[OpenTRV-dev] H-bridge transistor selection

[Mike Stirling]

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From: "Damon Hart-Davis" EMAIL ADDRESS HIDDEN 
To: "Closed list for developer discussions" EMAIL ADDRESS HIDDEN 
Date: Thu, 16 May 2013 10:45:51 +0100
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Interesting. The poor performing transistors do so because he is running them far too hard, although he does acknowledge this. He is also running out of gain at the lower voltages, and would get an improvement there by reducing the value of the 1k base resistor. This is evidenced by the reduction in voltage drop with increasing supply voltage.

The important figures in the datasheet are Ic from the absolute max ratings, which needs to be well above the expected stall current of the motor, Vce-sat, which should be small, and the worst case hFE (large signal current gain), which should be high enough to allow for an acceptably low base current during motor stall conditions.

Mike

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