Help proofing schematic

[charybdis9]

Hey guys,

I am trying to build a circuit that runs with two 4.2V batteries in parallel with a 30A max draw that will use a momentary push button while also powering an LED. The top resistor on the page is interchangeable from .2 ohm to say .7 ohm, pulling 21A to 6A respectively, on a 510 connector. The push button is rated for 12-240V at a max 3A while the LED is rated for 1.7V at a max 700mA. I ran each area to an n type mosfet shown at the bottom. The issue I am running in to is that the program I am using is showing that the connection will not function as I had hoped. I am not sure if I am missing something, or if the program is just confused at what I am doing. Any help is greatly appreciated. Thanks guys!

[KMoffett]

Is the intent to have the LED always lighted or just when the buttoned is pressed? Either way, the LED branch should not go to the MOSFET's gate. If always lighted, have the bottom of the 3.6Ω resistor connected to the MOSFET's source. If only lighted when the button is pressed, have it connected to the MOSFET's drain.

Ken

[charybdis9]

Thanks Ken, I can't believe I missed that last night. The idea is that once the master switch is on the LED will stay lit to show power to the circuit is on. Once the push button is pressed power should flow through the 510 connector at the top supplying power to the interchangeable resistor.

I did switch the wiring over to show that the LED connection ended on the Source of the MOSFET. That is now working that the LED is lit and once the button is pressed power flows to the 510 connector, however the program now shows that No Amperage is being carried across the line that the push button is connected to. Does that seem accurate?

[KMoffett]

Only an small current flows to the gate of a MOSFET when you first push the button. This charges the small internal capacitance between the gate and source. After that no current s flows. It's just the applied voltage that maintains conduction. This is unlike a regular transistor that requires a continuous base-emitter current to maintain the transistor conduction.

Ken

[charybdis9]

Ok, Thank you again Ken. I have all the parts on order, I guess next step will be theory in to practice. I'm sure it will go great thanks to your help

[KMoffett]

I would also recommend putting a high resistance resistor, 10KΩ to 100KΩ, from gate to source. That will assure that the MOSFET turns off after the pushbutton is off.

Ken