JP2004348216A - Dc stabilized power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a DC stabilized power supply capable of rising an output voltage from a negative voltage status without damaging any output short-circuit protecting function. <P>SOLUTION: This DC stabilized power supply is provided with a short-circuit protecting circuit part 62 which monitors the short-circuit or abnormality deterioration of an output voltage Vo based on a reference voltage Vadj, and limits the driving control of an output transistor 1 and a clamp circuit part 63 which clamps the lower limit value of the reference voltage Vref to a predetermined positive voltage. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a stabilized DC power supply having an output short-circuit protection function.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, many DC stabilized power supply devices having an overcurrent protection function and an output short-circuit protection function in addition to a regulator function of driving and controlling an output transistor to generate a desired output voltage from an input voltage have been disclosed and proposed. (See, for example, Patent Documents 1 to 3). In such a DC stabilized power supply device, a correlation called a so-called "" shape is established between the generated output voltage Vo and the drive current Ido for driving the output transistor (see FIG. 1). 3).
[0003]
[Patent Document 1]
JP 2002-318625 A [Patent Document 2]
JP-A-2-235121 [Patent Document 3]
JP-A-61-6719 [0004]
[Problems to be solved by the invention]
Indeed, if the DC stabilized power supply device has the above-described output short-circuit protection function, even if the output is short-circuited or abnormally reduced, the drive current Ido is reduced in accordance with the above-mentioned "character shape" characteristic. It is possible to limit the short circuit current.
[0005]
However, the short-circuit protection circuit unit provided in the conventional stabilized DC power supply device is designed on the assumption that the output voltage Vo is a positive voltage, and the drive current is reduced during a period when the output voltage Vo is a negative voltage. The configuration was such that Ido did not flow. Therefore, when the stabilized DC power supply device is started from a state where the output voltage Vo is a negative voltage, the drive current Ido does not flow even after the start, and the output voltage Vo is reduced according to the “F” shape characteristic in FIG. There was a problem of not standing up.
[0006]
The present invention has been made in view of the above problems, and has as its object to provide a stabilized DC power supply device capable of starting an output voltage from a negative voltage state without impairing an output short-circuit protection function.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a stabilized DC power supply according to the present invention drives and controls an output control element so that a reference voltage that fluctuates according to an output voltage matches a predetermined reference voltage. DC stabilization means for generating an output voltage of the output voltage, and a short-circuit protection means for monitoring a short circuit or abnormal drop of the output voltage based on the reference voltage, and limiting the drive control of the output control element by the DC stabilization means. And a clamp means for clamping the lower limit of the reference voltage to a predetermined positive voltage. More specifically, the clamp means is configured using a diode in which a predetermined positive voltage is applied to the anode and the reference voltage is applied to the cathode. With such a configuration, the reference voltage is a positive voltage even if the output voltage is a negative voltage, so that the output voltage can be raised from the negative voltage state without impairing the output short-circuit protection function.
[0008]
Further, in the stabilized DC power supply having the above-described configuration, the short-circuit protection unit may have a configuration that includes a resistor for limiting the operation current. With such a configuration, it is possible to arbitrarily adjust the threshold value of the output voltage at which the short-circuit protection operation is started according to the resistance value of the resistor.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a circuit diagram (partially including a circuit block) showing an embodiment of a stabilized DC power supply according to the present invention. As shown in the figure, the stabilized DC power supply according to the present embodiment includes a pnp bipolar transistor 1, an on / off circuit 2, a reference voltage generation circuit 3, an overheat protection circuit 4, an error amplifier 5, It comprises a base drive circuit 6, resistors 71 to 73, capacitors 81 to 82, and terminals 91 to 94.
[0010]
The transistor 1 is an output control element connected in series between an input terminal 91 to which an input voltage Vin is applied and an output terminal 93 for sending out an output voltage Vo.
[0011]
The on / off circuit 2 is connected between the input terminal 91 and the ground terminal 94 to which the ground potential GND is applied, and operates the reference voltage generation circuit 3 based on the switching voltage Vc applied to the signal terminal 92. Control.
[0012]
The reference voltage generation circuit 3 is connected between the input terminal 91 and the ground terminal 94 and generates a reference voltage Vref based on the bandgap voltage from the input voltage Vin.
[0013]
The overheat protection circuit 4 is connected between the output terminal of the reference voltage generation circuit 3 and the ground terminal 94, detects an overheat state of the device, and lowers the output level of the error amplifier 5.
[0014]
The error amplifier 5 is connected between the input terminal 91 and the ground terminal 94, and is connected to the reference voltage Vref and a reference voltage Vadj (a divided voltage of the output voltage Vo by the resistors 71 and 72) which varies according to the output voltage Vo. ) Is amplified and output.
