Voltage regulator and temperature / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Voltage regulator and temperature

1 2 next

Move Thread

LAN_403

Andy

Thu Feb 13 2014, 06:54PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Hi
I'm thinking about getting this regulator

and was planning on running it with 12volt.
Would the heat made be like a Mosfet with I2R losses formula, or some voltage one.

Thanks

HV Enthusiast

Thu Feb 13 2014, 07:11PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Heat dissipation is imply your (Vinput - Voutput) * Current

Its just a linear regulator.

Erlend^SE

Thu Feb 13 2014, 08:29PM

Registered Member #1565 Joined: Wed Jun 25 2008, 09:08PM
Location: Norway
Posts: 159

You would be better off getting a DC-DC module if you plan to have it battery-powered and some load on the regulator.

Andy

Fri Feb 14 2014, 06:24AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Thanks AllisonS

Erlend^SE, the price I could find for 9-16volt to 5volt was $130, couldn't I just cascaded a couple of voltage regulators?,
What would the voltage source be like for dc-dc converters, smooth?

Cheers

Sulaiman

Fri Feb 14 2014, 10:41AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

One way to reduce the dissipation per regulator is as you say,
cascade two regulators, e.g. 12V input to 8v regulator (78M08)
then 8v to 3.3v regulator (78M33)

for about the same cost you could use one of these

or similar.
which will reduce heating dramatically, and draw labout 1/3 the battery current.

For 'ultimate' regulation use a switchmode dc/dc converter to produce 5v dc
then use a low dropout 3.3v linear regulator.
This would draw about half the current from the battery of a linear regulator(s) only setup.

P.S. the cheap eBay dc/dc converters appear to have 'out-of-spec.' ic
I and some colleagues have independently bought/used similar converters
the internal clock frequency is commonly lower than expected
which causes more voltage ripple than the passive components were designed for,
not a problem with a linear regulator added to the output.

Andy

Sat Feb 15 2014, 06:02AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Hi Sulaiman
I can't buy products off ebay, for the final product anyway. Found these

With buck converters what type of problems even after a liner regulator, I could add a smoothing cap, but max of 10uF, won't the switching of the bucks be a problem?

Thanks

Sulaiman

Sat Feb 15 2014, 09:46AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

For a commercial product I would always advise a ready made dc/dc converter .. easier.
e.g. 3.3v regulated @ 1A isolated 9v to 18v dc input

(example only, not a brand endorsment)
For a quality product I recommend isolated regulated dc/dc converters,
and please do not try to run them at their full rated power.
(smpsu and dc/dc converters
are amongst the first things we check when doing industrial repairs !)
Ready made dc/dc converters save design/test/approve time,
so for low volume production are the best choice.
The isolation allows for separating power/digital/analogue sections from each other for noise or safety purposes. (with opto-couplers for data etc.)

For high volume,
a multi-output custom designed smpsu is the norm due to cost.
(usually following the smpsu ic manufacturer's application notes examples)
(there's rarely a prize for re-inventing the wheel)

P.S. a small led at 1mA on the output to indicate local power available can save debug time but only wastes a few mW and very small board area.

For low volume production you could also consider ac/dc converter modules,
or complete ready made ac/dc chassis power supplies,
or an external plug-pack etc.
For industrial equipment it is assumed that the customer can supply 24 Vdc
(noisy, unregulated, non-isolated generally 'dirty' supply) also.
Using pre-approved power sources is easier and less liability.

Alex M

Sat Feb 15 2014, 12:38PM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

Andy wrote ...

Thanks AllisonS

Erlend^SE, the price I could find for 9-16volt to 5volt was $130, couldn't I just cascaded a couple of voltage regulators?,
What would the voltage source be like for dc-dc converters, smooth?

Cheers

How about something like the LM2576? It is probably one of the easiest switching regulators out there to get a clean output from since it only switches at 52kHz.

Using a small additional pie filter + ferrite bead on one of the diode legs I could get well under 5mV of ripple under full load (3 amps). This was also on a piece of strip board too, so a half decent PCB design could easily beat that.

Image below is the ripple voltage I scoped on the converters output rails.

1392467472 3943 FT161295 Buck Ripple Pie Filter

When used under very light loads the IC drops into discontinuous mode so a small RC snubber should be used across the diode.

Thomas W

Sat Feb 15 2014, 02:38PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

Ive had a play with these things:

They are rather good, managed to get one running within 1 hour of getting the chip from a teacher (was bored in class, he gave me a chip and asked me what i could do with it)

Alex M

Sat Feb 15 2014, 03:00PM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

Thomas W wrote ...

Ive had a play with these things:

They are rather good, managed to get one running within 1 hour of getting the chip from a teacher (was bored in class, he gave me a chip and asked me what i could do with it)

Found one of those in an in car 12v to 5v USB charger, not a bad little IC for its package and simplicity. Would definitely recommend it if you don't need much more than 100mA or so.

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob