UCC28251: does it need an opto coupler in addition to current transformer?

Ras Sharif50

Genius 3455 points

Part Number: UCC28251

Hi Everybody,

please consider the schematics: ( form UCC28251 datasheet on the page 42 )

please notice the current feedback which is sensed by a resistor through a current transformer ( in the primary side ).

does it need really an opto coupler ( U6 ) in addition to the current transformer ( CT1 )?

is it possible to connect the secondary side of CT1 to the ground of the secondary side ( of half bridge ) to eliminate the U6?

Best Regards,

Ras

over 6 years ago

0 Teng Feng over 6 years ago

TI__Genius 13660 points

Hi Ras,

I have contacted one of my colleagues to answer this question.

Regards,
Teng

0 Frank TANG over 6 years ago

TI__Intellectual 1390 points

Hi Ras,

If the current transformer can meet isolation standard, the opto coupler can be removed. This is the way that many practical designs would take.

Best Regards

Frank

0 Ras Sharif50 over 6 years ago in reply to Frank TANG

Genius 3455 points

Hi Frank,

thank you. if found the answer.

it raises another question about the schematics.

why doesn't the current sense in the secondary? in this way the CT and opto coupler are eliminated.

Regards,

Ras

0 Frank TANG over 6 years ago in reply to Ras Sharif50

TI__Intellectual 1390 points

Ras,
The way without opto coupler is way that many practical designs adopt.

Regards,
Frank

0 Ras Sharif50 over 6 years ago in reply to Frank TANG

Genius 3455 points

Frank,
But the current transformers in the market don't specify isolation rating.

Regards,
Ras

0 Frank TANG over 6 years ago in reply to Ras Sharif50

TI__Intellectual 1390 points

Ras,

You may need to talk with the vendor of current transformer to see if they have product that can pass safety system certification such as basic isolation system or reinforced isolation system standard. If they do not have and you do need pass safety standard, you can look for other vendor or ask for a customized product.

Regards

Frank

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UCC28251: does it need an opto coupler in addition to current transformer?