High side and Low side switching

  • Thread starter Harrison G
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  • #1
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Main Question or Discussion Point

Hello! I just wanted to make sure i get this right. So we prefer to use pnp transistors for low side switch because since then we basicaly connect the load to the collector we dont have to worry that the load(say a dc motor) will influence the base voltage and by influence the base voltage i mean that the load will decrease the current and force us to use higher voltage or lower resistance. Something that is inevitable if you use an npn where a low side switch means to connect the load to the emitter. Is that right? To be clear we are talking about stuff that can cause a large voltage drop on them.
 

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  • #2
jim hardy
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So we prefer to use pnp transistors for low side switch..........
.....To be clear we are talking about stuff that can cause a large voltage drop on them.
It's not clear at all what you mean.
And what you say sounds backward.

here's a hobbyist level tutorial
https://learn.sparkfun.com/tutorials/transistors/applications-i-switches
and
here's a low side switch datasheet
http://www.st.com/content/ccc/resource/technical/document/datasheet/aa/9d/e5/b4/56/e6/41/92/CD00002001.pdf/files/CD00002001.pdf/jcr:content/translations/en.CD00002001.pdf
 
  • #3
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Thank you for the links and excuse me if i made it a bit hard to understand :-D but i got it. Im now learning about Ic's, op amps and such and i felt the need to go back and fortify some old knowledge.
 
  • #4
jim hardy
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i felt the need to go back and fortify some old knowledge.
Yes that's the way to do it, constantly refine and improve one's understanding.
I look at any new field as a fog with just a few solid points in it. The focus improves as i learn more vocabulary and understand the ties between those "solid rock anchors".

"The Very Basics rule !"

old jim
 

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