JPH0836430A - Power supply circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] The temperature hysteresis characteristic is added to the on / off operation of the output voltage accompanying the overheat protection operation of the reference voltage source that supplies the power supply voltage to the load, and the output voltage near the overheat protection operating temperature Prevent oscillation phenomenon. A reference voltage source 3 that receives a voltage input to supply a power supply voltage to a load, and a base is connected to a first voltage dividing node of a resistance voltage divider circuit that divides the voltage input, and a base is connected to an overheated state. Is connected between the collector of the transistor 25 for detecting the temperature, the collector of the overheat detecting transistor and the bias current source of the reference voltage source, and the emitter and base are connected to both ends of the collector current adjusting resistor 24. A transistor 22 connected to the second voltage division node of the transistor 22 and a transistor 20 for extracting a bias current to which a base current is supplied from the collector of a transistor 23 current-mirror connected to the transistor 22. .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit formed in a semiconductor integrated circuit, and more particularly to a power supply circuit using a reference voltage source requiring an overheat protection function.
Used in various electronic devices for industrial use.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional example of a power supply circuit using a reference voltage source requiring an overheat protection function. In this power supply circuit, 1 is a voltage input terminal to which a voltage input Vin is applied, 2 is a ground terminal to which a ground potential GND is applied, 3
Is a reference voltage source, 3a is a control input terminal of the reference voltage source, 3b
Is an output voltage terminal of the reference voltage source, and 40 is an overheat protection circuit.

The reference voltage source 3 is a reference voltage generation circuit 4
And the collector and emitter are connected between the voltage input terminal 1 and the output voltage terminal 3b, and the base is the control input terminal 3a.
Connected to the output NPN transistor 5, resistors 6 and 7 connected in series between the output voltage terminal 3b and the ground terminal 2, and connected between the voltage input terminal 1 and the control input terminal 3a. Bias current source 8 and control input terminal 3a
And an NPN transistor 9 for error output connected between the ground terminal 2 and the ground terminal 2.

The reference voltage generating circuit 4 includes a bias node connected to the output voltage terminal 3b and the ground terminal 2
Has a ground node connected to, a reference voltage node connected to the series connection node of the resistors 6 and 7, and an error output node connected to the base of the error output transistor 9.

The bias current source 8 is composed of a transistor and a resistor (both not shown), and the reference voltage generating circuit 4 is also a transistor and a resistor (both not shown).
It consists of and.

On the other hand, the overheat protection circuit 40 is supplied with a voltage input Vin of the voltage input terminal 1 to generate a bias voltage, and a bias voltage output node 41a of the bias voltage generation circuit 41. Resistors 12 and 13 connected in series with the ground terminal 2
And a base connected to a series connection node of the resistors 12 and 13 and a collector-emitter connected between the control input terminal 3a and the ground terminal 2 for overheat protection.
N transistor 10.

The bias voltage generating circuit 41 includes a resistor 14 and a Zener diode 15 connected in series between the voltage input terminal 1 and the ground terminal 2, and the resistor 14
Also, the base of the Zener diode 15 is connected to the serial connection node of the Zener diode 15, and the NPN transistor 11 is connected between the collector and the emitter between the voltage input terminal 1 and the bias voltage output node 41a.

In the overheat protection circuit 40 having the above structure, the overheat protection transistor 10 has the function of detecting when the reference voltage source 3 is overheated, and the bias current (bias current) of the output transistor 5 of the reference voltage source 3 when overheat is detected. The current of the source 8).

That is, the base potential VTSD of the overheat protection transistor 10 is set as shown in the following equation. VTSD = (Vz-VBE11) .R13 / (R12 + R13) (1) where Vz is the Zener voltage of the Zener diode 15 VBE11 is the forward voltage between the base and emitter of the transistor 11 R12 is the value of the resistor 12 R13 is the resistance The value is 13.

During normal operation of the reference voltage source 3, the overheat protection transistor 10 is off, and the output transistor 5 is biased by the bias current source 8. When the temperature rises, the forward voltage VBE10 between the base and the emitter of the overheat protection transistor 10 becomes smaller and becomes equal to the base potential VTSD expressed by the above equation (1), the overheat protection transistor 10 turns on and the output transistor The bias current of 5 is pulled out, and the output voltage terminal 3b
Voltage (output voltage) Vout decreases.

