JP3531605B2 - Constant voltage circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant voltage circuit which outputs a constant DC voltage by clamping a control terminal of an output transistor below a predetermined voltage.

[0002]

2. Description of the Related Art Conventionally, for example, in an automobile,
For a battery that is a DC power source, a starter motor, a horn,
Since many electric loads such as lights are connected, the power supply voltage (battery voltage) may suddenly change by several volts or more when these electric loads are turned on and off.

Particularly in an automobile whose battery has deteriorated over time, when the engine is started in cold weather, there is no power supply from the alternator to the battery and the voltage of the battery itself drops, so the starter motor must be driven. Allows the electronic control unit for engine control (engine EC
In some cases, the power supply voltage supplied to U) becomes extremely low, the engine ECU cannot operate, and the engine cannot be started.

Therefore, in order to prevent such a problem, it has been conventionally required to lower the minimum operating voltage of the engine ECU. In addition, lowering the minimum operating voltage in this way is not limited to the engine ECU, but may be another vehicle control device that controls an air conditioner, an automatic transmission, or the like mounted in a vehicle, or a portable type that has a built-in battery. There is a similar demand for a control device used in an environment in which the power supply voltage easily changes, such as a control device incorporated in the device.

On the other hand, in order to meet such a demand, conventionally, the minimum operating voltage of various functional circuits constituting the control device is set to be low so that the functional circuits do not malfunction due to a sudden change in the power supply voltage. It is considered that a constant voltage circuit that receives power from an external DC power source to generate a predetermined constant voltage is provided, and that the constant voltage circuit supplies power to various functional circuits.

For example, FIG. 8 shows that the engine ECU supplies a constant power supply voltage to a reference voltage generation circuit 50 which generates a reference voltage required for highly accurate A / D conversion. The configuration of the voltage circuit 10 is shown. Here, the reference voltage generation circuit 50 uses a constant voltage (bandgap voltage: about 1.2) having a zero temperature characteristic as the reference voltage Vc.
V) is provided for the bandgap circuit 52. In the bandgap circuit 52, the collector has a resistor R.
Connected to the output terminal Tc of the reference voltage Vc via 51,
An NPN transistor Q51 having an emitter-base connection, an emitter grounded to a ground line, a collector connected to an output terminal Tc of a reference voltage Vc via a resistor R52, and a base connected to the base of the NPN transistor Q51, It is a well-known one having an NPN transistor Q52 whose emitter is grounded to a ground line via a resistor R53.

In the reference voltage generation circuit 50, the collector is connected to the power supply line to which the output voltage Vout from the constant voltage circuit 10 is applied, the emitter is connected to the output terminal Tc of the reference voltage Vc, and the collector-base is connected. Resistance R50 between
The NPN transistor Q50 connected via the NPN transistor Q50 and the non-inverting input terminal (+) constitute the bandgap circuit 52.
The bases of the transistors Q51 and Q52 are connected to each other, the inverting input terminal (−) is connected to the collector of the NPN transistor Q52, and the output terminal Tc is connected to the NPN transistor Q5.
And an operational amplifier OP1 connected to the base of 0. This operational amplifier OP1 is an NPN transistor Q.
By controlling 50, the reference voltage Vc output from the output terminal Tc is always a constant voltage (bandgap voltage:
It is controlled to about 1.2V).

The reference voltage generating circuit 5 configured as described above
At 0, the reference voltage Vc, which is the output voltage, is about 1.2 V. To output this reference voltage Vc, the forward voltage Vf (about 0.7 V) is applied between the base and emitter of the NPN transistor Q50. Therefore, it is necessary to operate the NPN transistor Q50. Therefore, the reference voltage generation circuit 50
The minimum operating voltage for operation is about 1.9V (= Vc
+ Vf), and the reference voltage generation circuit 50 operates normally when the output voltage Vout from the constant voltage circuit 10 is equal to or higher than this voltage.

On the other hand, in the constant voltage circuit 10, as the output transistor Q0, the collector is connected to the power supply line which receives power supply from the positive electrode side of the battery which is the DC power supply through the power supply terminal T (+), and the emitter is An NPN transistor is provided, which is connected to the voltage output line to the reference voltage generation circuit 50 and has the collector and base connected to the emitter and collector of the PNP transistor Q1, respectively.

Further, the constant voltage circuit 10 is provided with a constant current circuit 12 which is supplied with power from a battery and flows a constant current. The base of the PNP transistor Q1 is a constant current energizing circuit which constitutes the constant current circuit 12. Is connected to the bases of the PNP transistors Q11 and Q12. Therefore, the PNP transistor Q1 is connected to the P in the constant current circuit 12.
A current mirror circuit is configured with the NP transistors Q11 and Q12, and it functions as a bias means for supplying the same constant bias current as the constant current flowing in the constant current circuit 12 to the base of the output transistor Q0.

Further, the base of the output transistor Q0,
The output transistor Q is connected between the ground line connected to the negative electrode side of the battery via the ground terminal T (-).
Seven diodes D1 connected in series with the base of 0 as an anode and the ground line as a cathode
~ D7 are provided. Therefore, when the voltage applied from the power supply line to the base of the output transistor Q0 through the PNP transistor Q1 exceeds the forward voltage “7 · Vf” (about 4.9V) for seven diodes, the diodes D1 to D7 are generated. A current flows through the output transistor Q0, and the base voltage of the output transistor Q0 is limited to this voltage or less.

Therefore, the seven diodes D1 to D7 are
The base voltage of the output transistor Q0 functions as a clamp means for limiting the base voltage to a predetermined clamp voltage (here, about 4.9 V) or less, and the constant voltage circuit 10 to the reference voltage generation circuit 5 are used.
The output voltage Vout to 0 is controlled to a constant voltage (here, about 4.2V) obtained by subtracting the forward voltage Vf between the base and emitter of the output transistor Q0 from the clamp voltage even if the battery voltage VB becomes high. Will be.

Next, in the constant current circuit 12, PN
The emitters of the P transistors Q11 and Q12 are connected to the power supply line connected to the positive side of the battery, like the PNP transistor Q1. The collector of the PNP transistor Q11 is grounded to the ground line connected to the negative electrode side of the battery via the ground terminal T (-) via the NPN transistor Q14, and to the power supply line via the resistor R11. Connected, PN
The collector of the P transistor Q12 is grounded to the ground line via the NPN transistor Q15 and the resistor R13.

