JPH0619686B2 - Power supply circuit - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a device, such as a telephone, which receives a power supply voltage from a power supply line and which superimposes and transmits a signal using the power supply line as a signal transmission path. Regarding improvement of power supply circuit.

[Technical background of the invention]

Conventionally, as this type of circuit, there is one configured as shown in FIG. 1, for example. This circuit starts with a pair of feeders 1
A constant current operation is performed by a power supply voltage generation circuit 2 that generates a power supply voltage V _CC of the device and a constant current control circuit 3 between a and 1b.
The PNP type transistor 4 and the PNP type transistor 5b which forms the switch circuit 5 together with the resistor 5a are connected in series to each other, and the PNP type transistor 4 separates the signal and the PNP type transistor 5b supplies the power supply voltage generating circuit 2 The direct current supply of the power supply lines 1a and 1b to the power supply is controlled. In addition, the DC voltage V _{L is} applied between the feeder lines 1a and 1b.
The voltage drop detection circuit 6 for detecting the drop of the voltage is provided, and the protection PNP transistor 7 is operated by this circuit 6.

With such a configuration, the voltage between the power supply lines 1a and 1b
When V _L is higher than the total value of the power supply voltage V _CC and the saturation voltage of the transistors 4 and 5b, the transistor 5b becomes conductive, so that the direct current of the power supply line 1a is generated through the transistor 4 which operates in constant current. It is supplied to the circuit 2.

On the other hand, the signal superimposed on the power supply lines 1a and 1b causes the voltage V _{L to rise.}
Becomes lower than the total value of the power supply voltage V _CC and the saturation voltage of the transistors 4 and 5b, the transistor 5b becomes non-conductive. However, at this time, the base potential of the transistor 7 is lowered by the capacitor 6a of the voltage drop detection circuit 6, so that the transistor 7 becomes conductive, and as a result, the direct current from the power supply line 1a is shunted via the transistor 7, The constant current operation of the transistor 4 is maintained. At this time, the output voltage V _CC of the power supply voltage generation circuit 2
Is held substantially constant by the power supply capacitor 2a. Therefore, with the above configuration, the power supply lines 1a, 1
No distortion occurs in the signal waveform superimposed on b.
Further, since the PNP transistors 4 and 5b are in series with each other, the constant current operation of the transistor 4 is maintained even if the voltage of the power supply lines 1a and 1b drops to about 1V.

[Problems of background technology]

However, in the case of integrating such a conventional circuit, the PNP transistors 4 and 5b for power supply are usually forced to be lateral PNP transistors. A relatively large current of, for example, 10 mA flows through the power supply transistors 4 and 5b. But like this lateral PN
Since the P-type transistor has a current capacity of about 1/20 of that of the NPN-type transistor of the same size, there is a drawback that the chip size becomes very large when the power-supplying PNP-type transistors 4 and 5b are integrated.

[Object of the Invention]

The present invention uses an NP for each of the transistors for power supply and side current.
An object of the present invention is to provide a power supply circuit that can perform stable constant current operation up to a low value of a power supply line voltage while using an N-type transistor.

[Outline of Invention]

In order to achieve the above object, the present invention provides a second NP for side current in parallel with a first NPN transistor for power supply.
An N-type transistor is provided and a voltage drop detection circuit is provided. And by this voltage drop detection circuit,
When the base potential of the first NPN-type transistor exceeds a predetermined potential, the first NPN-type transistor is made conductive, while the DC voltage of the power supply line is lowered, so that the base of the first NPN-type transistor is turned on. When the potential drops below the predetermined potential, the second NPN transistor is made conductive instead of the first NPN transistor so that the direct current from the power supply line is shunted.

Therefore, even if the first NPN transistor for power supply is cut off due to a decrease in the DC voltage of the power supply line, the second NPN transistor for side current is turned on instead, and the current path is always secured. As a result, stable constant current operation can be performed up to a low value of the power supply line voltage.

