555s require a different circuit if you want to adjust between 0 - 50% DC.Ok so I will try 10Khz, 50Khz, and 100Khz.
Bill, being the resident 555 expert, what is the best way to get as close to 0% duty cycle and as close to 100% duty cycle as possible with one pot and without changing the base frequency too much? Digipots are made in a wide range and I will be using one of those.
or perhaps something besides a 555?
So 5v on CMOS 555, 5v on comparator, 5v on complimentary transistors (what should I use for these?)Your 555 must use a 12V supply so that the gate voltage is +10V.
If you use the 555 plus a comparator and complementary transistors then they should also have a 12V supply.
If you use logic-level Mosfets then the 555 with a 5V supply will have a max voltage of only 3.5V which is too low to properly drive a logic-level Mosfet.
The 555 plus comparator plus complementary transistors all using a 5V supply will drive a logic-level Mosfet pretty well.
The gate resistor for a Mosfet is 10 ohms to 100 ohms and stops the Mosfet from ringing or oscillating at a VHF frequency. The resistor must be at the gate pin so that there is very low inductance in series with the gate.
The complementary transistors are emitter-followers that do not have voltage gain. The 5V p-p from the comparator will produce a high of 4.3V and a low of 0.8V at the output of the transistors.So 5v on CMOS 555, 5v on comparator, 5v on complimentary transistors (what should I use for these?)
Will the 5v comparator not switch a 12v signal on the complimentary transistors?
Yes, if you use a logic-level Mosfet.So 5V for everything though should work well?
DO NOT use darlington transistors. A 2N3904 is the NPN and a 2N3906 is the PNP.Darlington for the top one and a small signal one for the bottom one?
Simply look at its datasheet. The IRF510 is an old ordinary Mosfet with poor performance. It is not logic level because it is spec'd with a gate voltage of 10V. Some might turn on a little with a gate voltage of 5V.I got Bill's circuit completed and everything works good up until the complimentary transistors. I tried a 10k pullup and a 1k pullup. I also used a 100 ohm and a 22 ohm gate resistor. Not sure whats wrong. Oh and I'm using an IRF510 which apparently is logic level. I even tested this and it had turned on by 5v. Any ideas?
Is the Gate to Threshold Voltage not the spec I need to look at?Simply look at its datasheet. The IRF510 is an old ordinary Mosfet with poor performance. It is not logic level because it is spec'd with a gate voltage of 10V. Some might turn on a little with a gate voltage of 5V.