Datasheet

Main characteristics and circuit description AN3329
6/47 Doc ID 18376 Rev 1
1 Main characteristics and circuit description
The main features of the SMPS are:
● Universal input mains range: 90 ÷ 264 Vac - frequency 45 ÷ 65 Hz
● Output voltage 1: 24 V ± 5 % at 6 A for backlight and audio supply
● Output voltage 2: 12 V ± 3 % at 2 A for TV panel supply
● Output voltage 3: 5 V ± 2 % at 2 A for microprocessor supply
● Mains harmonics: acc. to EN61000-3-2 Class-D or JEITA-MITI Class-D
● Standby mains consumption: at 230 Vac <150 mW with 50 mW load
● Overall efficiency at full load: above 90 %
● EMI: according to EN55022-Class-B
● Safety: according to EN60065
● Dimensions: 197x115 mm, 25 mm maximum component height from PCB
● PCB: single side, 70 µm, CEM-1, mixed PTH/SMT.
The circuit is made up of two sections; a 10 W supply generating 5 V standby output,
dedicated to supplying the TV microprocessor and the logic circuitry, and a larger section
made up of a PFC front-end and an LLC resonant converter which provides two output
voltages, one dedicated to supplying the TV panel, and one for the backlight and audio
power amplifiers. The PFC stage delivers 400 V constant voltage and acts as a pre-
regulator for both the LLC stage and the standby supply. An external signal, referred to as
secondary ground, turns the PFC and LLC stages on and off.
Startup
At turn-on the standby supply starts up and delivers 5 V dedicated to the TV microprocessor
and other logic circuitry. It also generates the auxiliary supply voltage for the PFC and LLC
controllers at primary side via the linear regulator Q7. Q7 is activated by the optocoupler U5,
that is driven by the logic signal on/off (active high). At startup, the on/off signal (delivered by
the microprocessor) is supposed to be low, so the PFC and the LLC are off. Once the on/off
signal is asserted high, the regulator Q7 provides 14 V to the L6564 PFC controller and the
L6599A LLC controller; to always ensure proper operation of the LLC, the circuit is designed
so that the PFC starts first, then the downstream converter. The LINE pin of L6599A allows
the resonant stage to operate only if the PFC output is delivering its rated output voltage. It
prevents the resonant converter from working with an input voltage that is too low which may
cause the undesirable capacitive-mode operation. The L6599A LINE pin internal
comparator has a hysteresis allowing to set the turn-on and turn-off thresholds
independently. The LLC turn-on voltage (PFC output) and the turn-off threshold are set to
380 V and 300 V respectively. This last value prevents the LLC stage operating in
capacitive-mode but allows the resonant stage to operate even in the case of mains sag or
dips lowering the PFC output voltage.
Brownout protection
Brownout protection prevents the circuit from working with abnormal mains levels. It is
accomplished by both the Viper, through the brownout pin, and the L6564, through an
internal comparator internally connected to the VFF pin (#5), which detects the mains
voltage peak value. The internal comparators allow the IC operation with proper mains level
only, as defined by power supply specifications, therefore, if the input voltage is below
around 80 Vac (typ.), the circuit is not allowed to start up.