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Many thanks to the guys who answered about the LM2936 reg.
RS Components do have it - Rockby don't, haven't checked Farnell.
Hmmm ... looking at the data sheet, it only comes in SMD & T092 & only gives 50mA max so I don't know how usable it would be.
The problem is that I want to use it as power supply in a remote camera that's likely to be left out in the sticks for a month, may 2 months, so minimal current drain is essential. But the cct uses opto couplers to fire a solenoid & read input data when it goes active, so in its active state it'll pull maybe 100mA off the 5V rail. The solenoid & sensors work directly off the 12V gel battery so they don't affect the LM2936.
I thought i'd bonk up the 2936's current capcity with a pnp booster transistor - saw the idea in NS AN103. The idea is the PNP (BD140) only comes on when there's a demand for more than about 40mA.
The question is ....
... do u see any sneaky little current paths to GND in the attached gif that i haven't thought of?
Or is there some better way entirely to do it? Gotta keep the steady state drain real low in passive mode, which is most of the time. Thankz for advice - Debbie :)
---------------------------------
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>
> Many thanks to the guys who answered about the LM2936 reg.
> RS Components do have it - Rockby don't, haven't checked Farnell.
>
> Hmmm ... looking at the data sheet, it only comes in SMD & T092 & only
gives 50mA max so I don't know how usable it would be.
>
> The problem is that I want to use it as power supply in a remote camera
that's likely to be left out in the sticks for a month, may 2 months, so
minimal current drain is essential. But the cct uses opto couplers to fire a
solenoid & read input data when it goes active, so in its active state it'll
pull maybe 100mA off the 5V rail. The solenoid & sensors work directly off
the 12V gel battery so they don't affect the LM2936.
>
> I thought i'd bonk up the 2936's current capcity with a pnp booster
transistor - saw the idea in NS AN103. The idea is the PNP (BD140) only
comes on when there's a demand for more than about 40mA.
>
> The question is ....
> ... do u see any sneaky little current paths to GND in the attached gif
that i haven't thought of?
>
> Or is there some better way entirely to do it? Gotta keep the steady state
drain real low in passive mode, which is most of the time. Thankz for
advice - Debbie :) {Quote hidden}
>
>
>
>
> ---------------------------------
> Yahoo! Greetings
> - Send some online love this Valentine's Day.
>
> --
> http://www.piclist.com hint: PICList Posts must start with ONE topic:
> [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads
>
>
At 09:25 AM 2/6/03 -0400, Ray Gallant wrote:
>I've used 2 of the LM2951 for my last design. Consider the LM2950.
>Best Regards, {slewrate}
Actually, I think that you mean LP2950 and LP2951 (note: LP instead of LM).
The problem with those 2 devices is the high quiescent current (about 100
uA max). That's a lot power wasted over a period of time.
I actually prefer the LP2950 over the TC55 - the 2950 is more accurate
(0.5% initial accuracy) and much less expensive. But that quiescent
current is a real battery killer.
I mentioned in my earlier email that I use the TC55 series regulator in 2
products. By comparison, I use the LP2950 in dozens of products - anything
that uses a PIC with on-board a/d uses the 2950 if at all possible. The
quiescent current is not a problem for most of my stuff since the majority
is AC powered.
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thankz guys - i'll have a look for those chips locally (Melbourne, Australia)
the battery terminal volts are going down at ~0.1V per day which is gonna discharge it in ~10days. I'm using an LM74LS164 to drive an LCD (3lines from PIC). Trouble is, *it* pulls a lot of mA also - are there any really low current alternatives there?
I have the cam sealed inside a PVC tube with perspex windows and switch it on/off with a UHF tx/rx+decoder. Don't wanta put any holes in it for battery charging or for manually activating the LCD. There's a low temps & condensation involved so outside air needs to be xcluded. Seems a pain to write a routine to switch the LCD on by remote yet keep the cam in passive state - the LCD doesn't draw much current so it'd be good to just leave it on & readable.
Thankz again - Debbie :)
Dwayne Reid <dwaynerspam_OUTPLANET.EON.NET> wrote:At 09:25 AM 2/6/03 -0400, Ray Gallant wrote:
>I've used 2 of the LM2951 for my last design. Consider the LM2950.
>Best Regards, {slewrate}
Actually, I think that you mean LP2950 and LP2951 (note: LP instead of LM).
The problem with those 2 devices is the high quiescent current (about 100
uA max). That's a lot power wasted over a period of time.
---------------------------------
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- Send some online love this Valentine's Day.
> thankz guys - i'll have a look for those chips locally (Melbourne,
Australia)
> the battery terminal volts are going down at ~0.1V per day which is gonna
discharge it in ~10days. I'm using an LM74LS164 to drive an LCD (3lines from
PIC). Trouble is, *it* pulls a lot of mA also - are there any really low
current alternatives there?
> I have the cam sealed inside a PVC tube with perspex windows and switch it
on/off with a UHF tx/rx+decoder. Don't wanta put any holes in it for battery
charging or for manually activating the LCD. There's a low temps &
condensation involved so outside air needs to be xcluded. Seems a pain to
write a routine to switch the LCD on by remote yet keep the cam in passive
state - the LCD doesn't draw much current so it'd be good to just leave it
on & readable.
> Thankz again - Debbie :)
> Dwayne Reid <RemoveMEdwaynerTakeThisOuTPLANET.EON.NET> wrote:At 09:25 AM 2/6/03 -0400, Ray
Gallant wrote:
> >I've used 2 of the LM2951 for my last design. Consider the LM2950.
> >Best Regards, {slewrate}
>
> Actually, I think that you mean LP2950 and LP2951 (note: LP instead of
LM).
>
> The problem with those 2 devices is the high quiescent current (about 100
> uA max). That's a lot power wasted over a period of time.
At 06:47 AM 2/8/03 +1100, Debbie Hynes wrote:
>I'm using an LM74LS164 to drive an LCD (3lines from PIC).
Yeah - substitute HC for the LS: 74HC164 should drop the quiescent from
several mA to several uA (about 3 orders of magnitude difference). Also
look at 4094 and 74HC595 - they are similar and may have pin-outs easier to
work with.
The contrast control on the LCD may also be of concern to you - assuming a
10K contrast pot, about 0.5 mA. It may actually be easier to power the
whole LCD arrangement from a PIC pin (make sure you are using CMOS instead
of LS shift registers) and use a touch switch to wake the PIC up and turn
on the display. The QT11x series from Qprox works well for this - they
consume very little quiescent current and are relatively inexpensive. Dead
simple to use as well.
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*>thankz guys - i'll have a look for those chips locally (Melbourne,
*>Australia) the battery terminal volts are going down at ~0.1V per day
*>which is gonna discharge it in ~10days. I'm using an LM74LS164 to drive
*>an LCD (3lines from PIC). Trouble is, *it* pulls a lot of mA also - are
74C164 or 74HC164. The first is lower current. But CD4094 is even lower
still. You will need to change the strobe logic and the pinout for 4094.
The LCD will consume as much current when not displaying as when
displaying. The usual fix is a swithch in the power line of the LCD (pfet
works best for low current).
*>there any really low current alternatives there? I have the cam sealed
*>inside a PVC tube with perspex windows and switch it on/off with a UHF
*>tx/rx+decoder. Don't wanta put any holes in it for battery charging or
*>for manually activating the LCD. There's a low temps & condensation
A cheap fix: Mount a reed relay for alarm systems inside on the tube wall
and use its magnet from the outside to turn it on. Be sure the PIC knows
when the LCD is off and drives its relevant outputs off.
planet.eon.net>
