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Engineering
Electrical Engineering
Transistor questions in control a stepper motor
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[QUOTE="Baluncore, post: 5529882, member: 447632"] The value of Hfe is hard to control during manufacture so devices are sorted into different grades or ranks after manufacture. The value of Hfe is also current dependent, which is why they identify three different ranges. The min=120, typ=110, max=400 seems irrational since the typical is less than the minimum. Either there is a typo in the data sheet or the typical and the maximum refers to all classes of the device. Low Hfe increases the base current required to drive the output load. High Hfe slows down the transistor in high speed applications because it multiplies the miller capacitance between base and collector. You should always design for the worst case values. That is why the minimum and maximum values are given. An analogue circuit is designed to minimise gain variation due to Hfe. Hfe spread and variation is then not critical. A digital circuit will need some way of limiting the base current to the maximum required for the lowest Hfe. Can you post the circuit diagram that shows how you will use this transistor. [/QUOTE]
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Engineering
Electrical Engineering
Transistor questions in control a stepper motor
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