JPS61134118A - Excess current protecting circuit of voltage driving type semiconductor element - Google Patents

Abstract

PURPOSE:To enable protection against excess current without using a conventional current detecting element by connecting an integration circuit to a driving signal source in parallel, connecting a discharge circuit to a capacitor of this circuit and short-circuiting the controlling electrode of a driven element through other switching element when terminal voltage exceeds a specified value. CONSTITUTION:A normally off voltage driving type semiconductor element 11 is made a driven element. An integration circuit consisting of a resistance 13 and a capacitor 14 is connected in parallel to a driving signal source 12, and a diode 15 is connected to the capacitor 14. A resistance 18 for preventing short-circuiting of the output of the driving signal source 12 when a semiconductor switch 16 is made on is provided. Thus, the on voltage of the driven element 11 can be known exactly by terminal voltage of the capacitor 14, and when the terminal voltage exceeds voltage of a constant voltage diode 17, the semiconductor switch 16 is turned on and turns off the driven element 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an overcurrent protection circuit for a normally-off voltage-driven semiconductor device such as a power MO5FET.

[Conventional technology]

Fig. 3 is a block circuit diagram showing a conventional example, and if ■ in the figure is a driven element, a current detection element 2 such as an AC or DC current transformer such as ACCT or DCCT or a resistor.
:t- is provided, thereby detecting the current flowing to the element 1, and determining by the voltage comparator 3 that the current exceeds a predetermined value, the drive signal is narrowed down to O.

In the figure, 4 is an overcurrent setter that provides a set voltage value to the voltage comparator 3, 5 is an AND element that receives the output from the voltage comparator 3 and conditions the control signal, and 6 is an output from this AND element 5.
This is a drive circuit that drives the element 1.

[Problem that the invention seeks to solve]

Conventional overcurrent protection circuits using current detection elements 2 such as ACCT, DCCT, and resistors have the disadvantage that the detection elements 2 themselves are expensive and generate large losses, making the entire circuit complex and costly. was there.

The purpose of the present invention is to eliminate the disadvantages of the conventional example, and to detect and judge the overcurrent state of the element without using a current detection element (3).
i! The objective is to provide a circuit with a simple configuration that can be protected.

[Means for solving problems]

In order to achieve the above object, the present invention provides a power MO3FET.
In order to detect the on-voltage when a normally-off type voltage-driven semiconductor element such as
An integrating circuit of a resistor and a capacitor is connected in parallel to the drive signal source, and a discharge circuit is connected to the capacitor, and when the terminal voltage of the capacitor exceeds a predetermined value, the driven element is switched on via another switching element. The gist is to short-circuit the control electrodes.

[Effect]

According to the present invention, by appropriately selecting the constant of the integrating circuit, the terminal voltage of the capacitor is kept approximately equal to the on-voltage of the driven element during the on-period of the driven element, and the drive signal source is kept in the on-state. The terminal voltage of the capacitor after the signal is generated until the driven element completes turn-on can be prevented from exceeding the on-voltage of the driven element after turn-on is completed. Further, when the drive signal source generates an off signal, the driven element is turned off and its main electrode becomes a high voltage, whereas the terminal voltage of the capacitor is discharged to 0 and returns to the initial state.

Therefore, it is possible to accurately know the on-voltage of the driven element from the terminal voltage of the capacitor, and when the terminal voltage of this capacitor, that is, the on-voltage of the driven element, exceeds a predetermined value, another semiconductor switch is activated. By shorting the control electrodes of the driven element, the driven element can be turned off and protected from overcurrent.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows 1. of the overcurrent protection circuit of the present invention. 11 is a circuit diagram showing an embodiment, in which reference numeral 11 is a normally-off type voltage-driven semiconductor element as the driven element; in this case, the power M
This is an example of an OS FET. Reference numeral 12 indicates a drive signal source that controls this driven element 11.

An integrating circuit is constituted by a series circuit of a resistor 13 and a capacitor 14, and the integrating circuit is connected in parallel to the drive signal source 12. A diode 15 constitutes a discharge circuit together with the main electrode of the driven element 11, and this diode 15 is connected to the capacitor 14 of the integrating circuit.

A constant voltage diode 17 is connected between the control terminal of the semiconductor switch 16 connected between the control electrodes of the driven element 11 and the midpoint of the capacitor 14 and the resistor 13, and when the semiconductor switch 16 is turned on, the drive signal source 12 A resistor 18 is connected in series to the control electrode of the driven element 11 and the drive signal #12 to prevent the output from being short-circuited.

Note that when using an element such as a power MO3PET as the semiconductor switch 16 that does not turn on unless the control voltage exceeds a predetermined voltage (threshold voltage), the constant voltage diode 17 may be omitted.

Further, as another embodiment, as shown in FIG. 2, the semiconductor switch 16 may be made of Cyrisk, and in this way, the cost can be further reduced.

Next, to explain the operation, during the ON period of the driven element 11, the terminal voltage of the capacitor 14 is kept almost equal to the ON voltage of the driven element 11, and after the drive signal source 12 generates the ON signal, By appropriately selecting the integral constant, the terminal voltage of the capacitor 14 until the driven element 11 completes turn-on can be prevented from exceeding the on-voltage of the driven element 11 after the turn-on is completed.

Furthermore, when the drive signal source 12 generates an off signal (OV), the driven element 11 is turned off, and its main electrode becomes a high voltage.
is discharged through the battery and returns to its initial state.

In order to shorten this discharge time, a diode 19 may be connected in parallel with the resistor 13, as shown by broken lines in FIGS. 1 and 2.

In this way, the on-voltage of the driven element 11 can be accurately determined from the terminal voltage of the capacitor 14, and when the terminal voltage of the capacitor 14 exceeds the voltage of the voltage regulator diode 17, the semiconductor switch 16 is turned on and the driven element 11 is turned on. The drive element 11 is turned off.

〔Effect of the invention〕

As described above, the voltage-driven semiconductor element protection circuit of the present invention detects the occurrence of overcurrent in a normally-off type with a simple circuit consisting of an RC integration circuit and a diode, and uses this detection signal to detect overcurrent occurrence. Since the control electrode of the driven element can be turned off by turning on an additional semiconductor switch, it is possible to turn off the control electrode of the driven element, so it is inexpensive and generates little loss without requiring a special current detection element such as ACCT or DCCT.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the overcurrent protection circuit for a voltage-driven semiconductor device of the present invention, FIG. 2 is a circuit diagram showing another embodiment, and FIG. 3 is a block circuit diagram showing a conventional example. It is. l... Driven element 2... Current detection element 3.
...Voltage comparator 4...Overcurrent setting device 5...
AND element 6... Drive circuit 11... Driven element 12... Drive signal source 13... Resistor
14... Capacitor 15... Diode 16... Semiconductor switch 17... Constant voltage diode 18... Resistor 19... Diode Applicant Fuji Electric Co., Ltd. Figure 1. Inner Jushu Diagram 3

Claims (1)

[Claims] Power MOSFET (MOS field effect transistor)
In order to detect the on-voltage when a normally-off type voltage-driven semiconductor device such as
An integrating circuit of a resistor and a capacitor is connected in parallel to the drive signal source, and a discharge circuit is connected to the capacitor, and when the terminal voltage of the capacitor exceeds a predetermined value, the driven element is switched on via another switching element. An overcurrent protection circuit for voltage-driven semiconductor devices characterized by short-circuiting control electrodes.