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Regulator chip for 5V from 4x AA cells

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.

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Reply to
Hal Murray
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thought of adding a cap for the motor?

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Reply to
jim dorey

Maybe the LT1930 with SEPIC topology (two inductors).

Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

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.

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Reply to
Andrew Gabriel

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