JPH0758786B2 - Semiconductor device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to a semiconductor device that realizes overvoltage protection of an enhancement type field effect transistor in a monolithic manner.

[Conventional technology]

FIG. 4 shows an overvoltage protection circuit in a conventional semiconductor device. In FIG. 4, 1 is a switching element, 2 is a diode, 3 is a resistor, 4 is a capacitor, and 5 and 6 are main terminals.

This overvoltage protection circuit absorbs the overvoltage by utilizing the fact that the main component of the overvoltage is a high-frequency component, and is called a snubber. It is a high-pass filter and a overvoltage absorption by a series connection of a resistor 3 and a capacitor 4. And a diode 2 for speeding up the process.

Next, the operation will be described. The main terminals 5 and 6 of the switching element 1 are AC-coupled with respect to the voltage rise by the diode 2 and the capacitor 4, and are short-circuited to the high frequency component of the overvoltage. Therefore, the overvoltage is absorbed by the charging of the capacitor 4. The absorbed energy of the overvoltage is gradually discharged through the resistor 3 after passing the peak of the overvoltage. The resistor 3 is for preventing the switching operation itself from being absorbed.

[Problems to be solved by the invention]

The conventional overvoltage protection circuit configured as described above charges and discharges the capacitor 4 through the diode 2 and the resistor 3 each time switching is performed. Therefore, a large power loss occurs in both the diode 2 and the resistor 3. In addition, a large capacity is required to increase the surge absorption amount. However, the increase in the amount of surge absorption slows the switching speed and thus has a limit, and cannot cope with an overvoltage having a relatively long pulse width with respect to the switching frequency. Therefore, there is a problem that the field-effect transistor characterized by high-speed switching cannot be absorbed unless the surge has a particularly high frequency.

The present invention has been made in view of the above circumstances, and an object thereof is to absorb an overvoltage having a relatively long pulse width for switching in a semiconductor device having an enhancement-type field effect transistor cell in a monolithic manner. To obtain a possible overvoltage protection circuit.

[Means for solving problems]

In order to achieve such an object, the present invention makes the gates of some of the enhancement type field effect transistor cells formed on the same substrate independent of each other, and makes some gates of the transistor cells independent of each other. The voltage dividing point of the series voltage dividing resistor connected in parallel to the drain-source of is connected to the independent gate, and by some of the transistor cells and the capacitance connected in parallel to this drain-source, It is designed to absorb the overvoltage applied to the.

[Action]

The semiconductor device according to the present invention has extremely small power loss other than when overvoltage is absorbed, and can cope with overvoltage having a relatively long pulse width.

〔Example〕

First, the outline of the present invention will be described. The overvoltage protection circuit for a semiconductor device according to the present invention has a property that some of the enhancement-type field effect transistor cells have a low impedance at the time of overvoltage. The structure is simple because it is composed of the transistor cells on the same substrate as the main transistor cell to be performed, and the low impedance is maintained at the time of overvoltage, so that it is possible to cope with overvoltage having a relatively long pulse width with respect to the switching frequency.
The enhancement-type field effect transistor for overvoltage protection can be obtained only by making some gates of the transistor cells of the switching element independent.

An embodiment of an overvoltage protection circuit for a semiconductor device according to the present invention is shown in FIG. FIG. 4 shows the case of an n-channel enhancement type MOS field effect transistor. In FIG. 1, 5 is a main terminal as a drain terminal, 6 is a main terminal as a source terminal, 7 is a main transistor, 7a is a gate terminal connected to the gate of the main transistor 7, and 8 is an overvoltage protection with an independent gate. Transistor, 8a is the gate terminal connected to the gate of the overvoltage protection transistor, 9 is the combined capacitance between the drain and source of each transistor 7,8,
11 is a voltage dividing resistance, and N is a voltage dividing point.

Next, the operation of the overvoltage protection circuit configured as described above will be described. The overvoltage protection transistor 8 is electrically connected between the drain terminal 5 and the source terminal 6 when the gate terminal 8a has a positive potential higher than a certain value with respect to the source terminal 6. "Conduction potential").

