Lee Cross wrote:
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When you drive your NPN transistor into saturation, a typical value for Vce will be about 0.2V - not very close to 0V when your reference is 1.25V. And Vce is not gauranteed to stay constant.


Its more like 1.2, not .2 volts, so its worse than you said !


Due to my aversion to relays, I just have to throw out the suggestion of using a logic-level FET. Using a beefy one that can handle around 10A will give a respectable On Resistance in the neighborhood of 10mOhm. This is comparable or better than most relay contacts. Plus there is no clicking.

Neat solution.