# Full Bridge and Voltage Comparision

• posted

Hi,

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

The two rectifiers are getting inputs from two different sinusoidal sources of frequency 80 KHz who are in phase but could have different amplitudes. 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

Am I on the right thinking process?

Melissa

• posted

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

Cheers

Phil Hobbs

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Dr Philip C D Hobbs
Principal Consultant```
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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

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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```
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How would you compare the current from each bridge?

--Winston

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Homework?

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

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| James E.Thompson, CTO                            |    mens     |
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not a homework at all

Melissa

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

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

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| James E.Thompson, CTO                            |    mens     |
• posted

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.

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Regards, Joerg

http://www.analogconsultants.com/```
• posted

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.
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Who cares?

All she wants is to have the bridge with the highest output voltage```
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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

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

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Regards, Joerg

http://www.analogconsultants.com/```
• posted

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)

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?? 100% natural

--- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net```
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Oh, well...```
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Fair enough.

Maybe she'll tell us what she wants.```
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Unless someone else does her homework for her ;-) ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |