Simply to give a specific time delay, one NOP takes one instruction cycle, if it only need a fairly small delay it's often easier to use a number of NOP's rather than bothering writing a loop.

In fact my IR tutorial uses a number of NOP's for the 40KHz generation, but only with a 4MHz crystal, with a 20MHz crystal I switch to a loop instead.

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PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

Thanks for your explanation regarding NOP.

Would like to ask you about the using the PWM from my PIC microcontroller to control my boost DC/DC Converter. You mention before about adjusting the duty cycle of the PWM to avoid overcharge of the 12V battery. Initially, I was thinking to step-up the voltage to a level to 15V from 7.5V. Instead of stepping it up with a duty ratio of 50%, can I just step the voltage level of 7.5V to 13.5V to avoid overcharge? What are the consequences that I might face if I were to do this?

Thanks in advance.

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Yes, you can step it up as you like, it's up to you what value you choose. As I suggested before, you should look at the PICKit1 details, it generates 13V off a 5V USB supply, using the PIC A2D for feedback regulation.

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PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

Thanks.

ops: Sorry, forgotten about this "reading material". Will read it now...

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This absolutely will not work, because your output goes to a battery and you start from a solar cell. Either one of these components makes voltage feedback impractical.

The PWM feedback will be set up so you increase the duty if the voltage is too low and vice versa. What's going to happen is when you put a half-discharged battery on it, and your circuit has enough sun that it should be capable of a lot of current with optimum PWM freq, look at what happens. The battery voltage will rise to 12.6 volts, the PWM will increase and miss the maximum power point totally, and as it increases duty the output gets worse, not better! Your solar cell will see a short for a load and there is no charging current.

This type of circuit always has to use delta adjustments to find the max power point. The weird part is you don't know if your duty cycle is too high or too low by looking at the output. You just have to tweak the duty cycle in small increments one way or the other and see if it makes the output greater or lower. Now you can "sort of" use voltage feedback for this, but the problem is it's a lot slower to respond, whereas changes in current are much faster.

You can still use a voltage divider to read the battery voltage to sense overcharge, and cut back the current or shut off when it happens. But really, this isn't necessary with your setup at all.

 

Just to reconfirm, so, you're saying that I shouldn't tap a feedback from the battery to control the PWM signal? And have a fix PWM signal?

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A fixed PWM period will do a poor job of tracking the mpp of the solar cell. It'll work so-so, your system is low on power already so it may be close to nonfunctional if you lower performance any more.

You can use the battery voltage to shutoff the source to prevent overcharge, but it is not as useful as measuring current in order to provide PWM feedback to track the mpp.

 

Will the following incease the efficiency of the DC/DC converter?

I have a PWM signal that varies according to the voltage output at the solar panel instead of according to the 12V battery.

Meaning, example:
If the output voltage of the solar panel is 7.5V, I will step-up to 13.5V.
If the output voltage of the solar panel is 8.5V, I will step-up to 13.5V.

In the second case, where I step up the voltage level of 8.5V to 13.5V, meaning, I step-up lesser. Does this mean that I will obtain a higher value of current at the output of the converter? Is this known as increasing the efficiency of the DC/DC converter? Meaning, I'm close to the max. power point?

By the way, do you mind suggesting what should I do to enhance my DC/DC converter if as mentioned above is wrong?

Thanks in advance...

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Lord Robert Stephenson Smith Baden Powell\'s last message : -BE PREPARED-

 

That's varying the PWM based on the output voltage, keeping it constant as the input voltage changes - not based on the input voltage.

As you probably have gathered by now, it's a very complex subject, I suspect you may need to do considerable experimentation to try and get optimum power from your solar panel.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

Thank you very much for all the guidance...

At this moment, I'll do some reading about obtaining mpp from my panel and complete my PWM signal PIC code.

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The other thing is the PWM freq could probably be adjusted by solar cell voltage too, though this may seem odd. The mpp voltage changes somewhat with different light levels, but not a whole lot.

As you may have noticed, if the solar cell voltage is high, you're not loading it enough to take all the power it can give, and if it's low, you're taking too much current and the voltage suffers badly. So you know if you hit the mpp voltage, you're in the area of optimum load. It seems to me it won't accomodate the efficiency issues in the boost converter itself so it won't be as good as current feedback at the load.

 

Would like reconfirm with about the above statement. It seems that it would be a lot easier for me to tap the output voltage of the solar panel for me to determine the duty ratio of my PWM signal. Are you saying that it is sufficient to perform such feedback to manipulate my PWM signal?

Thanks in advance...

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