voltage (VBT) is supplied to the power supply IC 10 from the battery terminal TBT only, similarly to the conventional device shown in FIG. ) Is supplied, the two operational amplifiers OP1 and OP2
Only the second operational amplifier OP2 operates to cause the second output transistor Tr2 to output the second voltage V2 as the power supply voltage VOS of the ECU as shown in FIG.

In this state, when the ignition switch IG is turned on and the battery voltage (VIG) is supplied from the ignition terminal TIG to the power supply IC 10, the first operational amplifier OP1 starts operating. As shown in FIG. 2, as the power supply voltage VOS of the ECU,
The first output transistor Tr1 outputs a first voltage V1 higher than the second voltage V2.

In this state, the second operational amplifier O
Since the divided voltage VO2 input to P2 is higher than the reference voltage Vref, the output of the second operational amplifier OP2 is at the low level, the second control transistor Tr4 is turned off, and the ECU outputs only the first output transistor Tr1. As a result, the first voltage V1 for operation is supplied.

Therefore, according to the constant voltage power supply device of the present embodiment, as in the conventional device shown in FIG. 4, when the ignition switch IG is switched from the OFF state to the ON state, the operation to the ECU is performed. The required large current can be supplied promptly, and the ECU can be quickly operated immediately after the ignition switch IG is turned on.

In the constant voltage power supply of the present embodiment, the current paths (the output transistors Tr1 and Tr2) of the first control transistor Tr3 and the second control transistor Tr4 on the side opposite to the output transistors Tr1 and Tr2.
Base current path) and a single phase compensation capacitor C0 connected to the current path (specifically, between the resistors R01 and R02). Although the function described above can be realized, the device configuration can be simplified.

Further, the first operational amplifier OP1 and the second operational amplifier OP2
And a common connection terminal TS for the phase compensation capacitor provided in the power supply IC 10. Therefore, according to the constant voltage power supply of the present embodiment, it is possible to configure the constant voltage power supply inexpensively as compared with the conventional apparatus, and it is also possible to simplify the wiring when actually configuring the constant voltage power supply using the power supply IC 10. it can.

FIG. 2 shows a change in the power supply voltage VOS which changes in response to the rise of the battery voltage (VBT) input from the battery terminal TBT when the constant voltage power supply of this embodiment is connected to the battery BT. , And thereafter, when the ignition switch IG is turned on, the ignition terminal TIG
7 is a simulation result of a change in the power supply voltage VOS that changes in response to a rise in the battery voltage (VIG) input from the power supply. In FIG. 2, the power supply voltage VOS changes sharply immediately after connection to the battery BT and immediately after the ignition switch IG is turned on. However, actually, the power supply path LOS on the ECU side, which is an electric load, is changed. By providing an electrolytic capacitor or the like, such a steep change can be absorbed.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.
Various embodiments can be adopted. For example, in the above embodiment, the output terminals of the operational amplifiers OP1 and OP2 are described as being directly connected to the bases of the corresponding control transistors Tr3 and Tr4. For example, FIG.
As shown in FIG. 3, each control transistor Tr3, Tr2 is connected to a signal path connecting the output terminal of each operational amplifier OP1, OP2 to the base of the corresponding control transistor Tr3, Tr4.
Bias circuits B1 and B for regulating the rise of the base potential
2 may be provided to prevent the base current of the output transistors Tr1 and Tr2 from becoming unnecessarily large.

That is, for example, when some abnormality such as a short circuit occurs on the ECU side and the power supply voltage VOS decreases, the power supply voltage VOS is reduced to the set voltage V1 or V2 in the power supply IC 10.
Therefore, the output voltage of the operational amplifier OP1 or OP2 rises. If the voltage rise causes the base current of the output transistor Tr1 or Tr2 to rise more than necessary, the output transistor Tr1 or Tr2 may be destroyed. Usually, a current limiting circuit is provided in the power supply path to the ECU, and the current flowing through the output transistors Tr1 and Tr2 is also limited.
If b1 and B2 are provided, the output transistors Tr1 and Tr1 can be provided before the current limiting circuit operates in the event of a short circuit abnormality on the ECU side or the like.
By limiting the current flowing through Tr2, the output transistor Tr
1, Tr2 can be reliably protected from a large current.

