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What happend to 320K resistors ?
coppercone2:
link to 300mW 0805 320k thin film?
Siwastaja:
You need to realize TH technology is mostly obsolete, want it or not. So no matter how much you prefer TH over SMT, no matter how good reasons you have, the selection of parts available is poor and gets worse every day. You can whine about it until cows come home, or you can just use the parts that are available and get the job done. Side effects are almost all positive, but attitude needs to be fixed first.
My observation is that people who most whine about lack of TH parts are those who have no idea about circuit design and their designs would fail even if all the parts in the world would be available in TH. As always, coming up with excuses is a sign of something.
ogden:
--- Quote from: Siwastaja on February 20, 2021, 07:15:51 am ---My observation is that people who most whine about lack of TH parts are those who have no idea about circuit design and their designs would fail even if all the parts in the world would be available in TH.
--- End quote ---
Your observation is correct. People who have no idea about circuit design do exist. They are beginners. Even today it is nothing wrong about using breadboard or learning circuit design using through hole components and perfboard.
Thou beginners shall listen too. If many people are telling you that your approach is wrong - then most likely it is so. In this case apply best engineering practices - use your head and parts that are available (E24):
300 + 20 = 320 (0 %)
220 + 100 = 320 (0 %)
200 + 120 = 320 (0 %)
160 + 160 = 320 (0 %)
calc used: https://www.qsl.net/in3otd/parallr.html
srb1954:
--- Quote from: wraper on February 20, 2021, 03:19:44 am ---
--- Quote from: coppercone2 on February 20, 2021, 03:14:04 am ---stop forcing SMD on people for no reason other then its cheaper or desirable for YOUR process.. stop thumping the 'new testament' of SMD being better at everything, not everyone wants rice.
--- End quote ---
SMD is not only cheaper but also takes less space, is faster to assemble and have less of parasitic inductance. Not to say TH parts go away, you simply cannot find most of modern parts in TH.
--- End quote ---
SMD may have some advantages for non-critical applications but it has some severe disadvantages in high power circuitry:
* The power handling capability for pulse loads for most types of SMD resistors is abysmal
* The ability of SMD resistors to withstand high peak voltages is poor
* The ability to withstand thermal cycling stress with pulsed loads is poor, especially when using lead-free solder
* If the application requires power dissipations more than several watts the heating of the PCB material and surrounding components becomes excessive with SMD parts
If any of the above situations applies the best option is often to stick with leaded parts.
Siwastaja:
--- Quote from: srb1954 on February 20, 2021, 08:40:35 am ---
--- Quote from: wraper on February 20, 2021, 03:19:44 am ---
--- Quote from: coppercone2 on February 20, 2021, 03:14:04 am ---stop forcing SMD on people for no reason other then its cheaper or desirable for YOUR process.. stop thumping the 'new testament' of SMD being better at everything, not everyone wants rice.
--- End quote ---
SMD is not only cheaper but also takes less space, is faster to assemble and have less of parasitic inductance. Not to say TH parts go away, you simply cannot find most of modern parts in TH.
--- End quote ---
SMD may have some advantages for non-critical applications but it has some severe disadvantages in high power circuitry:
* The power handling capability for pulse loads for most types of SMD resistors is abysmal
* The ability of SMD resistors to withstand high peak voltages is poor
* The ability to withstand thermal cycling stress with pulsed loads is poor, especially when using lead-free solder
* If the application requires power dissipations more than several watts the heating of the PCB material and surrounding components becomes excessive with SMD parts
If any of the above situations applies the best option is often to stick with leaded parts.
--- End quote ---
Also large capacitors and connectors benefit from the mechanical support you get with THT.
90-99% of parts in such designs are still likely SMD. The control side tends to have large number of components, especially large number of pins.
It's not a choice whether to build the entire thing in THT or SMT, that would be stupid.
Right component is used for the job, each component chosen separately based on what is needed.
Fully SMT designs are rare in power electronics. Fully THT are even more rare.
It's all about availability and suitability. If you want a modern microcontroller, there is no TH type available. If you want a 10000uF 50V capacitor, there is no SM type available. If you have decided not to use certain technology for no good reason, you can't do the job because you need both types.
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