AN3339 datasheet(6/44 Pages) STMICROELECTRONICS

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Main characteristics and circuit description

AN3339

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Doc ID 18449 Rev 2

Main characteristics and circuit description

The main features of the SMPS are:

●

Universal input mains range: 90

÷ 264 Vac - frequency 45 ÷ 65 Hz

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Output voltage 1: 130 V ±8 % at 620 mA for backlight

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Output voltage 2: 24 V ±8 % at 2 A for audio supply

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Output voltage 3: 12 V ±1 % at 4 A for panel supply

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Output voltage 4: 5 V ±2 % at 2 A for microprocessor supply

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Mains harmonics: acc. to EN61000-3-2 Class-D or JEITA-MITI Class-D

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Standby mains consumption: <170 mW at 230 Vac with 50 mW load

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Overall efficiency at full load: >90 %

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EMI: acc. to EN55022-Class-B

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Safety: acc. to EN60065

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Dimensions: 115x204 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 standby supply delivering 5 V, dedicated to

supplying the microprocessor and the logic circuitry, and a bigger section made up of a

front-end PFC and an LLC resonant converter delivering three output voltages, 12 V is

dedicated to supplying the TV panel, 24 V to supplying the audio power amplifiers and 130

V is dedicated to the backlight.

The PFC stage delivers 400 V constant voltage and acts as the pre-regulator for both the

LLC stage and the standby supply.

An external signal, referred to secondary ground, turns the PFC and the LLC stage on and

off.

Startup

At turn-on the standby supply begins startup and delivers 5 V dedicated to the TV

microprocessor and other logic circuitry. It also generates the auxiliary voltage powering 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. At startup, the on/off signal (active

high) from the microprocessor is supposed to be low, so the PFC and the LLC do not work.

Once the on/off signal is asserted high, the regulator Q7 delivers 14 V powering the PFC

controller L6564 and the LLC controller L6599A; 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 too low input

voltage that can cause undesirable capacitive mode operation.

The L6599A LINE pin internal comparator has a hysteresis which allows to independently

set the turn-on and turn-off voltage. The LLC turn-on voltage (PFC output) has been set to

380 V while the turn-off threshold has been set to 300 V. This last value avoids capacitive

mode operation by the LLC stage but allows the resonant stage to operate even in the case

of mains sag and consequent lowering of PFC output voltage.

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