Author Topic: Power regulation options for 5V and 18V circuit  (Read 2208 times)

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Offline Audioguru

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Re: Power regulation options for 5V and 18V circuit
« Reply #25 on: January 10, 2018, 09:39:49 pm »
An error was posted above, here are the facts from the datasheets:
A TO220 package creates the same amount of heat from an LM317 as a 7805. Both will shut down within 1 minute when fed 20-24VDC and produce 5V at 200mA unless they have a medium size heatsink.
 
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Offline soubitos

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Re: Power regulation options for 5V and 18V circuit
« Reply #26 on: January 10, 2018, 09:48:50 pm »
if OP HAS a 20-24V (better be 24V) then by all means, 7818-7805 one feeding the other would be an option, he did mention small footprint requirement though.... and that would not be so with proper heatskinking...  I used an 7805CV recently in one of my boards, powered from 7,5V and drawing 0,4-0,5A tops, it reached 100C within few minutes... no heatsink, simply laying on the pcb with the GND soldered to a huge pad on it...

if OP wants to build something that requires 18V and 5V like he described then i insist its a hell of a lot easier to find a proper 5V-2A wall psu on the cheap like the one i mentioned, and a small boost module would make sure his non-demanding 18V rail was met again, on the VERY cheap..... you cannot beat this logic i am sure LOL....

As for the remark about how laptop power bricks come at high voltage etc, you do understand the smaller laptop power brick starts at around 40W power right? And that most chargers over 15V are used to charge 4S battery packs so a voltage of 16.8+drop on voltage regulator and charger circuit is required... so it is only natural to design with a higher voltage in mind, when you really use most of the power in form of 3,3-5-12V rails (and not only)....
 

Offline soubitos

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Re: Power regulation options for 5V and 18V circuit
« Reply #27 on: January 10, 2018, 09:56:22 pm »
Chip is expensive in small quantities, but then again if you add two linear regulators and heatsinks for both and the footprint those two heatsinks will use on your board ... maybe it's not so expensive.

Nice chip this one... and if you buy LM78xx from the same source or mouser etc, the cost of two LM78xx with heatsinks etc against the tps + proper inductors etc is very much comparable......
 

Offline james_s

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Re: Power regulation options for 5V and 18V circuit
« Reply #28 on: January 10, 2018, 10:34:40 pm »
I've used quite a few Chinese buck regulator modules that were 99c shipped, I think I got some once for only 90c. I haven't priced 78xx or LM317 regulators recently but they can't be much cheaper, and by the time you add the heatsink and capacitors it will cost more.
 

Offline soubitos

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Re: Power regulation options for 5V and 18V circuit
« Reply #29 on: January 10, 2018, 10:46:48 pm »
I've used quite a few Chinese buck regulator modules that were 99c shipped, I think I got some once for only 90c. I haven't priced 78xx or LM317 regulators recently but they can't be much cheaper, and by the time you add the heatsink and capacitors it will cost more.

I got LM7805CV from China recently, worked very well, cost 0,76$/10pcs ....  a module cost 99c shipped from China with an LM7805 on it is NOT a cheap deal LOL..  On the other hand, 78xx can set you back ~~0,8-1,5$ a piece ordered from "western"sites etc....
 

Online Zero999

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Re: Power regulation options for 5V and 18V circuit
« Reply #30 on: January 11, 2018, 10:11:48 am »
Just one question: why use the LM317 as well as the TL431 when the LM317 will do on its own?

Already mentioned: performance/precision. Reference of LM317 is specified as +/- 4% with +/- 0.7% additional temp drift for 0..125oC range. TL431 is 2%, B grade is 0.5%. In circuit TL431 does not dissipate heat, so circuit is much more thermally stable compared to LM317 alone. FYI circuit from TL431 datasheet.
Oh I see. The LM317 could also be replaced with a Darlington transistor, but then there will be no over-current or thermal protection.

if OP HAS a 20-24V (better be 24V) then by all means, 7818-7805 one feeding the other would be an option, he did mention small footprint requirement though.... and that would not be so with proper heatskinking...  I used an 7805CV recently in one of my boards, powered from 7,5V and drawing 0,4-0,5A tops, it reached 100C within few minutes... no heatsink, simply laying on the pcb with the GND soldered to a huge pad on it...

if OP wants to build something that requires 18V and 5V like he described then i insist its a hell of a lot easier to find a proper 5V-2A wall psu on the cheap like the one i mentioned, and a small boost module would make sure his non-demanding 18V rail was met again, on the VERY cheap..... you cannot beat this logic i am sure LOL....

