JP2003223231A - Constant-voltage power source circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a constant-voltage power source circuit capable of using an SMD transistor, even when a lead type transistor with a large loss is required. <P>SOLUTION: In the constant-voltage power source circuit 1 provided with first and second branch paths 3a and 3b provided to a power supply path 3 between a power source B and a load in parallel to each other for temporarily branching a load current from the power source B, first and second constant- voltage power source circuits 5a and 5b provided respectively to the first and second branch paths 3a and 3b for providing transistors Tr1 and Tr2 to the branching paths 3a and 3b, and a resistance R3 provided at the post stage of the first constant-voltage power source circuit 5a on the first branching path 3a, an output voltage V<SB>o</SB>1 of the first constant-voltage power source circuit 5a is set higher than an output voltage V<SB>o</SB>2 of the second constant-voltage power source circuit 5b. <P>COPYRIGHT: (C)2003,JPO

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 circuit having a transistor interposed in a power supply path, and more particularly to a technique for reducing loss (heat generation) due to a load current per transistor.

[0002]

2. Description of the Related Art In the field of in-vehicle equipment, a constant voltage power supply circuit of this type is used as a means for obtaining a constant voltage (for example, 9 [V]) for a circuit from a power supply voltage of 10 to 16 [V]. Has been.

A conventional constant voltage power supply circuit 100 includes, for example, as shown in FIG. 2, a transistor Tr provided between a collector and an emitter in a power supply path 103 between a power supply B and a load.
A resistor R connected between the collector and the base of the transistor Tr, and a Zener diode D connected in the reverse direction between the ground point and the intermediate point between the resistor R and the base of the transistor Tr.
_{And Z.}

In the figure, V _B is the power supply voltage, V _D and V _Z are the voltage across the zener diode D _Z and the zener voltage, and V ₀
(= V _D -V _BE) and I ₀ is the output voltage and output current of the circuit 100, V _BE and _{V CE (= V B -V 0} ) , the transistor T
The base-emitter voltage and the collector-emitter voltage of r are shown.

In this circuit 100, the power supply voltage V _B is applied across the resistor R and the zener diode D _Z at a voltage ratio of V _B -V _Z to V _Z (that is, V _D = V _Z ), and the zener diode D The voltage V _D across _Z is the base of the transistor Tr.
By being output from the emitter via between the emitters, V
A constant output voltage V _{0 of 0} = V _Z −V _BE is output to the load. In addition, the transistor Tr from the power source B via the resistor R
By inputting the base current to the base of, the output current I ₀ can be output from the power supply B to the load via the collector and the emitter of the transistor Tr.

The magnitude of the output current I ₀ (that is, the current flowing through the load) is determined by Ohm's law from the resistance of the load itself and the output voltage V ₀ (that is, the voltage applied to the load).
For example, when V ₀ = 9 [V] and the load is a valve, an inverter, or the like, I ₀ is, for example, about I ₀ = 0.2 [A]. In this case, in the range of V _B = 10 to 16 [V], the transistor Tr
The maximum loss P is P = I ₀ · V _CE = 1.4 [W].

[0007]

In recent years, in the field of in-vehicle equipment, SMD (Surface Mounted Devices) of electronic parts has been developed.
The constant voltage power supply circuit 100, as well as other components,
Transistor Tr and Zener diode D used in
It is also considered to make _Z into SMD.

Normally, the allowable loss of the SMD transistor is as small as 1 [W] or less. Therefore, as described above, in a usage environment in which the loss P of the transistor Tr exceeds 1 [W], the allowable loss of the transistor Tr becomes insufficient when the transistor Tr is made into an SMD. There is no choice but to use the transistor T
There is a problem that it is difficult to convert r into SMD.

Therefore, an object of the present invention is to provide an SMD even when a lead-type transistor with a large loss is required.
The purpose of the present invention is to provide a constant voltage power supply circuit that can use a transistor that has been made into a computer.

