Continue to Site

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

Register Log in
  • Congratulations waross on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Replacing through-hole type components with SMD components 1

Status
Not open for further replies.
sanvik

sanvik

Electrical
May 9, 2015
21
I want convert existing PCB design from through-hole type design to SMD design.
Is clear about selecting IC in SMD package selecting, but not fully clear about passive components: trimmer potentiometers,
Electrolytic Capacitors and resistors. There are 10 trim-pots are used to adjust frequency: 5pcs 50K trim-pots and 5pcs 5K trim-pots, and one 50K POT is used for adjust input signal level. Normally, it requires only once to adjust this. What type of SMD trim-pots can be used to replace these 50K and 5K through-hole type trim-pots? The SMD trim-pots are very small, not sure how handy is to adjust it. Also, what type of SMD capacitors and Electrolytic Capacitors can be used to replace existing ceramic and Electrolytic Capacitors?

PCB_sample.jpg
 
Replies continue below

Recommended for you

Sort by date Sort by votes
IRstuff said:
"Normal"
Seriously? Normal for me is MIL-STD-810. What is "normal" for you?
Click to expand...

Normal means "for indoor use". -10C to +60C / 14F to 140F Not in aerospace industry. :)

@BrianG For myself, yes. You are absolutely right, assembling SMD PCB professionally at home is very difficult, and also requires a very sharp vision, and solid hand-soldering skills. I didn't plan to assemble SMD boards myself. I have good contacts with small PCB assembler, and I'm expecting they can help me with that. If not, then I will go with through-hole PCB, or will looking for another assembler.

I find SMD equivalents for MOSFETs and transistors, so all can be done in SMD, except terminal connectors blocks. Two separate terminals on the left side will be moved to the other end of the board, so PCB will be twice less in width.
Can anyone advice about SMD Fuse 10A?
 
Upvote 0 Downvote
sanvik,
Go to digikey.com on the most basic search they yield 84 SMT/10A fuses..
BUT.. I'd suspect what you really want is a SMT fuse holder to accept the same/similar fuse.. again digikey and look for one that fits your needs..
Same with everything else.
 
Upvote 0 Downvote
For through-hole mounting trimpots, Digikey offer 120 models for given criteria. What type is better suitable for application? does Tolerance % matter?
 
Upvote 0 Downvote
Given that you are tweaking the pots anyway, the absolute tolerance isn't particularly relevant, since I assume that you'd remove the pot, measure its value, and replace with a fixed resistor that's closest to that value.

TTFN
faq731-376
7ofakss

Need help writing a question or understanding a reply? forum1529


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com:
 
Upvote 0 Downvote
For THT cdesign, would be fine to use resistors with 1/4W power rating for all elements or it need be calculated?
If use SMD design, what is common SMD resistor size (Code) that can be used here? (Imperial/ Mectric)

 
Upvote 0 Downvote
0805 are common, rated 1/10 to 1/8 watt, and fairly easy to hand solder. 0603 get trickier to solder and the power rating goes down. 0402...

If you need higher power ratings then you'll need to go to larger sizes.

Z
 
Upvote 0 Downvote
Can be 27N3LH5 Power Mosfet TO-220 replaced with DPAK version without heat sinks?
 
Upvote 0 Downvote
?? You've done nothing to make the power dissipation lower? So, how are you going to deal with the 15W lower power rating on the DPAK?

TTFN
faq731-376
7ofakss

Need help writing a question or understanding a reply? forum1529


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com:
 
Upvote 0 Downvote
Theoretically, max power is 2A x 12V = 24W per driver circuit: so I still have some power reserve?
Possibly, I can use copper area around DPAK Mosfet for heat dissipation?
 
Upvote 0 Downvote
The ST datasheet has numbers that don't make much sense; however, it's pretty clear that the 40ºC difference in junction to case temperature cannot be made up with external improvements. Therefore, if the ambient is going to get above 30ºC, you're going to have potential reliability problems with the DPAK.

TTFN
faq731-376
7ofakss

Need help writing a question or understanding a reply? forum1529


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com:
 
Upvote 0 Downvote
Should I consider another Mosfet with more power dissipation? Which model would be suitable?
 
Upvote 0 Downvote
The issue isn't the power dissipation spec, it's the thermal resistance of the dinky package you want to use.

TTFN
faq731-376
7ofakss

Need help writing a question or understanding a reply? forum1529


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com:
 
Upvote 0 Downvote
As I stated earlier you should stick with the existing thru-hole parts, not for the parts but for access
to the heatsinks those parts work with. I don't think that you're getting that the
whole game is surface area. Changing from a bunch of metal fingers exposed to the air down to no metal
fingers and just some flat board area is going to be a dissipative back-step. You can dissipate some
reasonable power that way as long as you trade up the area dedicated to it on the board, the opposite
of what I thought you were trying to do (smaller board). About the maximum area you can achieve with
standard circuit board materials is an area around the parts you contemplate of about two square inches
each on both sides of the board. That much space would probably account for about 1/2 of the existing
heatsinks.

You could make the switch to SMD and maybe a square inch per part if you had forced air blowing across
the heatsink pad area but that requires noise and a mechanical failure down the road.

Keith Cress
kcress -
 
Upvote 0 Downvote
You could go with a metal core board... but then you would be trading a higher cost for reduced space (not necessarily a bad thing, mind you, but that's a project-specific decision).

Dan - Owner
Footwell%20Animation%20Tiny.gif
 
Upvote 0 Downvote
It's possible that this design was created with a big reserve in mind, so using heat-sinks & fuse might be overkill for the purpose.
I saw similar device (SMD PCB), where output connected to IRF8313 Power Mosfet without heat-sinks. It max total current is 5A though.
 
Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

sunclipa
  • Locked
  • Question
micro components to drive a shaft
Replies
6
Views
107
biff44
biff44
satrevolution
  • Locked
  • Question
Looking for components
Replies
2
Views
242
satrevolution
satrevolution
jmacion
  • Locked
  • Question
relay wont close consistently with open collector input
Replies
16
Views
356
hacksaw
hacksaw
Willem19
  • Locked
  • Question
Voltage and power through steel pipe
Replies
8
Views
153
waross
waross
Total Novice
  • Locked
  • Question
How to calculate the EMF in a circuit with 2 opposing batteries? 2
2 3
Replies
41
Views
1K
Total Novice
Total Novice

Part and Inventory Search

Sponsor

Back
Top Bottom