LTC3723-1 130W Isolated Push-Pull Converter for PoE Applications with 93.5% Peak Efficiency

Jeoffrey (Zijian) Wang - Applications Engineer Oct 3rd 2016

This solution is a non-synchronous isolated push-pull converter designed for PoE applications, which can generate a 50V/2.6A output from a 34-38V (36V typical) input voltage range. A 93.5% peak efficiency is achieved for the whole isolated converter and the total solution can be fit into 1/8 brick footprint (2.3” x 0.9”) with proper layout. Half wave diode rectifier used for the secondary side results in a low part count, high reliability power supply. Transformer is optimized with the minimized leakage inductance to reduce the voltage spike and thus improve the overall efficiency. Figure 1 shows the efficiency performance of circuit. Figure 2 shows the full schematic. Figure 3 and Figure 4 show the output voltage ripple at full load and the half to full load transient response, respectively. Figure 5 and Figure 6 show the thermal performance.

The circuit uses the LTC3723-1 push-pull PWM controller which provides all of the control and protection functions necessary for compact and highly efficient, isolated power converters. The LTC3723-1 features peak current mode control with programmable slope compensation and leading edge blanking, extremely low operating and start-up currents and over-temperature protection. This high integration minimizes external component count, while preserving design flexibility. The LTC3723-1 is offered in a 16-pin SSOP package.

Figure 1 Efficiency vs Load Current at 36Vin, 50Vout

 

Figure 2 Schematic of 130W Isolated Push-Pull Converter for PoE Applications

 

Figure 3 Output Voltage Ripple at 36Vin, 50Vout, 2.6A Load

 

Figure 4 1.3A to 2.6A Load Transients at 36Vin, 50Vout

 

Figure 5 Top Side Thermal Performance at 36Vin, Full Load, 200LFM Air Flow, Ta = 23C

 

Figure 6 Bottom Side Thermal Performance at 36Vin, Full Load, 200LFM Air Flow, Ta = 23C

 

Software

LTspice