EVL150W-ADP-SR View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

EVL150W-ADP-SR

12 V - 150 W resonant converter with synchronous rectification using the L6563H, L6599A, and SRK2000

STMicroelectronics 

Main characteristics and circuit description

AN3233

RH

=

RL (1.25V −

VBM

VBM )

=

309kΩ

The value of the mounted resistor is 330 kΩ.

RHts sets a small de-bouncing hysteresis and is in the range of mega-ohms. Rlim is in the

range of tens of kilo-ohms and limits the current flowing through the optocoupler’s diode.

Both L6599A and L6563H implement their own burst mode function but, in order to improve

the overall power supply efficiency, at light load the L6599A drives the L6563H via the

PFC_STOP pin and enables the PFC burst mode: as soon as the L6599A stops switching

due to load drops, its PFC_STOP pin pulls down the L6563H’s PFC_OK pin disabling PFC

switching. Thanks to this simple circuit, the PFC is forced into idle state when the resonant

stage is not switching and rapidly wakes up when the downstream converter restarts

switching.

Fast voltage feed forward

The voltage on the L6563H VFF pin (pin 5) is the peak value of the voltage on the MULT pin

(pin 3). The RC network (R15+R26, C12) connected to VFF completes a peak-holding

circuit. This signal is necessary to derive information of the RMS input voltage to

compensate the loop gain that is mains voltage dependent.

Generally speaking, if the time constant is too small, the voltage generated is affected by a

considerable amount of ripple at twice the mains frequency causing distortion of the current

reference (resulting in higher THD and lower PF). If the time constant is too large, there is a

considerable delay in setting the right amount of feed-forward, resulting in excessive

overshoot or undershoot of the pre-regulator’s output voltage in response to large line

voltage changes.

To overcome this issue, the L6563H implements the fast voltage feed forward function. As

soon as the voltage on the VFF pin decreases by a set threshold (40 mV typically), a mains

dip is assumed and an internal switch rapidly discharges the VFF capacitor via a 10 kΩ

resistor. Thanks to this feature, it is possible to set an RC circuit with a long time constant,

assuring a low THD, keeping a fast response to mains dip.

Brownout protection

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

achieved using the RUN pin (pin 12) of the L6563H: this pin is connected through a resistor

divider to the VFF pin (pin 5), which provides the information of the mains voltage peak

value. 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.

Output voltage feedback loop

The feedback loop is implemented by means of a typical circuit using the dedicated

operational amplifier of TSM1014A modulating the current in the optocoupler’s diode. The

second comparator embedded in the TSM1014A - usually dedicated to constant current

regulation - is here utilized for burst mode as previously described.

On the primary side, R34 and D17 connect the RFMIN pin (pin 4) to the optocoupler’s

phototransistor closing the feedback loop. R31, which connects the same pin to ground, sets

8/35

Doc ID 17595 Rev 1

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