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whether I use Linear or a Switching regulator.

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Sep 25, 2012
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I do not know whether I should use a Linear drop out voltage regulator or a Switching one like TPS63021 to gain power to my circuit using a one cell LIPO (4.2 to 3.0 V 5000mAh)

both ARM and the SIM908 module needs 3.3 volts ideally.

SIM908 requires two 2Amp bursts a day to transmit two messages a day. And the ARM M4 will be in hibernation(@4uA) and wakes up(@100mA) two times a day to "tell" the SIM908 "what" to transmit via UART. yes, this is a data transmission circuit but the difference is that this is a solution to my countries elephant human conflict from which a number of people die every year. this cct is to replace the current extremely expensive cct which uses SAT communication and this is my final year project

this provides hardware support to the already built software model (an earlier project) which is a web server and a mobile android app. I will upload data(the location of an elephant) to a web server via GPRS/SMS.

I will use the highest available mAh LIPO battery and it will be charged using SOLAR/Kinetic energy which I havent thought about yet.

I understand that a LIPO battery has a voltages life per cycle ranging from 4.2 to around 3.0(safe operation)


from 4.2V to 3.4V (I require 3.3V) which regulator should I use? Linear drop out? or Switching
I know there are 0.1V drop out LDRs how about them?

Or is this( TPS63021) better because this can run down till 2.5V

Your help would save a life and also help me get a good grade :)


Since this is a battery energized system and power efficeincy is important using a switching regulator might be a more reosnable solution. It will increase the efficiency (less power loss on regulator). And this TI device can boost also, it means when your battery goes down to ie 3.1V can still supply 3.3V to your devices. But an LDO can do that. On the other hand, take care of good filtering of swtiching noise on the supply since you want to transmit wireless signal, that might be important (i am not sure), I mean, use shielded coil and low esr caps etc for switching device.
Good luck
compared to efficiency I do not mind the cost and the complexity at all

I just want it to be really really efficient to charge one cell of LIPO using solar. could you advice me with regard to this?

Here is an illustration of a buckboost converter, and how it might work to charge a 3.6v battery...

when the supply voltage is lower (left), and when it is greater (right).

The switches are simplifications. They represent control circuitry or a controlling IC.
Dear Emresel ,Crutschow , BradtheRad ,

thank you so much for these replies. they are really valuable to me. I am going almost insane these days trying to figure a proper charger for my circuit.

with deep searching I discovered that there are charging ICs that provide feature called " Power Path". some ICs i discovered are


and there are some chips that only charge the battery.


Im really confused and I had been trying to figure this mess as to how to learn to chose a ideal charger for my LIPO battery to charge it.

I think some ICs that do not allow Power Path mention that if current taken out of the battery whule its being chargd that the charging IC would be "fooled", as it has three major modes.
is that true? How do I overcome this ?

Well, I thought may be a sollution is to find a IC that has power path and can deliver more than 2A to the circuit to be powered. It has a microcontroler that switches on two times a day (RLT clock) and uses SIM908 to send an SMS. this is all what is does. So I just want 2A two times a day for around 3-5 seconds..

And the other problem I face is that some ICs offer Power path but they dont offer 3.3V output. I do not feel like using a Linear drop out to reduce this after the switching regulator becasue it feels like a loss. Even thought it would be a drop of 2mV @2A.

Can someone please tell me how to sue the TPS63021 along with a charging IC to automatically charge my batt when its low? is there a way to do this?

My second qustion is that, When I give an input to a charging IC using a solar if the Vin of the chip says e.g. max 5V 100mA, Am i supposed to use exactly a solar panel that has the same specs ? Am i supposed to use a higher voltage solar? at least a couple of Milli Volts?

Your response with regard to these would be so much appreciated.


- - - Updated - - -

im honestly sorry if this looks so long..

It happens to know about a very low drop voltage regulator that uses TL431 that I used. The only problem is that it can't supply high currents, but it can be adapted to work with higher currents by replacing the P-MOSFET and some resistors. Also the zener reference voltage should probably be changed with another TL431.

Here is the schematics:

As you can see, the voltage is maintained at 3.3 volts until voltage source gets to 3.3 volts. After that the voltage is maintained at whatever the voltage source is giving. If it drops below 3.08V, the LDO shuts down completely until higher voltage is available from the source.

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