SSL4120 datasheet(21/48 Pages) NXP

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SSL4120

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Product data sheet

Rev. 2 — 1 November 2012

21 of 48

NXP Semiconductors

SSL4120

Resonant power supply controller IC with PFC for LED lighting

7.8.3 HBC switch control

HBC switch control determines when the MOSFETs switch on and off. It uses the output

from several other blocks.

• A divider is used to alternate switching of the high and low-side MOSFETs for each

oscillator cycle. The oscillator frequency is twice the half-bridge frequency.

• The controlled oscillator determines the switch-off point.

• Adaptive non-overlap time sensing determines the switch-on point. This function is

the adaptive non-overlap time.

• Several protection circuits and the state of the SSHBC/EN input pin specify if the

resonant converter is allowed to start switching.

Figure 9 provides an overview of typical switching behavior.

7.8.4 HBC Adaptive Non-Overlap (ANO) time function (HB pin)

7.8.4.1

Inductive mode (normal operation)

The high efficiency characteristic of a resonant converter is the result of Zero-Voltage

Switching (ZVS) of the power MOSFETs. ZVS is also called soft switching. To allow soft

switching, a small non-overlap time is required between the high-side on-times and

low-side MOSFETs. During this non-overlap time, the primary resonant current charges or

discharges the half-bridge capacitance between ground and Vboost.

After the charge or discharge cycles, the MOSFET body diode starts conducting and

because the voltage across the MOSFET is zero, when the MOSFET is switched on there

are no switching losses. This operating mode is called inductive mode. In inductive mode,

the switching frequency is above the resonance frequency and the resonant tank has an

inductive impedance.

Fig 9.

Switching behavior of the HBC

GATELS

GATEHS

ITr(HBC)

CFMIN

Vboost

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