TOP245P_1 POWERINT [Power Integrations, Inc.], TOP245P_1 Datasheet - Page 7

• Manufacturer Part Number: TOP245P_1
• Description: Title 32W (47W peak) Multiple Output supply
• Manufacturer: POWERINT [Power Integrations, Inc.]

DER-19
4 Circuit Description
This power supply uses the latest generation TOPSwitch in a DIL08 package to minimize
heatsink requirements. It is designed for 32W continuous operation in a 50°C ambient
with magnetics designed to allow short peak power levels of up to 50W.
4.1 Input EMI Filtering
Due to the frequency jittering function of TOPSwitch, the input EMI filtering is minimal,
consisting of a 15mH common-mode choke and 220nF x-capacitor. Protection is
provided by a 1A, 250V antisurge fuse. Inrush limiting is provided by a thermistor. Surge
protection is provided by a VDR on the input. If only 4kV surge is required, this part can
be removed since the TOP245P incorporates over-voltage shutdown giving additional
protection.
4.2 TOPSwitch Primary
On the primary side of the supply, the TOPSwitch integrates a number of functions:-
A 47uF input capacitor has been used to provide the high peak power capability. If peak
power operation is not required, this can be reduced to 33uF, 400V which will save
further cost.
4.3 Output Rectification
A fully AC stacked design has been used to give good cross-regulation. A snubber is
placed across D7 to reduce high frequency common-mode EMI emissions. Post filters
are used on all outputs to meet noise and ripple requirements.
4.4 Output Feedback
Full PWM feedback has been implemented using a TL431 reference and opto-coupler.
Feedback is split over the 3V3 and 5V rails, each giving equal influence to the feedback
network. D10, R10 and C11 provide a soft-finish function, ensuring a monotonic rise in
the output voltages with zero overshoot.
Page 7 of 25
Frequency jitter which reduces the QP and AV EMI levels by up to 10dB
Soft-Start which prevents transformer saturation during start-up. This increases
long term reliability
Line UV and OV detection to give additional differential surge withstand capability
Regulation to zero load without pre-load due to very low minimum duty cycle
capability
Line feed forward which improves 100Hz ripple rejection
Hysteretic thermal and short circuit protection to increase long term reliability
TOP245P Multiple Output Set Top Box
Tel: [phone] Fax: [phone]
Power Integrations, Inc.
www.powerint.com
March 30, 2004