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AN1660 APPLICATION NOTE

We choose Np = 52T, n = 2

The turns of 24V winding is 6.

The turns of Vcc supply winding is 3.

Now design the resonant components.

Set normalize output voltage is M = 0.95

Set normalize output current is J = 0.2

(6)

(7)

(8)

Cr = C17+C18,

Choose C17 = C18 = 20nF, then Cr = 40nF

Recalculate Lr under Fr = 84KHz. Lr = L1 = 90uH

Choose primary inductance L2 as 5 ~ 10 times the resonant inductance. L2 = 500uH

Now the resonant frequency of total circuit is

(9)

3.3 conditions for resonance between L2 and resonant circuit (L1, C17+C18)

When the resonant between L2 and the resonant circuit starts, current IL2 varies from -I2 to +I1 during t2-

t1, and the voltage is nVout and constant. The operating waveforms are shown in Fig. 4

Figure 4. operating waveforms

Zo

V

inm ax

2

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





2

JM

⋅⋅

Vo Io

⋅

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

=

Zo

420

2

----------





2

0.2 0.95

⋅⋅

110 1.2

⋅

()

24 2

⋅

()

+

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

46.55

==

Lr

Zo

2

πfr

-----------

56.55

2

π 84 10

3

⋅⋅

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

88.2

µH

==

=

Cr

1

2

πfr Zo

⋅

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

1

2

π 84 10

3

46.55

⋅⋅

⋅

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

40.6n F

==

=

fo

1

2

π L2 L1

+

() Cr

⋅

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

32.5kHz

==

D03IN1428

∆T

∆

VC2

VC2

I2

I1

IL2

IL2

IL1

I

IL1

IL1

I

IL1p

VC max

VC min

L1C1