VCE

Vce, denoted V_CE, is the voltage between the collector and emitter terminals of a bipolar junction transistor (BJT). It is measured with respect to the emitter and is typically referenced in circuits with the emitter at ground or a fixed potential. In most analyses, Vce is positive for conventional NPN configurations when the collector is at a higher potential than the emitter, while the sign is reversed for PNP devices.

The value of Vce, together with the base drive, determines the transistor’s operating region. In active operation, Vce is sufficiently high to keep the transistor out of saturation, allowing the collector current to be controlled by the base current. In saturation, the base drive is strong enough that Vce drops to a small, minimum value, known as Vce(sat), typically on the order of a few hundred millivolts (roughly 0.1–0.3 V depending on device and current). In cutoff, the collector current is essentially zero and Vce tends to the supply voltage. Note that Vce can also approach a device’s maximum rating before breakdown if the voltage is excessive.

Maximum ratings for a transistor include Vce(max) or V_CEO, the maximum collector-emitter voltage the device can withstand. Exceeding this rating risks breakdown and failure. In practice, Vce is a key parameter in biasing and switching circuits; for example, in a common-emitter amplifier, Vce determines available output swing and linearity. In most MOSFET circuits, the analogous parameter is Vds (drain-to-source), since MOSFETs are voltage-controlled differently from BJTs.