# Which BJT-parameters need to be derated at raised ambient temperature?

I am designing a discrete MOSFET-driver stage based on BJTs in simple push-pull configurations and wondering, which of the values under absolute maximum ratings I have to derate at higher ambient temperatures. The device in consideration is the BC807W which only has to conduct during turn-off of the MOSFET.

The datasheet gives me a max value for I_{CM}=-1A. Can I drive this peak current only at 25°C of ambient temperatures or also at higher temperatures as long as the maximum junction temperature is not exceeded?

The background of this question is that I head a similar issue with diodes some time ago. The datasheet would give me a maximum surge-current which has to be linearly derated above 25°C (according to the very competent FAE). This current must not be exceeded, even if a nice margin of the junction temperature remained. The point there was, that not only the heat destroys the diode, but also the current density.

So, to bring this to an end: is it the same with the peak collector current of a BJT?

• That value of $I_{CM}$ is in the table of absolute maximum ratings (table.6 - limiting values). Those are values from which you must stay absolutely clear, so don't think of going nowhere near 1A, even at nominal 25°C. Designing against absolute maximum ratings is bad design practice. – Lorenzo Donati -- Codidact.org Aug 19 '15 at 21:28
• If you foresee 1A peaks (or something near that) probably you should select a tougher part if you want a reliable design. – Lorenzo Donati -- Codidact.org Aug 19 '15 at 21:30