| Electronics > Beginners |
| Operational Amplifier driving MOSFET |
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| Ian.M:
You can do it either way. Before I talked you into adding the 1N4007 diode, an inductive load would have killed the LED at turnoff if you left it in parallel to the load. I've got a mild preference for moving it to the output of the first stage OPAMP as if your load shorts and the MOSFET dies, the LED should still work (the OPAMP will survive a MOSFET failure as the 1K5 gate resistor will limit the current to under 10mA, well within the OPAMPs ratings no matter how the MOSFET shorts out as it dies or blows apart), telling you the failure to command the load is either a load problem or a blown MOSFET. If you aren't going to volume production, you may want to add a second LED on the board on the first stage OPAMP output instead of moving it as if the two LEDs don't match you know you've killed the MOSFET and its also handy for setting it up before you wire everything up as all you need to do is hook up power and the ORP 12 to test the board or set the threshold. How are you doing on rearranging the board to shorten the high current traces? One thing I forgot to mention - a fuse in the DC input would be a good idea. It wont be fast enough to save the MOSFET, unless you vastly over-spec the MOSFET, but will prevent a high current short burning traces off the board, keeping it easily repairable. |
| mike_mike:
I am sorry for the delayed response. I attached the updated schematic and layout. I tried to do my best, but I am not sure if I made them correct. All traces are 1.5mm wide. Please have a look and tell me if the schematic and layout are ok. |
| mike_mike:
I am attaching a new layout. I am not sure if I made it correctly. I tried to respect the instructions. I elongated the pads to make sure that will be enough copper on the board. I will make the PCB using transfer toner method. I tried to make the power traces shorter but I don't know if they are short enough. I arranged the power traces on the top of the PCB. The power traces width is 2mm and the rest of the traces are 1.5mm. Please have a look at the schematic and at the layout and tell me if they are ok. |
| mike_mike:
@Ian.M Are you still there ? Can you please respond ? |
| Zero999:
--- Quote from: mike_mike on May 01, 2018, 09:27:24 am ---@Ian.M Are you still there ? Can you please respond ? --- End quote --- People do have other things to do, than post here you know. If no one responds within a day or two, fair enough bump the thread, but you only waited a few hours, which demonstrates lack of patience. The last layout looks better than the others, but I haven't looked in great detail. |
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