Patent ID: 8319546

Claim:
A control circuit for a transistor arrangement for implementing protection of the transistor arrangement, comprising: a monitoring arrangement for monitoring the current flow and voltage across the transistor arrangement; and means for determining when the current and voltage values define an operating point which falls within a stable operating region, wherein the stable operating region comprises a region having a boundary is defined by a bipolar transistor collector current stability line I C crit which satisfies: I C crit = M n ⁢ V T - M n ⁢ R eq - R TH ⁢ V eq ⁢ φ , [ 1 ] R eq = R E + R E + R B M n ⁢ ( 1 β 0 - ( M n - 1 ) ) , [ 2 ] V eq = M n ⁢ V CB + V BE ⁡ ( 1 + 1 β 0 ) , [ 3 ] M n =multiplication factor, V T =thermal voltage (=kT/g), φ=the temperature dependence of the internal base-emitter voltage, R E =emitter resistance, R B =base resistance, R eq =equivalent resistance of R E and R B , β 0 =current gain in absence of avalanche, V CB =base-collector voltage, V BE =Base-emitter voltage, V eq =equivalent voltage of V CB and V BE , R TH =thermal resistance [K/W], wherein the stability line comprises the value of I C crit for different values of base-collector and base-emitter voltages and defines the boundary between electro-thermal stability and instability.