EPR-000013 Datasheet, PDF (8/56 Pages) Power Integrations, Inc. – Engineering Prototype Report (EP13) 43 W / 57 W pk, 5 Output TOPSwitch팜-GX (TOP246Y) Power Supply

EPR-000013 – 43 W Multiple Output TOP246 Power Supply
08-May-2001
voltage at the primary was fixed at 100 V to optimize output cross regulation, thus fixing
the number of primary turns. A design with fewer output voltages can take better
advantage of the design flexibility offered by the TOPSwitch-GX family.
D6 and C3 provide a DC voltage of approximately 12 V to power the TOP246Y. A
relatively large value of C3 (1 µF) is used to provide bias voltage ride-through during
severe output load transients.
Capacitor C4 filters the internal bias supply of the TOPSwitch-GX, providing the
necessary peak currents to drive the gate of its internal high-voltage MOSFET. Capacitor
C4 also determines the TOPSwitch-GX auto-restart frequency, and along with resistor
R3, helps to compensate the power supply control loop.
Transformer T1 utilizes a nine section slotted bobbin designed for an automated
production environment. Primary and secondary windings are applied in alternate bobbin
slots using ordinary magnet wire. The slots provide the necessary safety isolation and
creepage distance between the primary and secondary windings without the need for
additional insulation of any kind. The large number of winding slots provides sufficient
interleaving of primary and secondary windings to reduce the leakage inductance to a
tolerable value, while the open construction of the transformer reduces winding
temperature rise, allowing use of relatively fine wire, further facilitating automatic winding.
Diodes D7, 8, 9, 10 and 11, along with capacitors C7, 9, 11, 13, 14, 16 and 17 are used
to rectify and filter the five output secondary windings of T1.
Two techniques are used to properly center the output voltages of the supply and to
improve cross regulation between outputs. An ultrafast rectifier is used for D10 (5 V
output rectifier) instead of a Schottky rectifier. The extra voltage drop of the ultrafast
rectifier centers the 5 V output at precisely 5 V. Also, the 12 V, 18 V and 30 V secondary
windings are stacked on the cathode side of the 5 V output rectifier (DC stacking) rather
than the anode side (AC stacking). This means that the current for these outputs passes
through the 5 V output rectifier (D10) as well as their respective output rectifiers (D7, 8,
and 9). This increases the dissipation in D10, but has two beneficial effects. First, the
extra voltage drop imposed by D10 precisely centers the 12 V output. Also, since the
current for the 12 V, 18 V and 30 V outputs passes through D10 and its connecting
printed circuit traces, variations in the current from these outputs will modulate the
voltage drop across D10 to a certain extent. This change is passed on to the 5 V output,
causing the output control loop to change the duty cycle to compensate. This indirect
feedback improves the cross regulation of these outputs.
Inductors L2, 3, 4, 5 and 6 are used along with capacitors C8, 10, 12, 15 and 18 to
provide high frequency filtering for the five outputs of the supply. These filters greatly
reduce the switching frequency ripple and high frequency spike noise at the outputs of
the supply.
Power Integrations, Inc.
Tel: [phone] Fax: [phone]
www.powerint.com
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