JPH09305246A - Overcurrent control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely start up a power source and to miniaturize a component. SOLUTION: A maximum current detection resistance R12 and a relay contact r2 are connected to both the ends of an overcurrent detection resistance R11 in series to constitute the overcurrent detecting circuit 20 and once the power source is turned on with a switch 12 ON, a switch 18 is turned ON to start supplying the electric power from a battery 19. An overcurrent detection value setting circuit 27 composed of a delay relay 25 and a relay 26 sets a 1st overcurrent detection value based upon the parallel composite resistance value of the overcurrent detection resistance R11 and maximum current detection resistance R12 for a certain period after the power source is turned on, and break a relay contact r2 the certain period later to set a 2nd overcurrent detection value based upon the resistance value of the overcurrent detection resistance R11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent control circuit, and more particularly to an overcurrent control circuit in a DC stabilized power supply circuit.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional example of an overcurrent control circuit in a stabilized DC power supply circuit. In FIG. 4, one end of an input switch 42 is connected to the input terminals 41a and 41b to which an AC voltage is applied. The primary side of the transformer 43 is connected to the other end of the input switch 42. A diode rectifier circuit 44 and a battery charger 45 are connected to the secondary side of the transformer 43. One end of the smoothing coil L41 is connected to the positive output end of the diode rectifier circuit 44, and the negative output terminal 46b is connected to the negative output end thereof.

To the other end of the smoothing coil L41, one end of the smoothing capacitor C41, the cathode of the backflow prevention diode D41, one end of the overcurrent detection resistor R41 and the emitter of the overcurrent control transistor Q41 are connected. The other end of the smoothing capacitor C41 is connected to the negative output terminal 46b, and the smoothing circuit 4 together with the smoothing coil L41.
7. The anode of the backflow prevention diode D41 is connected to the output end of the battery charger 45. The output end of the battery charger 45 and the negative output terminal 4
A battery 48 is connected between 6b and 6b.

The base of the overcurrent control transistor Q41, the emitter of the drive transistor Q42, and the collectors of the n regulator transistors Q43-1 to Q43-n are connected to the other end of the overcurrent detection resistor R41. There is. The overcurrent detection resistor R41 and the overcurrent control transistor Q41 form an overcurrent detection circuit 49 that detects an overcurrent flowing through the load. The collector of the overcurrent control transistor Q41 and the base of the driving transistor Q42 are commonly connected, and further connected to the output terminal of the stabilizing block circuit 50.

Regulator transistors Q43-1 to Q4
43-n comprises the regulator circuit 51, and the radiation fin 52 is attached to these transistors. A resistor R42-1 for transistor balancing is provided to each emitter of the regulator transistors Q43-1 to Q43-n.
One end of each of R42-n is connected. The other ends of the transistor balancing resistors R42-1 to R42-n are commonly connected and further connected to the positive output terminal 46a. The stabilizing circuit 50 is connected to the positive and negative output terminals 46a and 46b.
Two input terminals of are connected.

When the input switch 42 is turned on, the DC stabilized power supply circuit having the above configuration steps down and rectifies the AC voltage input through the input terminals 41a and 41b, and is connected to the output terminals 46a and 46b. A stable power is supplied to a load (not shown), and when the supply of the AC voltage is stopped due to a power failure or the like, the battery 4 is supplied to the load.
Power is supplied from 8 onwards. The specific circuit operation will be described below.

First, when the input switch 42 is turned on, an AC voltage is applied to the transformer 43 via the input terminals 41a and 41b.
The voltage is input to the primary side of and is stepped down to a required voltage in this transformer 43. The reduced voltage is rectified by the diode rectifier circuit 44 and further smoothed by the smoothing circuit 47. The current based on the smoothed voltage flows through the overcurrent detection circuit 49, and further the regulator circuit 5
Flow into 1.

The voltage from the regulator circuit 51 is output from the positive output terminal 46a and is also supplied to the stabilizing circuit 50. In the stabilization circuit 50, the regulator transistors Q43-1 to Q43-1 through the drive transistor Q42 are adjusted so that the output voltage becomes the set voltage.
It controls Q43-n. Further, the battery 48 connected between the smoothing circuit 47 and the overcurrent detection circuit 49 is charged by the battery charger 45 during operation with the AC power supply.

Here, the operation of the overcurrent detection circuit 49 depends on the ratio of the voltage drop V _R41 of the overcurrent detection resistor _R41 and the base-emitter voltage V _BE of the overcurrent control transistor Q41 when an overcurrent state occurs. Decided. That is, V
_{When R41} > V _BE , the overcurrent control transistor Q41 turns on. As a result, the overcurrent control transistor Q4
The collector-emitter of 1 is short-circuited, and the drive transistor Q42 is turned off. When the drive transistor Q42 is turned off, the output voltage of the regulator transistors Q43-1 to Q43-n is lowered and the output of the DC voltage from the output terminal 46a is stopped.

