Description of SMPS

AN4414

10/20

DocID025611 Rev 1

Maximum DC bus voltage at flyback input:

Equation 20

Vdcmax ~ 360 VDC

Assuming efficiency,

 = 65 % (flyback stage):

Equation 21

fsw = 115 KHz

Equation 22

Equation 23

Let

VR = 10 V

Equation 24

Equation 25

this gives

Dmax = 9.1%

Ton = Dmax = 790 µs

Which is greater than Tonmin (= 400 ns), the device minimum turn-on time as per the

datasheet of the VIPER17HN.

Equation 26

Where the max. drain current limitation threshold of the VIPER17 is 400 mA, so at minimum

DC input voltage, the device will not enter into the hiccup mode.

Equation 27

Ts

1

fsw

---------

8.69

s

==

VR

Dmax

1Dmax

–



------------------------------ Vdcmin



10V

==

Ipkp

2Pout



 Vinmin Dmax





-----------------------------------------------------

0.169A

==

Lp

2 Pout



 Ipkp

2

fsw





----------------------------------------- 540

H



=