LM74700D-Q1: bridge rectifier

Jeff YANG

Part Number: LM74700D-Q1
Other Parts Discussed in Thread: LM74681

Hi,

Are there any solutions that support an input voltage VIN +/- 60V, where a bridge rectifier is used at the back end to convert the output to positive DC? Note that the input source will be a fixed positive or negative DC during use; there will be no dynamic switching between polarities during operation. Does TI offer such a product?

Or there have reference design?

Thanks!

Jeff

6 months ago

0 Shiven Dhir 6 months ago

TI__Guru 70951 points

Hi Jeff,

Please check LM74681

Regards,

Shiven Dhir

0 Jeff YANG 6 months ago in reply to Shiven Dhir

Mastermind 9085 points

Hi Shiven,

For +48 or-48V application, is it needs 48-(-48) =96V rating? or it only needs over 48V operation is enough?

Thanks!

Jeff

+1 Shiven Dhir 6 months ago in reply to Jeff YANG

TI__Guru 70951 points

Hi Jeff,

The assumption is that at all times, either +48V will be connected or -48V will be connected, basically for polarity agnostic systems.

This means no matter what the orientation of power supply is, output will always be powered.

LM74681 is the perfect fit.

Please check figure 8.2 and 8.3 in the datasheet.

Regards,

Shiven Dhir

0 Jeff YANG 6 months ago in reply to Shiven Dhir

Mastermind 9085 points

Hi Shiven,

Got it, thank you!

Jeff

0 Jeff YANG 6 months ago in reply to Jeff YANG

Mastermind 9085 points

Hi Shiven,

Sorry, I just found Vin range is -54~+54V, In Vin= -54V condtion, is the OUTP to INx = +54-(-54) = 108V, may over -80V rating?

Or my caculate is wrong?

Thanks!

Jeff

0 Shiven Dhir 6 months ago in reply to Jeff YANG

TI__Guru 70951 points

Hi Jeff,

My assumption was that once power is connected in power direction, it will not reverse. Or will only reverse when the output is discharged, which means a fresh start.

Surely 108V is a problem.

Regards,

Shiven Dhir

0 Jeff YANG 6 months ago in reply to Shiven Dhir

Mastermind 9085 points

Hi Shiven,

Correct, the polarity remains stable after power-on. But we're worried about the case where -54V enters the system. At that moment, the voltage across OUTP to INx becomes 108V. Does this mean the component requires a 108V rating? Thank you.

Jeff

+1 Shiven Dhir 6 months ago in reply to Jeff YANG

TI__Guru 70951 points

Hi Jeff,

Please simulate using our model on TI.com. From my understanding, it should not be a problem. Even with 80V rating, it should be okay.

Regards,

Shiven Dhir

0 Jeff YANG 6 months ago in reply to Shiven Dhir

Mastermind 9085 points

Hi Shiven,

You mean use PSPICE model to simulate? thanks!

Jeff

0 Shiven Dhir 6 months ago in reply to Jeff YANG

TI__Guru 70951 points

Hi Jeff,

Thats correct.

Regards,

Shiven Dhir

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LM74700D-Q1: bridge rectifier