JPH08292816A - Direct current stabilized power source - Google Patents

Abstract

PURPOSE: To provide a DC stabilized power source which can have both voltage and current characteristics controlled with high precision and high reliability and is inexpensive by actualizing constant voltage and constant current characteristics by using one reference voltage source which is connected to a ground line as to a series regulator type power circuit. CONSTITUTION: Protecting operation against an overvoltage and an overcurrent is performed by using the one reference voltage source Vcr which has its minus electrode side connected to the ground line or a minus power line. Namely, an error amplifier EA1 controls a transistor(TR) Q for series regulators so that an output voltage Vo becomes equal to a voltage represented as RZ*Vcr /(R1 +R2 ), and consequently the output voltage Vo has constant voltage characteristics. When a load current Io is larger than (Vcr -Vo)/rA (where rA is resistance for current detection), on the other hand, the error amplifier EA4 is saturated to the minus side and a diode D conducts to perform control so that Io =(Vcr -Vo)/rA, thereby obtaining constant current characteristics. When Io <(Vcr -Vo)/rA, the error amplifier EA4 is saturated to the plus side and the diode D turns off.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stabilized direct current power supply with improved overvoltage and overcurrent protection means.

[0002]

2. Description of the Related Art Conventional examples of a stabilized DC power supply circuit having overvoltage and overcurrent protection means are shown in FIGS. FIG.
In, In is a terminal to which the unstable DC voltage Vin is applied, Out is a terminal from which the stabilized DC voltage Vo is taken out, and GND is a ground line. Q is a transistor for series regulator, rA is a resistor for current detection, and these are connected in series between terminals In and Out. Q is a transistor for current control, EA1 is an error amplifier for voltage control, rB is a resistance element, Vr is a reference voltage source, and its negative side is connected to the ground line GND.

In the circuit of FIG. 3 having such a configuration,
The series regulator transistor Q is controlled by the output of the error amplifier EA1 so that the output voltage Vo becomes equal to the reference voltage Vr. In addition, the detection resistance r of the load current Io
When the voltage generated at A becomes larger than a predetermined value, the transistor Qc turns on, which prevents overload current. In this way, the stabilized DC voltage Vo is obtained from the output terminal Out.

Although the power supply circuit of FIG. 3 having such a configuration has been conventionally used, the accuracy of the overload current limiting threshold depends on the variation of the resistance rA and the base-emitter voltage of the transistor Qc. There is a problem that is bad.

FIG. 4 is obtained by eliminating the defect of FIG. 3, and controls the transistor Q via the error amplifier EA2 so that the voltage drop caused by the load current Io in the resistor rA becomes equal to the reference voltage Vcr. The load current Io is controlled to a constant value. The circuit of FIG. 4 having such a configuration does not have the problem that the threshold of overload limitation varies as in FIG. 3, but the control is only overcurrent protection, and the reference voltage source Vcr is floating. There are drawbacks.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and in a series regulator type power supply circuit, one constant voltage and constant current characteristic is connected to a ground line. It is an object of the present invention to provide an inexpensive DC stabilized power source which can be controlled with high accuracy and high reliability in terms of both voltage and current characteristics by implementing the above standard voltage source.

[0007]

According to claim 1 of the present invention,
Series regulator transistor and current detection resistor connected in series between input and output terminals, reference voltage source whose negative side is grounded, one end of the current detection resistor and the reference voltage dividing point are connected to the input end A first error amplifier whose output end is connected to the base of the transistor, and the other end of the current detection resistor and a reference voltage source are connected to the input end, and the output end is connected to the base of the transistor via a diode. It is composed of a second error amplifier.

According to a second aspect of the present invention, a series regulator transistor connected to the + power supply line, a current detection resistor connected to the − power supply line, and a reference voltage source having a negative electrode side connected to one end of the current detection resistor. A first error amplifier in which the other end of the current detection resistor and the voltage dividing point of the reference voltage are connected to the input end and the output end is connected to the base of the transistor; and the output side of the transistor and the reference voltage source are input. And a second error amplifier having an output terminal connected to the base of the transistor through a diode.

[0009]

In the present invention as described above, the overvoltage and overcurrent protection operation is performed by using one reference voltage source whose negative electrode side is connected to the ground line or the power source line.

