JPH03186909A - Stabilized power circuit - Google Patents

Abstract

PURPOSE:To highly precisely protect an overcurrent by converting a current taken out by means of a PNP type transistor into a voltage and restricting the base current of a voltage controlled transistor when the voltage reaches a prescribed reference voltage whose temperature is compensated. CONSTITUTION:When a transistor Tr2 is turned on, the current which is 1/N of an output current I0 flowing in the emitter of a transistor Tr1 flows in a resistance R3 in an overcurrent protection circuit 2, and it is converted into the voltage by the resistance R3. When the output current increases by an overload and output shorting, the current flowing in the resistance R3 increases. Thus, the potential difference of both ends of the resistance R3 increases. When the potential difference reaches the reference voltage, the output of a differential amplifier 6 reduces the base current of the transistor Tr3 in a control circuit 1. Thus, the transistor Tr3 restricts the base current of the transistor Tr1. Consequently, the output current I0 is nearly restricted to a prescribed value by the transistor Tr1. Thus, the precision of the overcurrent protection circuit 2 can be improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a stabilized power supply circuit applied to a power supply IC such as a regulator IC, and more specifically, a stabilized power supply circuit that uses a PNP transistor as a voltage control element. This invention relates to a stabilized power supply circuit for series control elements.

[Conventional technology]

In conventional series control type stabilized power supply circuits, in order to reduce the voltage difference between input and output, P is used as a series control element.
An NP type transistor is used. Such a stabilized power supply circuit will be explained based on FIG. 2.

As shown in FIG. 2, in the stabilized power supply circuit, the PNP type transistor Trz+ as a series control element has its base connected to the input terminal V, and its base connected to the collector of the transistor Tr2+ driving transistor Trz□. It is connected to the. Further, the collectors of the transistors Tr, , are connected to the output terminal V0, and are also grounded via a resistor R2R2□ connected in series. The transistor Trz□ has its emitter grounded via the resistor R23, and its base connected to the output terminal of the differential amplifier 21. A constant current source 22 is provided between the base of the transistor Trz□ and the input terminal V1.

The differential amplifier 21 has an inverting input terminal connected to the connection point between the resistor R2 and the resistor R2□, and a non-inverting input terminal connected to the output terminal of the reference voltage source 23. Reference voltage a! 23, the ground terminal is grounded and outputs a constant reference voltage. Then, the differential amplifier 21 compares the voltage generated at the connection point t between the resistor RZI and the resistor R2□ with the reference voltage of the reference voltage source 23,
By amplifying these voltage differences, the base current of the transistor Trz□ supplied from the constant current #22 is controlled. Further, the overcurrent protection transistor Trza has a collector connected to the base of the transistor Trz, a base connected to the emitter of the transistor Trz, and an emitter connected to the ground.

In the above stabilized power supply circuit, the operation of transistor Trz□ is controlled based on the voltage generated at the connection point between resistor RZI and resistor R2□ by differential amplifier 2■, that is, the feedback voltage obtained from the output voltage. Therefore, the transistor T
Transistor Tr by rzz.

The base current of is controlled. This makes the input voltage
l-transistor Tr2. is controlled by the reference voltage source 230
It is output as a constant voltage corresponding to the reference voltage.

Then, due to the increase in output current, transistor Tr2.
When the base current of transistor Tr23 increases, the transistor Tr23 becomes
The base potential becomes higher than normal and turns on. Therefore, the current flowing from the constant current source 22 to the base of the transistor Tr2 is reduced because it flows through the collector edge of the transistor Tr23. As a result, the transistor Tr2° reduces the base current of the transistor Trz+, so the transistor Tr limits the output current.

By the way, the base current IRQ of the transistor Trz when limited by the transistor Trz□ is the base current of the transistor Tr2□ and the transistor Tr,
If we ignore the base current of 3, we get: However, V B
E23 is the voltage across the transistor Tr23. Here, when the stabilized power supply circuit is implemented as an IC, the resistor R23 is normally formed by an emitter diffusion resistor, and its resistance value has a temperature characteristic of about 2000 pPm/'C.
The emitter voltage VBE2:l is approximately -3000 p pm
/'C temperature characteristics. Therefore, the base current r
Ilo will have a temperature characteristic of about -5000 ppm/''C.

[Problem to be solved by the invention]

However, in the above stabilized power supply circuit, the transistor T
Even if the base current of rz+ is accurately limited by the transistor Tr2°, the output current is limited by the transistor T
Due to variations in the DC current amplification factor hyi of r, , its value varies greatly. Therefore, transistor Tr2. Even if the overcurrent protection circuit is operated, a problem arises in that it is difficult to accurately limit the output current to a desired value.

Further, in the above stabilized power supply circuit, the transistor Tr,
3, the transistor Tr2. Because the temperature characteristic of the limited base current IEO becomes too large, approximately -5000 ppm/'C, the transistor Trzs turns on at high temperatures in the M region where the output current is less than the value that should be limited, resulting in overload. There was a risk that current protection could not be performed accurately.

