JPH073829Y2 - Buck chopper - Google Patents

Description

[Detailed Description of the Invention] A. Industrial Field of Application The present invention relates to a step-down chopper, and more particularly to an overcurrent protection circuit of a chopper section.

B. Outline of the Invention The present invention is a step-down chopper that obtains a DC output by controlling the conduction ratio of the chopper section.The thyristor and the electromagnetic contactor that are parallel to the chopper section are turned on when an overcurrent occurs. By switching to an electromagnetic contactor, the chopper part can be operated at high frequencies and the overcurrent withstand capability can be reduced, and overcurrent protection can be ensured and facilitated.

C. Conventional Technology A step-down chopper converts a direct current power supply into a direct current whose voltage has been lowered by the on / off operation of a switch element. FIG. 3 shows a conventional step-down chopper, in which a DC power supply 1 is passed through a power transistor 2 as a chopper section to a reactor 3
Is supplied with a chopping current, a circulating current of the reactor 3 is obtained through the flywheel diode 4 during the off period of the transistor 2, and continuous DC power is supplied to the load 5. 6 is a smoothing capacitor.

In this configuration, the output voltage control is performed by the on / off ratio of the transistor 2, that is, the conduction ratio control.

D. Problem to be Solved by the Invention In the conventional step-down chopper, in order to reduce the size and weight of the device, the high frequency switching operation of the transistor 2 can reduce the inductance of the reactor 3 and the capacitance of the capacitor 6. For this reason, power transistors and GTO thyristors that can switch at high speed are also used in the chopper section.

However, with the above-mentioned configuration, in an application in which an excessively large current is required to be supplied in the case of a load short circuit or the like, the transistor 2 having good high frequency characteristics and a large current withstanding capability should be used. It becomes an expensive device if necessary.

An object of the present invention is to provide a step-down chopper capable of operating the chopper portion at a high frequency, reducing the overcurrent withstanding capability, and reliably and easily overcurrent protection.

E. Means and Actions for Solving the Problems In order to achieve the above-mentioned object, the present invention has a DC current reduced in voltage to a load by a switch operation for controlling the conduction ratio of a chopper provided between a DC power supply and a load. In the step-down chopper for supplying the thyristor and the electromagnetic contactor provided in parallel with the chopper portion, the thyristor is turned on by giving an ON signal to the thyristor when the overcurrent of the direct current is detected, and the electromagnetic contact is made at the shortest. Current detection circuit for applying an ON signal to the electromagnetic contactor for a period of time or more necessary for the ON operation of the device to turn on the electromagnetic contactor, and recovering the ON signal applied to the electromagnetic contactor by overcurrent elimination When the overcurrent is generated, the current of the chopper portion is transferred to the thyristor and then to the electromagnetic contactor and the thyristor is naturally extinguished.

F. Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention. 3 is different from FIG. 3 in that the thyristor 7 and the electromagnetic contactor 8 are provided in parallel with the transistor 2 of the chopper part, and when the overcurrent detection circuit 9 detects the overcurrent, the thyristor 7 and the electromagnetic contactor 8 are turned on. There is a point to control.

In the above configuration, the overcurrent detection circuit 9 outputs the ON control signal to the thyristor 7 and the electromagnetic contactor 8 when the detection signal of the current detector 10 (for example, a hall current detector) capable of detecting the load current exceeds the set overcurrent. give. This ON control signal is applied to the thyristor 7 during the period required for its turn-on,
The electromagnetic contactor 8 is kept for longer than the time required to ensure it is on. Further, the circuit 9 gives an OFF control signal to the electromagnetic contactor 8 when the overcurrent is eliminated, and the thyristor 7 is turned off by spontaneous extinction.

In such a configuration, the thyristor 7 and the electromagnetic contactor 8 are turned off in the normal operation, and the step-down chopper operation similar to the conventional one is performed. Next, when an overcurrent starts to flow due to a short circuit of the load 5 or the like, the overcurrent detection circuit 9 controls the thyristor 7 and the electromagnetic contactor 8 to be turned on. The operation when this overcurrent occurs is as shown in FIG.

