# Can two bridge rectifiers with varying voltages be connected in parallel?

Discussion in 'General Electronics Chat' started by b2386, Nov 26, 2010.

1. ### b2386 Thread Starter New Member

Feb 9, 2010
13
0
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?

2. ### retched AAC Fanatic!

Dec 5, 2009
5,201
315
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.

3. ### SgtWookie Expert

Jul 17, 2007
22,194
1,764
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.

4. ### b2386 Thread Starter New Member

Feb 9, 2010
13
0
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.

5. ### retched AAC Fanatic!

Dec 5, 2009
5,201
315
So are you set? Or did you need further clarification?

6. ### b2386 Thread Starter New Member

Feb 9, 2010
13
0
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...

7. ### tom66 Senior Member

May 9, 2009
2,613
215
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.

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