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Old Sep 27, 2012, 08:10 AM
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Looking for a 4.2V 3A buck regulator

I'd like to power 1S applications with 2S batteries (or even 3S). As efficiently as possible (>90%). As light as possible (<2g). 3A should be OK.

I found some candidate circuits like MCP16323 and ADP2303 in their adjustable version (nothing between 3.3V and 5V seems ready to use). Unfortunatly I'm nowhere to design and solder a light and usable PCB with small components.
I also found the easier LM2576, but the resulting PCB would be bulky and heavy.
And there is the PTN78060W. A ready to use PCB to start with, but also too bulky as a definitive choice.

So maybe someone with knowledge in micro PCBs could make a small serie.

Why I'd like such circuit ?
Well, I noticed the small 1S batteries used in parkzone ultra-micros tend to become lazy quite quickly with brushed 8mm motors (mustang, 4site). Voltage drops to a value where parkzone's bricks (ar6400, etc) stop working, resulting in plane damages. The same batteries are still OK for 6mm motors (vapor, j3).

Pros: constant reliable voltage, constant motor power.
Cons: weight, cost.

Does this request make sense ?
Thanks
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Old Sep 27, 2012, 04:51 PM
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Bruce Abbott's Avatar
Hastings, New Zealand
Joined Jan 2001
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Quote:
Originally Posted by Camboui View Post
Unfortunately I'm nowhere to design and solder a light and usable PCB with small components. I also found the easier LM2576, but the resulting PCB would be bulky and heavy.
You don't need a PCB - just solder the parts directly to each other, 'dead bug' style! A chip with wire pins (eg. NCP3155) will be easier to connect to. The inductor will probably be the heaviest part.

You will also need a cutoff circuit to prevent over-discharging the battery. Implementing this on a stock Parkzone brick could be tricky.

Quote:
Does this request make sense?
Not really. You cannot get better performance from 2S without significantly increased weight. It would be easier to just use a better 1S battery, eg. Hyperion G3 CX 160mAh, and charge it slower for longer lifespan.
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Old Sep 28, 2012, 07:12 AM
C-c-c-custom!
United States, NM, Albuquerque
Joined Nov 2011
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You could also use a boost or buck/boost from 1S, here is a potentially suitable example: http://www.linear.com/product/LTC3113

Quote:
Originally Posted by Bruce Abbott View Post
Not really. You cannot get better performance from 2S without significantly increased weight. It would be easier to just use a better 1S battery, eg. Hyperion G3 CX 160mAh, and charge it slower for longer lifespan.
But I'd have to agree with Bruce here. The inductor and capacitors required have some mass to them, and will probably offset any performance increase you may gain.
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Old Sep 30, 2012, 04:52 AM
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So what are you trying to achieve?
Looks like longer flight times
Why don't you just put two 1s in parallel
100% efficiency
no weight penalty exceept for a connector
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Old Oct 01, 2012, 08:45 AM
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Brussels
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Thanks for suggestions.
I'm already replacing crap eflite 150mAh batteries by nanotech 160mAh and plan to use 300mAh in some cases (only 4g heavier).

Well, I just wanted try something different.
I may try the accessible NCP3155, but indeed it seems quite difficult to keep weight below 2g because of inductor.
Thanks.
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Old Nov 24, 2013, 03:36 AM
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Brussels
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Found !

I found a very small adjustable buck regulator.


The one in the middle weights 1.36g. After soldering some wires and micro plugs it weights 1.96g.
I tested it with a 2s LiPo input and about 4.0V and 1.2A constant charge output for half an hour. The inductor got barely warm. Specs say it can support 1.8A continuous and 3A peak, I think they can be trusted.
I have no precise enough instruments, but I calculated 90-95% efficiency.

Buck is based on MP2307 chip.
Now I'd like to see a similar sized regulator based on TPS54628. Same footprint chip with 6A capability and globally superior specs as the MP2307. It should allow 3A continuous without any heatsink.
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Last edited by Camboui; Nov 24, 2013 at 06:58 AM. Reason: tipo error
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Old Nov 27, 2013, 11:48 PM
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United States, NC, Chapel Hill
Joined May 2013
215 Posts
Quote:
Originally Posted by Camboui View Post
I found a very small adjustable buck regulator.


The one in the middle weights 1.36g. After soldering some wires and micro plugs it weights 1.96g.
I tested it with a 2s LiPo input and about 4.0V and 1.2A constant charge output for half an hour. The inductor got barely warm. Specs say it can support 1.8A continuous and 3A peak, I think they can be trusted.
I have no precise enough instruments, but I calculated 90-95% efficiency.

Buck is based on MP2307 chip.
Now I'd like to see a similar sized regulator based on TPS54628. Same footprint chip with 6A capability and globally superior specs as the MP2307. It should allow 3A continuous without any heatsink.
I've been looking for a buck converter like the one in the middle. Can you post a link to it? Thx
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Old Dec 07, 2013, 04:48 AM
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Brussels
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You can find them on ebay.
Look for "super mini dc-dc" or "supper mini" (with the typo).
Axeprice or comelili vendors.
I checked the smaller one, it barely warms at 1.2A continuous (tested for 30min).
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