JPH09233807A - Power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect a switching element and its peripheral circuit even if an overcurrent flows by driving the drive of the switching element thereby protecting the switching element when the detection value of a current detecting circuit amounts to a specified value or over. SOLUTION: A current detecting resistor 56 is connected in series to a switching element 51, and this output is inputted into a control circuit 55A. The control circuit 55A monitors the current value flowing to the switching element 51 by the current detecting circuit 56, and when the voltage of the current detecting resistor 56 amounts to reference voltage Vref2 , for example, a limit value or over where the switching element 51 does not break, it stops the drive of a drive circuit 54, and protects the switching element 51. Accordingly, even if an excessive current flows into the switching element by any reason, the switching element 51 can be protected from the stress caused by the excessive current at such abnormality.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device such as a boost converter, and more particularly to overcurrent protection.

[0002]

2. Description of the Related Art A conventional capacitor-input type switching power supply device has a drawback in that it has good efficiency but poor power factor. Therefore, recently, in order to improve the power factor, a power factor improving circuit has been provided.

An example of the conventional power supply device is shown in FIG.

A power supply device 1B shown in FIG. 1 has a full-wave rectifier circuit 3 for rectifying an AC power supply 2, a smoothing capacitor 4 for supplying electric power to a load LD, and a full-wave rectifier circuit 3 and a smoothing capacitor 4. It is a boost converter configured to include a connected power factor correction circuit 5B.

The power factor correction circuit 5B includes a reactor 50, for example, a switching element 51 formed of a MOSFET, a diode 52 connected in the forward direction, a current detection resistor 53 for detecting a current flowing from the AC power supply 2 to the load LD, and a drive circuit 5.
4 and a control circuit 55B.

The output voltage of the full-wave rectifier circuit 3, the terminal voltage of the smoothing capacitor 4, and the voltage value obtained from the current detection resistor 53 are input to the control circuit 55B. Then, they are compared with the level of the reference voltage Vref, and the drive circuit 5
4 is applied to the gate of the switching element 51 via ON / OFF to control ON / OFF, control the output voltage to the load LD, and protect the circuit in the device 1B and the load LD.

[0007]

However, the overcurrent protection in the conventional device 1B works only for the current passing through the AC power supply 2, the full-wave rectifier circuit 3, the reactor 50, the diode 52, the smoothing capacitor 4 or the load LD. , The current passing through the switching element 51 does not function.

That is, if the diode 52 is short-circuited for some reason while the switching element 51 is on, all the energy stored in the smoothing capacitor 4 is switched.
Will be discharged through. At this time, since the current flowing through the switching element 51 cannot be detected by the current detection resistor 53, if the current exceeds the allowable value of the switching element 51, the switching element 51 will fail.

As described above, usually, in the conventional boost converter, the current flowing through the switching element for boosting is not monitored to protect the circuit.
For this reason, there is no means for protecting the boosting switching element in the event of an abnormality, so it is expected that the switching element will fail in the worst case. Further, at that time, it is possible that the peripheral circuit of the switching element simultaneously fails due to the failure of the switching element, which may increase the scale of the failure.

Therefore, an object of the present invention is to provide a power supply device capable of protecting the switching element and its peripheral circuits even if an overcurrent flows through the boosting switching element for some reason.

[0011]

In order to achieve the above object, the present invention is to connect a reactor, a diode and a load to a power supply in series, and to connect a switching element in parallel to the series connection circuit. In a power supply device that drives a switching element to supply electric power to the load, a current detection circuit that detects a current flowing through the switching element, and the switching element when a detection value of the current detection circuit becomes a predetermined value or more. And a control circuit for controlling the driving of the device to protect the switching element.

According to the present invention having the above-described structure, by providing the current detection circuit for detecting the current flowing in the switching element for boosting, the switching element is driven when the detection value of the current detection circuit exceeds a predetermined value. Can be controlled to protect the boosting switching element from overcurrent. Further, by protecting the switching element, it is possible to protect the peripheral circuit of the switching element.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

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

This power supply device 1A has a full-wave rectifier circuit 3 for rectifying the AC power supply 2, a smoothing capacitor 4 for supplying electric power to the load LD, and a force connected between the full-wave rectifier circuit 3 and the smoothing capacitor 4. The rate improving circuit 5A is provided.