Here, the base potential VTSD can be expressed by using the increase ΔT from room temperature to the overheat protection operating temperature.
It becomes as shown in the following formula. VTSD = (ΦVBE10 / ΦT) · ΔT + VBE10− (VTSD / ΦT) · ΔT (2) where (ΦVBE10 / ΦT) · ΔT + VBE10 is the threshold voltage of VBE10 (ΦVTSD / ΦT) is the temperature coefficient of VTSD.

Therefore, from the above equations (1) and (2), the resistance R
By properly selecting the values of 12 and R13, it becomes possible to perform the overheat protection operation at any temperature. However, since VTSD set by the above equations (1) and (2) does not change by turning on / off the overheat protection transistor 10, the overheat protection transistor 10 turns on / off in the vicinity of the overheat protection operating temperature. Repeated operation, output voltage Vou
The phenomenon that t oscillates occurs.

In such a case, a load (not shown) using the output voltage Vout as a voltage source may malfunction. Further, since the overheat protection transistor 10 is gradually turned on, the output transistor 5 is not completely turned off even when the output voltage Vout falls below the rated value.
Again, the load using the output voltage Vout as a voltage source may malfunction.

[0014]

As described above, in the conventional power supply circuit, the overheat protection transistor repeats the on / off operation in the vicinity of the overheat protection operating temperature, and the output voltage Vout is output.
However, there is a problem that the oscillation phenomenon occurs.

The present invention has been made to solve the above-mentioned problems, and has a temperature hysteresis characteristic in the on / off operation of the output voltage accompanying the overheat protection operation of the reference voltage source for supplying the power supply voltage to the load. Accordingly, it is an object of the present invention to provide a power supply circuit capable of preventing the oscillation phenomenon of the output voltage near the overheat protection operating temperature.

[0016]

SUMMARY OF THE INVENTION The present invention is a reference having an output transistor supplied with a voltage input and supplying a power supply voltage to a load, and a bias current source for supplying a bias current to the base of the output transistor. In a power supply circuit comprising a voltage source and an overheat protection circuit that receives the voltage input and draws the bias current from the bias current source of the reference voltage source when an overheated state of the reference voltage source is detected, The protection circuit is supplied with the voltage input and generates a bias voltage, a bias voltage generating circuit, a resistance voltage dividing circuit connected between a bias voltage output node of the bias voltage generating circuit and a ground node, and the resistor. An overheat detecting transistor having a base connected to a first voltage dividing node of the voltage dividing circuit and an emitter connected to a ground node; A collector current adjusting resistor connected between the collector of the overheat detecting transistor and the bias current source of the reference voltage source, and an emitter connected to one end of the collector current adjusting resistor, and a base for detecting the overheat. For supplying a first current, the collector of which is connected to the collector, the collector of which is connected to the second voltage dividing node of the resistance voltage dividing circuit, and the emitter of which is connected to the emitter of the first current supplying transistor. A base current is supplied from a second current supply transistor whose base is connected to the collector of the overheat detection transistor and a collector of the second current supply PNP transistor, and a bias of the reference voltage source. A bias current drawing transistor connected between the collector and emitter between the current source and the ground node. Characterized in that it Bei.

[0017]

The overheat protection circuit includes an overheat detection transistor for detecting when the reference voltage source is overheated and a transistor for extracting the bias current of the output transistor of the reference voltage source when overheat is detected. We share. Since the base potential of the overheat detecting transistor is controlled to be different according to the on / off operation of the overheat detecting transistor, the on / off operation of the overheat detecting transistor has a temperature hysteresis characteristic.

As a result, the ON / OFF operation of the output voltage accompanying the overheat protection operation of the reference voltage source has a temperature hysteresis characteristic, and it is possible to prevent the oscillation phenomenon of the output voltage near the overheat protection operation temperature. become.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a power supply circuit according to the first embodiment of the present invention. In this power supply circuit, 1 is a voltage input terminal to which a voltage input Vin is applied, 2 is a ground terminal to which a ground potential GND is applied, 3 is a reference voltage source, 3a is a control input terminal of the reference voltage source, 3b is a reference voltage source. Output voltage terminal of
50 is an overheat protection circuit.

