Semiconductor device

Details Semiconductor device Semiconductor device

2001-09-04

2004-01-20

Sircus, Brian (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

With specific quantity comparison means

C361S079000

Reexamination Certificate

active

06680835

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device and more particularly to a semiconductor device having a short circuit protecting function for preventing a short circuit of a semiconductor element such as an insulated gate bipolar transistor (IGBT).
2. Description of the Background Art
In an IGBT in which a large current flows as a main current, a sense emitter to be used for measuring a current is provided separately from an emitter in which the main current flows, and the main current can be indirectly monitored by measuring a current (sense current) of the sense emitter with a conversion into a voltage through a current and voltage converting section.
As an example of the current and voltage conversion,
FIG. 9
shows a structure using a resistor. In
FIG. 9
, an IGBT
1
having a collector C connected to a terminal T
1
and an emitter E connected to a terminal T
2
is provided, and has a sense emitter SE connected to the terminal T
2
through a resistor R
101
to be a current and voltage converting section CV
1
. A terminal T
5
for outputting a sense emitter voltage is connected to an end on the sense emitter SE side of the resistor R
101
. The IGBT
1
has a gate connected to a terminal T
3
.
As an example of the current and voltage conversion,
FIG. 10
shows a structure using a current mirror circuit. In
FIG. 10
, the same structures as those in
FIG. 9
have the same reference numerals and repetitive description will be omitted.
In
FIG. 10
, a sense emitter SE of an IGBT
1
is connected to a collector of a transistor Q
2
constituting a current and voltage converting section CV
2
. The transistor Q
2
is paired with a transistor Q
1
to constitute the current mirror circuit, and both gates are connected to the sense emitter SE in common and both emitters are connected to a terminal T
2
in common.
A collector of the transistor Q
1
is connected to a positive electrode of a constant voltage source PS through a resistor R
102
, a negative electrode of the constant voltage source PS is connected to the terminal T
2
, and a terminal T
5
for outputting a sense emitter voltage is connected to an end on the transistor Q
1
side of the resistor R
102
.
The current and voltage converting section CV
2
constituted by the current mirror circuit can lessen a voltage drop with a current and voltage conversion to carry out a measurement.
FIG. 11
is a diagram showing a structure of a short circuit protecting circuit for measuring a sense emitter voltage to protect a short circuit by using a resistor R
101
as a current and voltage converting section.
In
FIG. 11
, a sense emitter voltage output from an end on the sense emitter SE side of the resistor R
101
is input to an input terminal on the positive side of a comparator C
101
and a positive electrode of a constant voltage source PS is connected to an input terminal on the negative side of the comparator C
101
.
An output terminal of the comparator C
101
is connected to a cathode of a diode D
101
and an anode of the diode C
101
is connected to a gate of an IGBT
1
.
In a short circuit protecting circuit having such a structure, a predetermined voltage supplied from the constant voltage source PS is compared with the sense emitter voltage. If the sense emitter voltage is higher than the predetermined voltage, it is decided that a sense emitter current abnormally flows. Consequently, a current is caused to flow from the gate of the IGBT
1
toward an emitter through the diode D
101
, thereby dropping a gate voltage and reducing a collector current of the IGBT
1
.
There is a problem in that the sense emitter current is assumed to have a uniquely simple correlation with the collector current.
More specifically, an electric potential of the sense emitter SE is increased with the detection of the sense current in an actual circuit. For example, therefore, in some cases in which an electric potential of a collector C is low, the electric potentials of the collector C and the sense emitter SE become insufficient so that the sense emitter current is measured to be small even if a large collector current flows. For this reason, the detection precision of the collector current is reduced and a sufficient protection cannot be obtained in some cases. In addition, a rise in a collector voltage rapidly increases the sense emitter current with a start of a protecting operation so that the protecting operation is promoted. Furthermore, a positive feedback in which the gate voltage is decreased to increase the collector voltage is generated and the sense emitter current is rapidly increased with a delay of the operation of a protection circuit, thereby causing a malfunction in some cases.
Moreover, the collector current is rapidly reduced by the inaccurate detection of the collector current. In the IGBT to be used for controlling a large current, for example, there is a problem in that a high surge voltage is generated.
In order to solve these problems, a structure for detecting a collector voltage has also been proposed. However, the collector of the IGBT is provided on the high potential side. Therefore, a detection circuit corresponding to a high voltage is required so that a manufacturing cost is increased and a large space for providing the detection circuit is required, resulting in an increase in a size of the device. Moreover, a countermeasure to be taken against a noise made from various circuits on the high potential side becomes complicated.
Japanese Patent Application Laid-Open No. 11-299218 (1999) has disclosed a structure in which a sense emitter and an emitter in an IGBT are imaginarily short-circuited by using an operational amplifier, thereby preventing a fluctuation in a sense emitter voltage. In order to implement such a structure, it is necessary to prepare a power supply having a lower potential than an emitter potential. In addition, in the case in which the structure is to be implemented as a monolithic IC, there is a problem in that a countermeasure to be taken against a noise becomes complicated because an emitter potential to be an original grounding potential is an intermediate potential of a power supply of the monolithic IC.
SUMMARY OF THE INVENTION
A first aspect of the present invention is directed to a semiconductor device comprising a transistor having a sense emitter, and a protecting system for carrying out a protecting operation for detecting a sense current flowing to the sense emitter to control a collector current, the protecting system including a current and voltage converting section having a variable resistor for converting the sense current into different voltages by change of a resistance value thereof, thereby generating a plurality of sense voltages, and a current ratio detecting section for receiving the sense voltages output from the current and voltage converting section and information about a resistance value of the variable resistor corresponding to the sense voltages, thereby calculating a ratio of each of the sense voltages to each of the resistance values and detecting an amount of change of the ratio thus calculated.
A second aspect of the present invention is directed to the semiconductor device according to the first aspect of the present invention, wherein a resistance value of the variable resistor is varied in response to a voltage signal which is changed on a time basis, the information about the resistance value of the variable resistor is the voltage signal which is changed on a time basis, and the resistance value of the variable resistor and the voltage signal which is changed on a time basis have a proportional relationship.
A third aspect of the present invention is directed to a semiconductor device comprising a transistor having a sense emitter, and a protecting system for carrying out a protecting operation for detecting a sense current flowing to the sense emitter to control a collector current, the protecting system including a current and voltage converting section for converting the sense current into

Affiliated with

Also associated with

Rating

Semiconductor device does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Semiconductor device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor device will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3209146