Further, a feedback circuit is provided, and by this feedback circuit, the DC voltage of the power supply line, the first NPN transistor and the second
Of the DC voltage at the point of parallel connection with the NPN transistor, and obtains the change information thereof, and when the first NPN transistor is conducting, the upper change information is given as the first change information.
Of the second NPN-type transistor, the second NPN-type transistor is fed back to the second NPN-type transistor to conduct the constant current operation.
The NPN type transistor is fed back to the transistor to perform a constant current operation.

Therefore, the constant current characteristics of the power supply transistor and the side-flow transistor can always be maintained by the feedback circuit, even though the power supply transistor and the side-flow transistor are configured by NPN transistors.

Example of Invention

FIG. 2 is a circuit configuration diagram of a power supply circuit in one embodiment of the present invention, and the same parts as those in FIG. 1 are designated by the same reference numerals.

In the figure, a power supply voltage generation circuit 2 and one power supply line 1a
A power supply circuit 10 in which a resistor 11 and a power supply NPN transistor 12 as a first NPN transistor are connected in series is provided between and. The NPN transistor 12 is provided with a power supply voltage generating circuit 2 from the power supply line 1a.
It has the capacity to withstand the current supplied to it (for example, 10 mA). A side-flow NPN transistor 21 serving as a second NPN transistor is inserted between the collector of the power feeding NPN transistor 12 and the power supply line 1b. The NPN transistor 21 constitutes a side-current circuit, and constitutes the protection circuit 20 together with the voltage drop detection circuit 22 which controls the on / off operation thereof. That is, the voltage drop detection circuit 22 is provided with the power supply lines 1a and 1b.
A resistor 23, a diode-connected PNP transistor 24 and a constant current circuit 25 connected in series, and the base of a PNP transistor 26 connected to the collector of the PNP transistor 24. . The PNP transistor 26 has a collector for the side flow N
A power supply NPN transistor 1 of the power supply circuit 10 connected to the base of the PN transistor 21 and having an emitter
When the base potential of the power supply NPN transistor 12 is lower than its own emitter potential + V _BE , that is, when the base potential of the PNP transistor 26 is lower than the emitter potential of the NPN transistor 12. The transistor 26 is turned on, and the side-flow NPN is
Form transistor 21 to conduct.

That is, the PNP-type transistor 26 is configured such that the second NPN-type transistor 26 operates when the base potential of the power-supplying NPN-type transistor 12 as the first NPN-type transistor decreases to a predetermined potential or less due to a decrease in the DC voltage of the power supply line. Functioning as a control transistor circuit for conducting the side-current NPN transistor 21 as a source transistor to cause a direct current from the power supply line to flow side-by-side.

The resistor 23 also functions as a resistor circuit for compensating for the characteristics of the PNP transistor 26 serving as the side-current controlling transistor circuit.

By the way, in the circuit of the present embodiment, the NP of the power supply circuit 10 is
N-type transistor 12 and NPN-type transistor 2 for side current
A feedback circuit 30 is provided to operate each of the 1's at a constant current. This feedback circuit 30 connects the connection point of the series circuit of the resistor 31 and the constant current circuit 32 connected between the power supply lines 1a and 1b to the non-inverting input terminal (+) of the differential amplifier 33, and The collector of the feeding NPN transistor 12 is connected to the inverting input terminal (-) of the amplifier 33 via the resistor 34, and the output terminal of the differential amplifier 33 is connected to the base of the PNP transistor 35. And this PN
The emitter of the P-type transistor 35 is connected to the power supply line 1a, and the collector is connected to the emitter of the control PNP-type transistor 26 of the voltage drop detection circuit 22.

FIG. 3 is a circuit diagram showing a more specific configuration of the above power supply circuit. In the figure, the differential amplifier 33 has a pair of NPN transistors 41 and 42 that form a differential amplifier circuit together with a transistor 40 that forms a constant current source. It is connected to the power supply line 1a through a pair of PNP type transistors 43 and 44 which form a mirror circuit. Reference numeral 50 in the drawing is a fixed bias circuit for causing the transistors 40, 32 and 51 to perform constant current operation.

