Electronic Components--Resistor

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Joined: 22 Aug 2019, 22:36

Electronic Components--Resistor

#1 Post by Joeyer » 03 Sep 2019, 04:43

For engineers in the electronics industry, electronic components are the basic element. There are several types of components, in this artical,I would like to share some basic knowledge about resistors.

Resistor is the most frequently used in all electronic circuits. Resistor is called a resistive material because it has a hindrance to the current. It can cause changes in electron flux. The smaller the resistor, the greater the flux of electrons and vice versa.

Most of the time, the resistors we used are with fixed values. For example,
Wire Wound Resistor can be made as a precision resistor with a tolerance of 0.005% and a very low temperature coefficient.The disadvantage is that the parasitic inductance of the wire wound resistor is relatively large and cannot be used for high frequencies. The volume of the wire wound resistor can be made very large, and then an external heat sink can be used as a high power resistor.
Carbon Composition Resistor is simple in process and easy to obtain raw materials, so the price is the cheapest. However, the performance of the carbon composite resistor is not so good, the tolerance is relatively large (that is, the precision resistor cannot be made), the temperature characteristics are not good, and the noise is usually large.
Carbon Film Resistor mainly forms a carbon mixture film on the ceramic rod, for example, directly coating a layer, the thickness of the carbon film and the carbon concentration thereof can control the size of the resistor.

I would appreciate it if you can complement more types.

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Joined: 13 Nov 2018, 02:19

Re: Electronic Components--Resistor

#2 Post by d1wang » 15 Sep 2019, 00:35

Resistors are complicated. You can’t talk about resistors without talking about inductance and capacitance, and that would just confuse a lot of people.

Here are a few things I have learnt regarding surface mount resistors and DFM:

- Beware of cost. A R0402 is usually cheaper than R0805. However, some PCBA suppliers charge more if you use small packages. Ask how your suppliers price things before doing any layout.

- Beware of cost. The cost of surface mounting can be many times of the cost of components. Don’t populate your boards with lots of jumper resistors.

- Beware of space penalties. If you work with 2-layer PCBs, you can save space by routing trace under 0603 or 0805, which translate to better grounding and layout.

- Check your footprint. It’s easy to change footprint in the middle of design. If you don’t check your BOM, you may get surprises when you get the final boards. Also, make your own footprints. DipTrace’s defaults are for wave soldering, and the footprints are too big for reflow process.

- Don’t set tolerance too tight. Some engineer would just specify 1% tolerance for everything when 5% are good enough. That’s bad because 1) 1% cost more, and 2) component shortage can happen, and tight tolerance limit your options when shortage happen.

- Beware of power rating. If you use resistors below 100 ohm, calculate the max current and power across the resistors. You may not be able to get the right component in the package you want!

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