Dear Robert,

At 21.13 2014.01.06, Robert Dvoracek wrote:
>----------------------------------------
>> Date: Mon, 6 Jan 2014 16:04:07 +0100
>> To: piclist@mit.edu
>> From: electron2k4@infinito.it
>> Subject: [EE] Boost SMPS turn-OFF best current value
>>
>>
>> Hello,
>> I'm playing with a self-made boost converter, all the logic
>> is made via a PIC and its ADC's.
>>
>> I'd like to ask some general questions:
>>
>> in my first experiments, I was turning ON the transistor switch,
>> then monitoring the current in the inductor, then turn OFF the
>> transistor till the current reached 0, and again in a loop.
>>
>> My aim is to get the most possible power out of the power supply.
>>
>> Now I think that if I turn OFF the transistor earlier, say 100mA
>> below the "OFF" threshold (maximum current), instead of reaching
>> 0, then the average current will be higher, and I will get more
>> power from the circuit.
>>
>> Is my reasoning correct?
>
>Yes.  If you view the current waveform of a properly designed bucking=20
>LED driver, you will see the current rising and falling, but never=20
>reaching zero.  Although it does not use a microcontroller, the=20
>Velleman K8071 is a good example.

Thanks, I will take a look into its datasheet, just for inspiration.


>> What is the criteria to choose the inductor? As my PIC-based
>> circuit is relatively slow, I noticed that only inductors around
>> 10mH work, whatever has a smaller inductance probably charges
>> and discharges too quickly to work.
>>
>> So the best inductor I should choose is the one that has (of
>> course) the least possible resistance, but an high enough
>> inductance to let my slow PIC work correctly?
>>
>> No other recommendations?
>>
>> For example, don't inductors have a maximum voltage rating?
>
>Since an inductor is just a coil of wire, there is usually only=20
>current to worry about.  The only time you have to worry about voltage=20
>is if something is near enough to the coil and is at such a different=20
>potential that the insulation might be punctured.  Most of the time=20
>this is a non-issue.  Just stay below the current rating of whatever=20
>gauge wire the inductor is wound with and you will be fine. 			   		 =20

But what if I use the inductor to generate very high voltages (e.g.
to charge a capacitor to 1000V): will any inductor withstand the voltage
that it will be "asked" to generate, or can it breakdown to itself?

If this is possible, are inductors rated for maximum voltage? Because
the ones that I saw weren't, however for some extreme boost applications
it may be needed.

Cheers,
Mario


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