EE 5522 UMD Fall, 2015
PROPOSAL: Take-Home Final Exam (Due 12-18-2014 at 4PM if accepted)
*** TWO Students may work together to prepare this examination ***
Problem Statement:
Create an engineering design document that provides the preliminary component and functional design for a portable USB re-charging station. It must have the following capabilities:
Energy storage will be accomplished using super-capacitors, namely Nichion
4000 farad, 2.5 V caps.
Two such caps will be used in series to make a 5 volt, 2000 F bank.
The device must be capable of fast re-charging from a standard 120 Vrms wall outlet
The device will supply a constant 5 volt output at up to USB 3.0 current specifications
The device will have a basic human-machine interface, such as indicator lights, to display “state-of-charge” in the capacitors, connection to AC source and connection to USB load.
A programmable device, such as arduino, will be used to measure output voltage and control the duty cycle that maintains output voltage.
Deliverables:
The document MUST contain the following components:
1.
A full electric schematic of the AC/DC conversion, storage capacitors, DC/DC converter that maintains 5.0 volts (even though the capacitor voltage drops as its charge depletes), over-current protection, circuitry for indicator lights, etc.
2.
Design calculations on sizing the filter inductor for the DC/DC converter to maintain CCM operation, etc. Also, make sure to calculate the time necessary to put a full charge on the capacitors for your design. It looks like the Nichion cap has an internal resistance of 2.2 milli-ohms. Assume you can have I 2 R heating of 1 watt during charging.
3.
Discussion about design choices, such as MOSFET vs. IGBT or Si Diode vs.
Schottky. Remember, you’re potentially only working with 5.0 volts DC, unless your design creates additional potentials.
4.
Discuss/show how your programmable device receives its power. If it is powered from the energy stored in the super-capacitors, demonstrate how the system will power-up reliably at the start of a new charging cycle and how it will shut -down at the end of a discharge cycle. If the device is
S.R.Norr

EE 5522 UMD Fall, 2015 powered by separate energy storage, demonstrate that it will re-charge faster than the super-capacitors and last longer under normal operation.
5.
At a minimum, the device should clearly indicate a state of full charge and a state of impending full discharge (you could use LEDs).
6.
The device should protect against overcurrent when connected to the AC power system (fuse, re-settable circuit breaker, etc). Relying on the circuit protection in the AC system is unwise.
7.
The device should protect against overvoltage conditions on the supercapacitor and the USB output. At least state how your programmable device would react to such an overvoltage. Good designs might include some sort of physical back-up to isolate the capacitors (or USB output) in the event of an un-resolvable overvoltage condition.
8.
The device must have three operating states: Charging, Dormant and
Discharging. Design steps should be taken to ensure that the Dormant state is a very low power condition for the super-capacitors.
9.
A Bill of Materials (BOM) listing the components and retail prices, summed to a total material cost.
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