JP2015232796A - Regulator circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve the simplification and cost reduction of a circuit configuration by enhancing stability in operation of drooping characteristics of the output current during overcurrent time in a regulator circuit in which the output voltage of a power semiconductor element inserted between DC current input and output terminals is stabilized by a constant voltage element.SOLUTION: A constant voltage element ZD21 is connected between a control terminal of a power semiconductor element Q21 for output control inserted between an input terminal and an output terminal of a DC voltage, and a ground. A resistance element R21 for vias is connected between the control terminal and an input-side terminal of the power semiconductor element. A resistance element R22 for overcurrent detection is inserted between an output-side terminal of the power semiconductor element and the output terminal of the DC voltage. Diodes D21, D22 for control voltage reduction are connected between a connection node N21 of the control terminal and the constant voltage element of the power semiconductor element and a connection node N22 of the resistance element for the overcurrent detection and the output terminal of the DC voltage.

Description

  In the present invention, a power semiconductor element for output control such as a transistor is inserted between a DC voltage input terminal and an output terminal, and the control voltage of the power semiconductor element is stabilized by a constant voltage element such as a Zener diode. Relates to a regulator circuit configured as described above.

  A regulator circuit X having a circuit configuration as shown in FIG. 3 is one example of a conventional regulator circuit used for controlling an internal circuit of a switching power supply device or for low power output. 3, T1p and T1n are DC voltage input terminals, T2p and T2n are DC voltage output terminals, C11 is an input side smoothing capacitor, C12 is an output side smoothing capacitor, and Q11 is for output control as a power semiconductor element. Bipolar transistor, ZD11 is a Zener diode as a constant voltage element, R11 is a biasing resistance element, A is a DC power supply, and B is a load circuit. A series circuit of the bias resistor element R11 and the Zener diode ZD11 is connected between both ends of the smoothing capacitor C11 on the input side, and a connection node N11 of the bias resistor element R11 and the Zener diode ZD11 is connected to the base (control terminal) of the transistor Q11. Has been.

  The DC power source A charges the input-side smoothing capacitor C11, and the current from the smoothing capacitor C11 is supplied to the load circuit B through the transistor Q11 while charging the output-side smoothing capacitor C12. Since the base voltage (control voltage) of the transistor Q11 is regulated to a constant value by the breakdown voltage (zener voltage) of the Zener diode ZD11, the output current Io flowing through the transistor Q11 is maintained at a constant value, and the output voltage Vo is stabilized. To do. 3 is disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 57-95179).

FIG. 4 is an operating characteristic diagram showing the relationship between the output current Io and the output voltage Vo when the regulator circuit X shown in FIG. Under normal conditions, the output voltage Vo changes with a linear characteristic (almost constant) that decreases slightly as the output current Io increases (range from zero current to the rated current). At the time of an overcurrent when an output short circuit occurs in the load circuit B, the emitter voltage of the transistor Q11 becomes the ground (GND) level, and the base-emitter voltage V _BE excessively increases. As a result, while the output current Io flowing through the transistor Q11 increases, the output voltage Vo decreases, and finally a drooping characteristic occurs in which the output voltage Vo disappears due to the output short-circuit current Is. At this time, the increase in the output current Io until the output short-circuit current Is is settled becomes considerably large. When the input voltage from the DC power source A is V _IN , the power loss P _loss in the transistor Q11 is proportional to V _IN × Is (P _loss ∝V _IN × Is). Since the output short-circuit current Is is considerably large, the power loss P _loss is also large, the amount of heat generated by the transistor Q11 is increased, and there is a risk of circuit breakage, heat generation, and ignition.

A regulator circuit Y disclosed in Japanese Patent Application Laid-Open No. 11-111219 shown in FIG. 5 is a solution to solve the above-mentioned problem found in the regulator circuit X of FIG. The regulator circuit Y corresponds to a configuration obtained by adding an overcurrent detection resistor element R12 and a protection transistor Q12 to the configuration of the regulator circuit X of FIG. That is, the overcurrent detection resistor element R12 is connected between the emitter of the transistor Q11 and the high-side DC voltage output terminal T2p. The protection transistor Q12 has its base connected to the emitter of the transistor Q11, its collector connected to the connection node N11 between the base of the transistor Q11 and the biasing resistance element R11, and its emitter connected to the overcurrent detection resistance element R12. It is connected to a connection node N12 with the output terminal T2p. In the regulator circuit Y, the protection transistor Q12 is normally non-conductive. That is, the value of the current Io flowing through the overcurrent detection resistor element R12 is small, and the protection transistor Q12 has a non-conducting state because its base-emitter voltage V _BE (= R12 × Io) is less than the on-voltage. It has become. However, when an output short circuit occurs, the voltage drop in the overcurrent detection resistor element R12 increases, and the protection transistor Q12 is turned on when its base-emitter voltage V _BE exceeds the on-voltage. As a result, the base current injected from the biasing resistance element R11 is bypassed with respect to the base of the transistor Q11 through the path of the protection transistor Q12 (node N11 → transistor Q12 → node N12). That is, the base voltage of the transistor Q11 is lowered to limit the output current Io flowing between the collector and the emitter, and the output voltage Vo is lowered.

