Would you like to elaborate on that a little? Maybe with some circuits or examples?A transistor has a wide range of hFE. So its circuit is designed with enough DC negative feedback so that any hFE value will work acceptably.
An emitter resistor with the base biased from a stable supply through a voltage divider, or a resistor from the collector to the base to bias it.
You can use the typical curves if you like to live dangerously, or the guaranteed specs if you are smart. You need to know the collector current and VCE to figure out the gain.How do you determine what the gain will be for a transistor. I have a PN2222A transistor and the datasheet give lots of different numbers. How can you determine what HFE number to use when designing a circuit?
Then ask a question with a finite answer like "how do you design XXX" or "I am trying to build a circuit that does XXX". You will get buried in answers when people know what you are asking.So sorry to ask a question about electronics in a forum about learning electronics.
Where on the datasheet where they show guaranteed gain?You can use the typical curves if you like to live dangerously, or the guaranteed specs if you are smart. You need to know the collector current and VCE to figure out the gain.
Here is the guaranteed gain on the Fairchild datasheet of the 2N3904 transistor.Where on the datasheet where they show guaranteed gain?
Your circuit design sets the Vce and collector current.Also to know what VCE and Collector Current(without measuring them in the circuit) are going to be, don't you need to know HFE and Base Current?
Thanks. Sounds like I need to read up some more on negative feedback, to get a good grip on this.Here is the guaranteed gain on the Fairchild datasheet of the 2N3904 transistor.
Your circuit design sets the Vce and collector current.
If you use negative feedback then the transistor can have any value of hFE and will work properly at many temperatures.
How do you determine what the gain will be for a transistor. I have a PN2222A transistor and the datasheet give lots of different numbers. How can you determine what HFE number to use when designing a circuit?
If you put a resistor in series with the emitter, you would then have a emitter follower correct? And then you would have no gain at all?A resistor in series with the emitter adds negative feedback and reduces the difference of the Vbe of different transistors.
A bias resistor from the collector to the base also adds negative feedback but then a resistor from the input to the base is needed.