The mosfet has a Vgs MAX value of 5V. I hesitate to recommend powering the DAC with 5 volts as I think that might cause problems if the output of the DAC opamp can't swing close to +5V rail.
This is good to know and even comforting in a way. Be ready to strap those puppies on at a moments notice......(oh i have heat sinks ready).
thanks
I take this to mean that your target optimum operating point is 20V at 0.5A. That agrees with your 10W figure.open circuit voltage - 20V
short circuit current - 0.5A
hgmjr said:The mosfet has a Vgs MAX value of 5V. I hesitate to recommend powering the DAC with 5 volts as I think that might cause problems if the output of the DAC opamp can't swing close to +5V rail.
This parameter Vgs is specified in the manufacturer's data sheet for the FDA79N15 mosfet.please can you throw more light on this?
yes it helps thanks.
and i'll ground the negative side.
how do you suggest i get a voltage difference of 5V to turn on the mosfet?
Yes.does this mean that to get more resistance i would need more voltage at the gate?
If you have a 10 volt source I see no harm in that. If you power the DAC with 10 volts you might as well use +-10 volts on the opamps also.oh also so if i use a 10v reference for my DAC, will that help?
You can use a 1K or a 10K in series with the gate. It should not be too critical. The gate signal is not high frequency so pretty much anything between 1K and 10K should be good.wow, cool then . ok , do i need the 1k resistor just before the mosfet?
We are almost to that point. The schematic needs to be cleaned up and solidified.so am i guessing the rest will now be software?
I would ditch the second opamp and just connect up the DAC as shown in the manufacturer's datasheet for the unipolar configuration as a starting point. The output of the DAC opamp will then be routed to the gate of the mosfet through a 1K or 10K resistor.please what do you have to say about my connections of the DAC:
i have the LSB to MSB connected to the microcontroller , using a +15supply and now a 10V reference, then the Rfb (pin16) is connected to the 2nd op-amp (did you say i shluld put it back to the 1st op-amp?), then the out1 (pin1) to the inverting input (-) of the op-amp and out2(pin2) to the non-inverting (+) input of the op-amp? and also (not shown in diagram) a 0.1uC capacitor between Rfb (pin16) and the inverting input?
I don't have any problems at the moment in the way you connected up the microcontroller to the DAC or the measurement points in the circuit.also for the microcontroller?
Can you define what P0 and P1 represent to help us understand you algorithm?attached is a flowchart for the proposed .
i am still working on the diagram as new modifications are made.
thanks for all your help
olu
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