Author Topic: DC-DC Convertors  (Read 1345 times)

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Offline Mattk

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DC-DC Convertors
« on: September 25, 2016, 06:11:48 AM »
In converting from 12 to ~5 volts @ <0.5w using small Dc-Dc convertors in the 3-5 to 15 watt bracket (around ~1 to 3A max) what makes the decision between using Linear or Switching devices?         

Offline DanS

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Re: DC-DC Convertors
« Reply #1 on: September 25, 2016, 09:39:53 AM »
Noise on the power line. Switchers are usually "noisey" while transformer types (linear) are quieter. If you are powering a device that doesn't mind the switcher noise, like charging a phone, then switcher types are fine. If you're powering a device like a MP3 FM transmitter then you will likely hear static/hum and a linear power supply will be needed.
« Last Edit: September 25, 2016, 09:42:45 AM by DanS »

Offline hankster

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Re: DC-DC Convertors
« Reply #2 on: September 25, 2016, 11:12:25 AM »
A switching converter is more efficient.

Offline Old Tele man

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Re: DC-DC Convertors
« Reply #3 on: September 25, 2016, 01:29:27 PM »
SUMMARY:

• SWITCHING = high efficiency (less power loss; less heat generation), but highly EMF noise.
• LINEAR = low efficiency (higher power loss; more heat generation), but almost NO noise.
• SYS: Davis VP2 Vue/WL-IP & Envoy8X/WL-USB;
• DBX2 & DBX1 Precision Digital Barographs
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Offline Mattk

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Re: DC-DC Convertors
« Reply #4 on: September 25, 2016, 06:05:48 PM »
Yes I have seen the reference to switching noise etc. This is power for Davis ISS/Envoy/MB etc

Offline DanS

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Re: DC-DC Convertors
« Reply #5 on: September 25, 2016, 06:54:54 PM »
Yes I have seen the reference to switching noise etc. This is power for Davis ISS/Envoy/MB etc

It appears that they use the linear type as shown here.

Offline Mattk

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Re: DC-DC Convertors
« Reply #6 on: September 25, 2016, 07:00:07 PM »
Yes I have seen the reference to switching noise etc. This is power for Davis ISS/Envoy/MB etc

It appears that they use the linear type as shown here.

That would be for mains power plug packs, how about convertors for 12v to 5v on solar power.

Offline SLOweather

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Re: DC-DC Convertors
« Reply #7 on: September 25, 2016, 07:29:09 PM »

That would be for mains power plug packs, how about convertors for 12v to 5v on solar power.

If commercial, probably switchers for efficiency. However, if you are powering Davis consoles off 12VDC, you can easily and affordably build your own linear converter from an LM7805 (datasheet at https://www.fairchildsemi.com/datasheets/LM/LM7805.pdf) and a couple of capacitors.

I have done this for a VP2 console and a Vue console on solar, and the regulator doesn't get warm unless the backlights are on. Still, it doesn't need a heat sink. The console power use is so low, the efficiency difference between switchers and linear is negligible.

Offline Mattk

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Re: DC-DC Convertors
« Reply #8 on: September 25, 2016, 10:08:59 PM »
What I have been using for quite some time are MeanWell SCW03A-05 modules (5v/600ma) which have really worked well but. There is a fair amount of info available on switch mode but not a lot on Linear especially with regard input drain.

A typical switch mode appears to draw about 50ma @12v for a 5 volt output @ 100ma give or take a bit for efficiency etc. This appears to be the case regardless if the unit is rated to 1A or 3A.

What I haven't been able to determine is for say a 1A or 3A Linear (12v to 5v) is the input draw on the 12 volt side. They say Linear's burn off excess power to achieve the output but how much input are they taking in? My guess is probably a lot more than the 50ma for a switcher at the same voltages but have not been able to find anything definitive.       

Offline hankster

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Re: DC-DC Convertors
« Reply #9 on: September 25, 2016, 11:16:20 PM »
Did a little searching since my electronics theory is a bit rusty, if I remember correctly is the current in is the same as current out on a linear. I found this info:

A Switching converter for 12v in to 5v out @ 1.5 A peak current looks about 91% efficient. If it's supplying 7.5 W at 91% efficiency, it would be wasting 0.7 W from itself.

A linear regulator dropping 12 V to 5 V at 1.5 A would waste 10.5 W while supplying 7.5 W, making it 42% efficient.


Offline Mattk

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Re: DC-DC Convertors
« Reply #10 on: September 26, 2016, 07:02:52 AM »
It would certainly appear then that the switch mode variety is the way to go for maximum efficiency and longer up time if on batteries only?