Electronics > Beginners
How to choose a resistor?
redgear:
I am trying to recreate a reference circuit that I found online. The circuit has a BOM which specifies the resistances to use.
I know the value of the resistor, case code and the tolerance. I assume case code won't matter much as long as I can solder the components properly(correct me if I am wrong). There is no info about the power rating, temperature coefficient and voltage rating.
How do I choose a resistor without these?
Thanks
tggzzz:
You need to understand how the circuit works. A well-designed circuit will minimise the dependencies, but can't eliminate them.
If you can't understand the (analogue?) circuit, you could simulate with, say, LTSpice. You could manually tweak component values, or set it up to do monte-carlo simulations.
redgear:
--- Quote from: tggzzz on November 01, 2019, 10:55:28 am ---You need to understand how the circuit works. A well-designed circuit will minimise the dependencies, but can't eliminate them.
If you can't understand the (analogue?) circuit, you could simulate with, say, LTSpice. You could manually tweak component values, or set it up to do monte-carlo simulations.
--- End quote ---
Thanks.
The resistors are directly connected to the pins of the IC. I only have access to the block diagram of the IC. I don't think I simulate it. Can I? The Datasheet is in Chinese which makes things more difficult. I am attaching the circuit below for reference.
EDIT: The power traces are thicker that the others, how do I determine the thickness that I would require?
tggzzz:
Most of those resistors maximum possible power dissipation can be easily calculated: V2/R, where R is the supply voltage. For R2/R7, reduce V by one LED forward voltage drop.
RNTC is interesting; NTC may mean negative temperature coefficient, which implies a thermistor. Unfortunately thermistors are made with differing tempcos, so the best bet would be one with a tempco in the middle of the possible values.
Google can be useful when looking at foreign language datasheets.
redgear:
--- Quote from: tggzzz on November 01, 2019, 11:46:33 am ---V2/R, where R is the supply voltage. For R2/R7, reduce V by one LED forward voltage drop.
--- End quote ---
Do you mean V is the supply voltage?
--- Quote from: tggzzz on November 01, 2019, 11:46:33 am ---RNTC is interesting; NTC may mean negative temperature coefficient, which implies a thermistor. Unfortunately thermistors are made with differing tempcos, so the best bet would be one with a tempco in the middle of the possible values.
--- End quote ---
Yep, RNTC is a thermistor and they are 100K @ 25deg with a material constant of 4200
--- Quote from: tggzzz on November 01, 2019, 11:46:33 am ---Google can be useful when looking at foreign language datasheets.
--- End quote ---
I have been using Google Translate. But a lot of information is given as a image and I am not able to translate them.
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