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Hi all,
Is this pic of a resistor? I have seen them before but never understood with the different case etc.
It has a RED band near one end and 2 x black in middle
Thanks
Steve
Yes, it is an SMD resistor. Try searching Google for 'minimelf resistors'.
The colour bands are just the same as for through-hole resistors.
...I agree, it looks like a resistor in a melf package.
...
seldom to see the value printed using colour bands. That one has a resistance of 270,000Ω or 270KΩ. The black markings are just spacings between value numbers.
First thanks for clarifying what it is, but why use a mini-melf what on same board they use 0805? it measures 269R (not 270k) I have read that some mini melfs are very high precision could this be why it's used?
thx
...
seldom to see the value printed using colour bands. That one has a resistance of 270,000Ω or 270KΩ. The black markings are just spacings between value numbers.
Power considerations would be the only reasons I would choose a mini melf resistor instead of a 0805 resistor there. R1 biases the 5.1V zener diode; depending on the value of Vcc, there could be a few milliamperes flowing through R1, hence the need of a higher power rating. Do you know that value?
On a side note, 0805 reistors are usually very precise (a tolerance of 0.1% is common). But that's not a requirement for R1.
It's 12v +-5%
Thx
True, but 1% metal films are about as good as you can commonly get cheaply in an axial package. In a chip package, you can get .5% about as cheap. Chips go even more precise (.1%, .05%, .02%), way more precise than the common axials, but it gets progressively more expensive. By the time you get to .02% they're horribly expensive.
FWIW, Yageo 1% axial metal films and Susumu 0.5% 0805 thin film chips are what I keep in my stock bins.
SMT capacitors is where we can really talk about both price and performance benefits over their leaded brethren, but that is for another thread![]()
That's correct, of course. I was exactly pointing out that 0805 resistors can be as precise as mini-melf resistors - regardless of the size, as you say - in response to this question:The precision of the resistor has nothing to do with it's size, as you well know.
So, precision was not the reason to choose a mini-melf resistor for R1; instead, that choice was caused by power dissipation as I supposed and as it's demonstrated by your calculations. A 1206 resistor rated for 0.75W would have been just fine.Scarr said:I have read that some mini melfs are very high precision could this be why it's used?