TPS23751: Adapter power range

Michael Gilge

Expert 1690 points

Part Number: TPS23751
Other Parts Discussed in Thread: PMP8812

Hello,

we have a TPS23751 low-cost design based on the PMP11254 (12V 2.1A), but are using the LinkCom transformer LDT8202-51R.

I am wondering how to calculate the allowable adapter voltage range? Is it strictly dependent on the transformer?

The datasheet for the transformer says 33-57V? We would want to go lower to support 24V inputs.

Best regards,

Michael

over 3 years ago

0 Michael Pahl over 3 years ago

TI__Mastermind 21320 points

Hello Michael,

No the transformer is not the only component that sets the input voltage range.

Since you want a 12V/2.1A with a 24V input adapter design, please consider the PMP8812. It is exactly what you want.

http://www.ti.com/tool/PMP8812

If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

Regards,

Michael P.

Applications Engineer

Texas Instruments

0 Michael Gilge over 3 years ago in reply to Michael Pahl

Expert 1690 points

Hello,

the PMP8812 is not a low cost design. I would just like to understand what parameters determine the lowest possible input voltage when using adapter power. I will measure it on my design.

Best regards,

Michael

0 Michael Pahl over 3 years ago in reply to Michael Gilge

TI__Mastermind 21320 points

Hello Michael,

The PMP8812 is the best starting place for the design you want. It is not listed as a cost optimized solution because it is a synchronous driven flyback. A cost optimized solution would be a diode rectified flyback, so the PMP8812 cannot compete with our other designs in this respect.

You could take the PMP8812 and make it low cost component by component, which in my opinion is easier than designing a new power stage but that is your call.

The following paper outlines how to design a flyback with one of our parts. To make it wide-Vin and a different device, just change the values in the parameters than the standard values. http://www.ti.com/lit/an/slva305c/slva305c.pdf

The biggest changes for a wide Vin design is the transformer, and the APD divider. You will want to ensure the bias winding is providing enough voltage for the IC to remain powered. Additionally the output inductance and the output capacitance should be checked to ensure the full load is available at the full input range and the ripple is not too high. You will also want to calculate the duty cycle for the full range of the input to ensure the design can support lower input voltages but not slip into DCM in higher input voltages.