The caps are just what I had, and only trying to test a concept. Disregard the cap voltage rating and charge capacity for the moment. What I'm after is effeciently bypassing series caps that have reached a certain target voltage, as well as info on why the caps at the end of the string seems to hold greater V than the caps at beginning of the string.Why are you bothering to charge 50V capacitors to only 3V and what will you do with the tiny amount of charge?
The voltage source stays constant, and the resistor stays constant, so wouldn't the current through R be constant? In series, how does the current increase? Shouldn't it be the same through all series components?The symbol for your battery has its polarity backwards. The long bar is the (+) terminal.
It looks like the current increases as each capacitor is bypassed because you have a resistor instead of a constant current source so of course the last LED is brighter.
I tried zener's but they just avalanched at their rated voltage and seemed to be turned on constantly (so cap bled to 0), whereas the LEDs wouldn't turn on until their Vf was met (cap bled to 2.8V-ish fast and then slowly to 0, maybe over a day).To charge each capacitor in a series string to a similar voltage the very simple way is to put similar resistors across each one. Not at all efficient, but sort of effective. It is routinely used in high voltage power supplies. Substituting a non-linear device like a zener diode can hold the charge to some value. Or use a gas-discharge tube to hold a specific voltage. Beyond that it gets fairly complex, similar to the mechanisms used to keep equal voltages in electric car battery packs. Researching those schemes will show how it is done.
EditThe voltage source stays constant, and the resistor stays constant, so wouldn't the current through R be constant? In series, how does the current increase? Shouldn't it be the same through all series components?
I anticipated seeing equal V on each cap. I thought it odd the uneven distribution. I switched LEDs around and was still seeing same V distribution (increasing). I guess I could try switching MOSFETs around too to see if the distribution seems to follow a particular component or not. Perhaps it is just a variation from component to component, but do you know that for sure? I'm just trying to double check with some people to make sure that there isn't some sort of anticipated uneven V distribution in the cct design except for minute component to component variation.Your parallel caps are 141uf- the current consumed by your voltmeter and circuit leakage discharges them rapidly while you measure.
Try much larger caps to prevent insanity in measurement.
The voltages you are reading vary less than 300 mV, the part-to-part variation of Vgs and the LED drops are to blame- what are you expecting to see?
More importantly, what are you REALLY trying to accomplish?
I'm going to try to increase regulation to 4.5V (18V source instead of 9V), or 3 LEDs per cap, but in an attempt to increase gate V of MOSFET so it can turn on harder. If I'm creating a low enough R pathway with MOSFET S to D, then I should be shorting the LEDs? Or some sort of oscillation maybe between MOSFET short and LED bypass?I calculate an equivalent capacitance of 47μF, is that correct? Is each 3 parallel cap bank only holding 47/3μF, or 15.67μF?
I wonder if I had my Zener's flipped. I'm going to try them again. Also looking into transistors.One more consideration is that as the voltage across each cap increases, the rising gate bias tends to decrease the effective resistance of the FET. That is functionally a negative resistance, and so it is possible that the circuit is unstable. (How this post returned after my tab crashed yesterday is unclear.)
There is a quite different set of harmonics produced between the two kinds of control. In addition the control circuits are quite different, quite often phase control is simpler. So the amount and type of filtering is very different between the two kinds of control. In addition there is the consideration of response time, since phase control can only change once per cycle, while PWM can be adjusted every pulse, which is much faster with normal PWM systems.Why can't you PWM a full bridge with a power MOSFET? Is phase angle control more effecient? Zero point switching only has to turn components on twice per period, while PWM-ing a full bridge output would require a higher freq of switching compared to diac+triac, which in turn draws more power?
Which is generally more effecient?
Phase angle control + full bridge
Full bridge + PWM MOSFET
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by Jake Hertz
by Luke James
by Luke James