[0010]

In order to solve the above-mentioned problems, first and second devices which are interposed in parallel with each other on a power feeding path from a power source to a load and temporarily divide a load current from the power source are provided. A shunt channel and first and second shunt channels respectively provided in the first and second shunt channels and having a transistor interposed in the shunt channel.
And a constant voltage power supply circuit.

The invention according to claim 2 is further the above-mentioned first
A resistor is provided at a stage subsequent to the first constant voltage power supply circuit on the shunt flow path, and the output voltage of the first constant voltage power supply circuit is set higher than the output voltage of the second constant voltage power supply circuit. Is.

According to a third aspect of the present invention, in the first and second constant voltage power supply circuits, the transistor in which the main electrodes are interposed between the first and second branch channels, and the transistor, respectively. A resistor connected between the upstream main electrode and the control electrode of
A zener diode reversely connected is provided between an intermediate point between the resistor and the control electrode of the transistor and a ground point.

[0013]

1 is a block diagram of a constant voltage power supply circuit according to an embodiment of the present invention.

Constant voltage power supply circuit 1 according to this embodiment
As shown in FIG. 1, the first and second branch flow paths 3a and 3b are provided in parallel on the power supply path 3 from the power source B to the load, and temporarily divide the load current from the power source B, Each 1st
The second branch channels 3a and 3b are provided with the branch channels 3a and 3b.
3b in which transistors Tr1 and Tr2 are interposed
Second constant voltage power supply circuits 5a and 5b, and first branch flow path 3a
And a resistor R3 provided in the subsequent stage of the first constant voltage power supply circuit 5a.

In this circuit 1, the output current I ₀ (that is, load current) of the circuit 1 is the first and second constant voltage power supply circuits 5a and 5a.
sum of output currents I ₀ 1 and I ₀ 2 of b (that is, I ₀ = I ₀ 1 + I
₀ 2), and its output voltage V ₀ becomes equal to the output voltage V ₀ 2 of the second constant voltage power supply circuit 5b (that is, V ₀ = V
₀ 2).

First and second constant voltage power supply circuits 5a and 5b
Are configured in the same circuit configuration as the conventional circuit 100, for example. That is, the first (second) constant voltage power supply circuit 5a (5
b) shows a transistor Tr1 (T1) in which the collector-emitter is interposed in the first (second) shunt channel 3a (3b).
r2) and the collector of the transistor Tr1 (Tr2)
A resistor R1 (R2) connected between the bases and a resistor R1
(R2) and the base of the transistor Tr1 (Tr2) and a Zener diode D _Z 1 (D _Z 2) connected in the reverse direction between the ground point and the ground point.

[0017] However, the output voltage V ₀ 1 of the first constant-voltage power supply circuit 5a, the output voltage V ₀ 2 of the second voltage regulator 5b
Set higher than. That is, Zener diode D _Z 1
Zener voltage V _Z 1 is set higher than Zener voltage V _Z 2 of Zener diode D _Z 2.

As a result, V is applied across the resistor R3.₀1-
V₀The voltage of 2 is the forward direction (the one where the voltage drops toward the downstream)
Therefore, according to Ohm's law, resistance R3 is fixed.
Definitely I ₀1 = (V₀1-V₀2) / R3 current goes downstream
It flows toward. As a result, in the first branch flow path 3a, there is no electric current.
Load current from source B (ie output current I₀) Out of₀1
= (V₀1-V₀2) / R3 current is I₀Against the fluctuation of
The flow is fixedly divided, and the remaining I₀
2 = I₀-I₀The current of 1 is I₀Variably according to
Shed

[0019] Here, the shunt ratio between I ₀ 1 and I ₀ 2, for example, when the value of V _B is the upper limit value of the variation of V _B, the loss of transistors _{Tr1, Tr2 P1 (= I 0} 1 · V _CE 1), P
2 (= I ₀ 2 · V _CE 2) is preferably set so as to be evenly distributed among them (that is, P1 = P2).
With this setting, both the losses P1 and P2 of the transistors Tr1 and Tr2 can be limited to the allowable loss or less with a margin for the fluctuation of V _B.

