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Okay so here's the deal I am using these items in parallel to power one load in order to supply enough current (3A max) at a constant 5V. I won't get into detail about why exactly I'm using 12v-8v-5v but during the summer in Texas ambient temperatures average at 35*C which does awful things to large metal clips that are supposed to be heat sinks, so it's best to dissipate heat this way than strait up 12v-5v 1.5A. Additionally I don't need help with heat dissipation, with preferential circuit design, or with buck converters. I would only like advice on how I am supposed to put these two 5v 1.5A supplies in line with either diodes or another method while keeping the 5v status. Since diodes have a voltage drop and I need a constant 5v continuous it will be a hassle to use those unless you can explain how to tie them in. Please provide the solution's part number and datasheet to your answer. The bottom half is not labeled as it is a replicated circuit of the top half.

Thank you for your time :)


closed as unclear what you're asking by tcrosley, pjc50, nidhin, PeterJ, Daniel Grillo Apr 23 '15 at 10:47

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ I don't understand the title of your post, "My Circuit is leaking voltage. What diodes\methods can I use to fix this problem". What is your actual problem that needs fixing? \$\endgroup\$ – tcrosley Apr 23 '15 at 8:03
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    \$\begingroup\$ @Darksun96 your question is meaningless - volts don't leak; current leaks. Also, do you have a proper circuit diagram and not some cartoon. \$\endgroup\$ – Andy aka Apr 23 '15 at 8:19
  • \$\begingroup\$ This is basically from what I can tell asking the same question or at least will have the same answers as this EE.SE question: electronics.stackexchange.com/questions/12801/… \$\endgroup\$ – Tom Carpenter Apr 23 '15 at 12:39

You can run multiple 780x style voltage regulators in parallel if you - as you've suggested - connect their outputs via a diode.

The voltage drop across the diode will reduce the total output voltage. Fortunately you can compensate for this drop by adding another diode into the ground path of the voltage translator like this: Schematic of two 7805 in parallel

The total output voltage will now be close to 5V again.

For the choice of the diodes I would pick some beefy Schottky diodes like the 1N5820 or the SB330. These can pass a continuous current of 3 Ampere, so you're on the safe side. The choice isn't critical though, any Schottky with enough current capability will be fine.

  • \$\begingroup\$ Exactly what i was looking for much appreciated \$\endgroup\$ – Darksun96 Apr 23 '15 at 8:42
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    \$\begingroup\$ One more thing: If you drive anything inductive like a motor or so: Do yourself a favor and connect another diode in blocking direction from pin 1 to 3 (e.g. diode does not pass current in normal operation). Inductive loads tend to generate a lot of voltage on their own if they're turned off, and the 780x regulators don't like that at all. A simple 20 cent diode would fix this problem. \$\endgroup\$ – Nils Pipenbrinck Apr 23 '15 at 8:46
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    \$\begingroup\$ @Darksun96 by the way, is there a reason why you're using 780x regulators? If you already have heat problems you should seriously consider using a 5V step down converter. These are much more efficient. \$\endgroup\$ – Nils Pipenbrinck Apr 23 '15 at 9:21
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    \$\begingroup\$ There is a flaw with this which is that is one of the regulators is generating a slightly higher voltage than the other, all that will happen is that one will pull the output voltage up causing less current to flow through the other regulator. This sort of inbalance in a high-current circuit will lead to one of the heating up more than the other. \$\endgroup\$ – Tom Carpenter Apr 23 '15 at 12:35
  • \$\begingroup\$ The second answer of this EE.SE question shows the way to wire up an external transistor to avoid the balancing problem - I believe the diagram is straight from the manufacturers datasheet. electronics.stackexchange.com/questions/12801/… \$\endgroup\$ – Tom Carpenter Apr 23 '15 at 12:40

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