  FIG. 6 is an operational characteristic diagram showing the relationship between the output current Io and the output voltage Vo when the regulator circuit Y is overcurrent. From this figure, in the case of the regulator circuit Y, the output short circuit current Is is reduced to about one third of that in the case of the regulator circuit X of FIG. 4, and the loss in the transistor Q11 at the time of abnormality such as an output short circuit can be greatly reduced. ing.

JP-A-57-95179 Japanese Patent Application Laid-Open No. 1-111219

However, in the case of the regulator circuit Y shown in FIG. 5, as apparent from the operating characteristic diagram of FIG. 6, the operating characteristic depends on the current amplification factor h _fe of the protection transistor Q12 and the magnitude of the base-emitter voltage V _BE . There is a feature that the influence appears greatly, and there is a problem that the fluctuation of the current value increases and decreases in the operating characteristic diagram from the start to the end of the overcurrent protection operation, and the operating characteristic becomes unstable. is there. Further, the transistor Q12 is used as a semiconductor element for protection, and improvement in cost is demanded.

  The present invention was created in view of such circumstances, and a power semiconductor element for output control is inserted between a DC voltage input terminal and an output terminal, and the control voltage of the power semiconductor element is set to a constant voltage. The regulator circuit configured to be stabilized by the element is intended to make the operation of the drooping characteristic of the output current at the time of overcurrent highly stable, and to simplify the circuit configuration and reduce the cost. .

  In order to solve the above problems, the present invention takes the following measures.

The regulator circuit according to the present invention comprises:
A power semiconductor element that is inserted between a DC voltage input terminal and an output terminal, and controls output by a control voltage applied to the control terminal;
A constant voltage element inserted between the control terminal of the power semiconductor element and the ground;
A regulator circuit comprising a bias resistance element connected between a control terminal and an input side terminal of the power semiconductor element,
further,
An overcurrent detection resistance element inserted between the output side terminal of the power semiconductor element and the output terminal of the DC voltage;
A control voltage reduction diode connected between a connection node between the control terminal of the power semiconductor element and the constant voltage element, and a connection node between the overcurrent detection resistance element and the output terminal of the DC voltage; It has the composition provided.

  The regulator circuit of the present invention having the above configuration exhibits the following operation.

  Under normal conditions, the control voltage reducing diode between the control terminal of the power semiconductor element and the output terminal of the DC voltage is kept in a non-conductive state and does not affect the operation. Since the voltage applied to the control terminal of the power semiconductor element is kept constant by the constant voltage element, the output of the power semiconductor element is stabilized.

  When an overcurrent state occurs due to an abnormality such as an output short circuit in the load circuit, the potential of the output terminal of the DC voltage is greatly reduced, and the control voltage reducing diode becomes conductive. Then, the state changes so that the total voltage of the voltage between the control terminal and the output side terminal in the power semiconductor element and the voltage across the overcurrent detection resistance element becomes equal to the voltage drop due to the control voltage reducing diode. The current that flows in the power semiconductor element at this time is the output short-circuit current. The output short-circuit current includes the forward voltage of the control voltage reduction diode, the voltage between the control terminal and the output side terminal of the power semiconductor element, and the overcurrent detection. It is determined by the resistance value of the resistance element. By appropriately determining these circuit constants, it is possible to limit the output short-circuit current to a required small value (solving the problem of the regulator circuit X).

  In the above description, the number of control voltage reduction diodes is singular or plural. In the case of a plurality, they are connected in series in the same direction. In this case, the forward voltage of the control voltage reducing diode is the sum of the forward voltages of all the diodes. Thereby, an overcurrent protection point can be adjusted appropriately.

