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looking for a good buck boost converter

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neilxavier

New Member
we are designing a battery charger from a solar panel. we have a power path battery charger which requires an input voltage of about 5V.

in this case, we need a buck boost converter with min Vin of maybe 0.3-0.8 and max Vin of maybe 6V (since that is the highest voltage our flexi solar panel can generate).

Maybe you have encountered a buck boost with these specs. Again here it is:
Vin (min) = 0.3- 0.8
Vin (max) = 6V
Vout = any range that would include 5V.

Your help will be very much appreciated. thanks in advance.
 

hotwaterwizard

Active Member
Are you looking to make your own?
What wattage do you need?
Less than 1 volt could be tuff,
 

mneary

New Member
Do you expect to receive substantial power at inputs below 1.0 volts? Or is 0.3V what you receive when it's almost dark?
 

neilxavier

New Member
Do you expect to receive substantial power at inputs below 1.0 volts? Or is 0.3V what you receive when it's almost dark?
yes. Its what we expect to receive when its almost dark. we just want to have the converter working (meaning running) with that amount of voltage.

do you think we dont need the power generated at inputs below 1.0V?

and in addition, we need the converter that can poower maybe up to 1A.

thanks again.
 

mneary

New Member
The power generated when it is almost dark is probably not useful.

[edit] Half of this thread is in another forum. This is very annoying. [/edit]
 
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Russell_McMahon

New Member
re Looking for a good buck boost converter

A 6 volt PV panel will provide negligible energy below 1 volt.
You should do some simple load tests to convince yourself that this is true.
And also - you should have datasheets for the panel and/or you can look at generic datasheets.

If you MUST go to such a low input voltage then something like an NCP1450 may suit your need. This is a bit inflexible but can be used with some thought. Use the 5V version for minimum work - or a lower voltage version with some voltage division on Vdd. See datasheet to see what I mean.
eg http://www.electro-tech-online.com/custompdfs/2009/07/NCP1450-DPDF.pdf
The external transistor can be sized to suit your application.
This device is boost only as shown. You could use a lower voltage PV panel eg 4V max.

If you use this IC to drive a SEPIC converter you can achieve buck-boost. Control may be 'interesting'.

regards

Russell McMahon
 

Russell_McMahon

New Member
It's the current sourcing that drops off with illumination, not the voltage. The max power point is set by the cell diodes, times the number of series stacked cells.
What you say about current/voltage/illumination is essentially true in "normal use" - But he is proposing an extreme example. Voltage falls somewhat with illumination but PV cells tend to act as current sources with the current roughly proportional to the illumination level. For a wide range of illuminations a loaded silicon cell will provide slightly more than 0.5 Volt per cell. That means a 6V nominal panel will require at least 12 cells, and it is usual for a serious 6V panel to use up to 18 cells. (Typical "12 volt" solar panels in the say 10W to 250 W range often have 36 cells).

However, if he has a 6V at full load panel then for it to be producing only 1 V (as requested) the illumination levels will be close to zero. It is extremely unusual in 'real world' applications to expect a 6V panel to deliver useful power at 1V.

One use for very low level output is to drive "turn off on sun" circuitry. eg in solar path lights or similar which provide lighting at night and then turn off the light automatically as soon as a mere smidgeon of light appears. At that stage a 6V nominal panel may be making only 1 Volt but the power level is about zero. I use this feature in this product which I designed: advertising deleted - moderator This allows it to be optionally used as a "street light" or to be left on until it runs flat and then start charging when there is enough light.


Russell McMahon
 
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RCinFLA

Well-Known Member
Yes, with a very cheap cells like amorphic, RadioShack specials, the Rp can be very low. This means the Rp becomes the dominate factor at low lillumination levels.
 
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