JP2701181B2 - Inrush current prevention circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a rush current prevention circuit for a switching power supply. 2. Description of the Related Art There is known a switching power supply device in which a plurality of switching power supply units are connected in parallel to supply a stabilized DC voltage to a load. In such a switching power supply device, each switching power supply unit is unitized so that it can be inserted and removed even during parallel operation.When inserted, a rush current is prevented by a resistor, and after a predetermined time, An inrush current prevention circuit for short-circuiting the resistor is provided.

[0002]

2. Description of the Related Art FIG. 3 is an explanatory view of a conventional example.
31-n are n switching power supply units, 32 is an inrush current prevention circuit, 33 is a resistor with a temperature fuse, 33A is a resistor, 33B is a fuse, 34 is a transistor for short-circuiting a resistor, 35 is a resistor, and 36 is a power switch. 37, a transistor control switch, 41, a main transformer, 42, a transistor as a switching element, 43, a rectifying and smoothing circuit, 44, a switching control circuit, 45, a capacitor, and 46, a DC power supply.

Switching power supply units 31-1 to 31-n
Has an input terminal and an output terminal connected in parallel,
The input voltage Vin from the DC power supply 46 is supplied to a load (not shown) as a predetermined stabilized output voltage Vout by switching control. In other words, even if the switching control operation of one switching power supply unit is stopped, the reliability of the switching power supply device can be improved as a redundant configuration capable of supplying a stabilized DC voltage to the load by another healthy switching power supply unit. is there. Further, a configuration is known in which the switching power supply units 31-1 to 31-n are unitized so that they can be inserted and removed even during parallel operation. In this case, the power switch 36 can be always on or omitted. . The switch 37 is configured to be turned on a predetermined time after the input voltage Vin from the DC power supply 46 is applied by a timer or the like (not shown) or a transistor is delayed from the application of the input voltage Vin by selecting a connector pin configuration. It is possible to adopt a configuration in which a gate voltage of 34 is applied.

FIG. 4 is a diagram for explaining the operation of the conventional example.
Are the switching power supply units 31-1 to 31-3 from the DC power supply 46.
1-n input voltage Vin, (b) is a power switch 36
(C) indicates on / off of the switch 37,
(D) is the terminal voltage of the capacitor 45, (e) is the source-drain voltage of the transistor 34, (f) is the start and stop of the switching control operation, and (g) is the output voltage Vout.
Are shown below.

When the power switch 36 is turned on at time t1 as shown in (b), since the transistor 34 is off, the charging current of the capacitor 45 flows through the resistor 33A, and the terminal voltage of the capacitor 45 becomes (d ) As shown in the figure. Further, the source-drain voltage of the transistor 34 once increases as shown in (e) and then gradually decreases.

At time t2 after a predetermined time T1, the switch 3
7 is turned on as shown in FIG.
4 turns on and short-circuits the resistor 33A. Then, the switching control circuit 44 is activated and the transistor 42
Is started, the DC current from the DC power supply 46 flowing through the primary winding of the main transformer 41 is interrupted, and the voltage induced in the secondary winding of the main transformer 41 is rectified by the rectifying / smoothing circuit 43. The output voltage is smoothed and becomes the output voltage Vout. This output voltage Vout is applied to the switching control circuit 44 so that the output voltage Vout becomes a set value.
The ON / OFF period of the transistor 42 is controlled.

[0007] If, for example, the transistor 42 fails to remain on at the time t3, the DC power supply 46 is short-circuited due to the small impedance of the path of the transistors 34, 42 and the primary winding of the main transformer 41.
As shown in (a), the input voltage Vin drops rapidly,
When the voltage drops below the threshold voltage Vth, the switching control operation stops as shown in (f). Therefore, the output voltage Vout decreases as shown in (g).

[0008]

When a plurality of switching power supply units 31-1 to 31-n operate in parallel and the transistor 42 as a switching element causes a short-circuit fault as described above, the faulty switching power supply unit Since the impedance becomes substantially zero, the voltage supplied from the DC power supply 46 to other sound switching power supply units also decreases at time t3 in FIG. The operation of all the switching power supplies stops, and the system goes down. When an overcurrent detection unit is provided in the DC power supply 46, an overcurrent flows to the switching power supply unit in which a short-circuit fault occurs, so that the DC power supply unit 46 cuts off the current supply. Also in this case, the switching control operation is stopped, and there is a disadvantage that the features of the redundantly configured switching power supply device provided with a plurality of switching power supply units cannot be exhibited. The present invention
An object of the present invention is to prevent a short-circuit fault from spreading to other sound switching power supply units.