As for the remark about how laptop power bricks come at high voltage etc, you do understand the smaller laptop power brick starts at around 40W power right? And that most chargers over 15V are used to charge 4S battery packs so a voltage of 16.8+drop on voltage regulator and charger circuit is required... so it is only natural to design with a higher voltage in mind, when you really use most of the power in form of 3,3-5-12V rails (and not only)....
Yes, I mentioned the availability of parts in my previous post:
https://www.eevblog.com/forum/beginners/power-regulation-options-for-5v-and-18v-circuit/msg1396846/#msg1396846

To simply things: an 18V PSU and 5V buck maybe optimum, but a 5V 2A PSU will be cheaper, than a potentially huge 18V PSU, so a 5V PSU and 18V boost, is more economical.

I've used quite a few Chinese buck regulator modules that were 99c shipped, I think I got some once for only 90c. I haven't priced 78xx or LM317 regulators recently but they can't be much cheaper, and by the time you add the heatsink and capacitors it will cost more.

I got LM7805CV from China recently, worked very well, cost 0,76$/10pcs ....  a module cost 99c shipped from China with an LM7805 on it is NOT a cheap deal LOL..  On the other hand, 78xx can set you back ~~0,8-1,5$ a piece ordered from "western"sites etc....
Except he was not talking about a 99c module with an LM7805 on it. He was referring to a 99c buck converter module, which will be much more efficient than the LM7805 and won't need a heatsink.
 

Online mariush

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Re: Power regulation options for 5V and 18V circuit
« Reply #31 on: January 11, 2018, 01:39:45 pm »
Boosting 5v to 18v is somewhat difficult to do with high efficiency and with cheap ICs .

He wants 18v up to 325mA so let's say we aim for 350mA  or 6.3w ... with a cheap boost regulator he's probably not gonna get more than 80% efficiency boosting 5v, so we're looking at around 7.5-8w from 5v, or around 1.5..1.6 A and naturally there's gonna be pulses/bursts higher than that.  Do you trust any usb 5v 2A adapter to give you around 1.8a..2A for 24/7 (or while your device runs)?

Considering the dubious quality of various 5v 2A usb adapters and the losses on the usb cables between adapters and devices (which means i won't even get 5v), I wouldn't trust that i'd get good 5v to use directly without some regulator, so that's why I'm saying it would make more sense to use something in the range of 7.5v and 12v. 
Allow for some voltage drop on cables, allow use of some LDO for the more "critical" part which is 5v, and make boosting to 18v more efficient by reducing the voltage differential.
 

Offline soubitos

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Re: Power regulation options for 5V and 18V circuit
« Reply #32 on: January 11, 2018, 01:59:57 pm »
MT3608 is cheap with small BOM around it and can deliver 18V/400mA from 5V no problems... (I tested mine with a led strip @ 12V/0.5A from 3,5-4,2V from 18650 batteries and it was solid - and its not as efficient with inputs under 5V) efficiency with proper inductor etc would be in the range of 85-90% say 80-85% in real life. And the ORICO 5V supply at least based on what i already have and abuse, is good to go for the VA it claims with what it delivers and of course, you can find several others between 2-3A which are both cheap and good quality so its still a cheap solution and definitely the one i'd go with any time.... This for example is a 2 port 5V/2,4A https://tinyurl.com/yb3nes2m max 15w total charger 5.27$ delivered!
 

