Bugfix for setting currents/voltages below 1A/1V for BK1688B
This MR fixes two issues:
- The formatting of commands sent to the BK1688B was incorrect when setting voltages or currents below 1V/1A.
- The output voltage of the BK1688B cannot be set below 0.8V. Trying to do so leads to no response from the PS (at least with the PS firmware version 3.3 that we have). Added an exception in setVoltageLevel for values less than 0.8V.