JP4627894B2 - Power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power supply device that supplies power from a power supply to a load.
[0002]
[Prior art]
In a power supply device such as an audio device mounted on a car, as shown in FIG. 4, an example of a conventional circuit configuration is to increase current capability and prevent backflow of current from a smoothing capacitor C to a battery side. The power supply voltage V _CC output from the battery is a diode connected in a forward direction between the collector of the transistor 112 and the power supply voltage V _CC while connecting the two NPN transistors 111 and 112 in a Darlington connection. It is output via a voltage follower 101 formed by connecting D. A resistor 114 is connected to the base of the transistor 111.
[0003]
The constant voltage generation circuit 102 outputs a constant voltage using the voltage V _CC ′ output from the voltage follower 101 as an operating voltage. The voltage V _OUT output from the constant voltage generation circuit 102 is supplied as an operating voltage to, for example, a microcomputer (not shown) such as a car stereo or a video device (hereinafter referred to as “microcomputer”).
[0004]
Here, the power supply voltage output from the car battery may greatly decrease when the engine is started or when the audio equipment is turned on. On the other hand, on the load side, if the supplied operating voltage falls outside the allowable range, for example, the microcomputer may be reset unintentionally. Hereinafter, the intended operation is referred to as “normal operation”.
[0005]
[Problems to be solved by the invention]
For such an event, the conventional power supply apparatus, the number of transistors constituting the voltage follower 101 n, the base of each transistor - the voltage drop between the emitter and V _F, the output voltage of the voltage follower decrease amount of the power supply voltage is as large as n × V _F, the amount of operating voltage supplied to the load is decreased with a decrease in power supply voltage is large, the power supply voltage in order to ensure the normal operation of the load side The allowable range for the decrease was low. From another viewpoint, on the load side, it is necessary to use a special one that lowers the minimum value of the operating voltage that guarantees normal operation, such as lowering the voltage that resets in the microcomputer, The cost was raised.
[0006]
SUMMARY OF THE INVENTION An object of the present invention is to provide a power supply apparatus that can expand a range allowed for a decrease in power supply voltage in order to guarantee normal operation on the load side.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, in a power supply device that outputs a predetermined voltage from a power supply voltage via a voltage follower composed of a plurality of transistors, any one other than the first stage constituting the voltage follower is provided. A switch circuit connected between the control electrode of the transistor and the power supply voltage, and a voltage drop detection circuit that turns on the switch circuit when the value of the power supply voltage is lower than a threshold value are provided.
[0008]
With this configuration, if the switch circuit is connected to the control electrode of the k-th stage transistor from the Darlington connection input side constituting the voltage follower, the amount of decrease in the voltage on the output side of the voltage follower from the power supply voltage Is n × V _F (n is the number of Darlington-connected transistors constituting the voltage follower) when the switch circuit is OFF, whereas (n−k + 1) × V _F when the switch circuit is ON. Therefore, if the above threshold is set appropriately, a large current capability can be secured in the range where the voltage supplied from the power supply unit to the load does not decrease. However, when the voltage supplied from the power supply device to the load decreases as the power supply voltage decreases, the amount of decrease can be reduced. .
[0009]
Further, in the present invention, in a power supply device that outputs a predetermined voltage from a power supply voltage via a voltage follower configured by a transistor, a switch circuit connected between the output side of the voltage follower and the power supply voltage; A reduced voltage detection circuit that turns on the switch circuit in a state where the value of the power supply voltage is lower than a threshold value.
[0010]
With this configuration, the amount of decrease in the supply voltage of the output side of the voltage of the voltage follower, whereas when the switch circuit is OFF is n × V _F, the voltage of the switch circuit when the switch circuit is turned ON If the threshold value is set appropriately, the load supplied from the power supply device to the load is ensured while ensuring a large current capability in a range where the voltage supplied from the power supply device to the load does not decrease. When the voltage supplied to the power supply voltage decreases as the power supply voltage decreases, the amount of decrease can be reduced.
[0011]
For example, a transistor on the output side of the current mirror circuit may be used as the switch circuit. Further, as the threshold value, for example, in the case of having a constant voltage generation circuit that outputs a constant voltage using the output voltage from the voltage follower as an operating voltage, the output voltage of the constant voltage generation circuit starts to decrease. A value may be set.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a circuit diagram of an in-vehicle power supply device according to the first embodiment of the present invention. The power supply device according to the first embodiment includes a voltage follower 1, a constant voltage generation circuit 2, a reduced voltage detection circuit 3, and a switch circuit 4. Each of these circuits forms a one-chip IC.
[0013]
The configuration of the voltage follower 1 will be described. The two NPN transistors 11 and 12 are Darlington connected. In the Darlington-connected first-stage transistor 11, the power supply voltage V _CC from the battery is applied to the base via the resistor 14, and the power supply voltage V _CC is directly applied to the collector.