[0015]
The base drive circuit 6 variably controls the base current of the transistor 1 based on the output level of the error amplifier 5 and performs control for stabilizing the output voltage Vo. The base drive circuit 6 of the present embodiment includes a clamp circuit section 63 which is a feature of the present invention, in addition to the overcurrent protection circuit section 61 and the short-circuit protection circuit section 62. The overcurrent protection circuit 61 includes npn-type bipolar transistors Qa to Qd and resistors Ra to Rc. The short-circuit protection circuit 62 includes a pnp-type bipolar transistor Qe and npn-type bipolar transistors Qf and Qg. And resistors Rd and Re. The clamp circuit section 63 includes an npn-type bipolar transistor Qh. The above transistors Qd, Qf, and Qh are all diode-connected, and are hereinafter appropriately referred to as diodes Qd, Qf, and Qh.
[0016]
The circuit connection of the stabilized DC power supply having the above configuration will be described in detail. The emitter of the output transistor 1 is connected to the input terminal 91. The collector of the output transistor 1 is connected to the output terminal 93, and is also connected to the ground terminal 94 via the resistors 71 and 72. The connection node between the resistors 71 and 72 is connected to the inverting input terminal (−) of the error amplifier 5. A phase compensation capacitor 81 is connected between both ends of the resistor 71, and an output stabilizing capacitor 82 is connected between the output terminal 93 and the ground terminal 94. The base of the output transistor 1 is connected to the collector of the transistor Qb, and also connected to the input terminal 91 and the collector of the transistor Qa via the resistor 73, respectively. The non-inverting input terminal (+) of the error amplifier 5 is connected to the output terminal of the reference voltage generation circuit 3.
[0017]
The emitter of the transistor Qa is connected to one end of the resistor Rb, and the connection node is connected to the base of the transistor Qb, while being connected to the emitter of the transistor Qe via the resistor Re. The other end of the resistor Rb is connected to the emitter of the transistor Qb, and the connection node is connected to the collector and base of the transistor Qd (the anode of the diode Qd) via the resistor Ra. The other end of the resistor Rb is also connected to the base of the transistor Qc via the resistor Rc. The base of the transistor Qa is connected to the output terminal of the error amplifier 5, while being connected to the collectors of the transistors Qc and Qg. The emitter of the transistor Qc is connected to the collector and the base of the transistor Qd (the anode of the diode Qd), and is also connected to the collector and the base of the transistor Qh (the anode of the diode Qh). The emitter of the transistor Qd (the cathode of the diode Qd) is connected to the ground terminal 94.
[0018]
The collector of the transistor Qe is connected to the ground terminal 94 via the resistor Rd, and is also connected to the base of the transistor Qg. The emitter of the transistor Qg is connected to the ground terminal 94. The base of the transistor Qe is connected to the collector and the base (the anode of the diode Qf) of the transistor Qf, respectively. The emitter of the transistor Qf (the cathode of the diode Qf) is connected to the emitter of the transistor Qh (the cathode of the diode Qh), and is also connected to the connection node between the resistors 71 and 72.
[0019]
Hereinafter, various operations (normal regulation operation, overcurrent protection operation, short-circuit protection operation, and clamp operation) of the DC stabilized power supply device having the above configuration will be described in detail.
[0020]
First, the normal regulation operation by the base drive circuit 6 will be described. When the output voltage Vo falls below the set value, the reference voltage Vref becomes higher than the reference voltage Vadj, so that the output level of the error amplifier 5 becomes high and the transistors Qa and Qb are turned on. Therefore, a base current flows through the output transistor 1, so that the output transistor 1 is turned on, and the output voltage Vo increases. Conversely, when the output voltage Vo exceeds the set value, the reference voltage Vref becomes lower than the reference voltage Vadj, so that the output level of the error amplifier 5 becomes low and the transistors Qa and Qb are turned off. Therefore, no base current flows through the output transistor 1, so that the output transistor 1 is turned off and the output voltage Vo decreases. Through the above operation, feedback control is performed so that the output voltage Vo becomes a desired set value.
[0021]
Next, a base drive current limiting operation by the overcurrent protection circuit unit 61 will be described. A base drive current Ido that varies according to the base current of the output transistor 1 flows through the resistor Ra. If the base current of the output transistor 1 is within the normal range and the voltage across the resistor Ra (Ido × Ra) is lower than the turn-on voltage VBE (Qc) of the transistor Qc, the transistor Qc will not be turned on first. The regulation operation by the base drive circuit 6 described above is performed normally. On the other hand, when the base current of the output transistor 1 becomes excessive and the voltage (Ido × Ra) across the resistor Ra reaches the turn-on voltage VBE (Qc) of the transistor Qc, the transistor Qc is turned on. The current is bypassed via transistor Qc, and the base current to transistor Qa is controlled. As a result, the base drive current Ido is limited, and the overcurrent state is eliminated. At this time, the output transistor 1 outputs a current (Ido × hFE).
