EP11 datasheet(8/46 Pages) POWERINT

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EPR-00011 - 70 W Adapter

22-Jan-01

Page 8 of 46

Power Integrations Inc

Tel: +1 408 414 9200 Fax: +1 408 414 9201

www: http://www.powerint.com

an under-voltage detect (100V), over-voltage shutdown (450V) and line feed forward with

DCMAX reduction features.

Two resistors are used in series to allow low cost ¼ W

resistors which have a lower voltage rating.

The under-voltage detect ensures that the output is glitch free at start-up and shutdown.

With the combined value of R14 and R15 as shown, the power supply does not start

operating until the DC rail voltage reaches 100 VDC. On removal of the AC input the UV

sense prevents the output glitching as C7 discharges turning off the TOPSwitch-GX when

output regulation is lost or when the input voltage falls to 40 V, whichever occurs first.

The over-voltage feature shuts down the supply if the rectified input voltage exceeds

approximately 450V. If exceeded this protects the TOPSwitch-GX from excessive drain

voltages providing an extended AC surge withstand to 700 VDC (BVDSS rating), ideal for

countries with poor power quality.

Finally the line feed forward feature reduces output line frequency ripple by modulating

the control loop with the line frequency ripple on the DC rail, ideal when using a relatively

small input capacitor.

Resistors R5, R6, and R12 connect to the EXTERNAL CURRENT LIMIT pin (X) and are

used to externally program the current limit level of the device to just above the operating

peak current at full load and low line. This allows use of a smaller transformer core and /

or higher transformer primary inductance for a given output power. Reducing transformer

size and TOPSwitch-GX power dissipation, while at the same time avoiding transformer

core saturation during start-up or output load transient.

This resistor network also

reduces the current limit with increasing line voltage. This limits the maximum available

power during overload conditions at high line (see Figure 10) removing the need for any

protection circuitry on the secondary.

The secondary windings are rectified and filtered by D1, D5, C1, and create the 19 V

output voltage. Two windings are used, with separate dual rectifiers (for equal current

sharing), to lower winding losses and maximise efficiency.

Inductor L1 provided

additional filtering in conjunction with C4 and C14.

The 19 V output is directly sensed by the series combination of R4 and R13 that form a

divider with R10. These resistors together with the reference node voltage of U3 set the

output voltage. Other output voltages are also possible by adjusting the transformer turns

ratios and value of R4 and R13. Resistor R2 sets the overall DC gain of the control loop

and R7 provides bias for voltage reference U3. Capacitor C11 is the main compensation

capacitor and together with R11, C9, R8 and C10 ensure stability of the control loop.

The TOPSwitch-GX control circuit allows the switching frequency to reduce at light or

zero load conditions, eliminating the need for a pre-load resistor to control the output

EP11 Datasheet(PDF) 8 Page - Power Integrations, Inc.

EP11 Datasheet(HTML) 8 Page - Power Integrations, Inc.

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