Introduction
Who
Reserved for Kevin Li co-op student
Robert Tang doing the engineering
high level architecture defined by Daniel Puratich
What
Buck Converter
6S LiHv input
27V absolute max on LiHv
5V output voltage
rpp
Kind of nice because autonomy software people like to use this hardware
5 A output current
30.5x30.5 mount pattern
usb-c (for rpi) and jst (for pixhawk) output conns
USB-C connects to the raspberry pi easily, can copy circuit from 12V->5V @ 5A Buck Converter Board
Pixhawk standard connector for POWERx style port so this can be used as a redundant supply
To be clear, both of these output connectors should be present. Only one will be used in any given system though (so both should be sized on the PCB to handle the full 5 A of current).
xt30 input connector or just solderpads for input
both in library already (2.54mm pitch solderpads)
if solderpads are used, give space for epoxy so we can strain relieve
clear polarity label would be nice if solderpads are used
Why
Powering the Raspberry Pi 5 for https://uwarg-docs.atlassian.net/wiki/spaces/ARCHS22/pages/2556133415/Fixed+Wing+2025?search_id=772ded46-862b-41b6-8115-093586821d0d if we decide we want to mount the RPi into this system and dont want to use https://uwarg-docs.atlassian.net/wiki/spaces/EL/pages/2701197313/RPi+Interface+Rev+C?search_id=b1053a4c-4ec7-47de-9489-d50daf49510a&additional_analytics=queryHash---7d2c48e78a27d21f150b620681696259928cd14daa6e640c84eaf507c582ec26 . Currently there is no plan to do this but it is nice. Ground testing power supply for the raspberry pi is also a use case, but 12V->5V @ 5A Buck Converter Board kind of accomplishes this already.
Redundant Pixhawk power supply for https://uwarg-docs.atlassian.net/wiki/spaces/ARCHS22/pages/2556133415/Fixed+Wing+2025?search_id=772ded46-862b-41b6-8115-093586821d0d . See https://docs.px4.io/main/en/flight_controller/pixhawk6x.html for details.
Engineering
Robert Tang to fill out when the time comes
Background Knowledge
Buck Converter
DC-DC Step-down voltage regulator.
Components:
Source (Vin)
Switch
Usually a MOSFET, because manually switching on/off the switch is tooo slow
Diode
In synchronous buck converter, a second MOSFET is added
Inductor
Stores and release energy (as current)
Capacitor
Smooth the voltage output
Calculating the conversion factor in CCM
*In this application we are only interested in Continuous Conduction Mode (CCM), where essentially i_L is larger than 0 for all time during CCM.
Some assumptions to be made before the calculation:
Assume CCM
Average steady state (Over period, the average values will be constant)
Vin and Vout constant with respect to time
Diodes and FETs are ideal
The calculation:
When the switch is on, during a time T_on the circuit looks like the following, where the diode acts like a open circuit (because of the reverse polarity).
The Inductor voltage, and the rate of change of current through the inductor can be tested using the following equation, their graphs are also shown.
When the switch is off, (after T_on) for a time T_offthe diode acts like a wire, and the voltage source (Vin) is replaced by an open circuit, the inductor is supplying current to the rest of the circuit.
Here the inductor voltage and the current will change
Combine the two we can get the graphs for the change in inductor voltage and current over a period T, and we also know that T_on+T_off=T
