Electronic load

The BC100 features two electronically controlled constant current loads (adjustable). The loads are meant for development purposes: One load can be used to load the output of the buck converters to verify that the ADC reads the expected current during "charging" (no battery connected while the load is connected). The other load can be used to verify that the correct current is read when the battery is discharged into the load.

Figure 1. The electronic constant current loads (section of the BC100 schematics).

The ATmega644 board controller controls the electronic loads. The load current is controlled by the duty cycle of the PWM (OC2A on TIMER 2). The electronic load is will NOT endure very high currents, and the current flowing through the loads should be limited so that it does not exceed the tolerances of the FETs (15W) and resistors (2W). Warning: the components do not have any cooling area and may suffer from thermal damage even below the recommended maximum power dissipation rating. Always keep the temperature of the FETs (Q404 and Q405) and the resistors (R444 and R445) below a reasonable temperature (very warm is ok, untouchable is bad).

The equations below can be used to determine the maximum currents for the load resistors and FET transistors - still, keep well below these values.