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I am a new member and have found lots of useful information on this forum whilst learning about electronics.

I am wondering if I connect a low voltage high current source to a high voltage low current source, if I might get a high voltage source that could use the current from the low voltage high current source.

I have previously joined similar low voltages through two independent bridge rectifiers and then placed them in series across a filtering capacitor which I could manipulate to a higher voltage (x2 volts) out or a higher current out (volts x 1). This worked well. But before I try combining a high voltage such as say 500VDC at 100ma with a low voltage say 1VDC at say 50amps, I would like an expert opinion of the possible outcome, given that each supply will be isolated.

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  • \$\begingroup\$ Not at DC, you can combine AC signals, but the relative impedances need to be within an order of magnitude or two. \$\endgroup\$ – George Herold Jul 25 '14 at 0:28
  • \$\begingroup\$ After taking into account the limitations, you would probably succeed in making a low voltage, low current source :^) \$\endgroup\$ – gbarry Jul 25 '14 at 1:28
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What you are proposing is not feasible based on power considerations. To use your example, a 500 VDC source at 100 ma can provide a maximum of 50 watts. A 1 VDC source at 50 amps can also provide a maximum of 50 watts. Let's say you could somehow borrow 1 amp from the 1 VDC source and give it to the 500 VDC source. Now you would have a 500 VDC source providing 1.1 amps or 550 watts from 2 sources that are limited to a total of only 100 watts.

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You can in theory combine the two sources to provide a single output with an output power equal to the sum of the power available from each of the sources, minus conversion losses and overhead.

You would have to use a switching converter to step up the low voltage source to a higher voltage, and a load sensing and balancing circuit to ensure sharing.

So you could get 500V at less than 200mA from 500V @ 100mA and 1V @ 50A. (The 1V to 500V conversion would be fairly inefficient.)

But as Barry noted you can't just create power or energy where it doesn't exist.

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  • \$\begingroup\$ Can you give an example of load sensing and balancing circuit? Just curious... The OP's thought process might be flawed but I think a more comprehensive answer could still be useful to those who are interested in energy harvesting, where power generation from multiple sources may be presented at different V/A. \$\endgroup\$ – Jarrod Christman Jul 25 '14 at 2:26
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    \$\begingroup\$ @JarrodChristman Sure, there are a lot of ways to accomplish it, from a simple droop resistor and diode-or circuit to an active load sharing circuit that senses the current in a sense resistor on each source and adjusts the voltage to maintain sharing: ti.com/lit/ds/symlink/lm5080.pdf \$\endgroup\$ – John D Jul 25 '14 at 14:48
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You can do exactly what you describe, but not with the results you expect.

You could connect the two sources to a common supply bus, isolated from each other by a pair of diodes. The higher voltage source would dominate, providing high voltage to the bus. If your load draws more current than the high-voltage source, the high voltage will droop further and further until its voltage equals that of the low-voltage source. At that point, the much higher current capacity of the lower-voltage source would dominate, preventing much lower droop on the bus.

If you graphed voltage versus loading on this bus, you'd see a very abrupt elbow at the low-voltage source's voltage.

You should be aware that this approach would be pretty brutal to the higher-voltage source.

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