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  1. G

    2 5V power source for a circuit

    I took the easy way out and simply placed 2 schottky diodes on the 2 voltage sources to prevent any back flow of current. It seems to work, except my voltages are down to ~4.75-4.85V. My device has a 5V tolerance of +/-5%, which puts me on a borderline case. I'm wondering if there are any low...
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    2 5V power source for a circuit

    bump?
  3. G

    2 5V power source for a circuit

    Sorry, that was what I meant by positive or negative polarity. Positive meaning the center pin is positive and negative meaning otherwise. It seems that most AC adapters out there have positive center pins.
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    2 5V power source for a circuit

    What about AC adapters with 3 pin plugs? Is the DC ground still isolated from the AC wall socket? Anyway, does it even matter? Will breaking the GND on the USB side cause it not to supply power to the circuit? Coz I did some googling and it seems that positive polarity AC adapters are a lot more...
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    2 5V power source for a circuit

    Hmm, I thought the adapters are pretty much standard. Is one more prevalent than the other? Also, I don't think switching the GND would work right? Since the USB ground is from the PC, which is from the wall socket, which is where the AC adapter GND is from too, so they sorta share a common GND.
  6. G

    2 5V power source for a circuit

    OK, so I tested 2 of the enclosures I have here that have DC jacks. They all have 3 pins, so I assume they're switched jack. I found 2 of the pins that are shorted with a multimeter, and then I plugged in the DC jack(unconnected to the mains of course) and tested for continuity on those 2 pins...
  7. G

    2 5V power source for a circuit

    OK, in that case pin 1 has to be Vcc then. I'll pull out my multimeter tomorrow, test it out, and report back! Thanks! :)
  8. G

    2 5V power source for a circuit

    Makes sense. I assume pin 1 is Vcc and pins 2 and 3 are GND? Hence the USB Vcc is actually shorted with the DC jack Vcc but the USB GND is disconnected from DC/system GND when a DC plug is inserted, hence disallowing power delivery from the USB connector?
  9. G

    2 5V power source for a circuit

    OK, that schematic looks like most I can find on DC jacks. How exactly does the switch work? I thought pins 3 and 2 are just shorted together.
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    2 5V power source for a circuit

    As far as I can tell, there's no switch. The circuitry for these cheap enclosures are pretty simple, and the PCB is small with very few components. What would happen when they are shorted? Worst case, would something blow up? Also, how's this for a solution? I'm thinking of either 2 FETs or...
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    2 5V power source for a circuit

    Hi, I'm wondering if it's possible for a circuit to have 2 different power sources for 5V? I've seen many USB bus powered drives that normally use the USB 5V voltage to power the drive, but they often also have a DC jack. All of the ones that I've seen have both the Vusb and the Vdcjack...
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    Help me choose a mosfet

    Thanks, but due to the existing design I have to use a P channel transistor. Is a low RDS and Vth all that I should be looking at? I guess I just need to know some guidelines on what parameters are important when choosing a transistor. I might even go for a PNP BJT since they seem to be more...
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    Help me choose a mosfet

    Hi, I have an application where I have to switch on/off 2 3.3V low power devices(~50mA max combined) with a 3.3V MCU signal. I am currently using a TP0610K that I have lying around with the following connections. Source - 3.3V Gate - 50K pullup to 3.3V, and MCU control signal Drain - 1M pulldown...
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