AN3014

Main characteristics and circuit description

Doc ID 16064 Rev 2

5/29

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Main characteristics and circuit description

The main features of the SMPS are:

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Universal input mains range: 90

− 264 Vac, frequency 45 − 65 Hz

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Output voltage: 19 V at 4.75 A continuous operation

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Mains harmonics: according to EN61000-3-2 class-D or JEITA-MITI class-D

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Standby mains consumption: < 0.26 W at 230 Vac

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Efficiency at nominal load: > 92% at 115 Vac

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EMI: according to EN55022-class-B

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Safety: according to EN60950

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Dimensions: 65 x 155 mm, 25 mm maximum component height

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PCB: double-sided, 70 µm, FR-4, mixed PTH/SMT

The circuit is composed of two stages: a front-end PFC using the L6563H, and a LLC

resonant converter based on the L6599A. The SRK2000 controls the synchronous

rectification on the secondary side. The PFC stage works as a preregulator and powers the

resonant stage with a constant voltage of 400 V. The downstream converter operates only if

the PFC is on and regulating. In this way, the resonant stage can be optimized for a narrow

input voltage range.

Startup sequence

As indicated previously, the PFC acts as master and the resonant stage can operate only if

the PFC output is delivering the nominal output voltage. Therefore the circuit is designed so

that at startup the PFC starts first, then the downstream converter turns on. Initially, the

L6563H is supplied by the integrated high voltage startup circuit, but as soon as the PFC

starts switching, a charge pump connected to the PFC inductor supplies both the PFC and

resonant controllers. Once both stages have been activated, the controllers are supplied

also by the auxiliary winding of the resonant transformer, assuring correct supply voltage

even during standby operation.

Because the L6563H integrated HV startup circuit is turned off and therefore is not

dissipative during normal operation, it significantly contributes to the reduction of power

consumption when the power supply operates at light load, in accordance with current

world-wide standby consumption standards.

Brownout protection

Brownout protection prevents the circuit from working with abnormal mains levels. It is easily

achieved using the RUN pin (pin12) of the L6563H. This pin is connected through a resistor

divider to the VFF pin (pin 5), which provides the mains voltage peak value information. An

internal comparator enables the IC operations if the mains level is correct, within the

nominal limits. At startup, if the input voltage is below 90 Vac (typ), circuit operations are

inhibited.

The L6599A has similar protection on the LINE pin (pin 7). It is used to prevent the resonant

converter from working with too low an input voltage, which can cause incorrect capacitive

mode operation. If the bulk voltage (PFC output) is below 380 V, the resonant startup is not

allowed. The L6599A internal comparator has a hysteresis which allows the turn-on and

turn-off voltage to be set independently. The turn-off threshold has been set to 300 V in