  According to the present invention, the path between the control terminal of the power semiconductor element and the output terminal of the DC voltage is cut off during normal times, and is turned on during overcurrent to reduce the control voltage of the power semiconductor element, In addition, a diode (control voltage reduction diode) is used as an element for shutting off and conducting, so that the operation of the drooping characteristics of the output current during overcurrent is highly stable and the circuit configuration is simplified. And cost reduction.

The circuit diagram which shows the structure of the regulator circuit of the Example of this invention Operation characteristic diagram showing the relationship between output current and output voltage at the time of overcurrent of the regulator circuit of the embodiment of the present invention 1 is a circuit diagram showing a configuration of a regulator circuit of a first conventional example Operation characteristic diagram showing relationship between output current and output voltage in overcurrent of regulator circuit of first conventional example The circuit diagram which shows the structure of the regulator circuit of a 2nd prior art example Operation characteristic diagram showing relationship between output current and output voltage in overcurrent of regulator circuit of second conventional example

  Hereinafter, embodiments of the regulator circuit of the present invention having the above configuration will be described in detail at the level of specific examples.

  FIG. 1 is a circuit diagram showing a configuration of a regulator circuit in an embodiment of the present invention, and FIG. 2 is an operation characteristic diagram showing a relationship between an output current Io and an output voltage Vo when the regulator circuit is overcurrent.

  First, the components in the circuit diagram of FIG. 1 are listed. 20 is a regulator circuit according to an embodiment of the present invention, T1p and T1n are DC voltage input terminals, T2p and T2n are DC voltage output terminals, C21 is an input side smoothing capacitor, C22 is an output side smoothing capacitor, and Q21 is power. An NPN bipolar transistor as a semiconductor element, ZD21 is a Zener diode as a constant voltage element, R21 is a biasing resistance element, R22 is an overcurrent detection resistance element, D21 and D22 are control voltage reduction diodes, and A is a DC power supply. , B are load circuits.

  Next, a specific configuration of the regulator circuit 20 will be described.

  An input-side smoothing capacitor C21 is connected between the DC voltage input terminals T1p and T1n, an output-side smoothing capacitor C22 is connected between the DC voltage output terminals T2p and T2n, and a high-side DC voltage input terminal T1p. A collector / emitter of a transistor Q21 as a power semiconductor element is connected between the DC voltage output terminal T2p (an overcurrent detection resistor element R22 described later is connected to the emitter of the transistor Q21). A biasing resistance element R21 is connected between the collector (input side terminal) and the base (control terminal) of the transistor Q21, and a Zener diode ZD21 is connected between the base and the low-side DC voltage input terminal T1n. The low-side DC voltage input terminal T1n side is connected. An overcurrent detection resistance element R22 is connected between the emitter (output side terminal) of the transistor Q21 and the positive terminal of the smoothing capacitor C22 on the output side. Two control voltage reducing diodes D21 and D22 are connected between a connection node N21 between the base of the transistor Q21 and the Zener diode ZD21, and a connection node N22 of the overcurrent detection resistor element R22 and the output-side smoothing capacitor C22. A series circuit is connected. The anode of the control voltage reduction diode D21 is connected to the base of the transistor Q21, the cathode of the control voltage reduction diode D21 is connected to the anode of the control voltage reduction diode D22, and the cathode of the control voltage reduction diode D22 is overcurrent detection. Is connected to a connection node N22 between the resistance element R22 and the output-side smoothing capacitor C22. A DC power source A is connected between the DC voltage input terminals T1p and T1n, and a load circuit B is connected between the DC voltage output terminals T2p and T2n.

  Next, the operation of the regulator circuit 20 of the embodiment of the present invention configured as described above will be described.

  A current from the DC power source A flows from the high-side DC voltage input terminal T1p, the input-side smoothing capacitor C21 is charged, and a smoothed input voltage is generated. A current due to the input voltage flows through the bias resistor element R21 and the Zener diode ZD21, and a base voltage (control voltage) defined by the breakdown voltage of the Zener diode ZD21 is applied to the base of the transistor Q21. Transistor Q21 is driven by its base voltage and outputs a constant controlled current. This output current is supplied to the load circuit B from the high-side DC voltage output terminal T2p while charging the output-side smoothing capacitor C22.

  Under normal conditions, the base voltage of the transistor Q21 is stabilized at a specified value by the action of the Zener diode ZD21, and the output current Io from the transistor Q21 is also stabilized. Therefore, the output voltage Vo is also kept constant.

