| Electronics > Beginners |
| Input protection and power feed |
| (1/1) |
| rrinker:
There's nothing really magic or critical about my circuit, it is just a micro with some pushbutton inputs, driving a couple of RC servos and relays. It's been a while, but I did post the original circuit for critique quite some time ago, and implemented the suggestions in my schematic. As it stands, it actually works just fine built on a breadboard - WITHOUT any of the attached power protection and bypass caps, other than the ones directly on the leads of the micro. The main difference is, on the breadboard, it is running off my lab power supply. "In the wild" I plan to use a higher voltage power bus, and tap off for each instance of the circuit using one of those small LM2596 modules. I've chosen this approach because the area that will have these circuits (a large model railway) is already too large to use just one master power supply, the voltage drop even with fairly heavy wire would be too much, so rather than try to distribute 5 volts, I feel it would be better to distribute a higher voltage that I can tap off for multiple uses. Plus if I use say 12 volts, and at the furthest distance from a given power supply, the voltage has fallen to 11 volts, I can still get a solid 5.5 or so from the buck converter. The reason I did what I did here - the MOSFET is for reverse protection. Do i need it? Well, I'm the only one using and wiring this circuit. It's to protect myself from being an idiot, mostly - no one else will be using this. I then have the capacitor to smooth out transients caused by the servo motors, which are fairly high current draw (relative to the rest of the circuit - worst case I have gotten is a bit over 1 amp total, with the servo stalled, which will quickly burn it out). So there is the tap off for the servo power lead. The diode is to prevent the surge to the servos from draining the bypass on the micro side and causing a voltage drop. Option 1 - what I originally designed for, was to put the buck converter off board, and since the servos are rated for up to 6 volts, set it a bit above 5 volts to compensate for the diode drop. Option 1A would be to make a footprint and put the buck on the main board - just needs 4 pin headers to mount it - and put the MOSFET in front of it to protect the buck. Option 2 would be to use 2 buck converters, either on or off the board, one supplying the servos and one supplying the rest. An additional thought - should I also use the servo power as the source for the relays? There are 4 relays, transistor driver with a suppression diode on each one. As I said, on a breadboard it works without any of this stuff, but I'd rather follow best design practices where practical. And I want to get it right, this will be the most complex PCB I have done and want to try to make it right. I need to build dozens of this circuit. And I have another that accompanies this, but I want to get one finished before starting the next. |
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