When a voltage is applied between the drain terminal 5 and the source terminal 6 and is increased, the voltage between the gate terminal 8a and the source terminal 6 divided by the resistors 10 and 11 rises. When the voltage between the gate terminal 8a and the source terminal 6 becomes the conduction potential,
The drain terminal 5 and the source terminal 6 are electrically connected to each other, and an electric current is caused to flow between them to reduce the voltage between the drain terminal 5 and the source terminal 6.

When the voltage between the drain terminal 5 and the source terminal 6 becomes lower than the limit voltage, the voltage between the gate terminal 8a and the source terminal 6 also drops due to the voltage dividing resistors 10 and 11, and the voltage between the drain terminal 5 and the source terminal 6 rises. Be restricted. Enhancement type
There is a limit to the on / off operation speed of the overvoltage protection transistor 8 that is a MOS field effect transistor. However, in the case of a high-speed overvoltage that causes a problem, that is, a high-frequency component overvoltage, the capacitance 9 of the entire transistor causes The drain terminal 5 and the source terminal 6 are always short-circuited at a high frequency, so that they are sufficiently absorbed.

FIG. 2 is an explanatory diagram showing a semiconductor device having the above-mentioned overvoltage protection circuit. In the semiconductor device shown in FIG. 2, a large number of n-channel enhancement type field effect transistor cells are formed as switching elements, and some of these transistor cells having independent gates are used as overvoltage protection transistor cells. It is a thing. In FIG. 2, reference numeral 12 is a substrate and 13 is an insulator, and the same or corresponding portions as those in FIG. 1 are designated by the same reference numerals.

Although FIG. 1 and FIG. 2 show the case where the n-channel enhancement type MOS field effect transistor is used, the present invention is not limited to this, and a p-channel enhancement type MOS field effect transistor as shown in FIG. 3 is used. However, the same can be applied.

〔The invention's effect〕

As described above, according to the present invention, the gates of some of the enhancement-type field effect transistor cells formed on the same substrate are made independent, and are connected in parallel to the drain / source of the some transistor cells. By connecting the voltage dividing point of the series voltage dividing resistor to the above independent gate, some of the transistor cells and the capacitance connected in parallel to the drain and source absorb the overvoltage applied between the drain and source. As a result, the overvoltage protection transistor is completely turned off except when overvoltage is absorbed.
There is an effect that power consumption is extremely small except when overvoltage is absorbed.

Also, unlike the filter operation based on the frequency, since the current flows purely by voltage, it is possible to cope with the overvoltage having a relatively long pulse width with respect to the switching frequency, and the overvoltage can be sufficiently applied even during the high frequency operation which is a characteristic of the field effect transistor. It has the effect of being absorbed.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an overvoltage protection circuit for a semiconductor device according to the present invention, and FIG. 2 is a semiconductor device having an n-channel enhancement type field effect transistor cell having the overvoltage protection circuit of FIG. Explanatory drawing, FIG. 3 shows the first
FIG. 4 is an explanatory view of a semiconductor device having a p-channel enhancement type field effect transistor cell having an overvoltage protection circuit shown in FIG. 4, and FIG. 4 is a circuit diagram showing an overvoltage protection circuit in a conventional semiconductor device. 5 ... Drain terminal, 6 ... Source terminal, 7 ... Main transistor, 7a, 8a ... Gate terminal, 8 ... Overvoltage protection transistor, 9 ... Capacitance, 10, 11 ... Voltage dividing resistor, N ...
… Partial pressure point.

Claims (1)

[Claims] 1. A series voltage divider in which the gates of some of the enhancement-type field effect transistor cells formed on the same substrate are made independent and are connected in parallel to the drain / source of the some transistor cells. A voltage dividing point of the resistance is connected to the gate of the part of the transistor cell, and the part of the transistor cell and the capacitance connected in parallel to the drain and the source absorb the overvoltage applied between the drain and the source. A semiconductor device characterized by: