Concept of "resistance" and "power dissipation" in a transistor - Explanation?
Ok, so I've got way more experience with mosfets than BJTs. I'd become very accustomed to the idea of mosfets having a specific 'on' resistance, which would allow me to calculate actual heat generation and operating conditions for the mosfet quite easily.
I understand a BJT doesn't have an actual 'on' state. Instead, it has a diminishing gain as you raise base current further and further. What I'm wondering about is how to get an idea of how much resistance there is in a BJT -or- how much it will heat up when I operate it in various conditions. I'm guessing that if I have a resistive load that allows 5 amps (for instance) and I am switching it with a BJT, then biasing the BJT on as high as possible will minimize heat generated in the BJT because you open the channel as wide as possible. But what I find awkward is the fact that the gain approaches zero once you get above a certain 'grey area'. So how do I figure out what is practical? Do I just have to look at the gain curve graphs on the datasheet and pick some reasonable range?
Ok, so I've got way more experience with mosfets than BJTs. I'd become very accustomed to the idea of mosfets having a specific 'on' resistance, which would allow me to calculate actual heat generation and operating conditions for the mosfet quite easily.
I understand a BJT doesn't have an actual 'on' state. Instead, it has a diminishing gain as you raise base current further and further. What I'm wondering about is how to get an idea of how much resistance there is in a BJT -or- how much it will heat up when I operate it in various conditions. I'm guessing that if I have a resistive load that allows 5 amps (for instance) and I am switching it with a BJT, then biasing the BJT on as high as possible will minimize heat generated in the BJT because you open the channel as wide as possible. But what I find awkward is the fact that the gain approaches zero once you get above a certain 'grey area'. So how do I figure out what is practical? Do I just have to look at the gain curve graphs on the datasheet and pick some reasonable range?
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