| Electronics > Beginners |
| Trying to understand voltage divider circuit |
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| David Hess:
Do your analysis in a different way using the Thévenin equivalent circuit to understand why this circuit configuration might be used. Ignore the diode for the moment. R1 and R2 form a voltage divider with an output voltage of Vin*R2/(R1+R2). The Thevenin equivalent resistance of R1 and R2 is calculated as if they are in parallel so 1/(1/R1+1/R2). What the diode actually sees then is the output voltage from the calculated voltage divider through the Thevenin equivalent resistance which is the parallel resistance of R1 and R2; we are down to a single voltage source, a single resistor, and a single diode. We can now pick what maximum voltage is applied independently of what current is applied. Why might this be used in real life? If the diode was an LED to which power might be applied backwards, the voltage divider limits the voltage applied to the LED but the forward current can still be set as if a higher voltage is used because the equivalent resistance is lower. This might also be done when forward biasing a base-emitter junction so that if power is reversed, the base-emitter junction cannot reach reverse breakdown which will damage it. |
| Youkai:
Ok well I guess let's continue a little more. The reason I was looking into voltage dividers is because I'm working on a project that will use RGB LED strips (9-14v) and Arduino (5v) to control it. I'd like to power it off of a single wall plug. So I was thinking about going to the local thrift shop and seeing if I can find any electronic device with a wall brick that outputs something like 12v and scavenging that. Then I would use a "thing" (voltage divider, voltage limiter, whatever the right thing is) to run the arduino and some transistors to control the LED strips so they can operate at 12v. A) will that even work? B) if so is a voltage limiter the thing I want to use there? Is the 7805 the right thing to use? |
| hamster_nz:
--- Quote from: Youkai on April 26, 2018, 12:51:08 am ---Ok well I guess let's continue a little more. The reason I was looking into voltage dividers is because I'm working on a project that will use RGB LED strips (9-14v) and Arduino (5v) to control it. I'd like to power it off of a single wall plug. So I was thinking about going to the local thrift shop and seeing if I can find any electronic device with a wall brick that outputs something like 12v and scavenging that. Then I would use a "thing" (voltage divider, voltage limiter, whatever the right thing is) to run the arduino and some transistors to control the LED strips so they can operate at 12v. A) will that even work? B) if so is a voltage limiter the thing I want to use there? Is the 7805 the right thing to use? --- End quote --- A) Yes. B) Yes, some sort of voltage regulator is what you want. You could even get an inexpensive prebuilt module such as https://www.aliexpress.com/wholesale?SearchText=lm7805+module&opensearch=true that includes an 7805 regulator and the other required components. Edit: Corrected link. |
| Youkai:
A while ago for a different project I got some thing which I think was a voltage regulator from a RC hobby shop so I could run my arduino from a LiPo RC battery pack. I can't seem to find that thing anymore but that's probably what you are talking about Hamster. |
| Youkai:
Started looking into the power supply for this project. Went to the local thrift shop and found a wall adapter from something that supplies 12VDC and 500mA. My RGB LED strip runs on 12v. Also got a food saver vacuum that runs on 5v but I scavenged the barrel plug from that so I can have something to plug into. Pulled the plug out of the sealer and connected it to my adapter. Was able to power the segment of LED strip using this setup. Yay! Now I just need to get a voltage regulator and some transistors and start working on a circuit diagram. |
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