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Old 11-26-2010, 06:31 AM
b2386 b2386 is offline
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Default Can two bridge rectifiers with varying voltages be connected in parallel?

I have two different AC voltage sources that produce randomly varying AC voltages from 2-3 volts (not necessarily in unison). I have a basic bridge rectifier circuit connected to each voltage source. Assuming no voltage drop across the bridge rectifiers, I will have two DC voltage outputs varying from 2-3 volts. Can I put these two DC voltages in parallel?
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Old 11-26-2010, 03:30 PM
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Why would you assume no voltage drop across the bridge rectifiers?

You should most DEFINITELY count on voltage drop, especially at such small voltages.

You are going to lose 1.4 or more volts across each bridge.

As for paralleling 2 different voltages, no you can't. They will fight.

You might consider a summing amplifier to add the two voltages together.

You really need to get the current into the equation. That will affect the voltage drop across the bridges also.

You may need to sum them to get a usable voltage.
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Old 11-26-2010, 03:57 PM
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How much current are you expecting from your AC voltage sources?

To minimize the voltage drop across the bridge, consider using Schottky diodes rated for the expected current. For even less voltage drop, consider synchronous rectification, where MOSFETs are used as "ideal diodes".

If you connect the two outputs in parallel, you will likely have problems. If you connect them in series, you will be OK.
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Old 11-26-2010, 04:43 PM
b2386 b2386 is offline
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lol, the reason I said assume no voltage drop was only because it's effect was not really relevant to my original question of could these two DC voltages be connected in parallel. I am using schottky diodes so the actual voltage drop will be around 0.5V in total.
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Old 11-26-2010, 04:45 PM
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So are you set? Or did you need further clarification?
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Old 11-26-2010, 05:40 PM
b2386 b2386 is offline
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I think I got it. If I put two or more of these rectifiers in parallel, the smoothing capacitors of each rectifier will be in parallel and at any given time, the capacitors at a higher voltage will begin charging the capacitors at a lower voltage. I am assuming this is not what I want.

On a side note, let's say I have ten of these AC voltage sources described in my previous post. They have random phases so summing before rectification is not really an option. What are my options for getting a 3V DC output voltage from this entire system? I can't use transistors...
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Old 11-26-2010, 07:49 PM
tom66 tom66 is offline
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What will happen is the AC input with a higher voltage will provide almost all of the current; it will effectively choose the maximum between two sets of voltages. See image. The two demo waveforms are 45 degrees out of phase.

Code:
$ 1 5.0E-6 10.20027730826997 53 5.0 50
d 464 240 528 176 1 0.805904783
d 400 176 464 112 1 0.805904783
d 400 384 464 320 1 0.805904783
d 464 448 528 384 1 0.805904783
w 464 288 576 288 0
w 576 80 464 80 0
w 464 80 464 112 0
g 464 240 464 256 0
w 576 288 576 80 0
d 464 240 400 176 1 0.805904783
d 528 176 464 112 1 0.805904783
d 464 448 400 384 1 0.805904783
d 528 384 464 320 1 0.805904783
w 464 320 464 288 0
g 464 448 464 464 0
w 528 384 560 384 0
w 400 384 368 384 0
w 368 384 368 512 0
w 560 384 560 512 0
v 368 512 560 512 0 1 40.0 5.0 0.0 0.0 0.5
w 576 288 656 288 0
r 656 288 656 368 0 100.0
g 656 368 656 384 0
v 368 48 560 48 0 1 40.0 5.0 0.0 0.7853981633974483 0.5
w 560 48 560 176 0
w 368 48 368 176 0
w 368 176 400 176 0
w 528 176 560 176 0
o 20 64 0 34 5.0 0.025 0 -1
o 23 64 0 35 10.0 0.05 1 -1
o 19 64 0 35 10.0 0.1 2 -1
Select All
Paste this into http://www.falstad.com/circuit.

This can be expanded to many bridges. Due to how diodes work, it will work like an N-input OR gate.
Attached Images
File Type: png Screenshot-Circuit Simulator v1.5m-1.png (17.7 KB, 10 views)
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