5 volt regulator recommendation?
Archiver
Posts: 46,084
Dear Friends,
I'm building a little circuit that uses solar power, and I'm looking
for a 5 volt regulator that wastes as little energy as possible. I've
used a 7805 before but I'm wondering if there is something more
thrifty. The current draw on the circuit is @200ma.
any advice appreciated!
thanks,
markallen
I'm building a little circuit that uses solar power, and I'm looking
for a 5 volt regulator that wastes as little energy as possible. I've
used a 7805 before but I'm wondering if there is something more
thrifty. The current draw on the circuit is @200ma.
any advice appreciated!
thanks,
markallen
Comments
effiecient regulators are switching regulators with effiencies in the
mid 90's for some.
Linear tech, TI, National semiconductor, and analog devices all make
switching regulator IC controllers. Some are easy to use like the
national semi's simple switchers and some, if not most, are difficult
to use but offer many special features.
Power Trends makes DC-DC converters that may work in this application.
Need a little more info here.
Jason
--- In basicstamps@yahoogroups.com, markallen <markallen@m...> wrote:
> Dear Friends,
>
> I'm building a little circuit that uses solar power, and I'm
looking
> for a 5 volt regulator that wastes as little energy as possible.
I've
> used a 7805 before but I'm wondering if there is something more
> thrifty. The current draw on the circuit is @200ma.
>
> any advice appreciated!
>
> thanks,
>
> markallen
>
> I'm building a little circuit that uses solar power, and I'm
> looking for a 5 volt regulator that wastes as little energy
> as possible. I've used a 7805 before but I'm wondering
> if there is something more thrifty. The current draw on
> the circuit is @200ma.
>
The minimum energy consumed by a linear regulator is determined by the
drop-out voltage. That is, the smallest difference between the source
voltage and the regulated voltage that will allow the chip to maintain
regulation. Minimizing this difference starts with a low-drop-out regulator.
In your case, you probably want an ultra-low-drop-out regulator.
A ULDO regulator, like National's LP3965, would have a drop-out voltage of
only 50mV or so at your design current. In other words, with 5.05 volts as
the source, you will deliver 5.00 volts to the load. Sounds great. And
something like that is probably the minimum dissipation you're going to get.
Now the catch:
No matter what you do, a linear regulator reduces the source voltage to the
target voltage by dissipating the difference in its own circuit as heat.
That 5.05V is only the minimum source voltage that will allow the 3965 to
maintain regulation. When the voltage is higher, the 3965 dissipates the
excess. So if you want to design for minimum loss in the regulator stage,
you first must find a way to keep the source voltage very close to the
minimum voltage that will let the regulator stay in regulation.
Second catch:
The ultra low drop-out regulators have a pretty low ceiling on the source
voltage. That LP3965 tops out at 7.0 volts. You'll fry it if your source
goes much over that, so you have to design to make sure that doesn't happen.
I'm doing a BS-1 controlled supply for my robot (just for the hell of it,
really), and I dealt with this by using an LDO regulator with a high ceiling
(15V I think it is) to reduce high voltages into the range the ULDO and the
servos can handle. (This way the servos run at the highest voltages they can
tolerate and the logic circuits are fed regulated power at their 5V and are
isolated from the surges and sags caused by servos.) When the source is
already within that 5 to 7 volt range, the BS1 takes the LDO out of the
circuit, so the losses are not endured unnecessarily. The servos run
directly off the source, and the logic is still protected by the ULDO.
In either case, at only 7V or at 15V, the regulators are dispersing the
excess source voltage as heat. If your load is operating at 200ma at 5V then
it's dissipating 1 watt itself, but the regulator is dissipating another 0.4
watts if the source is 7V. (200ma at 2V). At 15V, the regulators are
dissipating two watts for the load's one watt.
Switching regulators have different rules and I understand the new high
frequency switchers can be very efficient at such low currents as you have
in mind. Unless it's practical to design your system to keep the source
voltage close to the target voltage, you should look into one of those
switchers instead of a linear regulator.
Maybe someone else has worked with them and can offer tips.
Gary
switching power supply modules, many of which are drop in compatible with a
7805. They are a bit larger so you may have clearance problems. They can
take very large input voltages and have pretty high efficiency.
