AN3329 datasheet(6/47 Pages) STMICROELECTRONICS

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Main characteristics and circuit description

AN3329

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Doc ID 18376 Rev 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

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Safety: according to EN60065

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Dimensions: 197x115 mm, 25 mm maximum component height from PCB

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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.

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