Full Bridge and Voltage Comparision

Could you just wire the rectifier outputs in parallel, and not worry about it?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

For sensing the current through each bridge for comparison, I would delete D1 and D2, then place current - sense resistors in series with the ground connection to each bridge.

--Winston

--
If you remove D1 and D2 and connect the outputs of the two bridges
together, then when the output voltage of the upper bridge is higher
than the output voltage of the lower bridge, current out of the bottom
bridge will be blocked and the load will be fed by the upper bridge.

Conversely, if the output voltage of the lower bridge is higher than
that of the upper bridge, the upper bridge will be cut off by the
lower bridge and the load will get its current from the lower bridge.

Plus, you won't have to suffer the losses in D1 and D2.

How would you compare the current from each bridge?

--Winston

Homework?

Looks like it. Not enough detail if it were a _real_ two source situation. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
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I love to cook with wine.     Sometimes I even put it in the food.

not a homework at all

Melissa

Could you tell us why you need to know this information?

Please. Like what is the application? ...Jim Thompson

-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

| 1962 | I love to cook with wine. Sometimes I even put it in the food.

As others have said, you can get rid of D1 and D2. Their function is already being provided by the right two diodes in each rectifiers.

Now, instead of connecting the anodes in the rectifiers directly to ground place a shunt resistor into those connections. Both of them. Calculate the resistor so that at nominal load you get a voltage drop you can easily measure. If you use a comparator such as the LM339 then

50-100mV would suffice. Rate these shunt resistors accordingly for power.

Now you can compare the two and find out which source contributes more. You could also use meters or AD converters to find out the ratio. When the sources are within about a volt of each other then both will contribute some.

Remember that the signal on that shunt will pulsate at twice the input frequency.

--
Regards, Joerg

http://www.analogconsultants.com/

If the 2 bridge outputs are reasonably similar, the simplest way is load each in turn with a resistor and measure the resistor's temperature rise - DMMs with K-type thermocouples are quite reasonable these days.

80kHz is quite fast, so you want Shottky-barrier or silicon carbide rectifiers or their dissipation will be as high as the resistor.

--
Who cares?

All she wants is to have the bridge with the highest output voltage
drive the load.

Melissa the OP, yes? (Emphasis mine):

"I am trying to *compare the magnitude of the DC outputs* of two full bridge rectifiers."

"Based on the magnitude of the DC output, *I have to decide which bridge will be providing power* to the load as shown in the link."

"I posted the circuit at the following link *to compare the two output voltages*"

I didn't get that from her post. :)

--Winston

AFAIU Melissa wants to know which bridge is currently driving the load. If that is so then she needs a signal that tells her.

--
Regards, Joerg

http://www.analogconsultants.com/

It depends how the AC sources are correlated with one another and with the circuit ground, it also makes the assumption that you want to drw power from the source with the greatest amplitude.

also D1 and D2 serve no purpose, as they only duplicate the functionality of the diodes on the right half of the two bridges. the could be omitted (replaced with wire)

--
?? 100% natural

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--
Oh, well...

--
Fair enough.

Maybe she'll tell us what she wants.

Unless someone else does her homework for her ;-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

How much of a voltage difference of detection are you looking for?

Jamie