Maker Pro
Maker Pro

Buck switcher chips

P

Phil Hobbs

Jan 1, 1970
0
So we've got the +-40V sorted out, thanks to all. The next bit to
re-examine is the two buck regulators, both LM2594s, one for +5 and one
for -15.

The TI LM2594MX-ADJ is about $1.40 in 100s, and there are zillions in
stock. The ONsemi clone, LM2594D, is only 64 cents, but it looks like
Digikey is the only distributor with any stock, and they have less than
one reel.

I like the medium-old bipolar switchers, because their nice slow edges
make me less worried about switching junk getting into my low level
circuitry.

Any idea why the ONsemi ones are both cheap and apparently unpopular?

Any suggestions for buck chips that will handle at least 40V and 0.5 A?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
P

Phil Hobbs

Jan 1, 1970
0
Have you checked the ON Semi site? It could be that the LM2594 is
being discontinued.

Use an LM339 and be safe ;-)

Reminds me of a design of mine that produced both +5V and -12V...

http://www.analog-innovations.com/SED/OldStyleBuckSwitcherWithAddedNegativeOutput.pdf

What are the relative loads on your +5V and -15V?

...Jim Thompson

I looked on the ONsemi site, and they're discontinuing the DIP package
but not (so far) the SO8.

The +5 load is relatively light--it's running a 3.3V LDO for a small ARM
with a bit of external flash and sram, some optos, a display, and an
FDTI chip. So maybe 200 mA.

The -15 can be at least that, because there are beefy op amps driving
series-terminated 50 ohm BNCs that somebody might decide to terminate in
50 ohms. But no more than 250 mA.

Cheers

Phil Hobbs



--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
J

John Devereux

Jan 1, 1970
0
John Larkin said:
We use LM2574/SO14 and LM2576HV/TO263. Nice and slow.

I tend to go the other way! Higher magnetics frequencies are easier to
filter and are attentuated more by groundplanes. The fall in PSRR of the
opamps gets compensated by the improvement in local filtering.

Works best when signals are relatively slow I suppose, slower that the
SMPS.
 
J

Joerg

Jan 1, 1970
0
Phil said:
So we've got the +-40V sorted out, thanks to all. The next bit to
re-examine is the two buck regulators, both LM2594s, one for +5 and one
for -15.

The TI LM2594MX-ADJ is about $1.40 in 100s, and there are zillions in
stock. The ONsemi clone, LM2594D, is only 64 cents, but it looks like
Digikey is the only distributor with any stock, and they have less than
one reel.

I like the medium-old bipolar switchers, because their nice slow edges
make me less worried about switching junk getting into my low level
circuitry.

Any idea why the ONsemi ones are both cheap and apparently unpopular?

Any suggestions for buck chips that will handle at least 40V and 0.5 A?

There's always the old MC34063, almost dates back to Methusaleh, which
can be had for slightly above $0.10 in qties:

http://www.st.com/web/en/resource/technical/document/datasheet/CD00001232.pdf

The BD9876 is around $0.50, more efficient, but you'd have to see if ok
for the inverter job:

http://rohmfs.rohm.com/en/products/databook/datasheet/ic/power/switching_regulator/bd9876efj-e.pdf

The others I have encountered are mostly over a Dollar. If you can
stomach an external FET there may be some further penny-pinching
possible in case the MC34063 is not to your liking.
 
J

Joerg

Jan 1, 1970
0
Phil said:
I see that there's a 150 kHz version of the 34063 as well, the NCP3063,
which might be a win at 37 cents in hundreds. The switch burden voltage
is quite a bit higher than the TI part, and it has an external current
limit, which is obviously more accurate, but bumps the switch drop up to
1.6V, which is a chunk.

The current sense only adds 200mV. The switch drop is a pain but you'll
have that in almost almost all slow and old regulators.

(I'm quite fond of the LM2594--I still wish I knew why the On Semi one
is half the price.)

One way to find out would be to ask a TI app engineer :)
 
J

josephkk

Jan 1, 1970
0
Have you checked the ON Semi site? It could be that the LM2594 is being
discontinued.

Use an LM339 and be safe ;-)

Reminds me of a design of mine that produced both +5V and -12V...

http://www.analog-innovations.com/SED/ OldStyleBuckSwitcherWithAddedNegativeOutput.pdf

What are the relative loads on your +5V and -15V?

...Jim Thompson

That is elegant to a cruel level.

?-))
 
Top