The reference voltage source 3 has a collector-emitter connection between the reference voltage generating circuit 4 and the voltage input terminal 1 and the output voltage terminal 3b, like the reference voltage source 3 shown in FIG. And an NPN transistor 5 for output whose base is connected to the control input terminal 3a, and resistors 6 and 7 connected in series between the output voltage terminal 3b and the ground terminal 2,
The bias current source 8 is connected between the voltage input terminal 1 and the control input terminal 3a, and the error output NPN transistor 9 is connected between the control input terminal 3a and the ground terminal 2.

The reference voltage generating circuit 4 includes a bias node connected to the output voltage terminal 3b and the ground terminal 2
Has a ground node connected to, a reference voltage node connected to the series connection node of the resistors 6 and 7, and an error output node connected to the base of the error output transistor 9.

The bias current source 8 is composed of a transistor and a resistor (both not shown), and the reference voltage generating circuit 4 is also composed of a transistor and a resistor (both not shown).

On the other hand, the overheat protection circuit 50 is supplied with the voltage input Vin of the voltage input terminal 1 to generate a bias voltage, and a bias voltage output node 41a of the bias voltage generation circuit 41. The first resistor 26, the second resistor 26, which are connected in series with the ground terminal 2,
Of the resistor voltage divider circuit having the resistor 27 and the third resistor 28, and the first voltage divider node (the series connection node of the resistors 26 and 27) of the resistor voltage divider circuit, the base of which is connected, and the emitter of which is the ground terminal 2. To the control input terminal 3a, and a fourth resistor 24 for adjusting the collector current connected between the collector of the transistor 25 for overheat detection and the control input terminal 3a. Has an emitter connected to one end (a connection node with the control input terminal 3a), a base connected to the collector of the overheat detecting transistor 25, and a collector connected to a second voltage division node (second node) of the resistance voltage dividing circuit. Resistor 27 and third resistor 28
First P for current supply connected to
An NP transistor 22, a second PNP transistor 23 for current supply, the emitter of which is connected to the emitter of the first current supply transistor 22 and the base of which is connected to the collector of the overheat detection transistor 25, and 2 PNP transistor 23 collector and ground terminal 2
A base current is supplied from the fifth resistor 21 for bias connected between the control input terminal 3a and the ground terminal 2 between the collector and the emitter. And an NPN transistor 20 for extracting a bias current.

The bias voltage generating circuit 41, like the bias voltage generating circuit 41 shown in FIG. 4, has a resistor 14 and a zener diode 15 connected in series between the voltage input terminal 1 and the ground terminal 2. And a base connected to a series connection node of the resistor 14 and the Zener diode 15, and an NPN transistor 11 having a collector-emitter connected between the voltage input terminal 1 and the bias voltage output node 41a.

In the overheat protection circuit 50 having the above structure,
Transistor 2 for detecting overheating of reference voltage source 3
5 and the transistor 20 for drawing out the bias current (current of the bias current source 8) of the output transistor 5 of the reference voltage source 3 when overheat is detected, share the overheat protection action. Since the base potential of the first PNP transistor 22 is controlled to be different depending on the on / off operation of the overheat detection transistor 25, the on / off operation of the overheat detection transistor 25 is performed. Has a temperature hysteresis characteristic as shown in FIG.

As a result, the on / off operation of the output voltage accompanying the overheat protection operation of the reference voltage source 3 has a temperature hysteresis characteristic, and the oscillation phenomenon of the output voltage near the overheat protection operation temperature can be prevented. It will be possible.

That is, the base potential VTSD2 of the overheat detecting transistor 25 is set as in the following equation (3). VTSD2 = (Vz-VBE11). (R27 + R28) / (R26 + R27 + R28) (3) where Vz is the Zener voltage of the Zener diode 15, VBE11 is the forward voltage between the base and emitter of the transistor 11, and R26 is the first resistor 26. R27 is the value of the second resistor 27 and R28 is the value of the third resistor 28.

During normal operation of the reference voltage source 3, the overheat detection transistor 25, the first PNP transistor 22, the second PNP transistor 23 and the bias current drawing transistor 20 are off, respectively, and the reference voltage source 3 The output transistor 5 is biased by the bias current source 8.

