Series STR-F6600

OFF-LINE

QUASI-RESONANT FLYBACK

SWITCHING REGULATORS

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

™

14

TM

Capacitors

Electrolytic capacitors carrying large switching fre-

quency ripple currents (C1 and the output capacitors)

should be capable of handling the high rms currents

involved. Capacitors with low ESR are suitable. The

quasi-resonance capacitor C4 should be a high-voltage

ceramic type suitable for pulsed current operation.

The safety critical nature of the off-line application

must be considered when selecting both X and Y capaci-

tors for common- and differential-mode noise filtering.

Use of the low-noise quasi-resonant Series STR-F6600

will allow optimization of these capacitor values.

C5, the 470 pF filtering capacitor should be a 50 V

temperature-stable (COG) ceramic type.

Resistors

Resistor R5 carries high-frequency current, and so a low

internal inductance type of 1 W rating should be used.

Resistor R9 (R

All other resistors can be 1/4 watt or 1/2 watt metal

film.

Diodes

Diodes carrying the high-frequency flyback currents

(such as the transformer rectifier diodes) should have a fast

or ultrafast reverse-recovery characteristic, adequate

current handing and peak reverse-voltage rating. Allegro/

Sanken supplies a range of suitable diodes, and these are

described in the Allegro/Sanken short-form catalogue

(AMS-127) or latest issue of Bulletin D01EC0.

Optocoupler

Both Toshiba TLP 621 and Siemens SFH 610A2 or

615A2 are suitable. A current-transfer ratio of 50% to

200% is acceptable.

Error Amplifier

A standard TL431 transconductance amplifier or an

Allegro/Sanken Series SE error-amplifier IC can be used.

The Series SE is particularly well-suited to high-voltage

(70 V to 140 V) power outputs.

If a Series SE error-amplifier IC is used, normally phase

compensation is not required. Should additional high-

frequency attenuation be required, a capacitor (0.022

µF or

less) can be connected across the primary side (collector-

emitter) of the optocoupler, a diode to maintain quasi-

resonant operation should be added in series with the

phototransistor emitter.

Applications Information

The products described here are manufactured in Japan by Sanken

Electric Co., Ltd. for sale by Allegro MicroSystems, Inc.

Sanken Electric Co., Ltd. and Allegro MicroSystems, Inc. reserve the

right to make, from time to time, such departures from the detail

specifications as may be required to permit improvements in the

performance, reliability, or manufacturability of their products.

Therefore, the user is cautioned to verify that the information in this

publication is current before placing any order.

These products are not authorized for use as critical components in

life-support appliances, devices, or systems without express written

approval.

The information included herein is believed to be accurate and

reliable. However, Sanken Electric Co., Ltd. and Allegro

MicroSystems, Inc. assume no responsibility for its use; nor for any

infringements of patents or other rights of third parties which may

result from its use.