Can anyone recommend a good cheap LDO (2 Bucks or less small quantity
10 or 20), preferably one that doesn't need a $5 tant cap on the
output? I've been looking through the datasheets at Newark and
Digikey until my eyes are bleeding.

The specs are

Vin is a 9V alkaline initially, then the battery gets switched out and
a regulated 12V from a flyback takes over. The LDO output should be 5V
and be able to provide 80 to 100mA continuous.

I was thinking of just using a L78L05 but I want to be able to use the
battery until it's depleted. I know I'm cheap.

Thanks

On Feb 1, 8:34=A0pm, Hammy <spa...@hotmail.com> wrote:
> Can anyone recommend a good cheap LDO (2 Bucks or less small quantity
> 10 or 20), preferably one that doesn't need a $5 tant cap on the
> output? =A0I've been looking through the datasheets at Newark and
> Digikey until my eyes are bleeding.
>
> The specs are
>
> Vin is a 9V alkaline initially, then the battery gets switched out and
> a regulated 12V from a flyback takes over. The LDO output should be 5V
> and be able to provide 80 to 100mA continuous.
>
> I was thinking of just using a L78L05 but I want to be able to use the
> battery until it's depleted. I know I'm cheap.
>
> Thanks

Hi, Hammy. The 78L05 has a dropout voltage of 7.0V max, which should
do fine. There's not much power left in a 9V battery when it gets
down to 7.0V. But the problem will be when you switch over to the 12V
supply. You'll be dissipating 0.7 watts at 100mA, which will mean the
78L05 will get far too hot. (12V - 5V) * 0.1A =3D 0.7W

Now, if you go with an LM341/LM78M05C, your dropout voltage will be
7.2V at 0.5A, and should be comparable to the 78L05 at 100mA output
current. It's about $0.40 in single quantities from Mouser, and is
forgiving on the output cap issue -- an 0.1uF ceramic should be fine.

Cheers
Chris
=2E

On Fri, 1 Feb 2008 20:34:56 -0800 (PST), Chris <cfoley1064@yahoo.com>
wrote:


>
>Hi, Hammy. The 78L05 has a dropout voltage of 7.0V max, which should
>do fine. There's not much power left in a 9V battery when it gets
>down to 7.0V. But the problem will be when you switch over to the 12V
>supply. You'll be dissipating 0.7 watts at 100mA, which will mean the
>78L05 will get far too hot. (12V - 5V) * 0.1A = 0.7W
>
>Now, if you go with an LM341/LM78M05C, your dropout voltage will be
>7.2V at 0.5A, and should be comparable to the 78L05 at 100mA output
>current. It's about $0.40 in single quantities from Mouser, and is
>forgiving on the output cap issue -- an 0.1uF ceramic should be fine.
>
>Cheers
>Chris
>.

Thanks I wasnt sure when a 9V battery dies. I'll try your suggestion.

On Sat, 02 Feb 2008 02:34:48 GMT, Hammy <spamme@hotmail.com> wrote:

>Can anyone recommend a good cheap LDO (2 Bucks or less small quantity
>10 or 20), preferably one that doesn't need a $5 tant cap on the
>output? I've been looking through the datasheets at Newark and
>Digikey until my eyes are bleeding.
>
>The specs are
>
>Vin is a 9V alkaline initially, then the battery gets switched out and
>a regulated 12V from a flyback takes over. The LDO output should be 5V
>and be able to provide 80 to 100mA continuous.
>
>I was thinking of just using a L78L05 but I want to be able to use the
>battery until it's depleted. I know I'm cheap.
>
>Thanks

LM1117 is a cheap "mdo" regulator with a little lower dropout than a
317. It's happy with a 22 uF aluminum elec on its output.

Once the battery is down to 6 volts or so, it's dying fast, so using
that last volt won't buy much more time.

John

Hammy wrote:
> Can anyone recommend a good cheap LDO (2 Bucks or less small quantity
> 10 or 20), preferably one that doesn't need a $5 tant cap on the
> output? I've been looking through the datasheets at Newark and
> Digikey until my eyes are bleeding.
>
> The specs are
>
> Vin is a 9V alkaline initially, then the battery gets switched out and
> a regulated 12V from a flyback takes over. The LDO output should be 5V
> and be able to provide 80 to 100mA continuous.
>
> I was thinking of just using a L78L05 but I want to be able to use the
> battery until it's depleted. I know I'm cheap.

Maxim/Dallas MAX603 came to mind immediately because I'd just been
playing with one. It might not be able to compete with the (undoubtedly
good) options others have already mentioned, especially in price, but I
thought I'd throw it in.

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1131

PDIP/SOIC, modern protection circuitry, shutdown mode, samples, good
information imo etc.

Hammy <spamme@hotmail.com> writes:

>Can anyone recommend a good cheap LDO (2 Bucks or less small quantity
>10 or 20), preferably one that doesn't need a $5 tant cap on the
>output? I've been looking through the datasheets at Newark and
>Digikey until my eyes are bleeding.

>The specs are

>Vin is a 9V alkaline initially, then the battery gets switched out and
>a regulated 12V from a flyback takes over. The LDO output should be 5V
>and be able to provide 80 to 100mA continuous.

>I was thinking of just using a L78L05 but I want to be able to use the
>battery until it's depleted. I know I'm cheap.

>Thanks

If cheap and easy is what you want, try the MIC29xx series from Micrel.
They have a bunch of different styles and you can get them from Digi-Key.
Might be a bit more than you want to pay, depending upon package, but
they'll do the job.

Steve.
--
Steven D. Swift, novatech@eskimo.com, http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC. P.O. Box 55997
206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA

"Hammy" <spamme@hotmail.com> wrote in message
news:lel7q31mnl3chnb9gkohlq7v2fk1u5njml@4ax.com...
> Can anyone recommend a good cheap LDO (2 Bucks or less small quantity
> 10 or 20), preferably one that doesn't need a $5 tant cap on the
> output? I've been looking through the datasheets at Newark and
> Digikey until my eyes are bleeding.
>
> The specs are
>
> Vin is a 9V alkaline initially, then the battery gets switched out and
> a regulated 12V from a flyback takes over. The LDO output should be 5V
> and be able to provide 80 to 100mA continuous.
>
> I was thinking of just using a L78L05 but I want to be able to use the
> battery until it's depleted. I know I'm cheap.
>
> Thanks

Hi , you might want to check out the TS2950ct-5.0 ultra low dropout
5volt pos. regulator,from Taiwan Semiconductor. 150ma.,only needs 1uf,
quiescent current only 80microamps,and works right down to 5.2volts input!
regards all doug.(in U.K.)