Results

Utlimately, the results of this project is just an LED that turns on to indicate a charging status. The battery doesn’t charge – in fact, it slightly discharges. But on the bright side, the board is no longer fried, and the IC itself seems to be behaving properly for the most part. A video of the solar charger, showing the LED light on, and analysis of the gate of the HDRIV Mosfet via oscilloscope are recorded: Solar Charger Operation Video

Quantitative Test Results | The voltage readings I got with the latest test results are summarized in the table. As you can see, the end voltage of the battery is slightly lower than the starting voltage, the reason for this is still not understood.

Test Point	Voltage Reading
Vsolar	10.10V
VCC	10.07V
ToHIDRV	10.08V
TS	2.0V
VREF	3.27V
REGN	5.95V
BTST	7.96V
HIDRV	see image of oscilloscope
LODRV	see image of oscilloscope
VFB	1.788V
SRN	7.2V
SRP	7.2V
PH	7.2V (see image of oscilloscope)
Vbat-Start	7.23V
Vbat-End (30 minutes later)	7.18V

This image depicts the HIDRV gate( in yellow) plotted with the HIDRV soucre, or PH (in blue).

This figure shows the HIDRV gate in yellow, and the LODRV gate in blue when the circuit is attached to both the solar panel and battery. It appears to be trying to switch in Discontinuous Current Mode (DCM).

The scope shows the HIDRV gate in yellow, and the LODRV gate in blue when only the solar panel is attached to the circuit. Notice the drop in DC offset when when the battery is not connected. The buck converter still appears to be trying to operate in DCM

What I learned from this project | There's always something to learn

• Learning how to interpret datasheets
• New knowledge regarding the helpfulness of help forums such as E2E
• A better understanding of mosfets, their inherit body diode, and their application in switching mode regulators.
• A stronger grasp on the concepts of photovoltaic panels such as their I and V curve characteristics
• Trouble shooting practices - taking a methodical approach

Future Work |

1. a closer investigation of the layout of the board and how it may be affecting the PWM and turn on/off of the external mosfets at higher frequencies.
2. test the board with a solar panel with a known greater watt rating to see if I see the same behavior as before.
3. Further testing with the mosfets and different charge criteria to how their switching characteristics change
4. Maintain ongoing communication with TI application engineer to see if he can assist with trouble shooting
5. Once the circuit board operates to charge a battery, I plan to perform analysis on the efficiency of the MPPT, the charge rate of the battery and compare it to a typical charger that charges at 0.5A, then I plan to make improvements on the board, such as including a thermistor and adjusting the MPPT resistor divider set point appropriately once I have the means of testing my solar panel for the MPP.
6. Lastly, the long stretch goal will be to design the Inverter portion of the circuit where I take the battery, convert it to AC, then push it through a transformer before it travels through the electric fence.