I/O口是否不串电阻直接NPN三极管基极

晚***

I/O口是否不串电阻直接NPN三极管基极，使用准双向弱上拉模式，
这样可以省掉一个电阻省空间，如需要输出电流大些可以打开内部上拉电阻，
只是I/O口输出高电平时只有0.7V,不知会不会损伤I/O口,有这样做过的吗

神***

少创作一些奇闻异事的电路，按下图来



https://www.stcaimcu.com/forum.p ... ptid=4830&pid=33151

神***

Debu***

准双向弱上拉0变1有2个高电平推挽加速，有风险
内部4K上拉可以试试

晚***

还有这情况呀，那用开漏输出模式加内上拉电阻方式应该没风险了吧

jw***

驱动三极管最好不要直接接IO，防止电流过大

晚***

看来还是不能省保险些，谢谢各位

cdp***

看过论坛中,有不使用I/O, 用使能和禁止上拉电阻驱动LED的方法,
可以做个试验如果关闭上拉时候,驱动不了三极管,
那么使能电阻的话,应该可以驱动三极管.
如果是自己玩你可以试试, 如果是做产品就不建议这样搞了,
万一空载容易出意外就得不偿失了.

jm***

Sure, if you are careful, that can work.
There are limits, and some rules.

If your part has a PxPU support, you can enable the ~4k PullUp, which will give about 1mA added Icc, due to the base current.

If your part does not have a PxPU, the available base current drops to the light pullup level, which is quite low : ~5uA at 3v3 and ~18uA at 5V
With a moderate HFE of 200, that gives you ~1mA maximum collector current, but very temperature dependent.


Alternatively, digital transistors like DTC144 have no additional parts, draw < 100uA added Icc, and are close to the same price as BJT.
MOSFETs (often with ESD inbuilt), are also close to the price of a BJT, and have even less drive Icc cost.

小***

有种数字三极管，自带电阻