Author Topic: power amp  (Read 2163 times)

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Offline benjiTopic starter

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power amp
« on: August 28, 2008, 09:42:15 AM »
im building a robot that can charge stuff like batteries ....etc
the robot is able to detect how much voltage should it provde
now the problem is that i need a power amp so i can provide big currents (im fine with 1 amps at 5 volts)
5 volts is my maximum voltage to provide

anybody knows a good power amp IC ?
is it ok to use audio amplifier IC ? im not sure if they can supply dc current ..
good ol' BeNNy

Offline ArcMan

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Re: power amp
« Reply #1 on: August 28, 2008, 12:57:03 PM »
Here is a simple battery charging circuit used for constant-current battery charging.  Check out page 7.

http://www.sparkfun.com/datasheets/Components/LM317.pdf

I use this circuit to charge my NiMH batteries.  Works great.  Just make sure that you set your current to C/10 or less to avoid venting when the battery becomes fully charged. C is the battery capacity.  For example, if you are charging 2000 mAh batteries, set your current to 200 mA or less.

Offline benjiTopic starter

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Re: power amp
« Reply #2 on: August 28, 2008, 03:15:41 PM »
i know about the lm317 ,,the problem with it is that i want to supply low voltages also ,,like 0.5 and 0.3 volts in some applications
and the lm317 has a minimum out of 2.5 i guess
i need a variable source from 0 >> 5 v
good ol' BeNNy

Offline TrickyNekro

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Re: power amp
« Reply #3 on: August 28, 2008, 06:32:54 PM »
eeeexxxx.....

Try PWM a MOSFET.... and read on output...

You can do that with a DS2438.... not to be proud and all that stuff have a look at my tutorial...
Won't help you much with what you want but it will be a good guide on the IC...
The IC can display sum of current in or out of the pack... but I don't include that function..... yet......
For whom the interrupts toll...


P.S. I've been inactive for almost a year... Don't give promises but I'll try to complete my tutorials. I'll let you know when..

Cheers!

Offline ArcMan

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Re: power amp
« Reply #4 on: August 28, 2008, 07:55:46 PM »
i know about the lm317 ,,the problem with it is that i want to supply low voltages also ,,like 0.5 and 0.3 volts in some applications
and the lm317 has a minimum out of 2.5 i guess
i need a variable source from 0 >> 5 v

The LM317 has a minimum output voltage of 1.25V, but that's as a voltage regulator.  When used as a constant current battery charger, output voltage of the circuit doesn't come into play.  You need to understand how the LM317 works.  What it does is maintain a voltage of 1.2V between its Output and Adjust pins.  Take a look at the circuit diagram on page 7, Figure 9 - the 50 mA constant-current battery charger circuit.  Placing the 24 ohm resistor between the Output and Adjust pins produces 50 mA of output current because (24 ohm) * (50 mA) = 1.2V.  So you can even tie the output directly to ground (meaning 0V at the output of your circuit) and it will still produce 50 mA of output.  Capice??

Offline benjiTopic starter

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Re: power amp
« Reply #5 on: August 29, 2008, 04:31:45 AM »
yea arcman i understand,,what u do here is a current source,,my task is to do a variable voltage source (0>5 with current up to 1 amps)
i dont find a configuration to do that ,
i thought about hooking 2 0.6v diode in series at the output so i can drop the output voltage of the lm317 1.2 v
but this is not much reliable as different  currents would cause different voltage drops across the diodes and the output voltage would change.
good ol' BeNNy

Offline ArcMan

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Re: power amp
« Reply #6 on: August 29, 2008, 11:48:25 AM »
OK.  I see. I was just going off of your OP, which said:

im building a robot that can charge stuff like batteries

In which case, the simplest way to do that is with a constant current source.

Offline benjiTopic starter

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Re: power amp
« Reply #7 on: August 29, 2008, 03:34:32 PM »
im sorry for not making it quite clear
by the way ,,in the lm317 datasheet figure 6 is a voltage source from 0 >> 30
though im still trying to understand why the -10 v is there,,, i guess -1.25 would do ..
good ol' BeNNy

Offline RobD

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Re: power amp
« Reply #8 on: August 29, 2008, 10:02:02 PM »
Hi Benji

Look at the MIC69502.  Adjustable down to 0.5v @ 5A.



 


Offline benjiTopic starter

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Re: power amp
« Reply #9 on: August 31, 2008, 10:23:11 AM »
by the way, would a 20 m amp current source charge any battery?? even if the voltage is lower than the voltage of the battery?
good ol' BeNNy

 


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