| Electronics > Beginners |
| Operational Amplifier driving MOSFET |
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| mike_mike:
Thanks for the reply @Hero999. I am sorry for bothering you and @Ian.M with my questions. Have you looked at the schematic ? It is OK ? |
| Zero999:
--- Quote from: mike_mike on May 01, 2018, 10:23:37 am ---Thanks for the reply @Hero999. I am sorry for bothering you and @Ian.M with my questions. Have you looked at the schematic ? It is OK ? --- End quote --- I don't mind the questions, as long as you don't forget that people are not being paid for the advice they give. The schematic would be better if J9 and R8 were switched by the MOSFET, rather than being connected to the op-amp's output. |
| Ian.M:
Use a Polyfuse, they are much more compact, and self-reset when the power is switched off for a few minutes. @Hero999: the whole point of the second LED connected to the first stage OPAMP output is it should *ALWAYS* match the one switched by the MOSFET. If it doesn't it means the MOSFET's blown - which is difficult to avoid in such a simple circuit if its output is shorted, without incurring excessive losses or complexity protecting the MOSFET, so its useful to have an indication that there is a fault. |
| mike_mike:
Thanks for the reply. I think I will use for the moment a 5x20 mm fuse which I can find at the local electronics store. It is ok now to make the pcb, or there are any other modifications that I should do ? |
| Ian.M:
Looks reasonable. I'm sure I could tidy it up a bit 'hands on', and I'd probably use a ground plane, if not for the whole board, at least for the small signal stuff from a line across the board between J1 and J6 downwards, but its not worth the time to try to talk you through the changes, as you aren't PWMing anything so it isn't going to radiate significant EMI. Worst case it may flash a bit if you get a cellphone too close to it! If you've checked the high current trace widths and copper thickness are adequate with the calculator Hero999 linked in Reply #43, it passes the schematic package ERC and DRC, and you have sorted out how you will mount it without mounting holes, then go for it. I've seen worse in commercial products! |
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