When an abnormality such as an output short circuit occurs and the voltage at the output terminal T2p of the high-side DC voltage is greatly reduced, the output current Io flowing through the series circuit of the transistor Q21 and the overcurrent detection resistor element R22 increases rapidly. With reference to the base of the transistor Q21, the potential of the connection node N22 between the overcurrent detection resistor element R22 and the output-side smoothing capacitor C22 is observed. V _BE between the base and emitter voltage of the transistor Q21, Io an output current flowing through the overcurrent detection resistor element R22, the voltage across the V ₂₂ of the overcurrent detecting resistor element R22 (= R22 × Io), control voltage reduction the forward voltage of the diode D21 Vf _1, the forward voltage of the control voltage reduction diode D22 as Vf _2,
V _BE + R22 × Io ≦ Vf ₁ + Vf ₂
That is,
Io ≦ (Vf ₁ + Vf ₂ −V _BE ) / R22
If the output current Io is below a certain value as described above, both control voltage reduction diodes D21 and D22 maintain the non-conductive state. However, the output current Io exceeds a certain value due to an abnormality such as an output short circuit.
Io> (Vf ₁ + Vf ₂ −V _BE ) / R22
The two control voltage reduction diodes D21 and D22 are turned on. As a result, the base current injected from the bias resistor element R21 with respect to the base of the transistor Q21 is bypassed by the path of both control voltage reducing diodes D21 and D22, and the output flowing between the collector and emitter of the transistor Q21. The current Io is limited, the output voltage Vo is lowered, and the output power is narrowed down.

In the process of limiting the output current Io, the output current Io gradually decreases,
Io = (Vf ₁ + Vf ₂ −V _BE ) / R22
Then, the output current Io stops decreasing and settles down. The output current Io at this time is the output short-circuit current Is.

  From the operating characteristic diagram of FIG. 2 showing the relationship between the output current Io and the output voltage Vo of the regulator circuit 20, the destination where the current settles when the output current Io is increased in the short-circuit direction is indicated by “x”. The output short-circuit current Is. In the case of the regulator circuit 20 of the embodiment of the present invention, the output short-circuit current Is is reduced to about one-third that of the regulator circuit X shown in FIG. 4, and in the case of the regulator circuit Y shown in FIG. In comparison, the loss is substantially reduced in the transistor Q21 in the event of an abnormality such as an output short circuit. Therefore, heat generation at the time of abnormality can be effectively suppressed.

  In addition, there is no characteristic disturbance as in the case of the regulator circuit Y shown in FIG. 6, and the change characteristic of the output current Io at the time of abnormality is stable.

  The path connecting the base of the transistor Q21 and the output terminal T2p of the high-side DC voltage is cut off during normal times, and as a semiconductor element that conducts to reduce the base voltage during overcurrent, the regulator circuit Y shown in FIG. In this case, the protection transistor Q12 is used. On the other hand, in the embodiment of the present invention, two control voltage reducing diodes D21 and D22 are used. This enables a cheaper configuration than using a transistor.

  The present invention relates to a regulator circuit used for controlling an internal circuit of a switching power supply device or for low power output, and a power semiconductor element for output control such as a transistor between a DC voltage input terminal and an output terminal. In a regulator circuit configured to stabilize the control voltage of the power semiconductor element by a constant voltage element such as a Zener diode, the operation of the drooping characteristic of the output current at the time of overcurrent is stable. It is useful as a technique for increasing the cost and simplifying the circuit configuration and reducing the cost.

20 Regulator circuit A DC power supply B Load circuit C21 Smoothing capacitor on the input side C22 Smoothing capacitor on the output side D21, D22 Control voltage reduction diode Q21 Transistor (power semiconductor element)
R21 Bias resistance element R22 Overcurrent detection resistance element T1p, T1n DC voltage input terminal T2p, T2n DC voltage output terminal ZD21 Zener diode (constant voltage element)

Claims (2)

A power semiconductor element that is inserted between a DC voltage input terminal and an output terminal, and controls output by a control voltage applied to the control terminal;
A constant voltage element inserted between the control terminal of the power semiconductor element and the ground;
A regulator circuit comprising a bias resistance element connected between a control terminal and an input side terminal of the power semiconductor element,
further,
An overcurrent detection resistance element inserted between the output side terminal of the power semiconductor element and the output terminal of the DC voltage;
A control voltage reduction diode connected between a connection node between the control terminal of the power semiconductor element and the constant voltage element, and a connection node between the overcurrent detection resistance element and the output terminal of the DC voltage; Regulator circuit provided.   The regulator circuit according to claim 1, wherein the control voltage reduction diode is composed of a plurality of diodes connected in series in the same direction.

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