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The 8050NPN transistor has a problem with the level of the base voltage when the IO port has a pull-up resistor.

Hardware design
enero 15, 2021 by Bonnie 1156

The triode in the figure is an 8050 triode, which is a current control type. If the io port of the microcontroller has a 200K pull-up, is the base voltage high or low? Can the LED light up?

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Connie Publicado en January 15, 2021

High level

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Jaycee Publicado en January 15, 2021

There may be a problem with the actual circuit

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Alonzo Publicado en January 15, 2021

1. It is best to connect a resistor in the base of the triode;

2. There is no need to use a pull-up, it is better to add a pull-down resistor between the NPN transistor and BE; in fact, the MCU generally has a weak pull-up;

3. If the LED voltage of the load is relatively low, such as about 2V;

It is possible to use 3.3V for the LED power supply, otherwise it is best to use 5V;

If it is a low-voltage LED, the LED can be directly connected to the IO of the microcontroller, and then a resistor is connected to the power supply;

One resistor + 1 LED is enough, which is simple and reliable;

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