When the load current exceeds the overcurrent level I _oc due to the load short circuit, the ON control signal from the overcurrent detection circuit 9 is supplied,
The thyristor 7 is turned on immediately to bypass most of the overcurrent from the transistor 2. On the other hand, the electromagnetic contactor 8 is turned on after a delay of time T _d1 (generally several tens of milliseconds), and this on-voltage is sufficiently lower than the on-voltages of the thyristor 7 and the transistor 2, so that the overcurrent is electromagnetic. The current flows through the contactor 8 and the current in the thyristor 7 becomes almost zero. As a result, the thyristor 7 cannot maintain the holding current,
It extinguishes naturally without forced commutation.

Therefore, although there is a delay in the forced off control of the transistor 2 when an overcurrent occurs, most of the overcurrent is transferred to the thyristor 7 by the quick turn-on of the thyristor 7, and the overcurrent of this thyristor is also electromagnetically contacted with a delay of time T _d1. Move to container 8. As a result, the transistor 2 can be protected from an overcurrent by using a transistor having a low overcurrent withstanding capability, and the thyristor 7 can withstand the overcurrent only for a short time until the electromagnetic contactor 8 is turned on, and the short-time rating is short. A small size that exceeds the expected overcurrent is sufficient, and a complicated forced commutation circuit is unnecessary.

ON control signal to the effects of up to above minimum time Tmin may be larger than the on operation delay time T _d1 of the electromagnetic contactor 8.

Next, when the overcurrent state is restored by eliminating the load short circuit such as opening of the short-circuit load, the overcurrent detection circuit 9 restores the ON control signal. Along with this, the electromagnetic contactor 8 is turned off with a return operation delay time T _d2 . At this time, the thyristor 7
Has already extinguished spontaneously and returns to normal operation.

When the electromagnetic contactor 8 recovers, a high voltage close to the voltage of the power source 1 is applied to the load 5 during the recovery delay time T _d2 of the electromagnetic contactor 8, but this voltage period is as short as several tens of milliseconds. It's time and there is no problem under normal load.

Further, the ON signal of the electromagnetic contactor is set to a period of at least the time required for the ON operation at the shortest, and the electromagnetic contactor is once turned ON even when the overcurrent state is resolved within this period. The reason for this is that if the overcurrent state is resolved and the ON signal of the electromagnetic contactor is restored before the electromagnetic contactor is turned on,
To prevent the overcurrent condition from disappearing while the electromagnetic contactor is not operating (that is, the current in the thyristor is not transferred to the electromagnetic contactor), and the thyristor cannot be extinguished spontaneously even when the overcurrent condition is resolved. belongs to.

G. Effect of the Invention As described above, according to the present invention, a thyristor and an electromagnetic contactor are provided in parallel with the chopper part, and the thyristor and the electromagnetic contactor are ON-controlled by overcurrent detection, and the current of the chopper part is transferred to the thyristor. Since it is made to move to the electromagnetic contactor, there are the following effects.

(1) It is possible to use a chopper having a small overcurrent withstand capability, and a chopper having a high frequency characteristic can be used to reduce the size and weight of the reactor, but the cost of the chopper does not increase.

(2) Thyristors with a short-time rating can be used, and electromagnetic contactors that do not have a high response are unnecessary, so that they do not increase in size and cost.

(3) Since the thyristor can be extinguished spontaneously, its commutation circuit is unnecessary, the overcurrent protection circuit is simplified, and a reliable operation can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG.
FIG. 3 is a time chart when an overcurrent occurs, and FIG. 3 is a conventional circuit diagram. 2 ... Power transistor, 3 ... Reactor, 5 ...
Load, 6 ... Smoothing capacitor, 7 ... Thyristor, 8
…… Electromagnetic contactor, 9 …… Overcurrent detection circuit, 10 …… Hall current transformer.

Claims (1)

[Scope of utility model registration request] 1. A step-down chopper for supplying a direct current whose voltage has been reduced to a load by a switch operation for controlling the conduction ratio of a chopper provided between a DC power source and a load, and a thyristor provided in parallel with the chopper. And an electromagnetic contactor, which turns on the thyristor by giving an ON signal to the thyristor at the time of detecting an overcurrent of the DC current, and at least outputs an ON signal for a period of time or more required for an ON operation of the electromagnetic contactor. A step-down chopper, comprising: an overcurrent detection circuit which is applied to an electromagnetic contactor to turn on the electromagnetic contactor, and which restores an ON signal applied to the electromagnetic contactor when overcurrent is eliminated.