OK, So what is a "linear current booster"? It may be an expression that
we call something different in the UK. Mind you, I didn't quite
understand what you meant by a "PV module power", either.
Now 12V 2.5A bilge pumps, no problem. I could imagine that you have a
low current analogue control signal that you want to "boost" into
something in the range 0 <-> 2.5A in order to drive the bilge pump. Not,
I would imagine, for actually pumping out bilges as on/off is normally
quite enough. I assume that you won't want to reverse it, lol?
So, if you would like to explain what your inputs are and what outputs
you want, then I may be able to help.
Although, for boats, every watt is normally precious, so I would be
using switched mode controllers rather than linear. So you are perhaps
using this bilge pump for something else.
Linear current booster or "LCB" is used in solar energy photovoltaic
applications involving direct-drive systems, that is, a PV module wired
directly to a dc motor, usualloy a pump. PV modules basically produce
full voltage at reduced current during low light conditions such as
early morning, clouds, or shading. LCBs will convert power to lower
voltage at higher current to help the pump get started or avoid stalling
out, although at a lower voltage, lower speed. At full sunlight in low
ambient temps a PV module can produce much higher than their nominal
voltage. The LCB limits the voltage to protect the pump.
Here is an example of a typical LCB:
Typical PV module IC curve:
I like to roll my own components if it's not too advanced.
Thanks for that! As I understand it, it is basically two standard
applications rolled into one. One is to produce a fixed power, low
voltage, high current output to start the pump. The other is to produce
a fixed 12 volt, up to 2.5 A constant voltage supply to run it. Both
will need protection circuitry to deal with overloads.
I couldn't get your second link to work but found this one useful:
I have a bit of a credibility gap that anyone would choose a linear
solution for this over switched mode. So I am only going to suggest
Now you could do this by using the two standard application building
blocks and having a simple change-over control circuit that switches
between the two as the voltage output of the constant current starting
circuit reaches a preset limit. However, there is a neater way:
I would suggest looking at modifying a buck-boost switch mode power
supply design. Modify in the sense of adding a simple additional
control circuit and a second output winding, with its associated energy
recovery diode and filter. It would also need some additional, simple,
control circuits to protect things, for example, if the pump stalled or
did not come up to speed quickly enough.
Can I suggest that you try google on buck boost switch mode supplies
and, in particular, go to the web sites of some of the chip
manufacturers that produce ICs aimed at buck-boost reguators? They have
many application notes that I am sure will be useful.
You can email me (leave off the invalid bit) if you want more specific
help - but a 12V 2.5A buck boost design suitable for working with your
range of input voltages is a good place to start. For the high current,
low voltage, starting current, putting an extra winding on the
transformer would have advantages. That design should be very
efficient. The output from the two controllers could simply be
paralleled, with blocking diodes. A very simple control circuit
monitoring the output voltage could be used to disable the controller
not needed at the time.
Hi, thanks for the info. Bill Kaszeta also gave some good background on
LCBs. You've got the idea. I might add there is one more application
that precedes the two you mentioned. Maximum power point tracking
(MPPT). So the LCB: 1)Finds and utilizes the MPPT on the solar module
I-V curve as solar irradiance and cell temperature vary; 2)Boosts
current and lowers voltage (or the other way around if that setting is
available); and 3)regulates voltage output to a set point.
Why the device is called "linear" I don't know, but from what I have
found out, they are a fast switching pulse width modulation device with
IC controller. Much more to it than my PV Design and Installation
Thanks for those suggestions and I will research buck boost dc-dc
transformers, manufacturers websites, and the TL494 that Bill mentioned.
A linear current booster (LCM) is a special purpose switch mode 'buck' converter
that is used in photovoltaic (PV), solar electric, systems to provide a better
match between the PV array and a motor load (or lower voltage battery).
The voltage output of a PV is relatively fixed as the level of sunshine varies.
Motors on the other hand are basically constant current devices with the
voltage varying with power and speed. The LCM acts as an automatically
adjusting dc/dc converter to convert high voltage/low current pv array
outputs (low sun conditions) to lower voltage/higher current to better operate
a dc motor.
The original circuits were built using a TL494 integrated circuit as a controller
with a feedback loop to limit the output current. A Google search on
'TL494 integrated circuit' produces several application notes on this
device and its more modern replacements. Understanding a buck
converter is a good starting place.
This same basic circuit with more modern control of the pulse width
is used with solar charge controllers and inverters that offer maximun
Photovoltaic Resources Int'l
Tempe Arizona USA
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