[0009]

Referring to FIG. 1, the inrush current prevention circuit according to the present invention includes a resistor 3A for limiting a current flowing when input power to the switching power supply units 1-1 to 1-n is turned on. A first transistor 4 which is turned on by a switch 17 or the like a predetermined time after the input power is turned on to short-circuit the temperature-fused resistor 3 including the resistor 3A and the fuse 3B, and that the first transistor 4 is turned on. The second transistor 5 that turns on when the voltage drop when it becomes equal to or more than the threshold value turns off the first transistor 4 and the second transistor 5 that divides the voltage drop of the first transistor 4
And a detection circuit including a series circuit of a third resistor 8 and a capacitor 9 connected in parallel with the first resistor 6. It is a thing.

[0010]

When the input voltage from the DC power supply 20 is applied with the power switch 16 turned on, the switch 17 is turned off and the transistors 4 and 5 are also turned off, so that the current flowing through the capacitor 15 flows through the resistor 3A. Become. Therefore, the charging current of the capacitor 15 is limited by the resistor 3A. Then, after a predetermined time, when the switch 17 is turned on by a timer or the like as in the conventional example, the first transistor 4 is turned on and the resistor 3A is short-circuited, so that the source-drain voltage of the first transistor 4 is substantially It becomes zero, and the second transistor 5 continues to be off.

When the transistor 12 becomes an obstacle for continuing the ON state, a large current flows from the DC power supply 20,
The voltage drop of the first transistor 4, that is, the source-drain voltage increases. Due to the rise of the source-drain voltage, the potential of the connection point between the resistors 6 and 7 also rises, and the base current of the second transistor 5 flows to turn on. In that case, the capacitor 9 acts as a speed-up capacitor, and the second transistor 5 is rapidly turned on as the first source-drain voltage rises sharply.

When the second transistor 5 is turned on, the gate voltage of the first transistor 4 is bypassed, so that the first transistor 4 is turned off. Thereby, a current flows through the resistor 3A and the fuse 3B.
It is possible to suppress a decrease in the input voltage from the DC power supply 20. That is, the operation of another sound switching power supply unit can be continued. Also, a large current flows through the resistor 3A and the fuse 3B, and the fuse 3B
Is blown, the switching power supply unit having the short-circuit fault can be disconnected.

[0013]

FIG. 1 is an explanatory view of an embodiment of the present invention. The input terminals of a plurality of switching power supply units 1-1 to 1-n are connected in parallel, connected to a DC power supply 20, and the output terminals are connected in parallel. To a load (not shown) to constitute a switching power supply device that performs parallel operation. Each of the switching power supply units 1-1 to 1-n can be unitized as in the conventional example. In that case, the power switch 16 can be omitted. The inrush current prevention circuit 2 includes a temperature-fused resistor 3 including a resistor 3A and a fuse 3B.
, A first transistor 4 and a second transistor 5
And a first, second, and third resistors 6, 7, 8, a capacitor 9, a resistor 10, and a switch 17 that is operated by a timer or the like after the power switch 16 is turned on. , A first, second, third resistor 6, 7, 8 and a capacitor 9 constitute a detection circuit, and a connection point between the first and second resistors 6, 7 is connected to the base of the second transistor 5. A series circuit of a third resistor 8 and a capacitor 9 is connected in parallel with the first resistor 6. 11 is a main transformer, 12 is a transistor, 13 is a rectifying and smoothing circuit, 14 is a switching control circuit, and 15 is a capacitor.

When the power switch 16 is turned on or when a unitized switching power supply unit is inserted, a charging current flows from the DC power supply 20 to the capacitor 15.
At that time, since the switch 17 is off, the first and second transistors 4 and 5 are off. Therefore, since a current flows through the resistor 3A, an inrush current can be prevented. After a predetermined time, the switch 17 is turned on by a timer or the like, and the gate voltage of the first transistor 4 is applied. Therefore, the first transistor 4 is turned on, and the resistor 3A is short-circuited.

FIG. 2 is a diagram for explaining the operation of the embodiment of the present invention. FIG.
Input voltages Vin to −1 to 1-n, (b) ON / OFF of the power switch 16, (c) ON / OFF of the switch 17, (d) terminal voltage of the capacitor 15, (e) 1
(F) is the start and stop of the switching control operation, (g) is the base current of the second transistor 5, and (h) is the collector-emitter voltage of the second transistor 5. , (I) is the output voltage V
An example of each of out is shown.

When the power switch 16 is turned on at time t1 or when the unitized switching power supply is inserted, the switch 17 is turned off, so that the first and second transistors 4 and 5 are turned off. The charging current of the capacitor 15 flows through the resistor 3A as shown in (e), and the terminal voltage of the capacitor 15 rises as shown in (d). Further, since the voltage drop of the resistor 3A is large, the base current of the second transistor 5 flows as shown in (g), but since the switch 17 is off, the second transistor 5 remains off.