The bias circuits B1 and B2 may be of any type as long as they can limit the rise in the base potential of the control transistors Tr3 and Tr4. More specifically, for example, as shown in FIG. , Control transistor Tr3
(Or Tr4), an NPN-type bipolar transistor (NPN transistor) Trb is Darlington-connected, and the base of a control transistor Tr3 to which the emitter of the NPN transistor Trb is connected is grounded to a ground line via a resistor Rb. , The base of the NPN transistor Trb is connected to the output terminal of the operational amplifier OP1 (or OP2), and the connection point is grounded via a series circuit composed of, for example, seven diodes Db1 to Db7. In this case, seven diodes Db1
To Db7 are connected in the same direction, and the anode side is NP
It is provided so as to be a base of the N transistor Trb.

In this way, the operational amplifier O
During the operation of P1 (or OP2), the control transistor Tr
3 (or Tr4) is the sum of the forward voltages VF of the diodes Db1 to Db7 (VF.times.7), respectively.
, NPN transistor Trb and control transistor Tr
3 (or Tr4) can be regulated to a predetermined value VF.times.6, VF.times.5 or less determined by a forward voltage (approximately VF) between the base and the emitter of the base transistor 3 and the base current of the output transistor Tr1 (or Tr2). And the output transistors Tr1 and Tr2 can be protected from a large current.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram illustrating a configuration of an entire constant voltage power supply circuit according to an embodiment.

FIG. 2 is an explanatory diagram illustrating an operation of the constant voltage power supply circuit according to the embodiment.

FIG. 3 is an electric circuit diagram illustrating another configuration example of the constant voltage power supply circuit (power supply IC).

FIG. 4 is an electric circuit diagram showing the configuration of the entire conventional constant voltage power supply circuit.

[Description of Signs] BT: Battery, IG: Ignition switch, L1
.. 1st power supply path, L2 2nd power supply path, Tr1 1st output transistor, Tr2 2nd output transistor, LOS
... power supply path (ECU side), C0, C1, C2 ... phase compensation capacitors, 10, 20 ... power supply IC, R3-R5 ... voltage dividing resistors (voltage detection circuits), Tr3 ... first control transistor, Tr4 ... second Control transistor, OP1: first operational amplifier, OP2: second operational amplifier, TBT: battery terminal, TIG: ignition terminal, TGD: ground terminal,
TS, TS1, TS2 ... capacitor connection terminals, TC1, TC2 ...
Control terminal, TFB ... Voltage feedback terminal, B
1, B2 ... bias circuit.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H03K 17/62 H03K 17/62 DF term (Reference) 5H430 BB01 BB05 BB09 BB11 CC02 EE03 EE09 EE17 FF02 FF13 GG08 HH03 LA07 LA13 LB06 5J055 AX44 AX46 AX62 BX16 CX28 DX05 DX44 DX55 DX61 DX73 EX06 EY01 EY03 EY10 EY12 EY17 EZ09 EZ43 EZ51 EZ57 FX05 FX32 GX01

Claims (2)

[Claims] 1. A power supply connected to a DC power supply via a switch,
A first output transistor provided in a first power supply path for supplying power to the electric load when the switch is turned on, and a first output transistor directly connected to the DC power supply for supplying power to the electric load when the switch is turned off. A power supply voltage output to the electric load via each of the output transistors by controlling a second output transistor provided in the second power supply path and a base current of each of the first and second output transistors; A first control transistor and a second control transistor for controlling, a voltage detection circuit for detecting a power supply voltage output from each of the output transistors to the electric load, and receiving power from the first power supply path to operate; A first operational amplifier for driving the first control transistor so that the power supply voltage detected by the voltage detection circuit becomes the first voltage And operates by receiving power supply from the second power supply path, and drives the second control transistor so that the power supply voltage detected by the voltage detection circuit becomes a second voltage lower than the first voltage. A second operational amplifier, comprising: a base voltage path common to the first control transistor and the second control transistor on a side opposite to the output transistors; A constant-voltage power supply device, wherein a common phase compensation capacitor is provided between each of the operational amplifiers and a common power supply path from an output transistor to an electric load. 2. The semiconductor device according to claim 1, wherein the first control transistor, the second control transistor, the voltage detection circuit, the first operational amplifier, and the second operational amplifier are incorporated in one semiconductor integrated circuit. 2. The constant voltage power supply device according to claim 1, wherein the second output transistor and the phase compensation capacitor are externally connected to the semiconductor integrated circuit.