LM5015

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SNVS538C – NOVEMBER 2007 – REVISED APRIL 2013

48V ISOLATED TWO-SWITCH FORWARD

The Isolated Two-Switch Forward converter shown in Figure 25 utilizes a 1.24V voltage reference (LMV431A)

located on the isolated secondary side for the regulation set-point. The LM5015 internal error amplifier is

disabled by grounding the FB pin. The LMV431A controls the current through the opto-coupler LED, which sets

the COMP pin voltage. The output is +5V at 2.5A and the input voltage ranges from 36V to 72V. The switching

frequency is 300 kHz. The functions of the EN and SYNC inputs are the same as in the previous example circuit.

Figure 25. Isolated Two-Switch Forward

ISOLATED TWO-SWITCH FLYBACK

The Isolated Two-Switch Flyback converter shown in Figure 26 utilizes a 1.24V voltage reference (LMV431A)

located on the isolated secondary side for the regulation set-point. The LM5015 internal error amplifier is

disabled by grounding the FB pin. The LMV431A controls the current through the opto-coupler LED, which sets

the COMP pin voltage. The output is +5V at 2.5A and the input voltage ranges from 36V to 72V. The switching

frequency is 300 kHz. The Flyback converter is less complex than the previous Forward converter example in

Figure 25. However, the Flyback converter produces higher input and output ripples of voltage and currents, and

lower conversion efficiency by about 2%. The functions of the EN and SYNC inputs are the same as in the

previous example circuits.

This circuit can be used with the LM5073 for a low cost isolated Power over Ethernet (PoE) Power Device (PD)

application that does not require a discrete power MOSFET.

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