can i use a 220 ohms resistor in place of a 240 ohms resistor?


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seandogue7 years ago
Doh!...I should have known...lol, you just asked about the LM338K a little while ago...

My immediate thought is..."Nah...if that's all you have, don't worry too much. The 5 K pot should accommodate"

Then I think..."hmm... what is the adjustment range you need?"  It will change a little bit...hopefully not so much that you are negatively affected...

Worst case, if you have a 22ohm resistor in your box of goodies, you could wire it in series with the 220 ohm to "build your own" 240 ohm.
hillbillyboy_316 (author)  seandogue7 years ago
schematic says range of 1.2v - 32 volts.  how would i go about wiring in series and with what value of resistors?
like so...
In general though, I agree with Steve that you can just go ahead and use the 220 and leave it at that. A schematic would clarify whether it might make a difference, I just posted the "caveat" to cover all bases because I can't see what we're dealing with or what it's powering.

http://www.national.com/mpf/LM/LM338.html#Overview

Is the circuit shown on the right side of the linked datasheet the circuit you're using? If so, and this is a general purpose variable supply, I wouldn't worry too much about adding the other resistor.

240 isn't a common value in the EIA resistor series we tend to use here. At work I use E24 and the odd bit of E48

Steve
I have a full compliment of 1% values across the board..I'm spoilt that way. My last employer decided that the electronic parts the company they purchased (of which I was an acquired part) were worthless, so they tasked me with throwing everything out...When I objected they told me I had a choice... could toss them in the garbage or take them home...I chose the latter., but yeah, 220 is a pretty common value to have in one's basket...
hillbillyboy_316 (author)  seandogue7 years ago
k 220 it is thanks for all the help and advise

                thank you
hillbillyboy_316 (author)  seandogue7 years ago
yeah, that would be the same schematic
That'll be fine then.

Steve
seandogue7 years ago
if the design is tolerant to a 10% deviation from expected value.

LED?  prolly, as long as you're not calculating 240 ohms based on maxxing the LED's forward current. If that were the case, you'd exceed the mfg ratings and might let out the magic smoke.
Usually, but that might depend on the exact application.