Hi again,
Ok thanks.
I asked about that cap because it could play a crucial role in the stability.
I was out late last night partying so im a bit overtired this morning, unfortunately. I rarely go out anymore but when i do i like to party heartily
At my second look at this circuit it seems like the main stability issue will be how the LCR output reacts with the duty cycle AND frequency of the switch. This is unlike the regular buck because with a regular buck the frequency is constant and known at all times. It appears that we might first model this as a frequency controlled switch being controlled by the input source voltage because the output load is constant. We then have to think about the aliasing between the switch frequency and the plant reaction. For some values of frequency we may not even get the right output. Although this would be rare if it even happened once for a power supply during normal operation it could mean the lights dim, which we certainly dont want. Keeping the output capacitance as low as possible would help prevent any aliasing though because the switch would have to switch too fast to interact strongly with the plant reaction, and that means it would only be able to interact mildly for sub harmonics of the plant, which would not be as bad.
This leads me to believe that it would help to simply look at the points where there is strong or mild aliasing and see what it does to the output. This is what i believe an averaged model would show us. We then might take steps to avoid the worst operating areas, if they in fact ever can happen because after all the very low output capacitance of LED's means the plant main frequency is going to be very high. I'll try to look into this more though today or tomorrow. Right now im tired out and drinking coffee
In the mean time maybe you have some more thoughts on this stability issue too. I will also draw up a more simplified schematic showing the basic operation only, without focusing on individual part peculiarities with the exception that the switch frequency will have an implied limitation on how high it can go.
BTW, it couldnt hurt to start with a time domain analysis could it? We could look at the most critical operating points that way at the least, and try to determine if those operating points could ever be reached due to the limitations on the switching frequency. Obviously there has to be limitations on that or else the MOSFET would be forced to switch too fast and that would consume too much power.
Here's a simplified schematic.
BTW, do we have to use an N channel MOSFET? We then have to assume that the output of the SR latch is higher than +Vcc .
Ok thanks.
I asked about that cap because it could play a crucial role in the stability.
I was out late last night partying so im a bit overtired this morning, unfortunately. I rarely go out anymore but when i do i like to party heartily
At my second look at this circuit it seems like the main stability issue will be how the LCR output reacts with the duty cycle AND frequency of the switch. This is unlike the regular buck because with a regular buck the frequency is constant and known at all times. It appears that we might first model this as a frequency controlled switch being controlled by the input source voltage because the output load is constant. We then have to think about the aliasing between the switch frequency and the plant reaction. For some values of frequency we may not even get the right output. Although this would be rare if it even happened once for a power supply during normal operation it could mean the lights dim, which we certainly dont want. Keeping the output capacitance as low as possible would help prevent any aliasing though because the switch would have to switch too fast to interact strongly with the plant reaction, and that means it would only be able to interact mildly for sub harmonics of the plant, which would not be as bad.
This leads me to believe that it would help to simply look at the points where there is strong or mild aliasing and see what it does to the output. This is what i believe an averaged model would show us. We then might take steps to avoid the worst operating areas, if they in fact ever can happen because after all the very low output capacitance of LED's means the plant main frequency is going to be very high. I'll try to look into this more though today or tomorrow. Right now im tired out and drinking coffee
In the mean time maybe you have some more thoughts on this stability issue too. I will also draw up a more simplified schematic showing the basic operation only, without focusing on individual part peculiarities with the exception that the switch frequency will have an implied limitation on how high it can go.
BTW, it couldnt hurt to start with a time domain analysis could it? We could look at the most critical operating points that way at the least, and try to determine if those operating points could ever be reached due to the limitations on the switching frequency. Obviously there has to be limitations on that or else the MOSFET would be forced to switch too fast and that would consume too much power.
Here's a simplified schematic.
BTW, do we have to use an N channel MOSFET? We then have to assume that the output of the SR latch is higher than +Vcc .
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