Transistor 2 for overheat detection due to temperature rise
When the forward voltage VBE25 between the base and the emitter of 5 becomes small and becomes equal to the base potential VTSD2 represented by the above equation (3), the overheat detecting transistor 25 is turned on and the reference voltage is supplied via the fourth resistor 24. Output transistor 5 of source 3
To pull out the bias current of.

Here, the voltage drop of the fourth resistor 24 is the first
When the threshold voltage of the forward voltage between the emitter and the base of the PNP transistor 22 and the second PNP transistor 23 becomes equal to the threshold voltage of the first PNP transistor 22 and the second PNP transistor 23.
Since the NP transistor 23 is turned on, the bias current drawing transistor 20 is turned on by the collector current of the second PNP transistor 23, and the bias current of the output transistor 5 of the reference voltage source 3 is drawn.
The voltage (output voltage) Vout at the output voltage terminal 3b decreases.

In the above operation, the transistors 22 and 2 are
Since 5 and the resistors 24, 27 and 28 form a positive feedback loop until the operation of the bias current drawing transistor 20 is saturated, a rapid overheat protection operation is obtained.

Further, since the collector current of the overheat detecting transistor 25 can be set small by the fourth resistor 24, the error in the detected temperature due to the characteristics of the overheat detecting transistor 25 can be reduced.

In the collector current Ic23 of the second PNP transistor 23, the resistance value R21 of the fifth resistor 21 is larger than the resistance value R28 of the third resistor 28 (R21> R28).
Under the conditions, it can be set as the following expression (4).

Ic23 = VBE20 / R21 (4) However, VBE20 is the transistor 2 for extracting the bias current.
0 is a base-emitter forward voltage.

The first PNP transistor 22 and the second PNP
Since the base-emitter forward voltage of each NP transistor 23 is equal, the first PNP transistor 2
2, the collector currents Ic22 and Ic23 of the second PNP transistor 23 are equal.

Since the collector current Ic22 causes a voltage drop in the third resistor 28, the base potential VTSD2 of the overheat detecting transistor 25 is VTSD2 = (Vz-VBE11). (R27 + R28) / (R26 + R27 + R28) + Ic22.R26. R28 / (R26 + R27 + R28) ... (5)

Therefore, from the above equation (5), the base potential VTSD2 of the overheat detecting transistor 25 becomes higher by the second term of the equation (5) than before the on-operation, so that it is turned off at a temperature lower than that during the on-operation. It will return to the state. Since the hysteresis width at this time is obtained by dividing the second term of the equation (5) by the temperature coefficient of VBE25, the first resistance 26, the second resistance
By appropriately selecting the resistance values of the resistor 27, the third resistor 28, and the fifth resistor 21, the overheat protection operating temperature and the hysteresis width can be set arbitrarily.

In the above equation (5), the Zener voltage Vz of the Zener diode 15 has a positive temperature coefficient,
Base-emitter voltage VBE of NPN transistor 11
11 has a negative temperature coefficient, so NPN transistor 1
The emitter voltage of 1 (Vz-VBE11) has temperature dependence. An example for avoiding this is shown in FIG.

FIG. 3 shows a power supply circuit according to the second embodiment of the present invention. Compared with the power supply circuit shown in FIG. 1, this power supply circuit has a resistor 14, a Zener diode 15, and an NP.
Bias voltage generation circuit 41 including N-transistor 11
1 in that a bandgap reference voltage source 60 that is stable in temperature is used instead of the above, and the other points are the same.
The same symbols as in the inside are attached.

The bandgap type reference voltage source 60 is
A current supply circuit 36 connected between the voltage input terminal 1 and the reference voltage output terminal 60a, and resistors 31 and 3 each having one end connected to the reference voltage output terminal 60a.
4, an NPN transistor 35 having a collector and an emitter connected between the other end of the resistor 34 and the ground terminal 2, and a collector and a base connected to each other, and an NPN transistor 35 and a base connected to each other. Is an NPN transistor 32 connected to the other end of the resistor 31, and
A resistor 33 connected between the emitter of the NPN transistor 32 and the ground terminal 2, a base connected to the collector of the NPN transistor 32, and a collector-emitter between the reference voltage output terminal 60a and the ground terminal 2. And a PNP transistor 30 connected between them. The current supply circuit 36 is composed of a current source, or a voltage source and a resistor.

