Overcurrent protection
This is a subproject within my project lab for my teams autonomous robot. We were tasked with using the L298 H-Bridge and the Basys3 board to run a rover chassis and have it perform a task. Within the project an overcurrent protection circuit was to be applied to protect it from a 1[A] current.
This project was part of a school project lab, and I had to write a technical report. To read the report for this project it is attached below.
Design and Simulation
This is the first step to achieving the circuit. Using LTspice a rough view of the circuit and simulation was made. Using an comparator with a pull-up resistor connected at Vcc+ and the output, I was able to simulate that when the Vref of 3.3[V], connected to a 3.3[Ω] resistor, is compared to a higher voltage, the signal reads high. Having this data allowed for the next steps.
Physical Build
After simulations went the way I intended, it was time for a physical design to be made. Using a breadboard, a DC power box and, the LM339 comparator chip, I hooked up up the required voltages.
-Vcc being 5[V] - red wire
-Vref (negative terminal) being 3.3[V] - right side red jumper cable
-Vin (positive terminal) being 3-4[V] - left side red jumper cable
Vcc and Vref are constant voltages where as Vin changed, this was done to show that when Vin is lower than Vref it did not detect overcurrent, but when it was raised above the 3.3[V] value it did detect.
Physical Simulations
Using an O-scope to test the outputs of the physical prototype, we can see that when the Vref is compared to a lower voltage/signal, it reads at the middle of the sin wave (low output signal).
Using the slider on the image, moving it to the right we can see the next simulation done. On this simulation we can see the same sin wave but the yellow bar is now moved. This represents a high output (vref being compared to a higher voltage/signal).
Final design
Starting simulations, prototypes, and testing sims all showed good results, so the only thing left to do was create a more permanent design. Using solderable breadboards, the idea was finally a working piece of equipment.
After talking with my groupmates and others around the lab, it was decided to use inputs and outputs 1 and 3 to have an extra comparator at our disposal.
PCB Design
This is the PCB design for the overcurrent. The male header pins are used for the inputs and outputs of the circuit. I added the 5[V] regulator to drop down the voltage coming in from a 9.6[V] battery, going into the Vcc ports of the comparator chip. The battery will be connected to the screw terminal providing the circuits power. The 4 resistors connected to the inputs are there if needed, right now I am only using input and output port 1, but if need be they are there for an added layer of proficiency.