[Means to solve the problem]

In order to solve the above problems, the stabilized power supply circuit according to the present invention includes a PNP type voltage control transistor that controls the input voltage, and a feedback voltage that changes along with the output voltage is equal to a constant reference voltage. A stabilized power supply circuit equipped with a control means for controlling the base current of a PNP type I Landisk is characterized by being configured as shown below.

In other words, a PNP transistor forms a current mirror circuit together with a voltage control transistor to divide the output current at a fixed ratio, and the current taken out by the PNP transistor is converted into a voltage, and this voltage is a temperature-compensated constant voltage. and current limiting means for limiting the base current of the voltage control transistor when the reference voltage of the voltage control transistor is reached.

Note that the reference voltage source that generates the reference voltage to be supplied to the control means and the reference voltage source that generates the reference voltage to be supplied to the current limiting means may be different, but due to the circuit configuration, configured identically.

[For production]

According to the above configuration, the current taken out at a constant rate by the PNP transistor is converted into a voltage by the current limiting means and used for detecting the output current, but this voltage is used to increase the output current. When the voltage increases accordingly and reaches the reference voltage, the current limiting means similarly limits the base current of the voltage control transistor, thereby limiting the output current.

In the above operation, since the output current is detected on the side of the voltage control transistor by the PNP transistor and the current limiting means, there are variations in the DC current amplification factor hFE of the voltage control transistor. However, the base current of the voltage control transistor can be limited without being affected by this. Therefore, overcurrent protection can be performed with high precision without sacrificing the advantage of a stabilized power supply circuit using a PNP type voltage control transistor, which allows voltage control with a small voltage difference between input and output.

Furthermore, as described above, even in a configuration in which the output current is detected on the output side of the voltage control transistor to limit the base current of the voltage control transistor, the standard used as a criterion for operating the current limiting means Since the voltage is temperature compensated, the temperature dependence of the detected current can be significantly reduced. Therefore, the current limiting means, at high temperatures,
Current limiting operation can be performed accurately without operating in a region where the output current is less than the value to be limited.

〔Example〕

An embodiment of the present invention will be described below based on FIG.

As shown in FIG. 1, the stabilized power supply circuit according to the present embodiment includes a PNP transistor Tr as a voltage control transistor, a control circuit 1 as a control means for controlling the base current of the transistor Tr, and a transistor Tr. Tr+
, a PNP type transistor Trz forming a current mirror circuit, and an overcurrent protection circuit 2 as a current limiting means.
It is equipped with The emitter of the transistor Tr is connected to the input terminal V8 in the stabilized power supply circuit, and the collector is connected to the output terminal V8 in the stabilized power supply circuit. It is connected to the. The base current of this transistor Tr is controlled by the control circuit 1 to control the input voltage and stabilize the output voltage to be in accordance with a constant reference voltage, which will be described later.

The control circuit 1 includes a resistor RI'R2, a transistor Tr3,
It is composed of a differential amplifier 3, a constant current source 4, and a base Y# voltage source 5. The resistors R1 and R2 are connected in series, one end of the resistor R1 is connected to the collector of the transistor Tr+, and one end of the resistor R2 is grounded to generate a feedback voltage for negative feedback of the output voltage to the differential amplifier 3. It constitutes a voltage dividing resistor circuit. The transistor Tr has a collector connected to the base of the transistor Tr, an emitter grounded, and a base connected to the output terminal of the differential amplifier 3. This transistor Tr+ is operated by being supplied with a base current by a constant current source 4 provided between the base and the input terminal V8, and drives the transistor Tr.

The differential amplifier 3 has an inverting input terminal connected to the connection point between the resistors R1 and R2, and a non-inverting input terminal connected to the output terminal of the reference voltage source 5. In this differential amplifier 3, the feedback voltage obtained by the resistors R1 and R2 is connected to the reference voltage source 5.
The base current of transistor Tr3 is controlled by amplifying the difference between both voltages so that it becomes equal to the reference voltage of
The base current of the transistor Tr is indirectly controlled. Further, the reference voltage source 5 has a ground terminal connected to the ground. This reference voltage source 5 is temperature-compensated, and is configured, for example, by a bandgap reference circuit to generate a constant reference voltage.
The transistor Tr is connected to the emitter of the transistor Tr, and its base is connected to the base of the transistor Tr, thereby forming a current mirror circuit together with the transistor Tr. The transistor Tr2 has a current flowing through its emitter and a transistor Tr2.
The ratio of the current flowing to the emitter of , is l :N (N>1
), the area ratio of the transistors Tr and ξ is set to 1:N. For example, in a stabilized power supply circuit with a rated output current of I, N is set to 40.

Further, the base of the transistor T r z is grounded via a resistor R3 in the overcurrent protection circuit 2 .