Bandgap type reference voltage source 6 having the above structure
0, the voltage Vref at the reference voltage output terminal 60a is expressed by the following equation (6). Vref = (R31 / R33) VT ln (A32 / A35) (R31 / R34) + VBE365 (6) However, R31, R33, and R34 are resistance values of the resistors 31, 33 and 34. A32 / A35 is the transistor 32, The emitter area ratio VBE35 of the transistor 35 is the forward voltage between the base and the emitter of the transistor 35.

Here, VBE35 has a negative temperature coefficient, and
When 32 · R31> A35 · R34, the first term of the equation (6) has a positive temperature coefficient, so that the resistance value R of the resistors 31, 33, 34 is R.
By properly selecting 31, R33 and R34, the temperature coefficient of Vref can be made zero.

When the base potential VTSD2 of the overheat detecting transistor 25 is set by using Vref thus generated, the following equation (7) is obtained. VTSD2 = Vref (R27 + R28) / (R26 + R27 + R28) (7) In the above equation (7), since the temperature coefficient of Vref is zero, the increase ΔT from room temperature to the overheat protection operating temperature is expressed as follows: The above equation (7) is as shown in the following equation (8).

VTSD2 = (ΦVBE10 / ΦT) · ΔT + VBE25 (8) Further, VTSD2 during the overheat protection operation is expressed by the following expression (9). VTSD2 = Vref (R27 + R28) / (R26 + R27 + R28) + Ic22.R26.R28 / (R26 + R27 + R28) (9) By setting as described above, the overheat protection operation having the same characteristics as the first embodiment can be achieved. can get. Moreover, since the temperature-stable reference voltage source 60 is used,
Compared with the embodiment, there is an advantage that the overheat protection operating temperature can be easily set.

[0045]

As described above, according to the power supply circuit of the present invention, the temperature hysteresis characteristic is imparted to the ON / OFF operation of the output voltage accompanying the overheat protection operation of the reference voltage source which supplies the power supply voltage to the load. It is possible to prevent the oscillation phenomenon of the output voltage near the overheat protection operating temperature.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a power supply circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a temperature hysteresis characteristic of the operation of the overheat detection transistor in FIG.

FIG. 3 is a circuit diagram showing a power supply circuit according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a conventional power supply circuit.

[Explanation of symbols]

1 ... Voltage input terminal, 2 ... Ground terminal, 3 ... Reference voltage source, 3
a ... Control input terminal of reference voltage source, 3b ... Output voltage terminal of reference voltage source, 4 ... Reference voltage generating circuit, 5 ... NP for output
N-transistors, 6, 7, 14, 21, 24, 26, 2
7, 28 ... Resistor, 8 ... Bias current source, 9 ... NPN transistor for error output, 11 ... NPN transistor, 1
5 ... Zener diode, 20 ... NPN transistor for extracting bias current, 22 ... First PNP transistor, 23 ... Second PNP transistor, 25 ... NPN transistor for overheat detection, 41 ... Bias voltage generating circuit, 50 ... Overheat Protection circuit.

Claims (1)

[Claims] 1. A reference voltage source having an output transistor for supplying a power supply voltage to a load and a bias current source for supplying a bias current to the base of the output transistor, and the voltage input. In a power supply circuit provided with an overheat protection circuit for drawing the bias current from the bias current source of the reference voltage source when an overheat state of the reference voltage source is detected, the overheat protection circuit, the voltage input, A bias voltage generating circuit that generates a bias voltage, a resistance voltage dividing circuit connected between a bias voltage output node of the bias voltage generating circuit and a ground node, and a first voltage dividing circuit of the resistance voltage dividing circuit. Voltage detection node, whose base is connected to the voltage node, and whose emitter is connected to the ground node. A collector current adjusting resistor connected between the collector of the star and a bias current source of the reference voltage source, an emitter connected to one end of the collector current adjusting resistor, and a base of the overheat detecting transistor collector. A first current supply transistor having a collector connected to the second voltage division node of the resistance voltage divider circuit, an emitter connected to the emitter of the first current supply transistor, and a base A base current is supplied from a second current supply transistor connected to the collector of the overheat detection transistor, and a collector of the second current supply transistor, and a bias current source of the reference voltage source and a ground node. And a transistor for extracting a bias current, the collector and the emitter of which are connected to each other. Circuit.