DC2014A: 5V @ 2.2A, 10 ~ 30V in, Buck

Demonstration circuit 2014A is a micropower No-Opto isolated flyback converter featuring the LT®8302. This demo circuit outputs 5V, and maintains tight regulation with a load current from 10mA to 2.2A over an input voltage from 10V to 30V. The output current capability increases with the input voltage.

The LT8302 typically needs less than 0.5% of its full output power as a minimum load to maintain good output voltage regulation. On the DC2014A, in order to avoid pre-loading, a 5.6V Zener diode is placed between its VOUT + and VOUT– to serve as a minimum load.

Transformer leakage inductance causes a voltage spike on the primary side after the power switch turns off. To limit this leakage inductance spike within MOSFET voltage rating of 65V, an RC snubber and a TVS clamp are installed to damp the ringing and clamp the MOSFET drain voltage to a safe level.

The Performance Summary table summarizes the performance of the demo board at room temperature. The demo circuit can be easily modified for different applications with some pre-designed transformers.

The LT®8302 is a simple to use monolithic micropower isolated flyback converter. By sampling the isolated output voltage directly from the primary-side flyback waveform, the part requires no third winding or opto-isolator for regulation. The output voltage is programmed with two external resistors and a third optional temperature compensation resistor. By integrating the loop compensation and soft-start inside, the part reduces the number of external components. Boundary mode operation provides a small magnetic solution with excellent load regulation. Low ripple Burst Mode® operation maintains high efficiency at light load while minimizing the output voltage ripple. A 3.6A, 65V DMOS power switch is integrated along with all the high voltage circuitry and control logic into a thermally enhanced 8-lead SO package.

The LT8302 data sheet gives a complete description of the part, operation and application information. The data sheet must be read in conjunction with this quick start guide for demo circuit 2014A.