The power factor correction circuit 5A is a conventional power supply device 1B.
Similarly, the reactor 50 and the diode 52 connected in the forward direction are directly connected, and the switching element 51 such as MOSFET is connected in parallel to the series connection circuit,
A current detection resistor 53 that detects a current flowing to the load LD is connected in series to form a load LD, a full-wave rectifier circuit 3, and a current detection resistor 5.
The control circuit 55A for inputting each voltage of 3 and the switching element 51 controlled by the output of the control circuit 55A.
And a drive circuit 54 that outputs the control voltage. In the present invention, in particular, the current detection resistor 56 is connected in series to the switching element 51, and this output is input to the control circuit 55A.

Therefore, the output voltage of the full-wave rectifier circuit 3, the terminal voltage of the smoothing capacitor 4, the voltage of the current detection resistor 53, and the voltage of the current detection resistor 56 are input to the control circuit 55A.

The control circuit 55A monitors the terminal voltage of the smoothing capacitor 4, the terminal voltage of the full-wave rectifier circuit 2, and the detected value of the current detection resistor 53, and compares them with the reference voltage Vref ₁ to determine the terminal of the load LD. Adjust the voltage.

Further, the control circuit 55A includes a current detection resistor 5
The value of the current flowing through the switching element 51 is monitored at 6, and when the voltage of the current detection resistor 56 becomes equal to or higher than the reference voltage Vref ₂ , for example, the limit value at which the switching element 51 is not damaged, the driving of the drive circuit 54 is stopped. Let
The switching element 51 is protected.

As described above, according to the power supply device 1A, in addition to detecting the current flowing from the AC power supply 2 to the load LD, the current flowing only in the boosting switching element 51 is detected. Even if an excessive current flows through the switching element 51 for some reason, the switching element 5 is not affected by the stress caused by the excessive current during such an abnormality.
1 can be protected.

If the switching element 51 fails, depending on the failure state, the peripheral circuit of the switching element 51 in the power supply unit 1A may also fail and the damage increases, but if the switching element 51 stops normally. , You can prevent such things.

The present invention is not limited to the above-mentioned embodiment, and various embodiments are possible. For example, in the above-described embodiment, the case where the DC output of the full-wave rectifier circuit is used as the power source has been described, but the present invention can be similarly applied to the case of the DC power source. Further, in the above-described embodiment, the current detection resistor 56 is taken as an example of the current detection circuit that detects the current flowing in the switching element 51.
Other methods such as detecting the current flowing through the switching element 51 by using a current transformer instead of the resistor may be used. In addition, when the current flowing through the switching element is detected and the driving of the element is stopped, a means for notifying the fact may be added.

[0023]

According to the present invention described in detail above, since the current detecting circuit for detecting the current flowing through the boosting switching element is provided, the boosting switching element and its peripheral circuits are based on the detected value. Can be protected from overcurrent.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a power supply device according to the present invention.

FIG. 2 is a circuit diagram of a conventional power supply device.

[Explanation of symbols]

 1A power supply device 2 AC power supply 3 full-wave rectifier circuit 4 smoothing capacitor 5A power factor correction circuit 50 reactor 51 switching element 52 diode 53, 56 current detection resistor 54 drive circuit 55A control circuit LD load

Claims (2)

[Claims] 1. A power supply device in which a reactor, a diode, and a load are connected in series to a power supply, and a switching element is connected in parallel to the series connection circuit, and the switching element is driven to supply power to the load. In, a current detection circuit for detecting a current flowing through the switching element, and a control circuit for controlling the driving of the switching element to protect the switching element when a detection value of the current detection circuit becomes a predetermined value or more. A power supply device comprising: 2. The power supply device according to claim 1, wherein the power supply is a DC output of a full-wave rectifier circuit.