When I was simulating a bipolar transistor circuit, I needed parameters related to Vcbo and Vebo, but the bipolar transistor models in Qspice did not provide these parameters. However, the bipolar transistor models in LTspice do have these parameters. Could you add these simulation parameters that are needed in future updates?
Vcbo and Vebo(if they existed) would be ratings, not really electrical parameters or SPICE BJT model parameters. Modeling breakdown is not included in simulated BJT behavior because it’s counter productive to the design flow. That being, first do a simulation to find out what the voltages would be on the transistor would it not breakdown and then, secondly, auditing those voltages against the transistor ratings. Otherwise it’s difficult to find out if the circuit works as intended or works because it blew up a transistor.
That said, the models in QSPICE are annotated with BVceo, maybe more commonly called Vceo, which is the rating that useful – basically the voltage the transistor can withstand with the base open circuit. If you pull the current out of the base, it will withstand a quite higher voltage.
Thank you for your reply!The reason I used Vcbo and Vebo is because I saw an application using two bipolar transistors in a so-called clamp protection circuit, so I wanted to simulate it in a circuit simulator. In LTspice I can refer to the datasheet of the device to define the values of Vcbo and Vebo in the spice model myself, so that the simulation result matches what I expect. However, the same model does not work in Qspice, because I cannot find where to customize these two parameters.The simulation result also does not match the expectation.
You can replace the transistors with zeners. The base-emitter breakdown of all transistors is roughly 6.2V. You’ll find different opinions on whether or not using the breakdown as a zener is acceptable practice or not. It does cause some ion drift so if you later decide to use that device as a transistor, it’s beta will likely be somewhat degrades. You can choose to worry about it. Or not.
If cost is not important, I would use a zener in that voltage range because the breakdown mechanism is partly true zener and partly avalanche and the tempco of the breakdown voltage can be near zero.