FIG. 5 shows the relationship between the voltage and the load current when the power source is turned on in the circuit according to the above-mentioned conventional example. In the characteristic diagram of FIG. 5, the overcurrent characteristic is a "folded" characteristic like the F line. A is the current during normal operation (rated current), B is the overcurrent detection value when the power is turned on, C is the load current when the power is turned on, and D is the overcurrent detection value when the device is downsized. , E indicates the range in which the power supply cannot be turned on.

[0011]

However, in the above-described DC stabilized power supply circuit, the load current C flows when the power supply is turned on depending on the state of the load. Therefore, as is clear from the characteristic diagram of FIG. The maximum current at startup is about 2.5 to 3 times the rated current A. If the overcurrent control characteristic is set to the line B in FIG. 5 in consideration of the rated current A and the overcurrent control characteristic is set to the line B in FIG. Therefore, a large power supply must be designed in consideration of a current larger than the maximum current of the load.

Further, as a design condition, in consideration of the above matters, the maximum current must be set to three times or more of the rated current before the start. The set value for overcurrent detection in the overcurrent detection circuit 49 must be set to 110% or more of the maximum current of the load. For this reason, it cannot be miniaturized. Especially,
The transformer 43 and the smoothing coil L41 are large in size in consideration of the maximum current. Further, the heat radiation fins 52 are also large in view of the heat generation amount of the regulator transistors Q43-1 to Q43-n.

[0013]

In order to solve the above-mentioned problems, an overcurrent control circuit according to the present invention is a DC stabilized power supply circuit which rectifies and stabilizes an AC voltage and supplies it to a load when the power supply is turned on. Set a first overcurrent detection value that is equal to or greater than the maximum current value of the load for a certain period of time, and after the elapse of the certain time, the second overcurrent detection value that is equal to or greater than the rated current value of the load and is lower than the first overcurrent detection value. Overcurrent detection value setting circuit for setting a current detection value, and an overcurrent detection circuit for detecting an overcurrent flowing through a load based on the first or second overcurrent detection value set by the overcurrent detection value setting circuit It is configured with and.

In the overcurrent control circuit having the above structure, the overcurrent detection value setting circuit sets the first overcurrent detection value which is equal to or more than the maximum current value of the load for a certain period after the power is turned on. Detects the overcurrent flowing through the load based on the first overcurrent detection value. After a certain period of time, the overcurrent detection value setting circuit switches the overcurrent detection value to a second overcurrent detection value which is equal to or higher than the rated current value of the load and lower than the first overcurrent detection value, and the overcurrent detection circuit Detects the overcurrent flowing through the load based on the second overcurrent detection value. When the overcurrent is detected, the power supply to the load is stopped.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit diagram showing one embodiment of the present invention.

In FIG. 1, one end of an input switch (S1) 12 is connected to the input terminals 11a and 11b to which an AC voltage is applied. The primary side of the transformer 13 is connected to the other end of the input switch 12. A diode rectifier circuit 14 and a battery charger 15 are connected to the secondary side of the transformer 13. One end of the smoothing coil L11 is connected to the positive output end of the diode rectifier circuit 14, and the negative output terminal 46b is connected to the negative output end thereof.

At the other end of the smoothing coil L11, one end of the smoothing capacitor C11, the cathode of the backflow preventing diode D11, one end of the overcurrent detection resistor R11, one end of the maximum current detection resistor R12 and the emitter of the overcurrent control transistor Q11 are provided. Each is connected. Smoothing capacitor C1
The other end of No. 1 is connected to the negative output terminal 16b and constitutes a smoothing circuit 17 together with the smoothing coil L11. A switch (S) interlocking with the input switch (S1) 12 is provided between the output end of the battery charger 15 and the negative output terminal 16b.
2) A battery 19 as an auxiliary power source is connected via 18. The backflow prevention diode D11 has its anode connected to the output end of the battery charger 15 and functions to prevent backflow of the battery voltage.

The base of the overcurrent control transistor Q11, the emitter of the drive transistor Q12, and the collectors of the two regulator transistors Q13-1 and Q13-2 are connected to the other end of the overcurrent detection resistor R11. There is. The other end of the maximum current detection resistor R12 is connected to the other end of the overcurrent detection resistor R11 via a normally closed relay contact r2 of a relay (RL2) 25 described later. The overcurrent detection resistor R11, the maximum current detection resistor R12, the relay contact r2, and the overcurrent control transistor Q11 form an overcurrent detection circuit 20 that detects an overcurrent flowing through the load.