In FIG. 1, V _B = 10 to 16 [V], V ₀
2 (= V ₀ ) = 9 [V] (that is, V _Z 2 = 9.7 [V]), I ₀
= 0.2 [A], I ₀ 1 = I ₀ 2 = 0.1 [A]
So that, for example, V ₀ 1 = 10 [V] (that is, V _Z 1 = 1
0.7 [V]) and R3 = 10Ω. With this numerical setting, when V _B = 16 [V] (upper limit value), the losses P1 and P2 of the transistors Tr1 and Tr2 are P1 =
0.6 [W], P2 = 0.7 [W], and the particles are distributed approximately evenly, and both are kept at 1 [W] or less (allowable loss or less) with a margin.

Next, the numerical value setting of FIG. 1 (V _B = 10 to 16)
[V], V _Z 1 = 10.7 [V], V _Z 2 = 9.7 [V], V _CE
1 = 0.7 [V], V _CE 2 = 0.7 [V], R3 = 10Ω,
The operation of the constant voltage power supply circuit 1 will be described based on I ₀ = 0.2 [A]). In the following description, for convenience, the voltage drop across the resistors R1 and R2 due to the base current is ignored.

In the range of 10.7 [V] ≦ V _B ≦ 16 [V], the voltage V _D across the Zener diodes D _Z 1 and D _Z 2 is
Since both 1 and V _D 2 become the zener voltages V _Z 1 and V _Z 2, respectively, V ₀ from the first and second constant voltage power supply circuits 5a and 5b, respectively.
1 (= V _Z 1-V _BC 1) = 10 [V], V ₀ 2 (= V _Z 2−
An output voltage of V _BC 2) = 9 [V] is output.

As a result, the constant voltage power supply circuit 1 outputs V ₀
An output voltage of (= V ₀₂ ) = 9 [V] is output to the load.
Further, a constant voltage of V _R (= V ₀ 1-V ₀ 2) = 1 [V] is applied to the resistor R3, and according to Ohm's law, a current I ₀ that flows in the resistor R3 (that is, the first branch flow path 3a). 1 is I ₀ 1 (= V _R
/R3)=0.1 [A] is fixed. As a result, of the load current from the power supply B (0.2 [A] as in the conventional circuit 100), I ₀ 1 = 0.1 in the first branch flow path 3a.
The current of [A] is shunted and the transistor Tr1 and the resistor R
3, the remaining current I ₀ 2 (= I ₀ −I ₀ 1) = 0.1 [A] is shunted to the second branch flow path 3b and output from the transistor Tr2. Join me, I
An output current of ₀ (= I ₀ 1 + I ₀ 2) = 0.2 [A] is output to the load.

In this V _B range, each transistor Tr
A constant current of I ₀ 1 = I ₀ 2 = 0.1 [A] flows through 1 and Tr 2, respectively, and V _CE 1 = V _B −10 [V], V _CE 2 = V _B −9
A base-emitter voltage that varies depending on V _{B of} [V] is applied. Therefore, in each of the transistors Tr1 and Tr2, P1 = 0.1 × (V _B −10) [W] and P2 = 0.1, respectively.
A loss that increases / decreases in accordance with the increase / decrease in V _B of × (V _B −9) [W] occurs, but in the range of V _B , P1 ≦ 0.6 [W],
P2 ≦ 0.7 [W] and both are limited to 1 [W] or less (tolerable loss or less).

In the range of 10 [V] ≦ V _B <10.7 [V], the voltage V _D 2 across the Zener diode D _Z 2 becomes the Zener voltage V _Z 2, but the voltage across the Zener diode D _Z 1 is across. voltage V _D 1 of the supply voltage V _B becomes a Zener voltage V _Z less than 1. Therefore, the first and second constant voltage power supply circuits 5a and 5b
Output voltage of V ₀ 1 = V _B −0.7 [V] and V ₀ 2 = 9 [V], respectively.

