Mike,
Why did you change my circuit so that it is not a constant current sink (with an emitter resistor)?
You show it as a simple common-emitter transistor as a switch so of course it needs a series base resistor.
If you have an input that goes up to 3.3V then the emitter voltage goes up to about 2.6V and if you want 16mA then the emitter resistor value is 162.5 ohms. Use 160 ohms for 16.25mA.
But it is not a constant current sink if its supply voltage is too low. The transistor must not be allowed to saturate because then the circuit is not a constant current sink and the base current increases dramatically.
Why did you change my circuit so that it is not a constant current sink (with an emitter resistor)?
You show it as a simple common-emitter transistor as a switch so of course it needs a series base resistor.
If you have an input that goes up to 3.3V then the emitter voltage goes up to about 2.6V and if you want 16mA then the emitter resistor value is 162.5 ohms. Use 160 ohms for 16.25mA.
But it is not a constant current sink if its supply voltage is too low. The transistor must not be allowed to saturate because then the circuit is not a constant current sink and the base current increases dramatically.
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