Regulator chip for 5V from 4x AA cells

H

Hal Murray

Guest
Is there any obvious regulator chip that can do both boost and buck
mode at50 mA?

Fresh batteries are over 6 V. End of life is (say) 3.2 V.
I'm looking for something that will switch modes when the battery
voltage drops below the target output voltage. (Linear is fine
rather than buck with inductor.)

I'm actually looking for 3.3 V. With modern LDOs,
it's simple to just give up a bit of battery life and declare
end-of-life to be 3.4 V. But I've also got a bursty load (motor, LED)
which drop the battery voltage enough to cause troubles. Backing
off the EOL voltage enough to cover that makes the life too short.

I also need a disable pin to turn it off for close to zero power
when the system is idle.

--
The suespammers.org mail server is located in California. So are all my
other mailboxes. Please do not send unsolicited bulk e-mail or unsolicited
commercial e-mail to my suespammers.org address or any of my other addresses.
These are my opinions, not necessarily my employer's. I hate spam.
 
On Wed, 08 Jun 2005 23:10:44 -0300, Hal Murray <hmurray@suespammers.org>
wrote:

Is there any obvious regulator chip that can do both boost and buck
mode at50 mA?

Fresh batteries are over 6 V. End of life is (say) 3.2 V.
I'm looking for something that will switch modes when the battery
voltage drops below the target output voltage. (Linear is fine
rather than buck with inductor.)

I'm actually looking for 3.3 V. With modern LDOs,
it's simple to just give up a bit of battery life and declare
end-of-life to be 3.4 V. But I've also got a bursty load (motor, LED)
which drop the battery voltage enough to cause troubles. Backing
off the EOL voltage enough to cover that makes the life too short.

I also need a disable pin to turn it off for close to zero power
when the system is idle.
Click to expand...
thought of adding a cap for the motor?

--
Using Opera's revolutionary e-mail client: http://www.opera.com/mail/
 
On Wed, 08 Jun 2005 21:10:44 -0500, the renowned
hmurray@suespammers.org (Hal Murray) wrote:

Is there any obvious regulator chip that can do both boost and buck
mode at50 mA?

Fresh batteries are over 6 V. End of life is (say) 3.2 V.
I'm looking for something that will switch modes when the battery
voltage drops below the target output voltage. (Linear is fine
rather than buck with inductor.)

I'm actually looking for 3.3 V. With modern LDOs,
it's simple to just give up a bit of battery life and declare
end-of-life to be 3.4 V. But I've also got a bursty load (motor, LED)
which drop the battery voltage enough to cause troubles. Backing
off the EOL voltage enough to cover that makes the life too short.

I also need a disable pin to turn it off for close to zero power
when the system is idle.
Click to expand...
Maybe the LT1930 with SEPIC topology (two inductors).


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
In article <9ridnbBWOJa5ODrfRVn-qw@megapath.net>,
hmurray@suespammers.org (Hal Murray) writes:
Is there any obvious regulator chip that can do both boost and buck
mode at50 mA?

Fresh batteries are over 6 V. End of life is (say) 3.2 V.
I'm looking for something that will switch modes when the battery
voltage drops below the target output voltage. (Linear is fine
rather than buck with inductor.)

I'm actually looking for 3.3 V. With modern LDOs,
it's simple to just give up a bit of battery life and declare
end-of-life to be 3.4 V. But I've also got a bursty load (motor, LED)
which drop the battery voltage enough to cause troubles. Backing
off the EOL voltage enough to cover that makes the life too short.
Click to expand...
This doesn't make sense to me, at least with LDO type regulators.
In an effort to squeeze a tiny bit of extra life out of a battery,
you are wasting nearly half the energy in the battery as heat in
the voltage regulator. You would get double the life by using a
battery with same energy storage and half the voltage.

I would look at using PWM control. Firstly this will avoid the
losses inherent in resistive droppers. Secondly, PWM control is
particularly suitable for motor loads, where it can provide much
better torque control at low speeds (starting or running). Pick
a battery voltage such that you would not need to boost it when
the battery has run as flat as you want to take it. If you are
ever likely to use rechargeable batteries, include provision to
disable the deep discharge, which will wreck the cells which
discharge first and get reverse charged by the cells which still
have some juice in them.

You might actually be able to use an off-the-shelf motor control
IC to do this. One such chip I've used is the A3953. It is a
full-bridge chip (allows motor reversing control), but if you
don't need motor reversing, a half-bridge chip would be better.

--
Andrew Gabriel
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top