AN2530

Functional overview

3/13

1

Functional overview

The simplest way of describing the functioning of a resonant converter is to compare it with

principal DC bus through a capacitive divider network that creates a "false" ground to feed

one of the transformer's ends (Figure 1). In this way, the transformer is fed with a voltage

that swings (from the transformer's point of view) from zero to negative, negative to zero,

zero to positive, then back to zero (therefore repeating the cycle).

is quite straightforward alternating the turn-on of each transistor.

Figure 1.

SMPS half bridge simplified schematic

The resonant variation for this type of converter places an "external" inductor to cause a

resonance between the capacitive divider network and the external inductor (Figure 2),

which sums up to the already present leakage inductance of the main transformer.

These components are the ones that require most of the care for this variation of the

converter. Nevertheless, remember that every aspect of the design stage has an impact on

the overall behavior of the converter.

Figure 2.

Resonant SMPS half bridge simplified schematic

Table 1 gives the BOM (Bill of materials) for this converter. Most of the capacitors do not

have an operating voltage, as they operate in low voltage. As for the driver, any voltage

C1

C2

Q1

1

Q2

1

C3

D2

D3

D4

D1

T1

1

5

6

4

8

D5

D6

+

C4

220VAC

110VAC

D2

C1

D6

Q2

1

D1

Q1

1

C2

+

C4

D4

D5

T1

1

5

6

4

8

D3

L1

110VAC

220VAC