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| N-channel Mosfets in a charge pump, replacing diodes |
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| Buriedcode:
--- Quote from: TheBaconWizard on June 22, 2018, 05:37:30 pm ---Ah, no, the present arrangement clips the supply to the Zener voltage even if Vcc varies (within reason) because anything over that value is shunted by the Zener, with the resistor bearing the brunt of the current (protects the Zener) However, switching speed is of concern, and i’m certain I can find diodes that will easily handle the current without any issues, so perhaps your way is better, which would give a voltage of Vcc - Zener voltage --- End quote --- Perhaps I am misunderstanding you here, but your "present configuration" sets a maximum voltage on the MOSFET gate with respect to ground. This would be understandable for an N-channel MOSFET with its source connected to ground, but it isn't - its an N- channel MOSFET with an unknown source voltage. If you are hoping to replace the diodes with MOSFETs to reduce to forward voltage, then it would be better to use P-channel MOSFETs with a zener from gate to source, and a resistor to ground. This puts a limit on the gate-source (Vgs) voltage, which is what turns on the transistor (negative for P channel, positive for N channel). I mean no offence, but you seem to have misunderstood how transistors and MOSFET's work, and charge pumps for that matter, but so did I at first. Having LTspice is very handy, you can simulate almost anything and trust (within reason..you can get weird results sometimes as it deals with "ideal" components) but I would advise you to play about with MOSFET's and transistors on their own in LTspice, see how they work. Google and this forum can answer any questions and fill in any blanks. Also, for charge pumps, google charge pump IC's - often they will have in internal diagram, perhaps not at the transistor level, but often more detailed than a block diagram. |
| exe:
Just noticed you don't have part numbers set. In my experience with LTSpice this is not going to work and simulation will have nothing in common with reality. So, if it's diode, it needs to be set to something (e.h., 1N4007). If it's a mosfet, set it to, e.g., irfz44n or whatever you are going to use. Otherwise it will use some default models that are completely wrong. Bear in mind any simulator has limits. This one will not warn you if you, e.g., exceed voltage/current ratings on components (but it can show TDP). It also cannot produce correct results if you connect components wrong (like swapping in and out on a voltage regulator) because models have their own limits. |
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