In addition, NPN transistors Q14 and Q15
Of the PNP transistors Q11 and Q1 respectively.
It is connected to 2 collectors. The emitter of the NPN transistor Q14 is directly grounded to the ground line, and the emitter of the NPN transistor Q15 is a resistor R.
It is grounded to the ground line via 13. Also,
The base of the NPN transistor Q14 is connected to the connection point between the emitter of the NPN transistor Q15 and the resistor R13, and the base of the NPN transistor Q15 is the collector of the NPN transistor Q14 and the PNP transistor Q11.
It is connected to the connection point with the collector of.

Furthermore, PNP transistors Q1 and Q1
The emitter of the PNP transistor Q13 is connected to the connection point where the bases of 1 and Q12 are connected to each other via the resistor R12. The collector of the PNP transistor Q13 is grounded to the ground line, and the base is connected to the connection point of the collectors of the PNP transistor Q12 and the NPN transistor Q15.

In the constant current circuit 12, after the power supply voltage (battery voltage VB) is turned on, the resistance R11 is used to
A base current is supplied to the NPN transistors Q14 and Q15, and each of the NPN transistors Q14 and Q15 is turned on, so that a current starts to flow in the PNP transistor Q1 and the PNP transistors Q11 and Q12 that form a current mirror circuit. The current is the resistance R
13 resistance value and NPN transistor Q14 base-
A constant current (Vf determined by the forward voltage Vf between the emitters)
/ R13).

When the constant current circuit 12 starts the operation in this way, the base current is supplied from the PNP transistor Q1 to the output transistor Q0, the output transistor Q0 is turned on, and the reference voltage generating circuit 50 is generated from its emitter. Voltage will be output to the side.

Therefore, the minimum operating voltage of the constant voltage circuit 10 is the voltage at which the constant current circuit 12 starts to operate, more specifically, the NPN transistors Q14, Q in the constant current circuit 12.
The voltage becomes “2 · Vf” necessary to drive the battery 15, and the constant voltage circuit 10 determines that the battery voltage VB is the voltage “2 · Vf”.
When it becomes (about 1.4V) or more, the operation is started.

[0019]

However, the output voltage Vout from the constant voltage circuit 10 is calculated from the battery voltage VB as follows:
The forward voltage Vf between the base and emitter of the output transistor Q0 and the emitter when the PNP transistor Q1 is on-
It becomes the voltage "VB-Vf-Vce" which is obtained by subtracting the collector-to-collector voltage Vce (about 0.1 V).

Therefore, the output voltage V from the constant voltage circuit 10
In order to operate the reference voltage generation circuit 50 by out, the battery voltage VB is obtained by adding the voltage drop “Vf + Vce” in the constant voltage circuit 10 to the minimum operation voltage (about 1.9V) of the reference voltage generation circuit 50. It is necessary to be higher than the voltage (about 2.7V). Therefore, even if the minimum operating voltage is reduced by configuring the reference voltage generating circuit 50 using the bandgap circuit 52, the battery voltage VB required to operate the reference voltage generating circuit 50 is the voltage in the constant voltage circuit 10. It will be higher by the amount of descent.

That is, in the past, in order to stably operate a control device such as an engine ECU used in an environment in which the power supply voltage easily fluctuates without being affected by the fluctuation of the power supply voltage, Reference voltage generation circuit 50 incorporated
Each functional circuit is configured to operate at a low voltage, and the functional circuit does not malfunction due to fluctuations in the power supply voltage. Each functional circuit outputs a diode forward voltage Vf. It is considered that power is supplied using a so-called simple constant voltage circuit that generates a constant voltage by clamping the base voltage of the transistor.
In such a simple constant voltage circuit, in order to control the output voltage Vout by the voltage clamp, the output transistor Q0 has N
Since the PN transistor is used, the output voltage Vout has a voltage value which is a voltage drop of the forward voltage Vf of the diode or more from the power supply voltage, and this voltage drop sufficiently reduces the minimum operating voltage of the control device. There was a problem that they could not do it.

The present invention has been made in view of these problems, and in a constant voltage circuit which outputs a constant DC voltage by clamping a control terminal of an output transistor to a predetermined voltage or less, when the power supply voltage drops, the output transistor The purpose is to enable a higher voltage to be output without being affected by the voltage drop that occurs.

[0023]

In the constant voltage circuit according to claim 1, which is made to achieve the above object, when the power supply voltage is equal to or lower than a predetermined voltage, an external load is supplied from the DC power supply through the power supply means. A current is directly supplied to the side, and the output voltage at that time can be made approximately the power supply voltage.

Therefore, according to the constant voltage circuit of the present invention, it becomes possible to output a high voltage substantially the same as the power supply voltage without being affected by the voltage drop that occurs in the output transistor when the power supply voltage drops. It is possible to sufficiently reduce the minimum operating voltage of the control device by incorporating it into the various control devices.

The operating voltage of the output transistor is the base-emitter forward voltage Vf (about 0.7V) of the NPN transistor if the output transistor is the same NPN transistor as shown in FIG. If the present invention is applied to the constant voltage circuit in which the output transistors are NPN transistors, the output voltage when the power supply voltage drops can be increased by this Vf.

The constant voltage circuit of the present invention (so-called simple constant voltage circuit) which outputs a constant voltage by limiting the control terminal voltage of the output transistor to a predetermined clamp voltage or less.
Can also be configured by using an n-channel MOSFET for the output transistor, connecting the drain of the MOSFET to a DC power supply and connecting the source to an external load. And
In this case, the operating voltage of the output transistor is MOSFE
Since the threshold voltage of T (about 1.0 V) is obtained, if the present invention is applied to a constant voltage circuit in which the output transistor is an n-channel MOSFET, the output voltage when the power supply voltage drops is Threshold voltage (about 1.0V)
You can raise it by a minute.

Here, the power feeding means prevents the output voltage from becoming lower than the power supply voltage by the operating voltage of the output transistor when the output transistor cannot output a predetermined constant voltage due to the operation of the clamp means. Therefore, it is desirable that the power supply means is configured as described in claim 2.

That is, if the upper limit of the power supply voltage at which the power supply means operates is set to a voltage value lower than the clamp voltage, for example, when the power supply voltage rises, a predetermined constant voltage is output from the output transistor as the power supply voltage rises. By the time it becomes possible, the power supply means will stop operating, and the output voltage will drop sharply by the operating voltage of the output transistor while it rises, similar to approximately the power supply voltage. However, if the power supply means is configured as described in claim 2, the output voltage can be stably increased until it reaches a predetermined constant voltage.

