DC1322A: 300V Cap Charger, 8 ~ 40V in

Demonstration circuit 1322 is a high current capacitive charging circuit featuring the LT3751EUFD. It is a DC/DC flyback converter used to charge large capacitors to high voltages. The circuit implemented on the board is a simple example of how to charge a 400uF capacitor to 300V in approximately one second at 8Vin and 400ms at 40Vin. An output capacitor discharge circuit is included on the board for the convenience of the user. This discharge circuit can be disabled by the user or permanently enabled at the expense of a minor degradation in the charging profile.

The LT3751 is a current-mode flyback controller optimized for charging large value capacitors to a predetermined target voltage. This target voltage is set by the turns ratio of the flyback transformer and just three resistors in a simple, low voltage network, so there is no need to connect components to the high voltage output.

The charging current is set by an external sense resistor and is monitored on a cycle-by-cycle basis.

The LT3751 datasheet gives a complete description of the parts, operation and application information. The datasheet must be read in conjunction with this quick start guide for working on or modifying the demo circuit 1322.