The overcurrent protection circuit 2 includes the resistor R3 and the differential amplifier 6.
It is made up of. The differential amplifier 6 has an inverting input terminal connected to the output terminal of the reference voltage source 5 in the control circuit 1, and an inverting input terminal connected to the connection point between the collector of the transistor Trz and the resistor R3. Further, the output terminal of the differential amplifier 6 is the transistor Tr in the control circuit 1.

connected to the base of. The resistor R3 converts the current shunted from the output current at the above ratio by the transistor Trz into a voltage. The differential amplifier 3 then compares the detected voltage converted by the resistor R1 with the reference voltage of the reference voltage source 5, and when the detected voltage reaches the reference voltage, draws in the base current of the transistor Tr3 to reduce it. ing.

In the above configuration, the input voltage input from the input terminal V is controlled by the resistor Tr+ and output to the output terminal V0, and this output voltage is controlled by the resistor R1.
The voltage is divided by R2 and input to the differential amplifier 3 as a feedback voltage. At this time, when the output voltage fluctuates, the feedback voltage also fluctuates accordingly, but since the differential amplifier 3 amplifies the difference between the pressures of both types so that the feedback voltage is equal to the reference voltage of the reference voltage source 5, The transistor Tr3 adjusts the base current of the transistor Tr according to the output of the differential amplifier 3. As a result, transistor Tr+ controls the input voltage so as to cancel out fluctuations in the output voltage, and holds the output voltage constant.

At this time, since the transistor Trz is ON, a current equal to 1/N of the output current I0 flowing into the emitter of the transistor Tr flows through the resistor R3 in the overcurrent protection circuit 2, and is converted into a voltage by the resistor R3. Ru. Here, when the output current increases due to an overload or an output short circuit, the current flowing through the resistor R3 also increases, so that the potential difference between both ends of the resistor R3 increases. When this potential difference reaches the reference voltage, the output of the differential amplifier 6 reduces the base current of the transistor Tr3 in the control circuit 1, so that the transistor Tr+ limits the base current of the transistor Tr. Therefore, the output current ■.

is limited to a substantially constant value by the transistor T r + .

By the way, at this time, the current 1°/N flowing into the overcurrent protection circuit 2 via the transistor T r 2 is 1 (I Vl, 4 N R if the reference voltage is V rllf).

becomes. In the above equation, the resistor R3 is constituted by an emitter diffused resistor as in the conventional case, and therefore its resistance value has a temperature dependence of about 2000 ppm/''C.

Also, the reference voltage V18. has a temperature characteristic of about 200 ppm/''C because the reference voltage source 5 is temperature compensated. Therefore, the detection current 1,/N is about 22
Since it has a temperature characteristic of 00 ppm/''C, the current detection accuracy of the overcurrent protection circuit 2 can be improved.

〔Effect of the invention〕

As described above, the stabilized power supply circuit according to the present invention includes a PNP transistor that forms a current mirror circuit with a voltage control transistor so as to divide an output current at a fixed ratio, and a current extracted by the PNP transistor. is converted into a voltage, and when this voltage reaches a temperature-compensated constant reference voltage, the voltage control circuit 1-current limiting means limits the base current of the transistor.

As a result, the output current can be detected on the emitter side of the voltage control transistor, and even if there are variations in the DC current amplification factor of the PNP transistor, the base current of the voltage control transistor can be limited without being affected by it. be able to. Therefore, without sacrificing the advantage of a stabilized power supply circuit using a PNP type voltage control transistor, which allows voltage control with a small voltage difference between input and output,
Overcurrent protection can be performed with high precision.

Furthermore, since the reference voltage for operating the current limiting means is temperature compensated, the current detection accuracy of the current controlling means can be improved. Therefore, the current limiting means does not operate in a region where the output current is small at high temperatures, and can accurately perform the current limiting operation.

5. Therefore, according to the present invention, it is possible to provide a stabilized power supply circuit with a more advanced overcurrent protection function.

[Brief explanation of drawings]

FIG. 1 shows one embodiment of the present invention, and is a circuit diagram showing the configuration of a stabilized power supply circuit. FIG. 2 shows a conventional example, and is a circuit diagram showing the configuration of a stabilized power supply circuit. 1 is a control circuit (control means), 2 is an overcurrent protection circuit (current limiting means), Tr is a transistor (voltage control transistor), and Trz is a transistor (PNP type 1-transistor). 6

Claims (1)

[Claims] 1. A PNP voltage control transistor that controls the input voltage, and a base current of the PNP transistor so that the feedback voltage that changes with the output voltage is equal to a constant reference voltage. In a stabilized power supply circuit equipped with a control means, a PNP type transistor constitutes a current mirror circuit with a voltage control transistor so as to divide an output current at a fixed ratio, and a current taken out by the PNP type transistor is converted into a voltage. and current limiting means for converting the voltage and limiting the base current of the voltage control transistor when this voltage reaches a certain temperature compensated reference voltage.