Next, the operation of the circuit configured as described above will be described.
First, the voltage drops of the resistors 23 and 31 are Δ respectively.
The value is determined to be E, and the resistance 11 is N for power supply by the differential amplifier 33 and the PNP transistor 35.
The value is set so that the voltage drop becomes ΔE by the negative feedback given to the PN transistor 12.

With such a configuration, the base potential V _B of the control PNP transistor 26 is V _B = V _L −ΔE−V _BE24 . However, V _L : DC voltage between the power supply lines 1a and 1b V _BE24 : Base-emitter voltage of the transistor 24. On the other hand, the emitter potential of the control transistor 26
V _E is clamped to V _E = V _CC + V _BE12 or V _E = V _L −ΔE, whichever is lower. Here, V _{CC is} the output voltage of the power supply voltage generation circuit 2, V _{BE12 is} the base-emitter voltage of the power supply NPN transistor 12.

Thus, for example, power supply lines 1a, high DC voltage V _L between 1b, when the V _B> V _E -V _BE26, namely V _L> V _CC + ΔE + If it is V _BE12 is, PNP type transistor 26 is cut off for control As a result, the power supply NPN transistor 12 is turned on and the side-current NPN transistor 21 is turned off, so that the current is supplied from the power supply line 1a to the power supply voltage generation circuit 2 via the power supply transistor 12. It At this time, a current corresponding to the difference between the collector potential of the power feeding NPN transistor 12 and the reference potential (V _L −ΔE) is fed back from the differential amplifier 33 to the power feeding NPN transistor 12 via the transistor 35. Therefore, the voltage drop across the resistor 11 is maintained at ΔE. That is, in the circuit of this embodiment, the feedback circuit 30 performs negative feedback so that the voltage drop ΔE of the resistor 11 is always constant. Therefore, the constant current characteristic of the power feeding NPN transistor 12 is reliably maintained.

Now, in this state, when the DC voltage V _L of the power supply lines 1a and 1b temporarily drops due to signal superposition and V _B <V _E −V _BE26 , that is, V _L <V _CC + ΔE + V _BE12 , the power supply The NPN transistor 12 is turned off. However, at the same time, the control transistor 26
Becomes conductive and the side-flow NPN transistor 21 becomes conductive, whereby the power supply current is side-flowed through the side-flow transistor 21.

At this time, since the difference signal from the feedback circuit 30 is fed back to the side-current transistor 21 via the transistor 26, the voltage drop ΔE of the resistor 11 is constant like when the power feeding NPN transistor 12 is in the conductive state. Held in. Therefore, also in this case, the constant current property of the feeding current is maintained.

As described above, in the circuit of the present embodiment, the constant current characteristics of the power supply transistor 12 and the side-current NPN transistor 21 can be maintained up to the low voltage of the power supply line V _L , and as a result, the power supply lines 1a and 1b. Since the AC power supply circuit and the power supply circuit are reliably separated from each other, the signal waveforms superimposed on the power supply lines 1a and 1b are not distorted.

Further, in the case of the circuit of this embodiment, the power supply transistor 1
2 is an NPN type, so when integrated (in LSI), PN
Compared to the conventional circuit using P-type transistors 4 and 5b,
The chip area can be reduced to about 1/40 while securing the same current capacity. As a result, the chip area of the entire power supply circuit can be reduced, so that the size of the circuit board can be reduced and the device can be downsized. In addition, because the power supply transistor is composed of NPN, the current amplification factor of the NPN type is larger than that of the PNP type, so there is less variation in the element characteristics, so there is an advantage that a circuit with high operational stability can be provided. is there.

Further, in this embodiment, a direct current circuit including the resistor 23, the diode-connected transistor 24, and the constant current circuit 25 is connected to the base of the control transistor 26.
Therefore, even if the control transistor 26 has a variation in characteristics such as a current amplification factor, the variation can be compensated by appropriately selecting the resistance value of the resistor 23. Further, the operation of the control transistor can be compensated. The points can be set accurately.

