Problem Using Bipolar Transistor as a Switch

  • Thread starter lindhaw
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  • #1
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Main Question or Discussion Point

Im new here and Im currently working on a small IR encoder project. I have the encoder working great but now I need to use the 5vdc signal that comes from the encoder and make it 24vdc. I am currently trying to use a bipolar transistor but its not working. The basic diagram that Im going off of is attached along with the schematic of the optical encoder schematic. Am i way off track or am I missing something obvious.

BTW im using 20k for R1 and 200K for R2 for the switch
 

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  • #2
berkeman
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Im new here and Im currently working on a small IR encoder project. I have the encoder working great but now I need to use the 5vdc signal that comes from the encoder and make it 24vdc. I am currently trying to use a bipolar transistor but its not working. The basic diagram that Im going off of is attached along with the schematic of the optical encoder schematic. Am i way off track or am I missing something obvious.

BTW im using 20k for R1 and 200K for R2 for the switch
Welcome to the PF.

Can you run the first stage off of 24V? A 5V pullup stage will not shut off a 24V high-side switch stage...
 
  • #3
berkeman
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If you can't run the first stage at 24V, use an open-collector stage to convert from 5V to 24V.
 
  • #5
berkeman
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I dont think I can do that because I think it would just burn up the emitter and possibly the receiver. Ive also been looking into this http://www.goldmine-elec-products.com/prodinfo.asp?number=G18694 but ive never used anything like that so im not sure if the response time will be fast enough.
Your link is just a DC-DC converter to convert a 5V power supply to a 24V voltage source.

What you want is a way to convert a 5V logic signal to a 24V logic signal, correct?

The way to do that is with an open-collector BJT stage. Are you familiar with those yet?
 
  • #6
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Ya thats correct. Im not familiar with those yet. Is that something that I could make or is that something that I should just buy?
 
  • #7
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ok dumb question sorry I just looked it up and I think i can manage one of those. Thanks for the advice! Ill let you know how it goes!
 

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