Github Link: https://github.com/lhr-solar/Power-SecondaryPCB

BOM Link: https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=da938bf7b6
 

Brief Description/Purpose: 

What does this circuit do? Why do we need it?

This board takes inputs from the DCDC converter and the Supplemental Battery and selects which source to output to the fuse box. DCDC is the power from the high voltage primary battery pack that gets stepped down to 12V through the DCDC converter. The supplemental battery pack is the low voltage 12V NiMH battery pack. When DCDC is on, the board will select DCDC, and when DCDC is off, the board will select the Supplemental Battery. The supplemental should only be selected during the ignition and the fault states. The board selects the source using a 10V zener diode that will break down once DCDC reaches 10V.

This board also interfaces with both the Supplemental Monitoring PCB and Ignition Switch:

• For the Supplemental Monitoring PCB, this board sends the voltage of the Supplemental Battery out from J1.
• For the Ignition Switch, this board sends Supplemental Power to the Controls Board through J6, which is then routed back to this board through J7 when the Ignition Switch is switched from the off position. This signal is routed to the gate of Q3 which turns on the NMOS and starts sending power to the fuse box.

Pertinent Regulation(s) 

Link to Regs: https://www.americansolarchallenge.org/regulations/2024-american-solar-challenge-regulations/ 

Context

Location of the Board: The power board will be located in the electronics enclosure(HV section if the electronics enclosure is split).

List of I/O and Connections: 

Main

Schematic

List of Circuit Components  

SUP90P06-09L 

• Description: Power PMOS
• Why is it necessary: This MOSFET is placed on the power lines for each source and functions as a switch that is used to connect and disconnect each source from the output.
• Justification for selection of specific part: Able to handle high current. Should be changed in the next iteration for a smaller and less expensive MOSFET.
• Datasheet link: https://www.vishay.com/docs/73010/sup90p06-09l.pdf
• Associated passives/components: 
  • Precharge Aux Enable connector 
  • Main Contactor Enable connector 
  • 10k resistors
• Notes: Two of these MOSFETs are placed in series with each other with their directions switched to prevent current from flowing into one of the sources through the body diode while the MOSFET is deactivated. 

UM6K1N 

• Description: Logic NMOS 
• Why is it necessary: The first MOSFET in the package is used to flip the logic when the zener diode breaks down. Once the zener diode breaks down, the gate of this MOSFET will pull high and therefore pull the DCDC_Gate connection low, activating the PMOS on the DCDC power line and connecting DCDC to Fuse Out. The second MOSFET in the package is used in the inverter that flips the DCDC_Gate signal for the Supp_Gate signal.
• Justification for selection of specific part: Has the proper threshold voltage and comes in a dual package.
• Datasheet link: https://fscdn.rohm.com/en/products/databook/datasheet-nrnd/discrete/transistor/mosfet/um6k1n.pdf
• Associated passives/components: 
  • 10k pull-up resistor
  • 1M pull-down resistor
• Notes:

UM6J1N 

• Description: Logic PMOS
• Why is it necessary: The first MOSFET is used in the inverter that flips the DCDC_Gate signal for the Supp_Gate signal.
• Justification for selection of specific part: Has a similar threshold voltage to the Logic NMOS. For the next iteration we can probably buy an inverting IC for more reliability.
• Datasheet link: https://fscdn.rohm.com/en/products/databook/datasheet-nrnd/discrete/transistor/mosfet/um6k1n.pdf
• Associated passives/components: N/A
• Notes: N/A

BZX384-Q

• Description: Zener Diode
• Why is it necessary: This diode ensures that the gate of the logic NMOS is pulled low only once the DCDC voltage surpasses the breakdown voltage of the diode. This way, the source swap only occurs once the DCDC is ~11V as opposed to when it surpasses the threshold voltage of the logic NMOS.
• Justification for selection of specific part: Appropriate breakdown voltage.
• Datasheet link: https://www.mouser.com/datasheet/2/916/BZX384_Q_SER-2721638.pdf
• Associated passives/components: N/A
• Notes: Confirm the exact part number ordered in the mouser order.

Layout 

Dimensions: 82mm x 62mm

Requirements/Constraints:  N/A

Design Choices:  

• Heavy use of planes and large traces to sustain the high current flowing along the power lines
• Used MOSFETs for logic as opposed to Op-Amps due to fast switching time and to avoid feedback

PCB: 

3D Model:  

Additional Considerations 

Redesign for the next generation to avoid doing logic at 12V.