This application note describes a highly efficient 100kHz converter that can charge a Ni-Cd battery in 30 minutes. Battery charging is monitored by a low cost microcontroller (ST6210) that provides battery voltage identification, temperature monitoring and charge control.
The document details the design of an efficient 100kHz power converter capable of fully charging a common 7.2V/1.2Ah Ni-Cd battery pack in approximately 30 minutes. The system operates as a current source, providing a constant 3.5A charge current to the battery.
| Charging Time | 30 minutes for a 7.2V/1.2Ah pack |
|---|---|
| Output Power Capability | roughly 35W |
| Charge Current | constant 3.5A |
| Switching Frequency | 100kHz |
| Battery Voltage Range | 2.4V to 7.2V (2 to 6 cells) |
| Stand-by Current | around 100mA |
The negative delta voltage method (-AV), also called negative slope cut-off circuit, is recommended.
The system turns into burst mode when the battery temperature reaches 40°C.
The microcontroller detects whether the battery pack is connected or not and switches to burst mode if absent.