〔The invention's effect〕

As described above in detail, in the present invention, the first NPN for power feeding is used.
The second NPN-type transistor for side current is provided in parallel with the type-type transistor, and the voltage drop detection circuit is provided. When the base potential of the first NPN-type transistor exceeds a predetermined potential, the voltage drop detection circuit causes the first NPN-type transistor to conduct, while the DC voltage of the power supply line is lowered. When the base potential of the first NPN-type transistor drops below the predetermined potential, the second NPN-type transistor is turned on instead of the first NPN-type transistor so that the direct current from the power supply line is turned on. I am trying to let it flow.

Therefore, even if the first NPN transistor for power supply is cut off due to a decrease in the DC voltage of the power supply line, the second NPN transistor for side current conducts instead and the current path is always secured. As a result, stable constant current operation can be performed up to a low value of the power supply line voltage.

Further, a feedback circuit is provided, and the feedback circuit monitors the DC voltage of the power supply line and the DC voltage at the parallel connection point of the first NPN-type transistor and the second NPN-type transistor and changes information thereof. In the state where the first NPN transistor is conducting, the change information is fed back to the first NPN transistor to cause this transistor to perform a constant current operation, while the second NPN transistor is being operated. Is conducted, the change information is fed back to the second NPN type transistor so that this transistor can perform a constant current operation.

Therefore, the constant current characteristics of the power supply transistor and the side-flow transistor can always be maintained by the feedback circuit, even though the power supply transistor and the side-flow transistor are configured by NPN transistors.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a conventional power supply circuit, FIG. 2 is a circuit configuration diagram of a power supply circuit in one embodiment of the present invention, and FIG.
The figure is a circuit configuration diagram showing a more specific form of the circuit shown in FIG. 1a, 1b ... Power supply line, 2 ... Power supply voltage generation circuit, 10
...... Feeding circuit, 12 ...... NPN transistor for feeding, 2
0 …… Protection circuit, 21 …… Side-current NPN transistor,
22 ... Voltage drop detection circuit, 26 ... Control PNP transistor, 30 ... Feedback circuit, 33 ... Differential amplifier.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Saeki 1-3-1, Asahigaoka, Hino-shi, Tokyo Higashi factory, Higashi Kyoshiba Electric Co., Ltd. (72) Naoshi Yamada, Komukai Toshiba, Saiwai-ku, Kawasaki-shi, Kanagawa No. 1 in Higashi Kyoshibaura Electric Co., Ltd.

Claims (1)

[Claims] 1. A DC voltage is supplied from a pair of power supply lines,
In addition, in the power supply circuit of the equipment that transmits and receives signals by using this power supply line as a transmission line, the power supply voltage generation circuit that generates the power supply voltage of the equipment and the DC voltage of the power supply line is separated from the signal in this power supply voltage generation circuit. And a side-current circuit having a second NPN transistor provided in parallel with the first NPN transistor of the power supply circuit, and the first NPN transistor. -Type transistor has a base potential equal to or higher than a predetermined potential set to the DC voltage value of the power supply line, the first NPN-type transistor is rendered conductive, while the first NPN-type transistor is caused by a decrease in the DC voltage of the power supply line. When the base potential of the transistor drops below the predetermined potential, the second NPN transistor is conducted instead of the first NPN transistor. A voltage drop detection circuit including a control transistor circuit for allowing a direct current from the power supply line to flow by side, a direct current voltage of the power supply line, the first NPN transistor and the second NPN transistor Of the DC voltage at the point of parallel connection with the above, and obtains its change information, and when the first NPN transistor is conducting, the change information is fed back to the first NPN transistor and this transistor is returned. And a feedback circuit for feeding back the change information to the second NPN transistor to make the transistor perform the constant current operation while the second NPN transistor is conducting. A power supply circuit comprising: