Since the outputs are all isolated, the source power can be shared amongst any number of circuits so that a single bulk supply can conveniently provide power to an entire array. Such an array connection also consolidates the parasitic circuit losses so that it becomes unlikely that the source supply experiences a current reversal in normal usage (i.e. as long as net ‘charging’ power < total operating losses).
Figure 3. Synchronous Isolated Flyback Circuit Supports Bi-Directional Current Flow
Looking at the Details
One particularly well suited IC for this converter function is the Linear Technology LT3837. The typical application for this circuit is to provide low, battery-like voltages at several amps from higher voltage bulk supply rails. The only difference for the cell simulator function is that we would like an adjustable output voltage. Since turnkey high-power bulk supplies are available at 12V, we can optimize the design to use this as a source. Given that the range of Lithium cell chemistries is from just under 2V to just over 4V, we can establish a corresponding tuning range that provides versatile usage and the ability to simulate a wide range of SOC states.
Figure 4 shows one section of an array with all the part details. To provide voltage adjustment, the feedback network supports an op amp control signal such that zero volts represents about 4.2V output and 3V commands about 1.9V out. For good user control, each cell circuit is configured to have a ‘vernier’ fine tune, and then an array set is group controlled with a