[0029]

[0030]

By the way, the power supply means prevents the output voltage from being lowered by supplying a current from the DC power supply to the external load through a path different from the output transistor when the power supply voltage is low when the clamp means does not operate. Since it is for the purpose of whether or not the current flows through the clamp means,
The clamp means operates when the power supply voltage is
To determine whether the voltage has reached the specified voltage
Depending on the result, the power feeding means may be operated.

Then, in this way, the power supply voltage becomes
The power supply means is operated until the clamp means operates and reaches a voltage value at which a predetermined constant current is output from the output transistor, and when the power supply voltage reaches the voltage value, the operation of the power supply means can be quickly stopped. become able to.

[0033]

On the other hand, the bias means for driving the output transistor receives power from a DC power source.
Constant current that supplies a constant current to the control terminal of the output transistor
It can be configured using a circuit.

Therefore, in the present invention (Claim 1), the bias means is configured by using a constant current circuit, and the power supply means is switched between power supply / stop to the external load based on the current flowing in the clamp means. By configuring the above,
The effect of is obtained .

Further, in the constant voltage circuit of the present invention (claim 1), the constant current circuit forming the bias means supplies a current to the current control transistor by the constant current source in response to an operation stop command inputted from the outside. Can be shut off. Therefore, when the constant voltage output to the external load is not necessary, the operation stop command is input to the constant current circuit, so that the current control transistor in the constant current circuit and the two constant current transistors forming the transistor and the current mirror circuit. It becomes possible to set all the currents flowing through the current transistors to zero and put the constant voltage circuit in a sleep state with zero power consumption.

As described above, by inputting the operation stop command to the constant current circuit, the operation mode of the constant voltage circuit is changed from the normal mode for outputting the constant voltage to the sleep mode for stopping the output of the constant voltage. When it is possible to switch to the power supply means,
If the switching transistor, the second constant current transistor, the current detection resistor, and the current detection transistor are simply included, the power supply transistor is temporarily turned on immediately after switching the operation mode, and the external power supply transistor is turned on. An overvoltage may be applied to the load.

However, in the present invention (claim 1) , a bias resistor is provided between the control terminal of the switching transistor constituting the power feeding means and the ground, and the resistance value of this bias resistor constitutes the bias means. When the ratio between the current ia flowing in the first constant current transistor and the current ib flowing in the second constant current transistor is “m” and the resistance value of the current detection resistor is “r”, the resistance value is “m × Since it is set to be smaller than “r”, it is possible to reliably prevent an overvoltage from being output to an external load via the power supply transistor at the time of switching to the sleep state.
Incidentally, this operation will be described in detail in an embodiment described later .

[0039]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.
To do. In addition, in the following description, the six prerequisites of the present invention are described.
The constant voltage circuit of 1 is given as a reference example, and then the present invention is applied.
The constant voltage circuit of the used embodiment will be described. [First Reference Example] FIG. 1 shows a constant voltage circuit of a first reference example which is a premise of the present invention .

The constant voltage circuit of this reference example is an engine ECU.
Etc. Various functional circuits incorporated in a semiconductor integrated circuit that constitutes an electronic control device for a vehicle and supplied with power from a battery (DC power supply) mounted on the vehicle to configure the control device (the reference voltage generation circuit described above). 50) to generate a constant DC voltage.

The constant voltage circuit of this reference example has the configuration shown in FIG.
Similar to the conventional constant voltage circuit 10 shown in FIG. 1, an output transistor Q0 formed of an NPN transistor, a PNP transistor Q1 for supplying a bias current to the base of the output transistor Q0, and a bias current for the PNP transistor Q1 to flow to the output transistor Q0 are constant currents. Is provided between the base of the output transistor Q0 and the ground line.
Of seven diodes D1 to D7 for limiting the base voltage of the device to a predetermined clamp voltage (about 4.9 V) or less.

Since each of these parts is constructed in exactly the same way as each part of the constant voltage circuit 10 shown in FIG. 8, the description of the connection state and the internal structure will be omitted. In this reference example , the PNP transistor Q
1 and the constant current circuit 12 function as bias means,
The seven diodes D1 to D7 function as clamp means.

[0043] Further, the constant voltage circuit of the present embodiment, the power supply circuit 14 which functions as a feeding hand <br/> stage is provided. The power supply circuit 14 serves as a power supply path from the power supply line to the output terminal Tout to which the power supply line of the external load is connected.
A second power feeding path different from the power feeding path passing through the output transistor Q0 is formed. The emitter is connected to the power supply line and the collector is connected to the output terminal Tout.
An NP transistor Q2 is provided.

The base of the PNP transistor Q2 is connected to the power supply line through the resistor R3 and the collector of the NPN transistor Q7 whose emitter is grounded to the ground line. Further, the power feeding circuit 14 is provided with a series circuit of resistors R1 and R2 provided between the power supply line and the ground line.
This resistor series circuit is for dividing the battery voltage VB, which is the power supply voltage, by two resistors R1 and R2.
(Voltage dividing means) , and the base of the PNP transistor Q4 is connected to the connection point of these resistors R1 and R2.

The emitter of the PNP transistor Q4 is connected to the collector of the PNP transistor Q3 and the emitter of the PNP transistor Q5 whose collector is grounded to the ground line.
The PNP transistor Q3 is an output transistor Q.
Similar to the 0 bias PNP transistor Q1, the emitter is connected to the power supply line and the base is connected to the bases of the PNP transistors Q11 and Q12. Therefore, the constant current controlled by the constant current circuit 12 is supplied from the collector of the PNP transistor Q3 to the emitters of the PNP transistors Q4 and Q5.

The base of the PNP transistor Q5 is connected to the connection point between the third diode D5 from the ground line and the fourth diode D4 of the seven diodes D1 to D7 for voltage clamping. There is. On the other hand, the collector of the PNP transistor Q4 is connected to the collector of the NPN transistor Q6 whose emitter is grounded to the ground line. The base and collector of the NPN transistor Q6 are connected to each other, and the base of the NPN transistor Q7 described above is connected to the base thereof.

In the power feeding circuit 14 thus constructed,
When the battery voltage VB becomes “2 · Vf” or higher, the constant current circuit 12 starts to operate, and the PNP transistors Q3 to P
When a constant current is supplied to the NP transistors Q4 and Q5, one of the PNP transistors Q4 and Q5 having a lower base voltage is turned on.

