TPS23753A: TPS23753A to design a buck converter, Vin 36~57V，Vout 24V 400ma to ~500ma

Hi Rob,

You can refer the PMP22301's secondary side for the transformer and resistor value selection (www.ti.com/.../PMP22301). It is a 24-V 0.9A design, so the secondary sec side diode/FET rating, and the transformer saturation current rating can be lower for your case. Other circuit parameters can similar.

Best regards,

Diang

That you so much. I will look at it in more detail next week. One more question, it looks like the transformer may not be available anymore, if true what would be its replacement? I don't even see the winding info either? how does POE13P-24L winding compare to this one?

Hi Rob,

Thanks for your follow-up.

POE13P-24L looks good for 24-V ~500 mA application. The windings is

If you have a TPS23753AEVM-001, it looks easier to do some jump wires to only configure the secondary side. 

If you have a TPS23753AEVM-004, it may need more jumpers.

Best regards,

Diang

Thanks for the confirmation!!! 

I have converted the -004 to -005 (12V 1A) and  it works fine at the voltage level. I have ordered the transformer to get it to 24V @ 500ma. If you Please confirm  the following:

I don't need the sync feedback, remove Q1 and D6 and D7 jumping across Q1

Replace R19 (10K) and R24 (1.15K) for U3 ref voltage

Replace R8 (LED) 6K

I don't think I need to adjust Bias Feedback area - right?

One other question: I below the above is true if I put the secondary windings in serial and that would double the voltage and 1/2 the current - true?

Thanks for any response!

unless more question get raised I believe this address all my concerns

Rob

Hi Rob,

Thanks for your rely!

"I don't need the sync feedback, remove Q1 and D6 and D7 jumping across Q1": you may need to put a (>= 80V, >= 2 A) Schottky diode to replace Q1 to complete the flyback converter.

"I don't think I need to adjust Bias Feedback area - right?": You may need to change R22 to 2kOhm

"if I put the secondary windings in serial and that would double the voltage and 1/2 the current": Since the Vout is regulated by the U3's circuit, you may still have the same voltage and current even you change the turns ratio, as well as the other factors can fit (like duty cycle, flux density not saturated...) 

Besides, make the output capacitors (C12, C13...) higher than 30V.

Best regards,

Diang

yes, the caps that I change out per the 12V BOM may have to change to 30V. in the 12V BOM R22 goes to 2.49K and R21 moves to 15K. I'll cal the current but they may have to change too. I guess just jumper Q1 out of the equation is not enough? When I review the norm circuitry there is no drive secondary to deal with, or am I missing something?.

Last question does the R19 and R24 make sense to you and U1 side of the feedback can be left allow - right?

Hi Rob,

Just found the cathode voltage of  TLV431 is only 7 V.

TL431 with 37-V cathode volatge may be suitable for 24-V operation.

TL431 has ~2.5V reference. You may use the following parameters for compensation.

Best regards,

Diang

Hi! looks good and yes the tlv431 must move to tl431, which I have done when I move to 12Vdc.. Last question: what schem (where TL431 is at) did you pull the schem from, can I get the whole schem?

Hi Rob,

Glad to know you have changed the TL431!

Both of these designs are 24-V rated:

24-V/0.9-A using TPS23754 & flyback converter: www.ti.com/.../PMP22301

24-V/2.5-A using TPS23730 & ACF converter (the schematic used in last post): https://www.ti.com/tool/PMP23287

Best regards,

Diang