Electrical transmission or interconnection systems – Switching systems – Condition responsive
Patent
1996-07-23
1998-09-01
Shoop, Jr., William M.
Electrical transmission or interconnection systems
Switching systems
Condition responsive
307104, 307125, 327110, 361152, 361156, 257161, H01H 4722
Patent
active
058014586
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a direct current control circuit for turning on and off the flow of current in an inductive load power circuit by the control of a semiconductor switch.
REVIEW OF THE RELATED TECHNOLOGY
For switching direct current on and off the conventional arrangement is one including a series circuit arrangement with a power source, a semiconductor switch and a consumer or load. In the case of inductive loads a freewheel diode is placed in circuit parallel to the inductive part of the power circuit, this inductance being possibly also for example due completely or partly to the conductors of the power circuit.
A semiconductor switch in the form of a MOSFET for instance is controlled with the aid of the GATE-SOURCE voltage. As long as such a transistor is conducting, then essentially the supply potential will be present at the connection point between the transistor and the load--and accordingly also at the freewheel diode. If now the GATE-SOURCE voltage is reduced to turn off the transistor, the internal resistance of the transistor will increasingly rise and the power converted into heat will also become greater and greater, since owing to the action of the inductance of the load power circuit the current will only be reduced a small amount. It is therefore necessary for the flow of current to be switched through the freewheel diode before the transistor develops so much heat that it is damaged.
For this purpose the German patent publication 4,013,997 A1 discloses holding a switch off control current for the GATE of the transistor at a high value until an evaluating circuit indicates that the freewheel diode is near the switching point. The control current is now switched over to a lower value. Although this measure means that the undesired effects occurring on switching over are substantially avoided, namely power dissipation at the transistor and the production of interfering voltages and interfering pulses, the maximum switching rate is limited because on increasing the DRAIN-SOURCE voltage and then simultaneously reducing the effective GATE-SOURCE capacity of a MOSFET the switching off operation is accelerated and because of this the maximum switching off current can only be selected to be so large that timely switching over to the lower switching off current near the switching point of the diode is still possible.
On switching on the current another problem occurs that is to say the danger of short circuiting. If switching off took place only just prior to switching on again, the current will still be flowing in the load power circuit through the freewheel diode. If the resistance of the transistor drops with an increasing GATE-SOURCE voltage for switching on the transistor, then the potential at the connection point between the transistor and the freewheel diode will become positive so that the diode is turned off. However such turnoff will not take place immediately so that there is a danger that on increasing the GATE-SOURCE voltage of the transistor the same will already be fully conducting, if the diode is not yet turned off. This will obviously lead to a short circuit accompanied by the danger of damage to the transistor and/or the diode.
In order to prevent this there has already been a suggestion in the said German patent publication 4,013,997 A1 to firstly hold the control current at a low level or--in the case of the use of bipolar transistors--to only cause it to increase at a slow rate until the evaluating device has detected switching of the freewheel diode. It is only then that the control current is switched over to a substantially higher value. While this means effective prevention of a short circuit, with the constant turn off current provided in this case the GATE-SOURCE voltage of the transistor will be continuously increased. If same exceeds the trip voltage of the transistor then current will increasingly flow through the same. Accordingly the current through the diode will be reduced and owing to a further increase in the DRAIN-SOURCE curre
REFERENCES:
patent: 3748560 (1973-07-01), Sawa et al.
patent: 4186418 (1980-01-01), Seiler
patent: 4746813 (1988-05-01), Disser
patent: 4903188 (1990-02-01), Madhavan et al.
patent: 5390070 (1995-02-01), Niedermeier
patent: 5532526 (1996-07-01), Ricco et al.
Paladini Albert W.
Shoop Jr. William M.
LandOfFree
Direct current control circuit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Direct current control circuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Direct current control circuit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-272426