The base of the PNP transistor Q4 is a divided voltage obtained by dividing the battery voltage VB by the resistors R1 and R2, and the base of the PNP transistor Q5 is
Since it is limited to the reference voltage “3 · Vf” (about 2.1V) or less determined by the forward voltage Vf of the three diodes D5 to D7, the divided voltage divided by the resistors R1 and R2 is Below the reference voltage (in other words, the battery voltage V
If B is a predetermined voltage “3 · Vf · (R1 + R2) / R2” or less determined by this reference voltage and the voltage division value by the resistors R1 and R2), the PNP transistor Q4 is in the ON state, P
The NP transistor Q5 is turned off, otherwise the PNP transistor Q4 is turned off and the PNP transistor Q5 is turned on.

When the PNP transistor Q4 is turned on, the current supplied from the PNP transistor Q3 flows to the NPN transistor Q6 side via the PNP transistor Q4, and the NPN transistors Q6 and Q7 are both turned on. Further, when the NPN transistor Q7 is turned on in this way, a base current flows through the PNP transistor Q2 forming the second power feeding path, and PN
The P transistor Q2 is turned on, and a second power supply path is formed from the power supply line to the output terminal Tout (and thus the external load) through the PNP transistor Q2.

On the contrary, when the PNP transistor Q5 is turned on, the current supplied from the PNP transistor Q3 flows to the ground line side through the PNP transistor Q5, so that the NPN transistors Q6 and Q6.
7 and PNP transistor Q2 are both turned off,
The second power feeding path by the PNP transistor Q2 is not formed.

That is, in this reference example , the transistors Q3 to Q7 forming the power supply circuit 14 divide the battery voltage by the resistors R1 and R2 and the reference voltage "3.V".
f ”, which functions as a comparator (voltage determination means) for comparing the magnitude with“ f ”, and the battery voltage VB is a predetermined voltage“ 3 · Vf ·
When (R1 + R2) / R2 ”or less, the PNP transistor Q2 is turned on, and the power supply line outputs to the output terminal T.
It is designed to supply current to an external load via out.

Therefore, according to the constant voltage circuit of the present reference example ,
As shown by the solid line in FIG. 4A, the battery voltage VB is
If “2 · Vf” or more at which the constant current circuit 12 operates,
A voltage substantially equal to the battery voltage (specifically, a voltage obtained by subtracting the emitter-collector voltage Vce (about 0.1 V) of the PNP transistor Q2 from the battery voltage VB) is output from the output terminal Tout via the PNP transistor Q2. In that state, the battery voltage VB is a predetermined voltage “3 · V
f. (R1 + R2) / R2 ".

Therefore, according to the constant voltage circuit of the present reference example , as in the conventional circuit shown by the dotted line in FIG. 4A, the battery voltage VB becomes "2.Vf" or more and the constant current circuit 12
From the start of the operation until the base voltage of the output transistor is clamped by the seven diodes D1 to D7 and the output voltage Vout is controlled to a predetermined constant voltage, the output voltage Vout changes from the battery voltage VB. A voltage obtained by subtracting the operating voltage "Vf" of the output transistor Q0 (specifically,
The battery voltage VB is prevented from being limited to the operating voltage “Vf” of the output transistor Q0 and the emitter-collector voltage Vce of the PNP transistor Q1), and the output voltage Vout when the battery voltage drops is The forward voltage of the diode can be increased by “Vf” as compared with the conventional circuit.

Therefore, according to the constant voltage circuit of this reference example ,
For example, if it is used as a power supply circuit for various functional circuits such as the reference voltage generation circuit 50 shown in FIG. 8, the minimum operating voltage of the circuit can be lowered by "Vf". Further, the battery voltage VB is a predetermined voltage “3 · Vf · (R1 +
R2) / R2 "or more, PNP transistor Q2
Turns off, but in this state the output terminal Tout
Since the power is supplied to the (and by extension the external load) via the output transistor Q0, the output voltage Vout is controlled to a constant voltage as in the conventional constant voltage circuit, and the output terminal Tout is supplied to the output terminal Tout. The connected external load can operate stably without being affected by the fluctuation of the battery voltage VB.

The voltage "3Vf (R1 + R2) / R2" at which the PNP transistor Q2 is turned off is the voltage division value "R2 / (R1 + R2)" of the resistors R1 and R2 and the forward voltage of the diodes D5 to D7. 3 · Vf ”, and this voltage value is a divided voltage value of the battery voltage VB by the resistors R1 and R2 (in other words, the resistors R1 and R2).
4 (a) by appropriately adjusting the resistance value 2).
As shown in, it is desirable to set the base voltage of the output transistor Q0 to be a voltage value clamped by the diodes D1 to D7 (approximately clamp voltage “7 · Vf”) or more. This is because this voltage value “3 · Vf · (R1
+ R2) / R2 ”is set to a value smaller than the clamp voltage“ 7 · Vf ”, the output voltage Vout is increased while the output voltage Vout is increasing with the increase of the battery voltage VB.
However, it is considered that the output voltage sharply decreases to the conventional output voltage shown by the dotted line in FIG. 4A, and the external load connected to the output terminal Tout cannot be stably operated.

Second Reference Example Next, FIG. 2 shows a constant voltage circuit of the second reference example . Book
Constant voltage circuit of the reference example is basically the same as the constant voltage circuit of the first reference example, The difference constitutes the comparator as the voltage determination unit in the power supply circuit 14 of the first reference example An NPN transistor Q8 is provided instead of the PNP transistors Q4 and Q5 and the NPN transistor Q6. Therefore, in the following description, only this change will be described and the other description will be omitted.

As shown in FIG. 2, in the present reference example , NP is provided at both ends of the resistor R2 on the ground line side among the resistors R1 and R2 that divide the battery voltage in the power supply circuit 14, respectively.
When the base and emitter of the N transistor Q8 are connected and the voltage across the resistor R2 reaches the base-emitter forward voltage Vf of the NPN transistor Q8, the NPN
The transistor Q8 is turned on.
And, in the collector of this NPN transistor Q8,
The collector of the PNP transistor Q3 is connected and the base of the NPN transistor Q7 is connected.

Therefore, in the constant voltage circuit of this embodiment , the battery voltage VB is divided by the resistors R1 and R2 until the voltage across the resistor R2 reaches "Vf".
That is, the battery voltage VB is equal to the predetermined voltage “Vf · (R1 +
Until reaching R2) / R2 ", the NPN transistor Q8 is in the off state, and conversely, when the battery voltage VB reaches this voltage, the NPN transistor Q8 is in the on state.