The collector of the overcurrent control transistor Q11 and the base of the driving transistor Q12 are commonly connected, and further connected to the output terminal of the stabilizing circuit 21. The regulator transistors Q13-1 and Q13-2 form a regulator circuit 22, and a radiation fin 23 is attached to these transistors. The transistor balancing resistors R13-1 and R13-2 are connected to the emitters of the regulator transistors Q13-1 and Q13-2, respectively.
Each end of is connected.

Transistor balancing resistors R13-1, R
The other ends of 13-2 are commonly connected, and the positive output terminal 1
6a. Positive side, negative side output terminals 16a, 1
Two input terminals of the stabilizing circuit 21 are connected to 6b. In addition, the stabilization circuit 21 is connected to the other end of the smoothing coil L11.
A delay relay (RL1) 25 is connected between the line 24 and the output terminal 16b.
2) 26 and the normally open relay contact r1 of the delay relay 25 are connected in series. Delay relay 25
Has a configuration in which the relay contact r1 is closed when a certain delay time has elapsed after the start of the operation.

The delay relay 25 and the relay 26 are
An overcurrent detection value setting circuit 27 that sets different overcurrent detection values for the overcurrent detection circuit 20 when the power is turned on and after a lapse of a fixed time after the power is turned on is configured. That is, in the overcurrent detection circuit 20, when the power is turned on,
Since the relay contact r2 of the relay 26 is in the closed state, the overcurrent detection resistance R11 and the maximum current detection resistance R
The first overcurrent detection value determined based on the parallel combined resistance value of 12 is set, and when a certain time has elapsed from the start-up, the relay contact r1 of the delay relay 25 is closed, and thereby the relay 26 is activated. When the relay contact r2 is opened, the second overcurrent detection value determined based on the resistance value of only the overcurrent detection resistor R11 is set.

Here, an overcurrent detection value that is equal to or greater than the maximum current value of the load is set as the first overcurrent detection value, and a second overcurrent detection value that is equal to or greater than the rated current value of the load and is equal to or greater than the first overcurrent detection value. To set the overcurrent detection value lower than the detection value,
Each resistance value of the overcurrent detection resistor R11 and the maximum current detection resistor R12 is selected.

In this embodiment, a delay relay 25 and a relay 26 are used as the overcurrent detection value setting circuit 27 having a function as a timer, and the maximum current detection resistor R1 is used.
Although a relay contact r2 is connected in series to 2 is used, the invention is not limited to this.
It is also possible to use a configuration in which a switching element formed of a transistor or the like is connected in series to the maximum current detection resistor R12, and an electronic timer circuit controls ON / OFF of the switching element.

However, it can be said that it is preferable to connect a relay contact in series with the maximum current detection resistor R12 in the following point. That is, since the contact resistance value of the relay contact is extremely small compared to the resistance value of the transistor or the like and can be ignored, the first and second overcurrent detection values are set to the overcurrent detection resistance R11 and the maximum current detection value. There is an advantage that each resistance value of the resistor R12 can be set accurately.

Next, the circuit operation of the DC stabilized power supply circuit having the above configuration will be described. In addition, this DC stabilized power supply circuit includes switches (S1) 12 and (S2) 1 which are interlocked with each other.
8, the AC power source is turned on / off and the battery 19 is turned on / off at the same time.

First, when the input switch (S1) 12 is turned on, the AC voltage input to the input terminals 11a and 11b is supplied to the primary side of the transformer 13 and reduced to a required voltage by the transformer 13. The reduced AC voltage is rectified by the diode rectifier circuit 14 to be a DC voltage, and further smoothed by the smoothing circuit 17. The smoothed DC voltage is supplied to the regulator circuit 22 through the overcurrent detection circuit 20, and the delay relay (RL1) 25 for overcurrent control and the relay (R
L2) 26.

The voltage from the regulator circuit 22 is output from the output terminal 16a and is also supplied to the stabilizing circuit 21. In this stabilizing circuit 21, the driving transistor Q is adjusted so that the output voltage becomes the set voltage.
12 through regulator transistors Q13-1, Q
It controls 13-2. Further, the battery 19 connected between the smoothing circuit 17 and the overcurrent detection circuit 20 is charged by the battery charger 15 while operating with the AC power supply.

Next, the circuit operation when the power supply of the overcurrent control circuit in the above-described DC stabilized power supply circuit is turned on will be described based on the time chart of FIG.

At time t1, the switches (S1) 12, (S
2) When 18 is turned on, first, the battery of the battery 19
Voltage delayed relay (RL1) 25 and relay (RL
2) is supplied to 26. For the maximum current detection resistor R12
Relay contact r2 connected in series is normally closed
Since it is a contact, it detects overcurrent when the power is turned on.
The resistor R11 and the maximum current detection resistor R12 are connected in parallel.
In a state. In this state, the overcurrent detection resistor R11 and
And the current drop in the maximum current detection resistor R12
Pressure V_R11R12And the base of the overcurrent control transistor Q11
Voltage between emitters V _BEOvercurrent detection circuit 2 depending on the ratio
0 works.

