An analysis of generation mechanisms of the transitional peak current in sense-emitter current for IGBTs with current sense and techniques to remove it

Abstract

It is important to remove the transitional peak current in sense-emitter current which occurs by dynamic currents sharing during turn-on for a design of IGBTs with current sense used protection against overcurrent and short circuit. But this analysis has been scarcely investigated.
This paper makes clear generation mechanisms of the transitional peak current by simulations and experiments using a parallel operation model and reports on techniques to remove it.
The following results were obtained.
(1) In the two paralleling devices model which consists of a sense cell and main cells, the transitional peak current occurs during turn-on when a sense cell turns on faster than main cells do. In this case, main parameters that effect dynamic currents imbalance are gate resistance (Rg) and gate threshold voltage (Vth).
(2) In dynamic currents imbalance based on individual Rg and Vth among main cells, it may treat as a two paralleling devices model consists of a sense cell with Rgs and Vths, and main cells with average values Rgm and Vthm.
(3) The transitional peak current can be removed by the design that Rgs and Vths in a sense cell are larger than average values Rgm and Vthm in main cells.
(4) We manufactured on trial IGBTs with current sense that Vths in a sense cell is different from average value Vthm in main cells to change impurity concentrations of each channels. And we confirmed that the transitional peak current in senseemitter current can be removed by the design that Vths in a sense cell is larger than average value Vthm in main cells.