Unless you are making a large number of units, the cost of the TI modules
will not be a big deal since it would cost you more to reinvent it for one
or two.
http://focus.ti.com/docs/search/paramsearch.jhtml?familyId=563&tfsection=par
am_table&templateId=2&showAssociated=false
Regards,
Al Williams
AWC
* New Kits: http://www.al-williams.com/kits.htm
>
Original Message
> From: markallen [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=z_kun-s4dTCpqsUN3WzbO_WD3DIkyfIcAWnS_y0Nh_d4F0HPOqQ0n4_3q_SIk4M7x493PHyhQA-1Sgh--Dqa]markallen@m...[/url
> Sent: Thursday, December 11, 2003 5:09 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] 5 volt regulator recommendation?
>
>
> Dear Friends,
>
> I'm building a little circuit that uses solar power, and I'm looking
> for a 5 volt regulator that wastes as little energy as possible. I've
> used a 7805 before but I'm wondering if there is something more
> thrifty. The current draw on the circuit is @200ma.
>
> any advice appreciated!
>
> thanks,
>
> markallen
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the
> Subject and Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
>
>
>
>
> From: "markallen" <markallen@m...>
> >
> > I'm building a little circuit that uses solar power, and I'm
> > looking for a 5 volt regulator that wastes as little energy
> > as possible. I've used a 7805 before but I'm wondering
> > if there is something more thrifty. The current draw on
> > the circuit is @200ma.
> >
> The minimum energy consumed by a linear regulator is determined by the
> drop-out voltage. That is, the smallest difference between the source
> voltage and the regulated voltage that will allow the chip to maintain
> regulation. Minimizing this difference starts with a low-drop-out regulator.
> In your case, you probably want an ultra-low-drop-out regulator.
>
> A ULDO regulator, like National's LP3965, would have a drop-out voltage of
> only 50mV or so at your design current. In other words, with 5.05 volts as
> the source, you will deliver 5.00 volts to the load. Sounds great. And
> something like that is probably the minimum dissipation you're going to get.
>
> Now the catch:
>
> No matter what you do, a linear regulator reduces the source voltage to the
> target voltage by dissipating the difference in its own circuit as heat.
> That 5.05V is only the minimum source voltage that will allow the 3965 to
> maintain regulation. When the voltage is higher, the 3965 dissipates the
> excess. So if you want to design for minimum loss in the regulator stage,
> you first must find a way to keep the source voltage very close to the
> minimum voltage that will let the regulator stay in regulation.
>
It seems to me I saw something in the shape of a 7805 which was actually
a switched voltage source, not a linear regulator, but that it didn't
dissapate excess voltage as heat, but I don't remenber where I saw it. I
think it was around $20.
Sean T. Lamont, Chief Mad Scientist |-- lamont@a...
Zen Chemical Productions |-- http://www.zenchemical.com
Fabricators of Unnecessary Amazement
<lamont@a...> wrote:
> On Thu, 11 Dec 2003, Gary W. Sims wrote:
>
> > From: "markallen" <markallen@m...>
> > >
> > > I'm building a little circuit that uses solar power, and I'm
> > > looking for a 5 volt regulator that wastes as little energy
> > > as possible. I've used a 7805 before but I'm wondering
> > > if there is something more thrifty. The current draw on
> > > the circuit is @200ma.
> > >
> It seems to me I saw something in the shape of a 7805 which was actually
> a switched voltage source, not a linear regulator, but that it didn't
> dissapate excess voltage as heat, but I don't remenber where I saw it. I
> think it was around $20.
>
> Sean T. Lamont, Chief Mad Scientist |-- lamont@a...
> Zen Chemical Productions |--
http://www.zenchemical.com
> Fabricators of Unnecessary Amazement
I use the Power Trends(TI) PT78ST105H 1.5 Amp Switching regulator.
It's a bit larger than the 7805 TO-220 package but it's still
pretty compact (about 1" x 1" x 1/4")
However, it's not a low drop-out device.
It's rated input voltage is 9 to 38 Vdc for the 5 volt version.
The data sheet shows about 88% efficiency @ 9 volt input.
It's available at Digikey (Part Number PT78ST105H-ND) $13.66