[0014]
The collector of the Darlington-connected final stage transistor 12 is connected to the diode-connected emitter of the transistor 13. A power supply voltage V _CC is applied to the collector and base of the transistor 13. The output side of the voltage follower 1 (the emitter of the transistor 12) is grounded via a smoothing external capacitor C. The voltage V _CC ′ output from the voltage follower 1 is supplied as an operating voltage for the constant voltage generation circuit 2 and the reduced voltage detection circuit 3.
[0015]
The configuration of the constant voltage generation circuit 2 will be described. A reference voltage V _ref1 is applied to the inverting input terminal (−) of the operational amplifier 21. The base of a PNP transistor 22 is connected to the output terminal (O) of the operational amplifier 21. A voltage V _CC ′ is applied to the emitter of the transistor 22. The collector of the transistor 22 is connected to the ground via three resistors 23, 24 and 25 connected in series.
[0016]
The non-inverting input terminal (+) of the operational amplifier 21 is connected to the connection point a of the two resistors 24 and 25. A voltage V _{OUT at} a connection point c between the collector of the transistor 22 and the resistor 23 is output from the constant voltage generation circuit 2. The voltage V _OUT output from the constant voltage generation circuit 2 is supplied as an operating voltage to, for example, a microcomputer.
[0017]
The configuration of the operational amplifier 21 will be described. The PNP transistor 201 is diode-connected, and a voltage V _CC ′ is applied to its emitter via a resistor 203, and a constant current flows from the collector to the constant current source 202. The other end of the constant current source 202 is connected to the ground.
[0018]
The PNP transistor 204 has a base connected to the base of the transistor 201, a voltage V _CC ′ applied to the emitter via a resistor 205, and a collector connected to the emitter of the PNP transistor 206. Yes. The collector of the transistor 206 is connected to the ground.
[0019]
The PNP transistor 207 has a base connected to the base of the transistor 201, a voltage V _CC ′ applied to the emitter via a resistor 208, and a collector connected to the emitter of the PNP transistor 209. Yes. The collector of the transistor 209 is connected to the ground.
[0020]
The PNP transistor 210 has a base connected to the base of the transistor 201, a voltage V _CC ′ applied to the emitter via a resistor 211, and a collector connected to the PNP type transistor via resistors 212 and 213, respectively. The emitters of the transistors 214 and 215 are connected. The bases of the transistors 214 and 215 are connected to the emitters of the transistors 206 and 209, respectively.
[0021]
The NPN transistor 216 is diode-connected, the collector is connected to the collector of the transistor 214, and the emitter is grounded. The NPN transistor 217 has a base connected to the base of the transistor 216, an emitter grounded, and a collector connected to the collector of the transistor 215.
[0022]
The NPN transistor 218 has a base connected to a connection point between the collector of the transistor 215 and the collector of the transistor 217, and an emitter grounded via a resistor 219. A phase compensation capacitor 220 is connected between the base and collector of the transistor 218.
[0023]
The base of the NPN transistor 221 is connected to the connection point between the transistor 218 and the resistor 219, and the emitter is grounded. A voltage V _CC ′ is applied to the collector of the transistor 218 and the collector of the transistor 221 through a common resistor 222.
[0024]
The base of the transistor 209 becomes the non-inverting input terminal (+) of the operational amplifier 21, the base of the transistor 206 becomes the inverting input terminal (-) of the operational amplifier 21, and the connection point between the transistors 218 and 221 and the resistor 222 is calculated. It becomes the output terminal (O) of the amplifier 21.
[0025]
With this configuration, in the constant voltage generation circuit 2, the output voltage V _OUT is set to a predetermined value (specifically, the resistors 24 and 25) unless the power supply voltage V _CC decreases too much and the transistor 22 is saturated. Is automatically controlled so that the voltage at the connection point a becomes equal to the reference voltage V _ref1 .
[0026]
The reduced voltage detection circuit 3 will be described. The emitters of the PNP transistors 302 and 303 are connected in common to the output side of the constant current source 301. The base of the transistor 302 is connected to the emitter of a PNP transistor 304. The collector of the transistor 302 is connected to the collector of a diode-connected NPN transistor 306. The base of the transistor 304 is connected to a connection point b between the two resistors 23 and 24 of the constant voltage generation circuit 2. The collector of the transistor 304 is grounded.
[0027]
The base of the transistor 303 is connected to the emitter of a PNP transistor 305. The collector of the transistor 303 is connected to the collector of an NPN transistor 307. A reference voltage V _ref2 is applied to the base of the transistor 305. The collector of the transistor 305 is grounded.
[0028]
The base of the transistor 306 and the base of the transistor 307 are connected to form a current mirror circuit in which the transistor 306 is an input side and the transistor 307 is an output side. The emitters of transistors 306 and 307 are grounded.
