Hi All,
Thank you for taking a look.
I used TI webench for AC/DC power design and entered the following criteria:
VAC (RMS) min: 22
VAC (RMS) max: 26
VDC out: 24
Iout: 2A

I selected
UCC28C45
because it is one of the only designs that put a part number for T1, all others don't give a part number and I don't feel I can reliably select one.

Can you suggest if this is an appropriate design but more importantly, can you answer my question below:
How do I connect the transformer T1 as it is in the schematic? The part number from the BOM (VPH5-0083-R) has 6 coils, 3 on each side. Pictured below. The webench schematic shows only 3 coils, 2 on left and 1 on right and the orientation dots are reversed on the left side coils. No pin numbers. Thank you for your help.

Picture from VPH5 data sheet (above)

Picture from webench, closeup of T1 (above)

Picture from webench of overall AC/DC schematic.

 

Doing a little bit more research, Why do I need a transformer?

Can't I pass the 24vac through a full bridge rectifier, add a smoothing cap, and then that should be DC with ripple. Then I can use any DC/DC converter?

 

Yes you can just put a bridge rectifier and smoothing capacitor, but the voltage will need to be regulated to stabilise 24V output.
The circuit diagram shown is mainly for mains input to isolate the output side, it uses an optocoupler and tl431 Zener diode to regulate the output.

 

Yes you can just put a bridge rectifier and smoothing capacitor, but the voltage will need to be regulated to stabilise 24V output.
The circuit diagram shown is mainly for mains input to isolate the output side, it uses an optocoupler and tl431 Zener diode to regulate the output.

Thank you for your response.

That makes sense. This is for a 24vac output in a pool setting so it already goes through a transformer. Is that isolated enough?
If I put a full bridge rectifier and smoothing cap, I can then use a conventional dc to dc regulator circuit to further regulate it? Most converters can handle that 60hz ripple (between a couple volts).

On a side note, purely academic, is there a way to convert ac without a full bridge rectifier so load current doesn’t need to go through diodes? I suppose there must be some mosfet with a controller solution.

 

On a side note, purely academic, is there a way to convert ac without a full bridge rectifier so load current doesn’t need to go through diodes? I suppose there must be some mosfet with a controller solution.

Yes, look for 'active rectifier' solutions such as Analog Devices' LT4322 or NXP's TEA2208T to name two of many...

 

You can use thyristors to rectify AC to DC , but it's very complicated, it's mainly used on large three phase motor controls and welding equipment.
For small domestic work stick with the bridge rectifier method, for the regulator I would use a switching type like the LM 2596.

 

Yes, look for 'active rectifier' solutions such as Analog Devices' LT4322 or NXP's TEA2208T to name two of many...

Thank you for the suggestions!