I am studying the STMicroelectronic BUL216 NPN power transistor. Electrical specification like VCES is given by the Specification Sheet BUL216 Datasheet. Also, the VCEO spec. Both spec has to do with how much high voltage the transistor can withstand before breakdown. Specifications are marked as follow:

  • Symbol - Parameter - Value - Unit
  • VCES - Collector-Emitter Voltage (VBE = 0) 1600 Volts
  • VCEO - Collector-Emitter Voltage (IB = 0) 800 Volts

Technically speaking, what exactly is the difference between VCEO and VCES ?
And what are the exact definitions ?
I also found on the WEB an old Fairchild 1973 Data Book which states that VCES would stand for "Collector to Emitter Saturation Voltage", typically 0.2volt.
Obviously, these two specifications are totally different.
Can anyone clarify those information ? Appreciate your help :)


4 Answers 4


V_CES is not Collector-Emitter Saturation voltage, which is denoted by V_CE(Sat), but Collector-Emitter voltage with Base-Emitter short circuit.

V_CEO is Collector-Emitter voltage with Base being open circuit.

And there are more such as

V_CER, Collector-Emitter voltage with a resistor between the Base and the Emitter.

V_CEV, Collector-Emitter voltage with a voltage supply (battery) between the Base and the Emitter. For an NPN BJT, the battery negative pole is connected to the Base, and the battery positive pole to the Emitter.

V_CBO, Collector-Base voltage with Emitter being open circuit.

enter image description here

In the image,

V_BCEO is the Breakdown Collector-Emitter voltage with Base being open circuit.

Similarly for the other breakdown voltages.


breakdown of CollectorBase, with base Open or with base Shorted to Emitter


There is a difference between BVCES and BVCEO. This is because as VCE rises, some (small) breakdown current flows on the C-B junction. If the base is shored e to the emitter, then nothing else happens. However if the base is open circuit (or connected to a circuit that can't absorb this current, then it flows 'back into' the B-E junction where it it multiplied by beta of the transistor and contributes even more to the C-B breakdown current. The whole process accelerates and ultimately BVCEO breakdown voltage is lower the BVCES breakdown voltage.



The relative Importance of the VCES and usually VCEO ratings depends on the application. In a half-bridge converter, for instance, the rated VCEO is the dominant factor, whilst in a VCES forward converter is important. Which is most rating Also applicable may depend on Whether to slow laughed network or snubber is applied (see section 1.3.3).

May 2022 update: The original link above from 2018 seem to have died (it claims to require a login, but even then it doesn't show the original content).

However the quoted text seems to be from chapter 1 in an old Philips Semiconductor book: "Power Semiconductor Applications". The relevant PDF file can be downloaded from an old version of the NXP website via the Internet Archive here. See page 79 for the quoted text.


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