[0029]
The base of the NPN transistor 308 is connected to the connection point between the transistor 303 and the transistor 307. The emitter of the transistor 308 is grounded. A constant current output from a constant current source 309 having the other end connected to V _CC ′ is supplied to the collector of the transistor 308.
[0030]
The base of the NPN transistor 310 is connected to the collector of the transistor 308. The emitter of the transistor 310 is grounded. The collector of the transistor 310 is connected via a resistor 43 to the collector of the transistor 42 on the input side of a current mirror circuit constituting the switch circuit 4 described later.
[0031]
The configuration of the switch circuit 4 will be described. The PNP transistor 42 is diode-connected, and the base of the PNP transistor 41 is connected to the base thereof, and the two transistors 41 and 42 constitute a current mirror circuit.
[0032]
The power supply voltage V _CC is applied to the emitter of the transistor 42 on the input side, and the collector is connected to the collector of the transistor 310 of the reduced voltage detection circuit 3 via the resistor 43. The output side transistor 41 has a power supply voltage V _CC applied to its emitter, and a collector connected to the base of the transistor 12 of the voltage follower 1.
[0033]
With the above configuration, the voltage at the point b is higher than the reference voltage V _ref2 while the output voltage V _OUT of the constant voltage generating circuit 2 is maintained at a predetermined value. Since the current flowing through the transistor 303 becomes larger, the transistor 308 is turned on. For this reason, the transistor 310 of the voltage drop detection circuit 3 is turned off, and the transistor 41 on the output side of the current mirror circuit constituting the switch circuit 4 is also turned off. Therefore, the transistors 11 and 12 of the voltage follower 1 function and a large current flows. Capability is secured.
[0034]
On the other hand, when the power supply voltage V _CC decreases and the voltage at the point b of the constant voltage generating circuit 2 becomes lower than the reference voltage V _ref2 , in other words, when the output voltage V _OUT of the constant voltage generating circuit 2 becomes lower than a predetermined value. Therefore, the current flowing through the transistor 303 is smaller than the current flowing through the transistor 302 of the reduced voltage detection circuit 3, and the transistor 308 is turned off. Therefore, the transistor 310 is switched from OFF to ON, the transistor 42 constituting the current mirror circuit of the switch circuit 4 is switched from OFF to ON, and the transistor 41 on the output side of the current mirror circuit constituting the switch circuit 4 from the power supply voltage V _CC. Since the current is supplied to the base of the transistor 12 of the voltage follower 1 via Vs, the output voltage V _OUT of the constant voltage generation circuit 2 is V _CC when the voltage between the collector and the emitter when the transistor 41 is saturated is V _SAT. −V _SAT −V _F (conventional V _CC −2 × V _F ). That is, since V _F ≈ 0.7 [V] and V _SAT ≈ 0.1 [V], the voltage V _OUT output from the constant voltage generation circuit 2 is changed from V _CC −1.4 [V]. It will be able to V _CC -0.8 [V], it is possible to reduce the amount decreases with decrease of the power supply voltage V _CC.
[0035]
In the first embodiment, the number of Darlington-connected transistors of the voltage follower 1 may be three or more. The larger the required current capability, the more the switch circuit 4 is provided at the base of the previous transistor. What is necessary is just to make it connect. Further, the constant voltage generation circuit 2 may be eliminated and the voltage V _CC ′ may be used as a power supply voltage for other circuits.
[0036]
The circuit diagram of the power supply device which is 2nd Embodiment of this invention is shown in FIG. In addition, the same code | symbol is attached | subjected to the same part as the said 1st Embodiment, and description is abbreviate | omitted. The collector of the transistor 41 on the output side of the current mirror circuit constituting the switch circuit 4 is connected to the output side of the voltage follower 1 (the emitter of the transistor 12 in the final stage), which is different from the first embodiment. .
[0037]
With this configuration, when the power supply voltage V _CC decreases and the voltage at the non-inverting input terminal (+) of the operational amplifier 21 of the constant voltage generating circuit 2 becomes lower than the voltage at the inverting input terminal (−), in other words, the constant voltage When the output voltage V _OUT of the generation circuit 2 becomes lower than a predetermined value, the transistor 310 of the reduced voltage detection circuit 3 is switched from OFF to ON, and the transistor 42 of the current mirror circuit constituting the switch circuit 4 is switched from OFF to ON. Thus, since the power supply voltage V _CC is supplied to the constant voltage generation circuit 2 via the transistor 41, the output voltage V _OUT of the constant voltage generation circuit 2 becomes V _CC −V _SAT , compared with the first embodiment. Although the current capability is reduced, the amount by which the voltage _VOUT output from the constant voltage generation circuit 2 decreases as the power supply voltage V _CC decreases can be further reduced.