As a result, even in this V _B range, the constant voltage power supply circuit 1 outputs an output voltage of V ₀ = 9 [V] to the load. However, in this range of V _B , the voltage V _R across the resistor R3 is V _R = V _B −9.7 [V]. Therefore, according to Ohm's law, the current I ₀ 1 flowing through the resistor R 3 is I _0. 1 (= V
_R / _R3) = 0.1 × V _B −0.97 [A], which is fixed to a current that fluctuates according to V _B. As a result, of the load current (0.2 [A]) from the power source B, to the first branch flow path 3a,
The current that fluctuates according to V _B of I ₀ 1 = 0.1 × V _B −0.97 [A] is fixedly shunted and output via the transistor Tr1 and the resistor R3. The remaining current of I ₀ 2 = 1.17−0.1 × V _B [A] is shunted and output from the transistor Tr2. The respective currents are merged to output I ₀ = 0.2 [A]. It is output to the load as a current.

In this range of V _B , each transistor Tr
1, Tr2 respectively _{to, I 0 1 = 0.1 × V} B -0.97
[A], I ₀ 2 = 1.17-0.1 × V _B [A] increases / decreases in accordance with the increase / decrease in V _B , and V _CE 1 = 0.7.
[V], V _CE 2 = V _B −9 [V] constant according to increase or decrease of V _B ,
A base-emitter voltage that increases or decreases is applied. Therefore, P1 = (0.1
× V _B −0.97) × 0.7 [W], P2 = (1.17−
_{0.1 × V B) × (V} B -9) but losses increase or decrease occurs in response to V _B of [W], in the scope of this V _B, P1 <0.
Since 6 [W] and P2 <0.7 [W], both are limited to 1 [W] or less (allowable loss or less).

Incidentally, the range of 9.7 [V] ≦ V _B <10 [V] has the same conclusion as the range of 10 [V] ≦ V _B <10.7 [V].

Further, in the range of V _B <9.7 [V], the voltage V _D across the Zener diodes D _Z 1 and D _Z 2 is
1 and V _D 2 are both less than zener voltages V _Z 1 and V _Z 2,
Both become the power supply voltage V _B. Therefore, V ₀ 1 = V ₀ 2 = V _B − from each of the first and second constant voltage power supply circuits 5a and 5b.
An output voltage of 0.7 [V] is output.

As a result, in this V _B range, the constant voltage power supply circuit 1 outputs an output voltage of V ₀ = V _B -0.7 [V] to the load. As a result, the output voltage V ₀ becomes less than 9 [V], and the current I ₀ flowing through the load becomes less than 0.2 [A] (I ₀ <0.2 [A]). Since the voltage V _R across the resistor R3 is V _R = 0, according to Ohm's law, the resistor R3 is
Current does not flow through (ie, I ₀ 1 = 0). This allows
All of the load current (<0.2 [A]) from the power source B flows to the second branch flow path 3b and is output from the transistor Tr2,
An output current of I ₀ = I ₀ 2 <0.2 [A] is output to the load.

In this range of V _B , the transistor Tr1
Current does not flow to the transistor Tr2 (I ₀ 1 = 0).
Current of all current I ₀ 2 = I ₀ (<0.2 [A]) flows, but the base-emitter voltage V of the transistor Tr2 is
_CE 2 is V _CE 2 = 0.7 [V], so P2 <0.14
[W], and even within this V _B range, P1 <0.6 [W],
P2 <0.7 [W] and both are limited to 1 [W] or less (tolerable loss or less).

Although the voltage drop in the resistors R1 and R2 due to the base current is neglected in the above description for the sake of convenience of description, when the voltage drop is taken into consideration, the range of each V _B is slightly shifted. It goes without saying that there is.

