Electronics > Beginners

High-side vs. low-side NPN transistor

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spec:
+ permal

Can you connect a 1k resistor from the emitter of the ZXTN25050x transistor to 0V and measure the voltages between the transistor's emitter and 0V and between the transistor's base and 0V. If you post the readings that will help with the explanation.

permal:

--- Quote from: spec on January 12, 2019, 04:57:26 pm ---+ permal

Can you connect a 1k resistor from the emitter of the ZXTN25050x transistor to 0V and measure the voltages between the transistor's emitter and 0V and between the transistor's base and 0V. If you post the readings that will help with the explanation.

--- End quote ---
Absolutely, as soon as I finish dinner. Sorry for the delay and thanks so much for your time.

spec:

--- Quote from: permal on January 12, 2019, 05:00:40 pm ---
--- Quote from: spec on January 12, 2019, 04:57:26 pm ---+ permal

Can you connect a 1k resistor from the emitter of the ZXTN25050x transistor to 0V and measure the voltages between the transistor's emitter and 0V and between the transistor's base and 0V. If you post the readings that will help with the explanation.

--- End quote ---
Absolutely, as soon as I finish dinner. Sorry for the delay and thanks so much for your time.

--- End quote ---
No sweat. Take your time and enjoy dinner.  :)

iMo:
I think there has been an answer already - the base of an NPN is always by Vbe (0.5-0.65V) higher than the emitter. With pretty low emitter currents the Vbe is a bit lower.

Zero999:
2.7V what you should expect with a base voltage of 3.3V.

The base voltage is 3.3V

The base-emitter voltage is 0.6V

So the emitter voltage will be 0.6V less than the base.

See the simple formulae below:
VBE = 0.6V
VB = 3.3V
VE = VB = VBE = 3.3  - 0.6 = 2.7V

Working back:
VB = 2.7V + 0.6 = 3.3V


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