[0038]
In the second embodiment, the number of Darlington-connected transistors of the voltage follower 1 may be one or three or more. In each of the above embodiments, the configuration of the switch circuit 4 is not limited to the current mirror circuit, and can switch between supplying and not supplying current from the power supply voltage, and can prevent backflow. That's fine. Further, if the transistor 41 is configured with a Darlington connection having a smaller number of stages than the number of transistors of the voltage follower 1, the current capability can be increased. Further, the constant voltage generation circuit 2 and the reduced voltage detection circuit 3 may have other configurations.
[0039]
In summary, according to the power supply device of each of the above-described embodiments, it is possible to reduce the decrease in the power supply voltage V _CC ′ supplied to the load, so that the power supply voltage V that can guarantee normal operation on the load side. The range of _CC can be expanded on the low voltage side. From another perspective, the load side needs to have a particularly low minimum operating voltage that guarantees normal operation, such as using a general microcomputer with a high reset voltage. The cost can be reduced.
[0040]
FIG. 3 is a block diagram showing the power supply apparatus including a battery, a load circuit and the like. In the figure, reference numeral 8 denotes a battery mounted on the vehicle. Reference numeral 6 denotes a microcomputer that operates using the output voltage V _OUT of the constant voltage generation circuit 2 as an operating voltage, and controls, for example, a predetermined function of the audio equipment. Reference numeral 7 denotes a circuit other than the microcomputer, which can be operated by the voltage V _OUT . _{Reference numeral} 5 denotes another system using the voltage V _CC ′ as an operating voltage.
[0041]
【The invention's effect】
As described above, according to the present invention, it is possible to reduce the amount that the voltage supplied from the power supply device decreases as the power supply voltage decreases, so that the power supply voltage that can guarantee normal operation on the load side Can be expanded on the low voltage side. From another perspective, the load side needs to have a particularly low minimum operating voltage that guarantees normal operation, such as using a general microcomputer with a high reset voltage. The cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a power supply device according to a first embodiment of the present invention.
FIG. 2 is a circuit diagram of a power supply device according to a second embodiment of the present invention.
FIG. 3 is a block diagram showing a power supply device of the present invention including a battery, a load circuit, and the like.
FIG. 4 is a circuit diagram of a conventional power supply device.

Claims (4)

A voltage follower including a plurality of transistors connected to a power source and connected in a Darlington connection ;
An external terminal for connecting an external capacitor for smoothing to the output of the voltage follower;
A constant voltage generating circuit connected to the output of the voltage follower and using the voltage of the external capacitor as an operating voltage;
A comparator connected to the output of the voltage follower to set the voltage of the external capacitor as an operating voltage, and compares the output of the constant voltage generating circuit with a threshold applied from the outside, and the constant voltage generating circuit according to the output of the comparator A reduced voltage detection circuit including a first transistor that is turned on when the output of
A second transistor and a third transistor are connected to the power source and constitute a current mirror circuit. The collector current of the first transistor is used as the collector current of the second transistor, and the current from the power source is the third transistor. directly supplies the switching circuit to the base of one of the transistors other than the first stage constituting the voltage follower as the collector current of the transistor,
Configured as an IC circuit,
When the output of the constant voltage generation circuit is lower than the threshold value, the current path via the voltage follower is switched to the current path via the base of any one of the transistors other than the first stage constituting the switch circuit and the voltage follower. A power supply device characterized by that . A voltage follower including a plurality of transistors connected to a power source and connected in a Darlington connection ;
An external terminal for connecting an external capacitor for smoothing to the output of the voltage follower;
A constant voltage generating circuit connected to the output of the voltage follower and using the voltage of the external capacitor as an operating voltage;
A comparator connected to the output of the voltage follower to set the voltage of the external capacitor as an operating voltage, and compares the output of the constant voltage generating circuit with a threshold applied from the outside, and the constant voltage generating circuit according to the output of the comparator A reduced voltage detection circuit including a first transistor that is turned on when the output of
A second transistor and a third transistor are connected to the power source and constitute a current mirror circuit. The collector current of the first transistor is used as the collector current of the second transistor, and the current from the power source is the third transistor. directly supplies the switching circuit to the output of the voltage follower as the collector current of the transistor,
Configured as an IC circuit,
When the output of the constant voltage generation circuit is lower than the threshold value, the power supply device switches from a current path via the voltage follower to a current path via the switch circuit . 3. The power supply device according to claim 1, wherein the threshold value is set to a value when an output voltage of the constant voltage generation circuit starts to decrease due to a decrease in the power supply voltage.   The power supply apparatus according to any one of claims 1 to 3, wherein the voltage follower has a function of preventing a current from flowing backward to a battery that supplies a power supply voltage.

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