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How to get 5 volts from 6.4 volts

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Hi, everyone.

I have a battery pack that takes 4 x AA batteries. If those batteries are alkaline, the output is 6.4 volts. If they're nickel-Mh, the output is 4.8V.

I have a microcontroller that takes +5V. It is rated at 1.8V to 5.5V. So I guess it could take anything in that range, but I'd like to aim at 5V.

Voltage regulators seem to need decent 'headroom' - for example, I could easily get 5V from a 9V battery. How do I get 5V from 4 AA batteries?

Richard
 

MrAl

Well-Known Member
Most Helpful Member
Hi,

There are low dropout regulators on the market, however you cant get 5v from 4.8v unless you use a boost circuit.
If you run your uC at a lower voltage it would be much easier. Like say 3 to 4 volts.

I run mine straight from 3xAA cells with no regulator sometimes.
 
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audioguru

Well-Known Member
Most Helpful Member
Four alkaline battery cells in series make 6.4V only when they are brand new. Their total voltage continues to drop as they are used until the voltage is 4V or less.
Adding a voltage regulator will make the voltage drop more.
 

RODALCO

Well-Known Member
Just use one or two diodes in series, when the battery voltage drops they can be switched out off the circuit.
 

ikelectro

Member
Hi, everyone.

I have a battery pack that takes 4 x AA batteries. If those batteries are alkaline, the output is 6.4 volts. If they're nickel-Mh, the output is 4.8V.

I have a microcontroller that takes +5V. It is rated at 1.8V to 5.5V. So I guess it could take anything in that range, but I'd like to aim at 5V.

Voltage regulators seem to need decent 'headroom' - for example, I could easily get 5V from a 9V battery. How do I get 5V from 4 AA batteries?

Richard

If there are 6.4 V. then you can use a zener diode of 5.1V and a 120Ω 1watt resistor to down the voltage in the supply pin, and it will aslo stable the voltage. If you want the circuit tell me i'll post it here.
 

japanjot

New Member
Hi, everyone.

I have a battery pack that takes 4 x AA batteries. If those batteries are alkaline, the output is 6.4 volts. If they're nickel-Mh, the output is 4.8V.

I have a microcontroller that takes +5V. It is rated at 1.8V to 5.5V. So I guess it could take anything in that range, but I'd like to aim at 5V.

Voltage regulators seem to need decent 'headroom' - for example, I could easily get 5V from a 9V battery. How do I get 5V from 4 AA batteries?

Richard

hey bro just simply use LM2940-5v,The LM2940 positive voltage regulator features the
ability to source 1A of output current with a dropout voltage of
typically 0.5V

that means you would get 5v constant from even 5.5v :) and of-course 6.0v and even 6.4v
this is the datasheet http://www.datasheetcatalog.org/datasheet/nationalsemiconductor/DS008822.PDF
this is the one i have been using for such 5v application from 6v battery
 
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ikelectro

Member
or you can also use LM7805, a simple voltage regulator IC.
 

Mikebits

Well-Known Member

japanjot

New Member
or you can also use LM7805, a simple voltage regulator IC.
as the input voltage is only 6-6.4, the lm7805 will need minimum 7v to 7.5 volt to give output of 5 v,
to overcome this disadvantage lm2940-5v ,a low dropout regulater was invented,as its name state its a low dropout regulator ,it can give 5v output even from as low as 5.5v ;)
so lm7805 wont solve the problem.
 
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WTP Pepper

Active Member
If you use Lithium Manganese Dioxide cells on the market due their near 3AH capacity, you get 1.75volts/cell All thrown away if you use a linear regulator.
 

ikelectro

Member
as the input voltage is only 6-6.4, the lm7805 will need minimum 7v to 7.5 volt to give output of 5 v,
to overcome this disadvantage lm2940-5v ,a low dropout regulater was invented,as its name state its a low dropout regulator ,it can give 5v output even from as low as 5.5v ;)
so lm7805 wont solve the problem.

ok..
if there are not requirement too much of current in the circuit he can simply use 5.1V Zener diode and resitor to drop and stable the voltage.
 
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MikeMl

Well-Known Member
Most Helpful Member
ok..
if there are not requirement too much of current in the circuit he can simply use 5.1V Zener diode and resitor to drop and stable the voltage.
Poor suggestion: Zeners do not provide very good regulation when the drop across the series resistor is a small fraction of the Zener voltage...
 

Mikebits

Well-Known Member
Poor suggestion: Zeners do not provide very good regulation when the drop across the series resistor is a small fraction of the Zener voltage...

Hey Mike! Your back :)
 

MikeMl

Well-Known Member
Most Helpful Member
Yep, it took me over a year to move from Utah to Northern Arizona. Selling a house, building a house, erecting ham radio tower, building a ham/hobby shack, the list goes on....
 

Mikebits

Well-Known Member
Yep, it took me over a year to move from Utah to Northern Arizona. Selling a house, building a house, erecting ham radio tower, building a ham/hobby shack, the list goes on....

Well, damn nice to have you back.
 

Boncuk

New Member
I don't quite understand all that discussion.

The μc requires supply voltages between 1.8 and 5.5V.

Fresh alkaline batteries supply 1.6V for a short time. Using 3 batteries (4.8V) they could be connected for supply without any additional electronic trick.

They are considered depleted at 1.2V per cell which equals 3.6V battery voltage, still well within supply volt range of the the μc.

My suggestion: Do nothing unnecessary and just connect three Alkali batteries. Saves money and headaches.

Boncuk


P.S. Welcome back, MikeMI :)
 
Boncuk,

I have several rechargeable Nickel-metal hydride batteries. My workplace encourages us to use them as a gesture for the environment. They produce 1.2 volts when fully charged. If you want to allow the end user to use rechargeables, you couldn't use the voltage as an indicator of charge status. Really, the cell is depleted when it produces 0 volts. It is useless when the combined output is less than the requirements of your components (in this case, 1.8 volts total). Assuming the microcontroller and all other components still work acceptably at 1.8 volts, then that's all you need the cells to produce.

Richard
 

Mikebits

Well-Known Member
So you are designing this for an end user product?
 
No, I'm just an amateur mucking about at home. But I've built my own oscillator using RC components, and it occurs to me that the frequency of the oscillator will change depending on the voltage going into it. One way to counteract this is to ensure a constant, regulated, voltage.

Richard
 
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