When the NPN transistor Q8 is off, the constant current supplied from the PNP transistor Q3 flows into the base of the NPN transistor Q7 as a bias current. Therefore, the NPN transistors Q7, P
Both the NP transistors Q2 are turned on, and the output terminal Tout is passed from the power supply line through the PNP transistor Q2.
A second power feeding path reaching (and extending to the power line of the external load) is formed.

On the contrary, when the NPN transistor Q8 is in the ON state, the constant current supplied from the PNP transistor Q3 flows through the NPN transistor Q8 to the ground line side, so that the NPN transistors Q7, PN
Both the P transistors Q2 are turned off, and the second power feeding path by the PNP transistor Q2 is not formed.

Therefore, in the constant voltage circuit of this reference example , if the battery voltage VB is equal to or higher than "2Vf" at which the constant current circuit 12 operates, the battery voltage VB is output from the output terminal Tout via the PNP transistor Q2 to the battery A voltage substantially the same as the voltage (specifically, from the battery voltage VB to the emitter-collector voltage Vce (about 0.1 V) of the PNP transistor Q2)
Is output, and that state continues until the battery voltage VB reaches a predetermined voltage “Vf · (R1 + R2) / R2”, and the relationship between the battery voltage VB and the output voltage Vout is The same effect as that of the first reference example can be obtained in substantially the same manner as that shown in FIG.

In this reference example , the NPN transistor Q
8 functions as a voltage determination means. Further, in the case of the present reference example , the battery voltage VB is a predetermined voltage “Vf (R1 + R)” at the timing when the output voltage Vout sharply drops while rising due to the PNP transistor Q2 being turned off.
2) / R2 ”, but as shown in FIG. 4A, at this timing, in order to output the predetermined constant voltage“ clamp voltage −Vf ”from the output transistor Q0, the battery voltage It suffices to adjust the voltage division value “R2 / (R1 + R2)” of the resistors R1 and R2 for VB voltage division.

Third Reference Example Next, FIG. 3A shows a constant voltage circuit of the third reference example . The constant voltage circuit of this reference example has an output transistor Q composed of NPN transistors as in the above-mentioned reference examples.
0 and a constant current source 20 as a bias means for supplying a constant bias current to the base side of the output transistor Q0.
And six diodes D1 to D6 and a resistor R provided between the base of the output transistor Q0 and the ground line.
A series circuit with 20 and a power feeding circuit 14 as a power feeding means are provided.

Here, in the series circuit of the diode and the resistor, each of the six diodes D1 to D6 has the base side of the output transistor Q0 as the anode and the ground line side as the cathode, and is closer to the base side of the output transistor Q0. The resistors R20 are connected in order, and are arranged between the cathode of the diode D6 at the final stage and the ground line. The base of the NPN transistor Q8 in the power feeding circuit 14 whose emitter is grounded to the ground line is connected to the connection point between the cathode of the diode D6 and the resistor R20.

On the other hand, in the power supply circuit 14, as in each of the above-described reference examples , the PNP transistor Q2 having the emitter connected to the power supply line and the collector connected to the output terminal Tout, and the base of the PNP transistor Q2 and the power supply line. A resistor R3 to be connected and an NPN transistor Q7 having a collector connected to the base of the PNP transistor Q2 and an emitter grounded to the ground line are provided. The base of the NPN transistor Q7 is connected to the power supply line via the constant current source 21, and the collector of the NPN transistor Q8 is connected.

Further, the constant current sources 20 and 21 are for respectively pouring a constant current from the power supply line to the base side of the output transistor Q0 and the NPN transistor Q7, and more specifically, in the above-mentioned reference examples . The PNP transistors Q1 and Q3 are configured in the same manner as the constant current supply transistor, and a constant current circuit that controls the current flowing through the transistor to a constant current.

In the constant voltage circuit of this embodiment having such a configuration, as shown in FIG. 4B, the constant current source 2
0, 21 until the operation starts, in other words, until the battery voltage VB reaches a voltage value (generally “2 · Vf”) at which the constant current sources 20, 21 can operate, the output transistor Q0. When the constant current sources 20 and 21 start operating, both the output transistor Q0 and the NPN transistor Q7 are turned on, but when the NPN transistor Q7 is turned on, the PNP transistor Q2 is also turned on. Since it is turned on, the output transistor Q0 is turned off, and the output voltage Vout (specifically from the battery voltage VB to the PNP transistor is transferred from the output terminal Tout to the external load via the PNP transistor Q2). Q2 emitter-collector voltage Vce (about 0.1V) is output) It will be.

In this state, the base voltage of the output transistor Q0 rises as the battery voltage VB rises,
This voltage is the forward voltage “6 · V for 6 diodes”.
When f "(about 4.2V) is reached, the diodes D1 to D6 are
A current begins to flow in the series circuit composed of the resistor R20 and the resistor R20.
Since the base-emitter of the NPN transistor Q8 is connected in parallel to the resistor R20, the resistor R20 increases as the base voltage of the output transistor Q0 increases.
Of the NPN transistor Q8 reaches the base-emitter forward voltage Vf of the NPN transistor Q8 (in other words, the base voltage of the output transistor Q0 is a predetermined voltage “7 · Vf”).
(When reaching about 4.9V), NPN transistor Q8
Turns on. Further, when the NPN transistor Q8 is turned on, the constant current supplied from the constant current source 21 flows to the ground line via the NPN transistor Q8, so that the NPN transistor Q7 is turned off, and in conjunction with this, the PNP is linked. The transistor Q2 is also turned off.

Therefore, as the battery voltage VB rises, the base voltage of the output transistor Q0 is changed to the diodes D1 to D.
6 and the forward voltage between the base and emitter of the NPN transistor Q8, which is a clamp voltage "7.V"
After reaching "f", the PNP transistor Q2 is turned off, and the output terminal Tout is applied to the external load via the output transistor Q0 from the clamp voltage "7.Vf" to the base-emitter of the output transistor Q0. A constant voltage "clamp voltage-Vf" obtained by subtracting the forward voltage Vf is output.

Therefore, also in the constant voltage circuit of this reference example , the output voltage Vout when the battery voltage drops is increased by the forward voltage "Vf" of the diode as compared with the conventional circuit, as in each of the above reference examples. When used as a power supply circuit for various functional circuits such as the reference voltage generation circuit 50 shown in FIG. 8, the minimum operating voltage of the circuit can be set to “V
It is possible to lower by "f".

