How to size the resonant tank of the Induction Cooking Evaluation Board

The resonant converter

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2

The resonant converter

Figure 1.

The series resonant circuit

Formula 1

Formula 2

Formula 3

when the switching frequency becomes identical to the resonance frequency. In the case of

the Induction Cooking evaluation board, the switching frequency is set by MCU, and the

signal sent directly to the IGBT driver.

The resonance frequency can be calculated as shown in the following formula:

Formula 4

There are two areas around the resonant frequency: the area where the switching frequency

is lower than the resonant frequency and the area where the switching frequency is higher

than the resonant frequency. In an Induction Cooking application, the system works always

on the right side of the curve, therefore in the inductive area (Figure 2).

The value of the capacitive reactance becomes smaller according to Formula 2. In this

situation, a higher switching frequency is followed by an increase in impedance (Formula 3),

causing the output energy to be lower (as shown in Figure 2).

AI12618

LC

R

v

i

X

c

1

j

ωC

---------

1

j2

πfC

--------------- Ω

==

ZR

2

ωL

1

ωC

-------

–

⎝⎠

⎛⎞

2

+

Ω

=

2

πfL

1

2

πfC

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

=

1

2

π LC

------------------- Hz

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⇒