Forward Topology

(See Figure 2)

B

Beenneeffiitt:: Lowest cost for >6A output currents.

W

Whheenn ttoo U

Ussee:: Typically for output voltages less than 12 V.

Recommended for multi-output voltages (<2.5V) and for applications

requiring highest efficiency.

Advantages:

• Low output ripple current results in lower output capacitor cost.

• Higher efficiency due to lower peak and rms currents can utilize

synchronous rectification.

• Isolated output.

Disadvantages:

Requires additional components including an output energy storage

inductor and additional rectifying device (diode or MOSFET).

Figure 2. Transformer Forward Topology.

Cooper Bussmann Coiltronics 4 to 13 Watt PoE Transformers.

The Coiltronics lines of RoHS compliant PoE configurable transformers

are available for use with a wide variety of PWM controllers from

several IC manufacturers, providing PD supply solutions that utilize

either

flyback or forward converter topologies.

Flyback and forward DC-DC converters solve the isolation

requirements of the PoE standard.

Forward and flyback switcher

topologies can use Coiltronics PoE transformers to isolate the PDs PoE

interface from the rest of its circuitry while stepping down the PoE

input voltage to power the PD circuits.

Coiltronics

flyback PoE transformers support 1500Vac isolation in the

power converter with feedback voltage of 11V at 0.1A. Available in

4W, 7W and 13W, the transformers accept input voltage ranging from

29.5V to 60V using a nominal 250kHz switching frequency.

Coiltronics PoE transformers feature split primary and secondary

windings to minimize leakage inductance (the result of imperfect

magnetic linking of one winding to another). These transformers allow

multiple output variations. 3.3V and 5V PoE transformers support

three outputs while 12V transformers support two outputs. These

three transformers have parallel windings with identical output voltage.

These enable the windings to be used:

• Independently for isolated circuits

• Paralleled for higher current

• Connected in series to generate higher voltages.

Cooper Bussmann Coiltronics 26 Watt PoE Transformers.

Coiltronics also offers transformers for

forward converters with

synchronous rectification support, 1500Vac isolation, isolated

feedback voltage and can deliver up to 26W. These transformers

accept an input voltage range from 29.5V to 60V using a nominal

300kHz switching frequency.

These components operate in ambient temperatures between -40°C

and +85°C with a maximum operating temperature of 125°C.

inductor or transformer configurations. This same user-configurable

concept is used in the PoE transformer family (VER suffix devices).

Connecting the windings in parallel increases the current carrying

capability while connecting in series increases the output voltage.

These devices provide even greater flexibility in the number of voltage

and current combinations than are available in this standard off-the-

shelf transformer series.

Typical PoE/PD Configurable Transformer Applications

• For IEEE 802.3af-compliant Power-over-Ethernet applications.

• UPS, VoiP Phone, wireless LAN access point, Bluetooth access point,

network camera, building access systems.

• Retail point-of-information systems.

• Vending/gaming machines.

Input

Output

Vo

Vin

N1

N2

C

L

+

+

_

_