JP2873643B2 - Series regulator protection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection circuit for a series regulator in which transistors are connected in parallel. In a series regulator that controls a transistor connected in series with a load so that an output voltage is constant, a configuration in which a plurality of transistors are connected in parallel when a load current is large is employed. If the output voltage cannot be controlled due to the transistor failure, it is necessary to protect the load from overvoltage.

[0002]

2. Description of the Related Art A large-capacity series regulator employs a configuration in which transistors are connected in parallel. For example, a conventional configuration has a configuration shown in FIG. In the figure, 31-1 to 31-n are transistors, 32
-1 to 32-n are balance resistors, 34 is an overvoltage detection unit,
35 is a switch circuit, 36 is an output voltage controller, 37 is a power supply, and 38 is a load.

[0003] Balance resistors 32-1 to 32-n are connected in series to the transistors 31-1 to 31-n, respectively.
To 31-n. The output voltage controller 36 detects the output voltage and controls the transistors 31-1 to 31-n so that the voltage applied to the load 38 of various electronic circuits or the like has a set value.

If the collector and the emitter of any one of the plurality of transistors 31-1 to 31-n are short-circuited, the control of the transistor cannot be performed.
The voltage applied to 8 becomes an overvoltage state. Such an overvoltage is detected by the overvoltage detection unit 34 and the switch circuit 34
To protect the load 38 by interrupting the current supplied from the power supply 37 to the load 38.

[0005]

Problems to be Solved by the Invention Transistor 31-
In order to protect the load 38 from an overvoltage caused by a short circuit between the collector and the emitter of the collectors 31 to 31-n, it is necessary to increase the detection speed of the overvoltage detection unit 34 and to configure the switch circuit 35 to operate at a high speed. Become. However, when the detection speed of the overvoltage detection unit 34 is increased, the switch circuit 35 is opened in response to a temporary voltage increase such as noise mixed into the output voltage, and the power supplied to the load 38 is often reduced. There is a problem of being shut off. An object of the present invention is to protect a load by detecting a short-circuit failure of a transistor, excluding the influence of noise or the like.

[0006]

Referring to FIG. 1, a protection circuit for a series regulator according to the present invention includes a plurality of transistors 1-1 to 1-n each having a balance resistor 2-1 to 2-n. In a series regulator connected and connected in parallel to simultaneously control a plurality of transistors 1-1 to 1-n to stabilize an output voltage, at least one of the plurality of transistors 1-1 to 1-n Transistors 1-1 when the other transistor is short-circuited
1-n and a voltage drop detecting section 3 for detecting a drop in voltage across the balance resistors 2-1 to 2-n, and a switch circuit 5 operated by a detection signal of the voltage drop detecting section 3. is there.

In addition, diodes 4-1 to 4-n to which voltages at both ends of the balance resistors 2-1 to 2-n are applied in a forward direction are connected in parallel with the balance resistors 2-1 to 2-n, respectively. It is.

A voltage stabilizing circuit having an output overvoltage detecting section is connected between the switch circuit 5 and the series regulator, and the output overvoltage detecting section detects the output overvoltage detecting signal of the voltage stabilizing circuit and the voltage drop detection of the series regulator. It has a configuration in which the switch circuit 5 is controlled by the detection signal of the unit 3.

[0009]

The transistors 1-1 to 1-n generated by the current supplied from the power supply 7 to the load 8 and the balance resistor 2-1
To 2-n, the voltage V _S across the transistors 1-1 to 1-1
1-n and the voltage V _CE between the collector and the emitter of the sum of the voltage V _R across the balancing resistor 2-1 to 2-n. In a normal state, the collector-emitter voltage V _CE is controlled by the output voltage controller 6 to stabilize the output voltage. However, if the collector-emitter short circuit occurs, the collector-emitter voltage becomes lower. The voltage V _CE becomes zero or a value close to zero. Therefore, the voltage V _S will be reduced compared to normal. The voltage drop detection unit 3 detects this voltage drop and opens the switch circuit 5 to protect the load 8 from overvoltage.

Further, by connecting the diodes 4-1 to 4-n in parallel with the balance resistors 2-1 to 2-n, when a large current flows through the balance resistors via the transistor whose collector and emitter are short-circuited. The voltage V _R at both ends of the balance resistor increases, but the voltage V _R is shunted to the diode so as not to exceed the forward voltage of the diode. Detection is assured.