Online Zero999

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Re: Power regulation options for 5V and 18V circuit
« Reply #33 on: January 11, 2018, 05:47:40 pm »
MT3608 is cheap with small BOM around it and can deliver 18V/400mA from 5V no problems... (I tested mine with a led strip @ 12V/0.5A from 3,5-4,2V from 18650 batteries and it was solid - and its not as efficient with inputs under 5V) efficiency with proper inductor etc would be in the range of 85-90% say 80-85% in real life. And the ORICO 5V supply at least based on what i already have and abuse, is good to go for the VA it claims with what it delivers and of course, you can find several others between 2-3A which are both cheap and good quality so its still a cheap solution and definitely the one i'd go with any time.... This for example is a 2 port 5V/2,4A https://tinyurl.com/yb3nes2m max 15w total charger 5.27$ delivered!
Too cheap. It might work and be safe, or it could be deadly but is it worth the risk?

I'd go to my local supplier and buy something more pricey but more likely to be safe and comply with the relevant EMC standards.

The 18V PSU is more expensive, than the 5V, but I'd probably go with it anyway, for the reasons mentioned in my previous posts.
http://cpc.farnell.com/stontronics/t6090dv/psu-raspberry-pi-5v-2-5a-uk-euro/dp/SC14026
http://cpc.farnell.com/stontronics/t6369st/ac-dc-power-supply-18v-1a-2-1mm/dp/PW02850
 

Offline soubitos

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Re: Power regulation options for 5V and 18V circuit
« Reply #34 on: January 11, 2018, 05:57:53 pm »
deadly? what makes you say that? i am using MT3608 quite a lot in my designs lately and have not had any issues with them in terms of safety (overshooting in the output for example) even when they eventually failed from (physical) abuse.... what makes an expensive part safer than a cheap one? i really am curious to know if for example the too cheap MT3608 has safety issues as that means i have to redesign half my designs so far......
 

Online Zero999

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Re: Power regulation options for 5V and 18V circuit
« Reply #35 on: January 11, 2018, 06:41:53 pm »
deadly? what makes you say that? i am using MT3608 quite a lot in my designs lately and have not had any issues with them in terms of safety (overshooting in the output for example) even when they eventually failed from (physical) abuse.... what makes an expensive part safer than a cheap one? i really am curious to know if for example the too cheap MT3608 has safety issues as that means i have to redesign half my designs so far......
Don't be silly, I wasn't referring to the MT3608, but the crappy USB charger on AliExpress of course, hence the links to mains power supplies.

Don't cheap out on safety critical components like that.
 

Offline soubitos

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Re: Power regulation options for 5V and 18V circuit
« Reply #36 on: January 11, 2018, 07:52:17 pm »
deadly? what makes you say that? i am using MT3608 quite a lot in my designs lately and have not had any issues with them in terms of safety (overshooting in the output for example) even when they eventually failed from (physical) abuse.... what makes an expensive part safer than a cheap one? i really am curious to know if for example the too cheap MT3608 has safety issues as that means i have to redesign half my designs so far......
Don't be silly, I wasn't referring to the MT3608, but the crappy USB charger on AliExpress of course, hence the links to mains power supplies.

Don't cheap out on safety critical components like that.

Oh.... silly me  :P
On the other hand.... Orico is a very good brand .. Chinese brand .... but a very good one... I have a 4 port 34W (max outp 2.4A you can draw 2,4A from any two channels but must keep it under 1A for the other two) I am so confident for the brand and products I would gladly tear apart the charger i got to show you and possibly others but i can't replace it with anything else and it will take a month or two before i get another ....   

Mine is different than this one but trust me, its really good

And a teardown... shows orico quality
« Last Edit: January 11, 2018, 08:00:53 pm by soubitos »
 

Offline james_s

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Re: Power regulation options for 5V and 18V circuit
« Reply #37 on: January 11, 2018, 10:08:41 pm »
There are some Chinese brands that are quite good, although you do have to be careful of counterfeits. China seems to have a very lax attitude toward counterfeit products, something will get a good reputation and then dozens of other companies try to cash in by making cheaper copies.
 
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