That is, when V _R11R12 > V _BE , the overcurrent control transistor Q11 is turned on and the drive transistor Q12 is turned off. When the drive transistor Q12 is turned off, the output voltage of the regulator transistors Q13-1 and Q13-2 is lowered and the output of the DC voltage from the output terminal 16a is stopped. V _{R1
When 1R12} > V _BE , the overcurrent control transistor Q11 is turned off and the overcurrent control circuit does not operate.

When the delay period of the delay relay 25 elapses from the time t1 when the switches (S1) 12 and (S2) 18 are turned on, the normally open relay contact r1 of the delay relay 25 is closed, whereby the relay contact r1 and the relay contact r1 are closed. The relays 26 connected in series are turned on. Relay 26
Is turned on, the normally closed relay contact r2 is opened, and the parallel connection state of the maximum current detection resistor R12 and the overcurrent detection resistor R11 is released.

During a fixed period T from the power-on time t1 to the overcurrent control relay contact r2 opening time t2, the overcurrent detection resistor R11 and the maximum current detection resistor R12 are connected in parallel, V _R11R12 at maximum current
> V _BE . Then, when the relay contact r2 opens after a lapse of a certain period of time, the overcurrent detection value at the rated current is V _R11 due to the drop voltage V _R11 of the overcurrent detection resistor _R11.
It becomes overcurrent control operation at> V _BE .

FIG. 3 shows the relationship between the voltage and the load current when the power source is turned on in the circuit according to the present invention described above. In the characteristic diagram of FIG. 3, A is the rated current during normal operation, and B is
Shows the overcurrent detection value at the rated current, C shows the load current curve at the time of power supply startup, and D shows the overcurrent detection value at the time of power supply startup.

As described above, in the overcurrent detection circuit 20, the overcurrent detection value is set to be equal to or higher than the maximum current value of the load when the power is turned on, and is equal to or higher than the rated current value of the load during normal operation. As is clear from the characteristic diagram, since the non-startable range does not occur, the power supply can be surely started up.

In particular, the battery 19 is turned on at the same time when the power is turned on.
Since the battery 19 is supplied with the maximum current when the power is turned on, the components such as the transistor 13, the smoothing coil L11, and the transistors Q13-1 and Q13-2 for the regulator are rated. The current can be taken into consideration, and since the amount of heat generated by the transistor and the like is reduced, the heat radiation fin 23 can also be made smaller. Along with this, the power supply body can be downsized.

[0036]

As described in detail above, according to the present invention, in the DC stabilized power supply circuit in which the overcurrent at power-on is taken into consideration, the overcurrent detection value is the maximum current value of the load at power-up. As above, in normal operation it should be more than the rated current value of the load, and by considering the average current,
Since the power supply can be reliably started up and the parts used can be made small, the power supply main body can be downsized and the material cost can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a time chart for explaining an operation of overcurrent control.

FIG. 3 is a characteristic diagram of a voltage and a load current when the power source is turned on according to the present invention.

FIG. 4 is a circuit diagram showing a conventional example.

FIG. 5 is a characteristic diagram of a voltage and a load current when the power source is turned on according to the conventional example.

[Explanation of symbols]

 14 Diode Rectifier Circuit 17 Smoothing Circuit 19 Battery 20 Overcurrent Detection Circuit 21 Stabilization Circuit 22 Regulator Circuit 23 Radiating Fin 25 Delay Relay 27 Overcurrent Detection Value Setting Circuit L11 Smoothing Coil r1, r2 Relay Contact

Claims (2)

[Claims] 1. A stabilized direct current power supply circuit for rectifying and stabilizing an alternating voltage and supplying the same to a load, the overcurrent control circuit detecting an overcurrent flowing in the load and stopping the power supply to the load at the time of detection. Then, a first overcurrent detection value that is equal to or greater than the maximum current value of the load is set for a certain period of time after the power is turned on, and after the elapse of the certain period of time, the first overcurrent detection value that is equal to or greater than the rated current value of the load and that the first overcurrent detection value is set. Lower overcurrent detection value setting circuit for setting a lower overcurrent detection value, and an overcurrent flowing through a load based on the first or second overcurrent detection value set by the overcurrent detection value setting circuit. And an overcurrent detection circuit for detecting the current. 2. The stabilized direct-current power supply circuit has an auxiliary power supply that supplies power to a load when no AC voltage is input, and the auxiliary power supply starts power supply at the same time when the power is turned on. The overcurrent control circuit according to claim 1.