Further, by providing a voltage stabilizing circuit having an overvoltage detecting section at a stage preceding the series regulator, the input voltage to the series regulator can be stabilized, and the output voltage of the series regulator can be further stabilized. The section can protect the series regulator from overvoltage. In that case, the overvoltage detection unit
Since it does not detect that the output voltage applied to the load 8 has become overvoltage, there is no need for high-speed operation. Therefore, the stabilized voltage can be applied to the load 8 without the overvoltage detecting section operating due to noise or the like.

[0012]

FIG. 1 is an explanatory view of an embodiment of the present invention.
-1 to 1-n are transistors, 2-1 to 2-n are balance resistors, 3 is a voltage drop detector, 4 is a diode, 5 is a switch circuit, 6 is an output voltage controller, 7 is a power supply, and 8 is a load. It is. The collectors of the plurality of transistors 1-1 to 1-n are commonly connected to the switch circuit 5, the base is also commonly connected to the output voltage control unit 6, and the collectors are respectively connected via the balance resistors 2-1 to 2-n. Output voltage controller 6 in common
And the load 8. The diode 4 may be a Schottky diode having a small forward voltage drop.

The voltage drop detector 3 includes a transistor 1-1
To 1-n and the voltage V across the balance resistors 2-1 to 2-n
_S is detected so as to detect _{S. When the} voltage V _S falls below a predetermined threshold value V _TH , the transistor 1-
When it is determined that any one of 1 to 1-n is short-circuited between the collector and the emitter, the switch circuit 5 is controlled to shut off the power. Therefore, it is possible to prevent an overvoltage output state due to control failure due to a collector-emitter short circuit, and to protect the load 8.

The above-mentioned voltage drop detecting section 3 includes, for example, a comparator for comparing the voltage V _S with the threshold value V _TH or a voltage applied to the collectors of the transistors 1-1 to 1-n and a balance resistor 2-1. ２−2-n. Further, since the overvoltage output state is not detected based on the output voltage, a malfunction does not occur due to noise.

[0015] The balancing resistor 2-1 to 2-n is selected as small as possible resistance, since the in the voltage drop V _R to the normal is small, the diode 4-1 to 4-n
Is cut off. Therefore, the balance resistors 2-1 to 2-n act so that the load current is balanced and shunted to each of the transistors 1-1 to 1-n. Also, the collector-emitter voltage V _{CE of the} transistors 1-1 to 1-n
Is controlled by the output voltage control unit 6 so that a constant voltage is applied to the load 8 even when the voltage of the power supply 7 fluctuates.
Therefore, the voltage V _S = V _CE + V _R is the difference between the voltage of the power supply 7 and the voltage applied to the load 8.
V is selected.

For example, the collector of the transistor 1-1
If the emitters are short-circuited, the output voltage will increase, and the output voltage control unit 6 sets each of the transistors 1-1 to
Since a control voltage that increases the collector-emitter voltage V _{CE of} 1-n is applied to the base, the transistor 1-1 cannot be controlled.
1 concentrates the load current. Therefore, the resistance 2-
1 is about to rise, but this voltage V _R
When _R exceeds the forward voltage drop V _F of the diode 4-1, was also run current minute diode 4-1, the voltage V _R is limited to the forward voltage drop V _F of the diode 4-1.

Since the forward voltage drop of the Schottky diode is about 0.4 to 0.5 V, the transistor 1
The voltage V _S becomes 2 due to the collector-emitter short circuit of -1.
V to 0.5V. Therefore, the voltage drop detection unit 3 determines that the voltage V _S is equal to the threshold V _TH (for example, 1.5
V) Since it is possible to detect that the voltage has decreased to below, control is performed to open the switch circuit 5.

FIG. 2 is an explanatory view of another embodiment of the present invention. The same reference numerals as in FIG. 1 denote the same parts, 9 is a voltage stabilizing circuit, and 10 is an overvoltage detecting section. Inside the chain line, as in the above-described embodiment, a plurality of transistors 1-1 to 1-n, a plurality of balance resistors 2-1 to 2-n, and a plurality of diodes 4
−1 to 4-n, a voltage drop detection unit 3, and an output voltage control unit 6. The transistors 1-1 to 1-n are controlled by the output voltage control unit 6, and the voltage applied to the load 8 It will stabilize. When the voltage drop detector 3 detects a drop in the voltage across the transistors 1-1 to 1-n and the balance resistors 2-1 to 2-n, that is, when a short circuit between the collector and the emitter of the transistor is detected. , So that the switch circuit 5 is opened.