After turning on the power switch 16 or inserting the unitized switching power supply unit, at time t2 after a lapse of a predetermined time T1 by a timer or the like, the switch 17 is turned on as shown in FIG. Become. Thereby,
Since the gate voltage of the first transistor 4 is applied, it is turned on, and the resistor 3A is short-circuited. At that time, the terminal voltage of the capacitor 15 increases and the charging current decreases, so that the base current of the second transistor 5 becomes extremely small, and the second transistor 5 maintains the off state.
Then, as shown in (f), the switching control circuit 1
4, the on / off control of the transistor 12 connected to the primary winding of the main transformer 11 is performed, and the voltage induced in the secondary winding of the main transformer 11 is
The on / off period of the transistor 12 is controlled by the switching control circuit 14 so that the output voltage Vout becomes a set value and is stabilized by the rectifying and smoothing circuit 13 so that the output voltage Vout becomes a set value. Output voltage Vou
t is supplied.

If a failure to keep the transistor 12 on at the time t3 occurs, the input voltage Vin from the DC power supply 20 starts to decrease as in the above-described conventional example. At this time, since a large current flows through the transistor 12 having the short-circuit fault via the first transistor 4, the source-drain voltage of the first transistor 4 rises as shown in (e). Due to the rise of the source-drain voltage,
The potential at the connection point between the first and second resistors 6, 7 rises. That is, the base current of the second transistor 5 flows through the capacitor 9 and the resistor 8 in response to a sudden change in the source-drain voltage as shown in FIG. Thereby, the second
Transistor 5 is turned on quickly, the gate voltage of the first transistor 4 is bypassed, and the first transistor 4 is turned off.

When the first transistor 4 is turned off, current flows from the short-circuited transistor 12 to the primary winding of the main transformer 11 via the resistor 3A, and the fuse 3B is blown at time t4. Alternatively, the temperature rises due to a large current flowing through the resistor 3A, and the fuse 3B is blown by the temperature and the flowing current. As a result, the switching power supply unit in which the short circuit fault has occurred is disconnected from the DC power supply 20. In this case, after a short-circuit fault occurs,
A second transistor to which a base current is supplied via the speed-up capacitor 9 before the input voltage Vin from the DC power supply 20 drops below the threshold voltage Vth for continuing the operation of the sound switching power supply unit. 5 is turned on, thereby turning off the first transistor 4;
Since the current can be reduced in a state where the resistor 3A is inserted in series, the switching control operation of another healthy switching power supply can be continued even if a short-circuit fault occurs, so that a system down can be avoided.

The present invention is not limited to the above-described embodiment, but can be variously modified.
For example, the first transistor 4 for short-circuiting the resistor 3A
Is shown as a field effect transistor, but a bipolar transistor or the like can also be used. Similarly,
Although the second transistor 6 and the transistor 12 connected to the primary winding of the main transformer 11 are shown as bipolar transistors, field effect transistors can also be used.

[0021]

As described above, according to the present invention, the rush current at power-on is limited by the resistor 3A, and after a predetermined time, the resistor 3A is short-circuited by the first transistor 4 to switch the switching power supply unit 1-1. To 1-n as a normal operation state,
When a short-circuit fault occurs in the transistor 12 connected to the primary winding of the main transformer 11, the first transistor 4
Is detected by a detection circuit, the second transistor 5 is turned on, the first transistor 4 is turned off, and the resistor 3A is connected in series in the same manner as when the power is turned on. This prevents the input voltage Vin from the DC power supply 20 from decreasing. Thereby, the other healthy switching power supply units can continuously perform the switching control operation, so that the system down can be avoided, and the plurality of switching power supply units 1-1 to 1-1 can be avoided.
There is an advantage that the reliability of the switching power supply device that operates the -n in parallel can be improved.

[Brief description of the drawings]

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

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

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

FIG. 4 is an operation explanatory diagram of a conventional example.

[Explanation of symbols]

 1-1 to 1-n Switching power supply unit 2 Inrush prevention circuit 3 Temperature-fused resistor 3A resistor 3B fuse 4 First transistor 5 Second transistor 6 First resistor 7 Second resistor 8 Third resistor 9 Capacitor DESCRIPTION OF SYMBOLS 11 Main transformer 12 Transistor 13 Rectification smoothing circuit 14 Switching control circuit 15 Capacitor 16 Power switch 17 Switch 20 DC power supply

Claims (1)

(57) [Claims] A plurality of switching power supply units (1- 1) for connecting a DC output terminal in parallel to supply a stabilized DC voltage to a load.
In the inrush current prevention circuit (2) provided for each of the switching power supply units (1-1 to 1-n), a resistance (3 )
A first transistor (4) that turns on a predetermined time after the input power is turned on to short-circuit the temperature-fused resistor (3), and a voltage drop of the first transistor (4) in an on state is a threshold value. A second transistor for turning on at the above time to turn off the first transistor; and a second transistor for dividing a voltage drop of the first transistor to divide the voltage drop of the first transistor. A series circuit of first and second resistors (6, 7) added to the base of (5), and a third resistor (8) and a capacitor (9) connected in parallel to the first resistor (6). And a detection circuit including: a rush current prevention circuit.