Further, in the constant voltage circuit of this reference example ,
From the current flowing through the diodes D1 to D6 as the clamping means for clamping the base voltage of the output transistor Q0, it is determined whether or not the battery voltage VB is equal to or higher than the voltage at which the base voltage of the output transistor Q0 can be clamped to the predetermined voltage "7Vf". Until the base voltage of the output transistor Q0 is judged and the base voltage of the output transistor Q0 is clamped, power is supplied to the external load via the PNP transistor Q2.
Since the power is supplied to the external load via the
2 The circuit configuration can be simplified as compared with the case where the battery voltage VB is detected by resistance voltage division as in the reference example .

In this reference example , the resistor R20 and the NPN
The transistor Q8 corresponds to the current detecting means, of which the resistor R20 is the current detecting resistor and the NPN transistor Q8 is
It functions as a current detection transistor. The resistor R20 and the NPN transistor Q8 also function as a clamp means together with the diodes D1 to D6.

Fourth Reference Example Next, FIG. 3B shows a constant voltage circuit of the fourth reference example . Constant voltage circuit of the present embodiment is basically the same as the constant voltage circuit of the third reference example <br/>, differs, in the constant voltage circuit of the third reference example, the resistor R20 and an NPN transistor The six diodes D1 to D6 that form the clamping means together with Q8 are changed to a Zener diode ZD1, and the breakdown voltage of the Zener diode ZD1 is used to limit the base voltage of the output transistor to a predetermined clamp voltage or less. This is the point I chose to do.

Therefore, in the constant voltage circuit of this reference example , as shown in FIG. 3B, the cathode of the Zener diode ZD1 is connected to the base of the output transistor Q0,
The anode of the Zener diode ZD1 is connected to the connection point between the resistor R20 and the base of the NPN transistor Q8.

Therefore, in the constant voltage circuit of this reference example , the output transistor Q increases as the battery voltage VB increases.
When the base voltage of 0 rises and this voltage reaches the breakdown voltage VZD of the Zener diode ZD1, current starts to flow in the series circuit composed of the Zener diode ZD1 and the resistor R20, and further, the voltage across the resistor R20 becomes NPN. When the base-emitter forward voltage Vf of the transistor Q8 is reached, the NPN transistor Q8 is turned on and the base voltage of the output transistor Q0 is the voltage "V" at that time.
It will be clamped to "ZD + Vf".

[0076] Thus, the constant voltage circuit of the present embodiment, although that the clamp voltage is determined by the breakdown voltage of the Zener diode ZD1 is different, otherwise, all third ginseng
Because it is configured in the same manner as Reference Example, the change characteristics with respect to the battery voltage VB of the output voltage Vout becomes the same characteristics as the third reference example shown in FIG. 4 (b), according to the constant voltage circuit of the present embodiment Thus, the same effect as that of the third reference example can be obtained.

In this reference example , in the constant voltage circuit of the third reference example , the Zener diode Z is used as the clamping means.
The case of using D1 has been described, but it is shown in FIG.
In the constant voltage circuit of the first reference example , a Zener diode may be used instead of the seven diodes D1 to D7 forming the clamp means. Further, in the constant voltage circuit of the second reference example shown in FIG. 2, among the seven diodes D1 to D7 forming the clamp means, the diodes D5 to D for generating the reference voltage for battery voltage VB determination.
7 and / or the other diodes D1 to D4, or both, may be used as a Zener diode.

[ Fifth Reference Example] Next, FIG. 5 shows a constant voltage circuit of a fifth reference example . Book
Constant voltage circuit of the reference example is basically the same as the constant voltage circuit of the fourth reference example, different from, in the constant voltage circuit of the fourth reference example, the base of the output transistor Q0 and NPN transistors Q7 The point is that the constant current sources 20 and 21 respectively provided between the power supply line and the power supply line are changed to resistors R22 and R23.

As described above, the constant current sources 20 and 21 are connected to the resistor R.
22 and R23, the output transistor Q0
A bias current is supplied to the bases of the NPN transistor Q7 and the NPN transistor Q7 via the resistors R22 and R23, respectively. The resistors R22 and R23 are provided between the bases of the transistors Q0 and Q7 and the power supply line. Since a bias current flows when a potential difference occurs, a bias current is supplied to each of these transistors Q0 and Q7 if the battery voltage VB is equal to or higher than the base-emitter forward voltage Vf.

Therefore, in the constant voltage circuit of the present reference example , as shown in FIG. 5B, when the battery voltage VB reaches approximately "Vf" as the battery voltage VB rises,
The output voltage Vout that is substantially the same as the battery voltage VB is output from the output terminal Tout via the PNP transistor Q2. According to this reference example , a voltage is output from the output terminal Tout as compared with the above reference examples. The lowest possible battery voltage VB can be lowered.

In this reference example , the resistor R22 functions as a bias means. And in this reference example , the 4th reference
In the constant voltage circuit of the example, the case where the resistors R22 and R23 are used instead of the constant current sources 21 and 22 has been described, but in the constant voltage circuit of the third reference example , the constant current source 21 and
Even if resistors R22 and R23 are used instead of 22, the same effect can be obtained.

Further, in the constant voltage circuits of the first and second reference examples , the resistors R22 and R23 may be used instead of the PNP transistors Q1 and Q3. And
In this case, since it is not necessary to provide the constant current circuit 12, the configuration of the constant voltage circuit can be simplified.

Sixth Reference Example Next, FIG. 6A shows a constant voltage circuit of the sixth reference example . The constant voltage circuit of this reference example is the fourth voltage circuit shown in FIG.
In the constant voltage circuit of the reference example , when it is not necessary to supply a constant voltage to the external load, such as when the external load stops operating, the constant voltage circuit is put into a so-called sleep state to reduce the power consumption of the constant voltage circuit to zero. It was made possible.

That is, as shown in FIG. 6A, the constant voltage circuit of the present reference example has the constant current sources 20 and 21 in the constant voltage circuit shown in FIG. 3B, respectively. First reference example or second
The same PNP transistors Q1 and Q3 as in the reference example are used, and the current flowing through each of the PNP transistors Q1 and Q3 is controlled by the constant current circuit 30 to be a constant current.

Further, in the constant current circuit 30, the emitter is connected to the power supply line, the base is connected to the bases of the PNP transistors Q1 and Q3, and the PNP transistor Q10 and the base-collector are connected to each other.
A constant current source 32 is connected to the collector of the transistor Q10 via a switching circuit (hereinafter simply referred to as SW) 34 and supplies a constant current from the collector of the PNP transistor Q10 to the ground line side when the SW34 is turned on.

