Teardown: Outback FM40 MPPT

4. Mai 2023 Uncategorized

stm32f103c8t6 mcu
Switching FETS 075n15n (7,5mΩ, 150V, 2 parallel)
HYG007N03LS1C2 as low-side protection?
LMV932ma OP-AMP for current sensing (wires to „shunt“ in the drawing). OP’s Vcc is connected to battery (+). OP Amp V(-) uses some transistor voltage stabilisation (Vcc-5V, source or emitter follower?). The output current at the collector is then flows through a 2k resistor to the MCU ADC pin, which is pulled down with 3.3k, which is the current gain resistor.
Caps: In: 4x 470uF 160V AISHI HL 105°C 2218JPET

from the LMV93x-N data sheet. instead of connecting OP’s GND to ground, use a Vcc-5V supply. R3 still connects to ground and it doesn’t change V_out because Q1 collector current is not affected by the OP’s GND shift.

2channel OP amp current sensing with (Vcc-5V) supply circuit

Low-side cascode

By using 2 MOSFET, one high-voltage and one low-voltage in a cascode configuration, we can reduce the reverse recovered charge to the Qrr of the low-voltage device. This will reduce Qrr loss but add additional dead-time loss due to ~2x Vsd. The additional conduction loss is expected to be rather low, if the low-voltage switch has a Rds_on much smaller than the high-voltage switch.

When the HS switch turns on, pulling D high. Now both LS body diodes begin reverse recovery, until the body diode of the low-voltage switch, with the lower Qrr and trr will stop conduction. The HV body diode is still powered at this time and the gate is discharged. The HV fet prevents LV channel break-down.

from Improving the Reverse-Recovery Performance of Si SJ-MOSFETs with a Low-Voltage GaN HEMT in a Cascode Configuration

Paper: Improving the Third Quadrant Operation of Superjunction MOSFETs by Using the Cascode Configuration

Power Measurement

Idle Power: 2.3 W @ 28V

Input: 58V, 4A, 225W
Output: 26.6V, 8.4A, 231W
Loss: 2.69% (eff= 97.3%)
HS Duty Cycle: 45%

Efficiency Curve over various input powers (at 58V / 26.6V, peak is at ~300W). spreadsheet

Inductor

2 toroidal coils in serial. inner/outer diameter: ~25/~50mm .
turns 15 (or 16?), total 30 (32) turns.
Wire: 2 parallel, 2.25mm diameter
120uH, 10mOhm DC resistance