#### Magnethicc

##### Member level 2

I need to design an isolated 30W housekeeping power supply:

Topology = Flyback

Input Voltage = +30VDC (Primary)

Output Voltage = +17VDC (Secondary), +12V (Primary Sensing)

Output Power = ~30W (Almost all of it to the +17VDC secondary output)

Efficiency = ~90%

Control = Peak Current Mode Control with Primary side sensing

Switching Frequency = 120kHz

__X'mer:__Magnetic Core = PC40-EER28L, AL=240nH/N^2

Peak Flux Density = 200mT

Number of Primary Turns = 30 (Lprimary = 216uH)

Number of Secondary Turns = 15

Number of Sensing Turns = 11

Build -

1- Primary - 2 Wires x 15Turns

2- Primary Sensing - 1 Wire x 11Turns

3- Secondary - 2 Wires x 15T

4- Secondary - 2 Wires x 15T (In parallel with 3)

5- Primary - 2 Wires x 15Turns (In series with 1)

__Input Calculations:__Duty came out to be 0.522

Input Average Current = ~1A

Input Peak Current =2.2A

Input RMS Current = 1.35A

Input Winding Current Density = 5.5A/mm^2

__Output Calculations__+17V Ripple Current = 1.25A

+17V Winding RMS current = 2.3A

+17V Winding Current Density = 4.5A/mm^2

__Notes:__* MOSFET - TPH5900CNH,L1Q - 64mOhms

* +17V Output Diode - 3x RF201LAM2S - Fast Recovery, 3 In parallel

* The +17V is supplying 3 Fans as well as a Buck Converter (Stable +12V)

Questions:

1. Does anyone have any notes regarding the design above?

2. Does anyone have any experience with low input voltage flybacks and could give me some tips to consider while

__designing__and

__laying it out__?

Thank You.