EP-85 6 V, 330 mA Low Cost Charger
04-Oct-2005
1 Introduction
This document describes a universal input charger power supply designed to replace
linear transformer based chargers/adapters in low power applications. The power supply
utilizes a LinkSwitch-LP IC, LNK564P. The document contains the power supply
specification, schematic, bill of materials, transformer documentation, printed circuit
layout, and performance data.
The LinkSwitch-LP IC has been developed to replace linear transformers in low power
charger applications. The integrated 700 V switching MOSFET and ON/OFF control
function achieve very high efficiency operation under all load conditions with simple bias
winding voltage feedback. No-load and operating efficiency performance exceeds all
international energy efficiency standards either present or proposed in the future.
Thermal shutdown is included as a minimum requirement to match the safety thermal cut
out (thermal fuse) in linear transformers. The IC’s intelligent thermal shutdown feature is
specified with a very tight tolerance (142 ˚C +/-5%) and includes a hysteretic auto-
recovery feature to automatically restart the power supply while maintaining the average
pcb temperature at safe levels under all conditions. This auto-recovery is designed to
eliminate the potential for field returns since the power supply automatically recovers
when ambient temperatures return to the normal operating range. However, with latching
thermal shutdown, often used in RCC discrete switching power supply designs, the input
AC typically needs to be removed to reset the thermal latching function. With RCCs,
there is therefore a potential that power supplies will be returned after a thermal latch off,
as customers are often unaware of the need to reset by unplugging the power supply.
The auto-recovery thermal shutdown also eliminates noise sensitivity associated with
discrete latch circuits, which can be sensitive to circuit design, environmental conditions
and component age.
The IC package provides extended creepage distance between high and low voltage pins
(both at the package and pcb), which is required in high humidity conditions to prevent
arcing. Other features include pulsed auto-restart operation under output short circuit and
open loop conditions.
Worst-case no-load power consumption is approximately 140 mW at 265 VAC, well
within the 300 mW European standards and even 150 mW at 230 VAC targets set in
some customer specifications. Heat generation is minimized with high operating
efficiency under all load and line conditions.
The EE16 transformer bobbin provides extended creepage to meet safety spacing
requirements.
Power Integrations
Tel: +1 408 414 9200 Fax: +1 408 414 9201
www.powerint.com
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