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24V relay transistor drive problem.

Hardware design
October 20, 2020 by Hector 1371

As shown in the figure, will it be a problem if I change it like this?

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Erik Posted on October 20, 2020

There should be no problem, but your R14 and R17 may be too small in resistance, generally around 10K.

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Raymond Posted on October 20, 2020

You can use the N-channel low-power MOS tube, AO3402. The MOS tube is a voltage-type control switch. I generally use this to control the relay. It works!

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Eliza Posted on October 20, 2020

The drive current requirements for the port are quite high. For example, if the port of 430 is pushed, the port will be damaged. The maximum output current of the 430 is also 6MA. In this design, the current of the general 24V relay is 20MA, which is estimated to be the working current of 30MA. The current multiple is 100, the base current is 0.03MA, (3.3-0.7)/0.03=12k, which is 10K, to prevent action, the shunt current is a quarter of the working base current, instant 0.003MA, shunt resistance 0.6/0.03*4=80k, light load on the port, and can be controlled correctly.

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