AN2590

Board description

9/17

As a consequence of that, we have the following.

Equation 2

Equation 3

●

Step 2: The input ac current (Iac) equals half of the average inductor current due to two

divider capacitors, so,

Equation 4

●

Step 3: The input power Pin is determined by,

Equation 5

Where Vac is the input voltage. With the above three steps, the values of L1 and Ipk can be

found if the input/output conditions and switching frequency are given.

●

Step 4: For the half bridge resonant circuit, the equivalent resistance of the lamp is

given by:

Equation 6

obtained.

●

Step 5: MOSFET selection. In order to select an adequate MOSFET parameters

Vc1 with a certain safe margin. In a compact application, the thermal issue becomes

t'

Vin

4Vc1

--------------Ts

=

Ipk

Ts

4L1

----------

1

Vin

2Vc1

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

–

⎝⎠

⎛⎞

•

Vin

•

=

Iac

1

2

---i

L1

⎝⎠

⎛⎞

ave

1

4

---Ipk

Ts

16L1

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

1

Vin

2Vc1

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

–

⎝⎠

⎛⎞

•

Vin

•

=

=

=

Pin

1

π

---

Vac

Iac

•θ

d

0

π

∫

=

R

lamp

V

rms lamp

,

I

rms lamp

,

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

=