Patent ID: 11942926
Assignee: SIEMENS AKTIENGESELLSCHAFT
Field: Basic communication processes (Electrical engineering)
Classification: CPC H | IPC H

Claim 0:
1. A protection circuit for a semiconductor switch, the semiconductor switch having a gate which is controllable by a gate driver, the protection circuit comprising:
an integrator connected to the gate and detecting a gate charge of the gate based on an integrator output voltage of the integrator,
a comparator unit for switching off the semiconductor switch when the gate charge falls below a time-independent reference charge, the comparator unit comprising a pnp-bipolar transistor, an npn-bipolar transistor having a collector connected to a base of the pnp-bipolar transistor, a first comparator diode, a second comparator diode, a comparator capacitor, a first comparator resistor, a second comparator resistor and a third comparator resistor and to an anode of the first comparator diode, with the comparator capacitor and the first comparator resistor each connected in parallel with a base-emitter path of the pnp-bipolar transistor, and with the second comparator resistor connected in parallel with a base-emitter path of the npn-bipolar transistor, and
a timer element for setting a minimum duration between a switching-on of the semiconductor switch by the comparator unit and a switching-off of the semiconductor switch by the comparator unit, wherein the minimum duration is selected such that, during the minimum duration, a gate capacitance and a Miller capacitance of the semiconductor switch, after the semiconductor switch into a normal operation, are substantially completely, but at least 90%, recharged,
wherein the timer element comprises a timer element resistor, a timer element capacitor and a timer element diode, wherein an anode of the timer element diode is connected to a first terminal of the timer element resistor and to a first electrode of the timer element capacitor, and an output of the integrator is connected to a cathode of an output diode, with an anode of the output diode being connected to the anode of the timer element diode, to the first terminal of the timer element resistor and to the first electrode of the timer element capacitor, and
wherein a cathode of the first comparator diode is connected to the anode of the output diode, an emitter of the npn-bipolar transistor is connected to a second electrode of the timer element capacitor, an emitter of the pnp-bipolar transistor is connected via the third comparator resistor to a second terminal of the timer element resistor, and a base of the pnp-bipolar transistor is connected to a cathode of the second comparator diode.