In this embodiment, a voltage stabilizing circuit 9 is provided before the above-mentioned series regulator. This voltage stabilizing circuit 9 is a circuit for stabilizing an output voltage of a series regulator, a switching regulator or the like. If the output voltage stabilizes and cannot be controlled due to the failure of the internal transistors, etc.
The overvoltage detector 10 detects this and controls the switch circuit 5 to open.

The overvoltage detecting section 10 in this case is different from the overvoltage detecting section 34 in the conventional example shown in FIG. Therefore, the voltage stabilizing circuit 9
Even if noise is mixed in the output voltage of the voltage stabilizing circuit 9, the overvoltage detecting unit 10 does not respond.
Can be detected when an overvoltage occurs due to the occurrence of a failure. That is, even when there is much noise, a stabilized voltage can be continuously supplied to the load 8.

[0021]

As described above, according to the present invention, the plurality of transistors 1-1 to 1-n and the plurality of balance resistors 2-
A voltage V _S across the 1 to 2-n is detected by the voltage drop detection section 3, since the voltage V _S drops when inter also the collector-emitter with one in the transistors 1-1 to 1-n are shorted , by a decrease in the voltage V _S, the transistor 1-1
1 to n can be detected, and an overvoltage output state due to the collector-emitter short circuit can be avoided by controlling the switch circuit 5 to open. Further, as described above, since the overvoltage is not directly detected, there is an advantage that a malfunction due to mixing of noise does not occur.

Further, by connecting diodes 4-1 to 4-n in parallel with the balance resistors 2-1 to 2-n, the balance resistors 2-2 when the collectors and emitters of the transistors 1-1 to 1-n are short-circuited. 1 to 2-n to suppress the increase in the voltage drop V _R, it is possible to facilitate the drop detection voltage V _S.
Further, since the current can be diverted to the diodes 4-1 to 4-n, there is an advantage that even if the balance resistors 2-1 to 2-n are miniaturized, burning does not occur.

Further, a voltage stabilizing circuit 9 such as a switching regulator is provided at a stage preceding the series regulator, and when the output voltage of the series regulator becomes overvoltage, it is detected by the overvoltage detecting section 10 to open the switch circuit 5, thereby providing a structure.
The operation of the series regulator can be further stabilized. In this case, the overvoltage detection unit 10 may have a configuration in which the detection speed is low, so that a malfunction due to mixing of noise does not occur.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of one embodiment of the present invention.

FIG. 2 is an explanatory diagram of another embodiment of the present invention.

FIG. 3 is an explanatory diagram of a conventional example.

[Explanation of symbols]

 1-1 to 1-n transistor 2-1 to 2-n balance resistance 3 voltage drop detection unit 4-1 to 4-n diode 5 switch circuit 6 output voltage control unit 7 power supply 8 load

Claims (2)

(57) [Claims] 1. A plurality of transistors (1-1 to 1-n)
Are connected in parallel with each other, and the plurality of transistors (1-1 to 1-n) are connected in parallel.
Are simultaneously controlled to stabilize the output voltage, and the plurality of balance resistors (2-1 to 2-n)
In parallel, the voltage at both ends of the balance resistors (2-1 to 2-n) is
Diode (4) connected so that pressure is applied in the forward direction.
-1 to 4-n) and the plurality of transistors (1-1 to 1-n) when at least one of the plurality of transistors (1-1 to 1-n) is short-circuited. ) And a voltage resistance detecting section (3) for detecting the resistance of the voltage between both ends of the plurality of balance resistors (2-1 to 2-n); and a detection signal of the voltage drop detecting section (3). Switch circuit for interrupting input voltage (5)
A protection circuit for a series regulator, comprising: 2. The switch circuit (5) and the series.
A voltage with an output overvoltage detector between the regulator
A stabilizing circuit is connected, and the output overvoltage
The output overvoltage detection signal of the voltage stabilization circuit and the series
Before the detection signal of the voltage drop detector (3)
2. A protection circuit for a series regulator according to claim 1, wherein said protection circuit is configured to control said switch circuit.