Constant voltage power supply circuit 1 configured as described above
According to this, the first and second branch channels 3a and 3b are provided in parallel on the power supply path 3 from the power source B to the load, and the branch channels are respectively provided in the first and second branch channels 3a and 3b. 3a, 3
Since the first and second constant voltage power supply circuits 5a and 5b in which the transistors Tr1 and Tr2 are interposed are provided in b, the load current from the power supply B is shunted and flows to the transistors Tr1 and Tr2. And each transistor T
The load current flowing through r1 and Tr2 can be reduced, and the loss of each transistor Tr1 and Tr2 (that is, temperature rise)
Can be reduced. Therefore, it is possible to prevent the allowable loss from being insufficient even if the transistors Tr1 and Tr2 are SMD.

Further, a resistor R3 is provided at the subsequent stage of the first constant voltage power supply circuit 5a on the first shunt flow path 3a, and the output voltage V ₀ 1 of the first constant voltage power supply circuit 5a is the second constant voltage. Since it is set higher than the output voltage V ₀ 2 of the power supply circuit 5b, it is possible to prevent the load current from the power supply B from concentrating and flowing in one of the first and second branch flow paths 3a and 3b.

Further, the first and second constant voltage power supply circuits 3a,
3b are transistors Tr1 and Tr2, resistors R1 and
R2 and Zener diode D _Z 1, because it is constituted by a D _Z 2, it can be constructed with a simple circuit configuration.

The numerical setting of this embodiment is an example, and the present invention is not limited to this numerical setting.

[0037]

According to the first aspect of the present invention, the first and second branch flow paths are provided in parallel with each other on the power feeding path from the power supply to the load, and the first and second branch flow paths are respectively provided. Since the first and second constant voltage power supply circuits with transistors interposed in the shunt flow path are provided, the load current from the power supply is shunted to each transistor, and each transistor is supplied to each transistor. The flowing load current can be reduced, and the loss per transistor (that is, temperature rise) can be reduced. Therefore, it is possible to prevent the allowable loss from being insufficient even if the transistors Tr1 and Tr2 are SMD.

According to the second aspect of the invention, the resistor is provided at the subsequent stage of the first constant voltage power supply circuit on the first branch flow path, and the output voltage of the first constant voltage power supply circuit is the second constant voltage. Since it is set higher than the output voltage of the voltage power supply circuit, it is possible to prevent the load current from concentrating and flowing in one of the first and second branch flow paths.

According to the third aspect of the invention, each of the first and second constant voltage power supply circuits is composed of a transistor, a resistor and a zener diode, so that the circuit can be constructed with a simple circuit configuration.

[Brief description of drawings]

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

FIG. 2 is a configuration diagram of a conventional constant voltage power supply circuit.

[Explanation of symbols]

1 Constant Voltage Power Supply Circuit 3 Power Supply Line 3a First Shunt Flow Path 3b Second Shunt Flow Path 5a First Constant Voltage Power Supply Circuit 5b Second Constant Voltage Power Supply Circuit D _Z 1, D _Z 2 Zener Diodes R 1, R 2, R 3 Resistors Tr1 and Tr2 Transistor V ₀ 1 Output voltage of first constant voltage power supply circuit V ₀ 2 Output voltage of second constant voltage power supply circuit

Claims (3)

[Claims] 1. A first and a second shunt flow path, which are interposed in parallel on a power supply path from a power supply to a load, for temporarily shunting a load current from the power supply, and the first and second shunts, respectively. A constant voltage power supply circuit, which is provided in a path and has a first flow path and a second constant voltage power supply circuit in which a transistor is interposed in the flow path. 2. A resistor is provided at a subsequent stage of the first constant voltage power supply circuit on the first branch flow path, and an output voltage of the first constant voltage power supply circuit is the second constant voltage power supply circuit. The constant voltage power supply circuit according to claim 1, wherein the constant voltage power supply circuit is set higher than the output voltage of the constant voltage power supply. 3. A first constant voltage power supply circuit and a second constant voltage power supply circuit, wherein the main electrodes of the transistor are interposed between the first and second branch flow paths, and the upstream main electrode / control of the transistor. 3. A resistor connected between electrodes, and a Zener diode connected in a reverse direction between an intermediate point between the resistor and a control electrode of the transistor and a ground point. Constant voltage power supply circuit described in.