ICE3B0565
Application Note 7 2006-03-28
4 Circuit Description
4.1 Line Input
The AC line input side comprises the input fuse F1 as over-current protection. The choke L1, X2-capacitors
C1 and Y2-capacitor C4 act as radio interference suppressors. After the bridge rectifier BR1 and the input
capacitor C2, a voltage of 80 to 380 VDC depending on input voltage is available.
4.2 PWM Control and Power Stage
The PWM pulse is generated by 8-pin CoolSET™F3 ICE3B0565. ICE3B0565 is an integrated power IC
which includes both of the current- mode PWM controller and a CoolMOS
TM
with 650V breakdown voltage.
The control IC and CoolMOS
TM
are fabricated by the different optimized chip technologies respectively and
no compromise like monolithic approaches is necessary.
4.3 Clamping Network
R1, C3 and D1 dissipate the energy of the leakage inductance.
4.4 Primary Current Sense
The primary current is sensed by the external shunt resistor R4. The sense voltage is fed into ICE3B0565
and a cycle by cycle current limiting is achieved. Primary current is being converted to a corresponding
voltage level at CS pin. A 220ns leading edge blanking is provided to avoid leading edge spikes from
distorting the current limiting.
4.5 Output Stage
On the secondary side the power is coupled out by an ultra-fast diode UF5401. The capacitor C21, provide
energy buffering following with the LC filter, L21 and C22 to reduce the output voltage ripple considerably.
Storage capacitor C21 is selected to have an internal resistance as small as possible (ESR) to minimizes the
output voltage ripple
4.6 Feedback Loop
The output voltage is sensed by the voltage divider of Rc1, Rc2 and Rc3 and compare to TL431 internal
reference voltage. The output voltage of TL431, IC3 is transferred to the primary via an optocoupler, IC2 for
regulation control. The secondary regulation control is adopted with TL431 and optocoupler. Cc1, Cc2, Rc4
being the compensation network constitutes the external circuitry of the error amplifier of TL431. This
circuitry allows the feedback to be precisely matched to dynamically varying load conditions, thereby
providing stable control. The maximum current through the optocoupler diode and the voltage reference is
limited by the resistor Rc6 and Rc5. Optocoupler IC2 is used for floating transmission of the control signal to
the “FB” input of the ICE3B0565.
4.7 Blanking Window for Load Jump / Active Burst Mode
In case of Load Jumps the Controller provides a Blanking Window before activating the Overvoltage
Protection and entering the Auto Restart Mode. This time is generated by charging up the Soft Start
capacitor from 4.4V to 5.4V. Within this timeframe the voltage at Feedback pin can rise up above 4.8V,
without switching off due to Overload Protection. During this operation the transferred power is limited to the
maximum peak current defined by the value of the sense resistor. The same procedure happens to the