Further, the SW 34 is composed of, for example, a switching transistor and the like, and the control terminal Tin has a Hi level.
When the gh level control signal Vin is input, the constant current source 32 is operated by forming a current path from the collector of the PNP transistor Q10 to the constant current source 32,
When a constant current is passed through the PNP transistor Q10 and the low-level control signal Vin is input to the control terminal Tin, PN
By interrupting the current path from the collector of the P transistor Q10 to the constant current source 32, the operation of the constant current source 32 is stopped, and the current flowing through the PNP transistor Q10 is interrupted.

Therefore, in the constant voltage circuit of the sixth reference example shown in FIG. 6A, if the high-level control signal Vin is input to the control terminal Tin, the constant current circuit 12 and, by extension, P.
Constant current flows through the NP transistors Q1, Q3, fourth ginseng
Works as a constant voltage circuit of Reference Example, the external load from the output terminal Tout, the output transistor Q0 or via the PNP transistor Q2, so that the power supply is made.

Further, if a low level control signal Vin is input to the control terminal Tin, the constant current circuit 12, and eventually the PNP.
The current flowing through the transistors Q1 and Q3 becomes zero, the output transistor Q0 for supplying power to the external load and the PNP transistor Q2 are both turned off, and the constant voltage circuit stops the power supply from the output terminal Tout to the external load. Go to sleep. In this sleep state, current does not flow in all the elements constituting the constant voltage circuit, so that the power consumption in the constant voltage circuit can be reduced to zero.

[Embodiment] As described above , according to the constant voltage circuit of the sixth reference example shown in FIG. 6A, when the power supply to the external load is unnecessary,
It is possible to enter a sleep state with zero power consumption, but with this constant voltage circuit, when the operation mode is switched from the normal mode for supplying power to the external load to the sleep mode for stopping power supply, The output voltage Vout may temporarily jump to the battery voltage VB.

That is, as shown in FIG. 7A, in the normal state in which the output voltage Vout is controlled to the constant voltage "clamp voltage-Vf", the control signal Vin changes from the high level to the low level.
When switched to level, PNP transistor Q1,
The currents I1 and I3 flowing through Q3 decrease with a substantially constant slope and finally become zero.

When each of the currents I1 and I3 is decreasing in this way, the current I1 changes to the NPN transistor Q.
When the voltage drops below the threshold value at which 8 can be turned on, the NPN transistor Q8 is turned off. In addition, NPN transistor Q8
Since the resistor R20 is connected between the base and emitter of the transistor, the threshold value of the current I1 at which the NPN transistor Q8 can be turned on is a value obtained by dividing the base-emitter forward voltage Vf of the transistor by the resistance value of the resistor R20. (Vf / R2
0).

Further, in this way, the NPN transistor Q8
Is turned off, the current I3 flows into the base of the NPN transistor Q7, so that the NPN transistor Q7 is turned on this time, and thereafter, when the current I3 drops below the threshold at which the NPN transistor Q7 can be turned on. , NPN transistor Q7 is turned off.

As a result, the output voltage Vout sharply rises from the constant voltage "clamp voltage-Vf" to the battery voltage VB when the NPN transistor Q8 turns off and the NPN transistor Q7 turns on, and then the NPN transistor Q7. When it turns off, it drops to 0V.

When the output voltage Vout jumps to the battery voltage VB even temporarily, the device may be destroyed by an overvoltage when a low withstand voltage device is connected to the output terminal Tout. is there. Further, it is possible that the circuit connected to the output terminal Tout malfunctions due to the noise caused by the rapid increase in the voltage.

Therefore, in order to prevent such a problem,
In the constant voltage circuit of the embodiment to which the present invention is applied, FIG.
As shown in , in addition to the constant voltage circuit of the sixth reference example,
A resistor R30 is also provided between the base and emitter of the NPN transistor Q7 in the power feeding circuit 14 so that the current I3 flows through this resistor R30 when the NPN transistor Q8 is turned off. voltage across (I3 × R30) is, the base needed to turn on the NPN transistor Q7 - way lower than emitter forward voltage Vf, sets the resistance value of the resistor R30
It

Specifically, the resistance value of the resistor R30 is "I
It may be set so that the relationship of 1 × R20> I3 × R30 ”is established. That is, each PNP transistor Q1, Q
The ratio of the currents flowing in 3 is "I1 / I3" (corresponding to "ia / ib" in claim 9, the so-called PNP transistor Q).
1 is the collector ratio of Q3) is "m", and the resistor R2
When the resistance value of 0 is “r”, the resistance value of the resistor R30 may be set to a value smaller than “m × r”.

That is, in this way, as shown in FIG. 7B, the threshold value (Vf / R30) at which the NPN transistor Q7 can be turned on and the threshold value (Vf / R20) at which the NPN transistor Q8 can be turned on. Even if the currents I1 and I3 decrease and the NPN transistor Q8 turns off, the NPN transistor Q7 is held in the off state to prevent the output voltage Vout from jumping up to the battery voltage VB. You will be able to do it.

The constant voltage circuit of the sixth reference example and this embodiment
Then, based on the constant voltage circuit of the fourth reference example , it is possible to switch from the normal operating state to the sleep state of zero power consumption . However, the constant voltage of the first reference example and the second reference example is changed. Even if it is a circuit, if a switching circuit for stopping its operation is provided in the constant current circuit 12, a constant voltage circuit capable of switching to a sleep state can be realized as in the constant voltage circuit of this embodiment.

Further, since the third reference example and the fourth reference example are different only in the configuration of the clamp means, the constant voltage circuit of the third reference example is also configured in the same manner as this embodiment , Can be changed to a constant voltage circuit that can be switched to sleep mode
It

Here, the sixth reference example and the example are the same as the present invention.
The specific configuration and operation of the
Then, the correspondence relationship between the circuit elements shown in FIGS. 6A and 6B and the constituent elements of the present invention will be clarified. First, the PNP transistor Q10 in the constant current circuit 30 corresponds to the current control transistor of the present invention, and the constant current source 32 is the present invention.
The low-level control signal Vin input to the control terminal Tin for turning off the SW 34 in the constant current circuit 30 corresponds to the operation stop command of the present invention . The PNP transistor Q1 that forms a current mirror circuit with the PNP transistor Q10 corresponds to the first constant current transistor of the present invention, and the PNP transistor Q3 that also forms a current mirror circuit corresponds to the second constant current transistor of the present invention . Equivalent to.