[0010]

The present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of an embodiment of a power supply circuit according to the present invention. In the figure, In is a terminal to which an unstable DC voltage Vin is applied, Out is a terminal for taking out the stabilized DC voltage Vo, and GND is a ground line. Q is a transistor for a series regulator, rA is a resistor for current detection, and these are connected in series between terminals In and Out as in the conventional example of FIG. EA1 and EA4 are error amplifiers, Vcr is a reference voltage source, and the positive electrode side is amplifier EA.
4 is connected to the + input terminal, and the negative electrode side is connected to the ground line. R1 and R2 are voltage dividing resistors for dividing the reference voltage Vcr, and the voltage dividing points are connected to the + input terminal of the error amplifier EA1. The-input terminal of the error amplifier EA1 is connected to the connection point of the resistor rA and the output terminal Out, and EA1
Is connected to the base of the transistor Q via the resistor rB. D is a diode, the anode of which is the base of the transistor Q and the cathode of which is the error amplifier EA4.
, And the negative input terminal of EA4 is connected to the connection point of the transistor Q and the resistor rA.

The operation of the circuit of FIG. 1 having such a configuration will be described as follows. The error amplifier EA1 outputs the output voltage Vo.
And R2 * Vcr / (R1 + R2), the series regulator transistor Q is controlled so that the voltages are equal, and the output voltage Vo has a constant voltage characteristic.
On the other hand, the load current Io is Io> (Vcr-Vo) / rA
Error amplifier EA4 saturates on the negative side and diode D
Is turned on and the transistor Q is controlled so that Io = (Vcr-Vo) / rA, resulting in a constant current characteristic.
Error amplifier EA when Io <(Vcr-Vo) / rA
4 saturates to the positive side, so diode D is turned off.
Thus, the load current Io is (Vcr-Vo) / rA
= {R1 / (R1 + R2)} * Vcr / rA is protected so as not to exceed, and the constant current drooping characteristic is provided at the time of overcurrent.

FIG. 2 is a circuit diagram of another embodiment of the present invention. 2, the same elements as those of FIG. 1 are designated by the same reference numerals as those of FIG. 1, and their re-explanation is omitted. In FIG. 2, the series regulator transistor Q has an unstable DC voltage -Vi.
terminal In 'to which n is applied and stabilized DC voltage -V
It is connected to the + power supply line connecting the terminal Out ′ for taking out o. rc is a resistance for detecting an overcurrent, and this resistance element connects a terminal In ′ to which an unstable DC voltage −Vin is applied and a terminal Out ′ for taking out the stabilized DC voltage −Vo− connected to a power supply line. ing. The negative side of the reference voltage source Vr is connected to this-power supply line.

The operation of the power supply circuit of FIG. 2 having such a configuration is similar to that of the circuit of FIG. 1, and the overvoltage droop threshold Vo (max) = {R1
/ (R1 + R2)} * Vr constant current output current Io = {R2 / (R1 + R2)} * V
It has a constant voltage characteristic and a constant current load characteristic represented by r / rc. The circuit of FIG. 2 has a feature that it can be applied to a negative output power supply in a relative relationship.

[0014]

According to the present invention, in a series regulator type power supply circuit, constant voltage and constant current characteristics are realized by using one reference voltage source whose one end is grounded or-is connected to a power supply line to obtain a voltage and It is possible to obtain an inexpensive stabilized DC power supply that can be controlled with high accuracy and high reliability in terms of current characteristics.

[Brief description of drawings]

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

FIG. 2 is a circuit configuration diagram showing another embodiment of the power supply circuit according to the present invention.

FIG. 3 is a circuit configuration diagram of an example of a conventional power supply circuit.

FIG. 4 is a circuit configuration diagram of another example of a conventional power supply circuit.

[Explanation of symbols]

 In Input terminal Out Output terminal GND Ground line Q series regulator rA, rc Current detection resistance Vr, Vcr Reference voltage source EA1, EA4 Error amplifier D Diode

Claims (2)

[Claims] 1. A series regulator transistor and a current detecting resistor connected in series between input and output terminals, a reference voltage source whose negative side is connected to a ground line, one end of the current detecting resistor and a reference voltage. A voltage dividing point connected to an input terminal and an output terminal connected to the base of the transistor;
A stabilized DC power supply comprising: an error amplifier; and a second error amplifier having the other end of the current detection resistor and a reference voltage source connected to the input end and the output end connected to the base of the transistor through a diode. 2. A series regulator transistor connected to the + power supply line, a current detection resistor connected to the − power supply line, a reference voltage source whose negative side is connected to one end of the current detection resistor, and a current detection resistor. A first error amplifier in which the other end of the resistor and the voltage dividing point of the reference voltage are connected to the input end and the output end is connected to the base of the transistor, and the output side of the transistor and the reference voltage source are connected to the input end. A stabilized direct-current power supply comprising a second error amplifier whose output end is connected to the base of the transistor via a diode.