A circuit cannot have negative static resistance (be active) over an infinite voltage or current range, because it would have to be able to produce infinite power. Any active circuit or device with a finite power source is " eventually passive ". This property means if a large enough external voltage or current of either polarity is applied to it, its static resistance becomes positive and it consumes power ∃ ∃ V , I : | v | > V or | i | > I ⇒ ⇒ R s t a t i c = v / i ≥ ≥ 0 where P max = I V is the maximum power the device can produce.