Of the other transistors forming the power feeding circuit 14 as the power feeding means, the PNP transistor Q2 is used.
Corresponds to the transistor for feeding of the invention, NPN transistor Q7 is equivalent to switching transistor of the present invention, the resistor R20 as a current detecting resistor is the base - NPN transistor Q8 connected between the emitter, the invention
Corresponds to the current detection transistor of. And, in particular,
The resistor R30 provided only in the constant voltage circuit shown in FIG. 6B, which is an embodiment of the present invention , corresponds to the bias resistor of the present invention .

The above six reference examples and the premise of the present invention
Although the embodiments have been described, the present invention is not limited to the above embodiments, and various modes can be adopted. For example, in the above-described reference examples and embodiments , the constant voltage circuit using all bipolar transistors as transistors has been described as an example. However, for example, some or all of the transistors may be configured by MOSFETs.

Specifically, for example, the output transistor Q
Even if the constant voltage circuit has an n-channel MOSFET in which the drain is connected to the power supply line and the source is connected to the output terminal Tout, instead of the NPN transistor, the present invention is applied to the above-mentioned embodiment. The same effect as can be obtained. In this case, the n-channel MOSF
The threshold voltage (gate-source voltage) for operating ET is about 1.0 V, and the output transistor Q
When power is supplied to an external load via 0, a voltage drop of at least this threshold voltage occurs, so that the present invention can be applied to a constant voltage circuit using an n-channel MOSFET for the output transistor Q0. It is possible to increase the output voltage by about 1.0 V when the power supply voltage drops.

For example, instead of the PNP transistor Q2, the source is connected to the power supply line and the drain is connected to the output terminal Tout as an output element for supplying a current to an external load through a path different from the output transistor Q0. p-channel MOSFET or n-channel MOSFE
It is also possible to use T. However, as an output element, n
In the case of using the channel MOSFET, in order to drive it, it is necessary to apply a voltage higher than the power supply voltage by a threshold voltage, so that it is necessary to separately provide a charge pump for boosting the power supply voltage.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a configuration of a constant voltage circuit of a first reference example .

FIG. 2 is an electric circuit diagram showing a configuration of a constant voltage circuit of a second reference example .

FIG. 3 is an electric circuit diagram showing a configuration of constant voltage circuits of a third reference example and a fourth reference example .

FIG. 4 is an explanatory diagram showing change characteristics of an output voltage from the constant voltage circuit according to the first reference example to the fourth reference example .

FIG. 5 is an explanatory diagram showing a configuration of a constant voltage circuit of a fifth reference example and a change characteristic of its output voltage.

FIG. 6 shows a sixth reference example and an example to which the present invention is applied.
It is an electric circuit diagram showing the composition of a constant voltage circuit .

FIG. 7 is an explanatory diagram showing change characteristics of the output voltage at the time of transition to the sleep state in each circuit shown in FIG.

FIG. 8 is an electric circuit diagram showing a configuration of a conventional constant voltage circuit and a reference voltage generation circuit that operates by receiving power supply from the constant voltage circuit.

[Explanation of symbols]

10 ... Constant voltage circuit, 12, 30 ... Constant current circuit, 14 ... Feeding circuit, 20, 21, 32 ... Constant current source, 34 ... SW (switching circuit), D1-D7 ... Diode, Q0 ... Output transistor, Q1, Q2, Q3, Q4, Q5, Q1
0, Q11, Q12, Q13 ... PNP transistor, Q
6, Q7, Q8, Q14, Q15 ... NPN transistor, R1, R2, R3, R11, R12, R13, R2
0, R22, R23, R30 ... Resistance, ZD1 ... Zener diode.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-344509 (JP, A) JP-A-3-252806 (JP, A) JP-A-4-212782 (JP, A) Jitsukaihei 4- 58720 (JP, U) (58) Fields surveyed (Int.Cl. ⁷ , DB name) G05F 1 / 445,1 / 56 G05F 1 / 613,1 / 618

Claims (2)

(57) [Claims] 1. An output transistor provided on a power supply path from a DC power supply to an external load, bias means for receiving a power supply from the DC power supply and supplying a bias current to a control terminal of the output transistor, the output. It is provided between the control terminal of the transistor and the ground, and when the control terminal voltage of the output transistor exceeds a predetermined clamp voltage, a current is passed from the control terminal to the ground side to reduce the control terminal voltage to a predetermined clamp voltage or less. By limiting, the clamp means for controlling the output voltage from the output transistor to the external load to a constant voltage, and when the power supply voltage supplied from the DC power supply is equal to or lower than a predetermined voltage, the path is different from that of the output transistor. , a constant voltage circuit and a power supply means for supplying a current to an external load from the DC power source, said bar Ass unit includes a current control transistor, the power supply from the DC power supply
Receiving a constant current through the current control transistor
It has a flow source and is operated by an operation stop command input from the outside.
The constant current source supplies to the current control transistor.
Constant current circuit capable of interrupting current, a current control transistor of the constant current circuit, and a current mirror
-Constitutes a circuit and flows to the current control transistor
A constant current proportional to the current is applied to the control terminal of the output transistor.
It includes a first constant current transistor for supplying to the child, wherein the power supply means is provided on the second feed path to the external load from the DC power supply
And a control terminal connected to the control terminal of the power supply transistor.
A switching tiger that switches whether or not to apply a bias current to the child
Transistor, the current control transistor, and the first constant current transistor.
Comprising a current mirror circuit with a transistor to control the current
Flowed through the transistor and the first constant current transistor
A constant current proportional to the current is controlled by the switching transistor.
The second constant current transistor supplied to the control terminal side and the current path from the clamp means to the ground are provided.
Current detection resistor and control at the connection point of the current detection resistor and the clamp means
The terminal is connected, and the voltage across the current detection resistor is
When the operating voltage is reached, it is turned on and the second constant
From the current transistor to the control end of the switching transistor
The constant current supplied to the child is sent to the ground side for switching
Between the current detection transistor that turns off the transistor and the control terminal of the switching transistor and the ground
A current i that is provided and flows through the first constant current transistor
a and a current ib flowing through the second constant current transistor
The ratio (ia / ib) is set to “m”, and the current detection resistor
When the resistance value is “r”, the resistance value is more than “m × r”
A constant voltage circuit comprising: a bias resistor set to be small . 2. The constant current supply device according to claim 1, wherein the power supply unit supplies a current from the DC power supply to an external load when the power supply voltage is equal to or lower than a predetermined voltage higher than the clamp voltage. Voltage circuit.