[0022]
Next, the protection operation performed by the short-circuit protection circuit 62 when an output is short-circuited will be described. If there is no short circuit or abnormal drop in the output voltage Vo and Vadj> Ido · Ra ≒ VBE (Qc) is satisfied, the relationship Vadj + VBE (Qf) + VBE (Qe)> VBE (Qd) + Ido · Ra + VBE (Qb) is satisfied. Since the condition is established between both ends of the resistor Re, the current Ix does not flow through the resistor Re, and the above-described regulation operation by the base drive circuit 6 is performed normally. On the other hand, if a short circuit or abnormal drop occurs in the output voltage Vo and Vadj ≦ Ido · Ra, the resistance Re is Vadj + VBE (Qf) + VBE (Qe) + Ix · Re = VBE (Qd) + Ido · Ra + VBE (Qb ), The current Ix flows to turn on the transistor Qg, so that the output current of the error amplifier 5 is bypassed via the transistor Qg, and the base current to the transistor Qa is controlled. As a result, the base drive current Ido is limited, and output short-circuit protection / output drop protection is performed.
[0023]
Note that the short-circuit protection circuit section 62 of the present embodiment has a configuration in which a resistor Re is connected between the base of the transistor Qb and the emitter of the transistor Qe. With such a configuration, it is possible to arbitrarily adjust the threshold value of the output voltage Vo for starting the short-circuit protection operation according to the resistance value of the resistor Re (see FIG. 2).
[0024]
Finally, a clamp operation by the clamp circuit unit 63, which is a characteristic part of the present invention, will be described. As described above, in the stabilized DC power supply according to the present embodiment, when the output voltage Vo is short-circuited or abnormally lowered, the short-circuit protection circuit 62 causes Vadj + VBE (Qf) + VBE (Qe) + Ix · Re = The base drive current Ido is limited so that VBE (Qd) + Ido · Ra + VBE (Qb) holds.
[0025]
Here, consider the case where the output voltage Vo is a negative voltage. In this case, in the conventional configuration having no clamp circuit section 63, as described above, the reference voltage Vadj becomes a negative voltage together with the output voltage Vo, so that the base drive current Ido does not flow from the above equation, and the above-described FIG. , The output voltage Vo does not rise.
[0026]
On the other hand, in the DC stabilized power supply device according to the present embodiment, which has a clamp circuit unit 63 including a diode Qh (VBE (Qh) ≒ VBE (Qd)) between the anode of the diode Qd and the reference voltage detection terminal, Even if the output voltage Vo is a negative voltage, the reference voltage Vadj becomes a positive voltage, and the base drive current Ido becomes Ix · Re / Ra according to the above equation. Therefore, by adjusting the circuit constants, the base drive current Ido does not flow so that the output voltage does not flow. The state where Vo does not rise can be avoided.
[0027]
In the above embodiment, the case where the clamp circuit unit 63 is configured using the diode-connected transistor Qh has been described as an example. However, the configuration of the present invention is not limited to this. The clamp circuit section 63 may be configured using a Schottky barrier diode. In this case, even if the output voltage Vo decreases, it is clamped by Vadj ≧ VBE (Qd) · VF (SBD), so that the Vo-Ido characteristic is clamped from the higher output voltage Vo.
[0028]
【The invention's effect】
As described above, with the stabilized DC power supply according to the present invention, the output voltage can be raised from the negative voltage state without impairing the output short-circuit protection function.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an embodiment of a stabilized DC power supply device according to the present invention.
FIG. 2 is a diagram for describing arbitrary adjustment of a short-circuit protection start voltage according to a resistance Re.
FIG. 3 is a diagram illustrating a correlation between output voltage Vo and drive current Ido (“character shape” characteristic).
[Explanation of symbols]
1 pnp bipolar transistor (output transistor)
2 ON / OFF circuit 3 Reference voltage generation circuit 4 Overheat protection circuit 5 Error amplifier 6 Base drive circuit 61 Overcurrent protection circuit section 62 Short circuit protection circuit section 63 Clamp circuit sections 71 to 73 Resistance 81, 82 Capacitors 91 to 94 Terminal (input) Terminal, output terminal, signal terminal, ground terminal)
Qa to Qd, Qf to Qh Npn-type bipolar transistor Qepnp-type bipolar transistor Ra-Re Resistance

Claims (3)

DC stabilizing means for driving and controlling an output control element so that a reference voltage that varies according to an output voltage matches a predetermined reference voltage, and generating a desired output voltage from an input voltage; A short-circuit protection means for monitoring a short-circuit or abnormal drop of the output voltage, and limiting the drive control of the output control element by the DC stabilization means;
A stabilized DC power supply device comprising: a clamp unit for clamping a lower limit value of the reference voltage to a predetermined positive voltage. 2. The stabilized DC power supply according to claim 1, wherein the clamping unit is a diode having a predetermined positive voltage applied to an anode and the reference voltage applied to a cathode. 3. The stabilized DC power supply device according to claim 1, wherein the short-circuit protection means has a resistor for limiting an operation current thereof.

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