What is this page for?
This page contains research into updating the lights boards for MSXV.
Main Considerations
Number of driver boards (try to minimize this and keep it to 1-2)
Making sure that the lights come on (part of regulations)
Aesthetics count for points
General Notes from reading
We will likely be using parallel led strings (this is pretty common in lights now days) so we need a good way to deal with this. We want to balance led strings. One example would be if there are leds in parallel and they have a forward voltage of 3.3V, since there is up to 20% variation it could be a huge difference in the voltage needed.
In general, if temp goes up, the forward voltage will drop and it will draw a lot more current → we should mount on a common heat sink (I believe this is being done in the current boards)
We can use a current mirror (this is being done in the current boards) for regulating current
if using dimmable lights, pwm is the way to go
Potential upgrades
Use independent opamps for each string instead of a current mirror, might have extra voltage but the current level should be good. More effective, less efficient, other considerations include needing a FET in a power package and that the switching frequency will be lower
We could add balsast resistors though this is probably not needed since we are using the current mirrors
increase power efficiency
Vary threshold voltages (use low voltage thresholds)
stack transistors in series
if we are using linear regulators switch to switching regulators
we can use fast switching mosfets
add more thermal vias if possible.
Make sure we keep the ground and power planes for low impedance paths
Adding decoupling and bypass capacitors (for filtering) near power pins of components
Center high power components for better thermal efficiency
even thought the driver boards are small, try to keep things away from the edge of the board
if necessary add heat sinks
Test the current boards with a PDN analyzer?
PCB Layout Considerations
Cap near the supply voltage
check signal integrity
keep path length short
Notes for our led driver
we can apply a 0.2V or lower to enter standby saving power
choose low esr cap (place it as close to the IC as possible) (on avg 4.7 to 10uf)
caps should be X7R or X5R for stability
diode showld be fast low cap. schottky with low reverse leakage
Recommendations for minimizing radiated EMI and other transients and thermal considerations are:
The decoupling capacitor (C1) has to be placed as close as possible to the VIN pin and D1 Cathode
The freewheeling diode’s (D1) anode, the SW pin and the inductor have to be placed as close as possible to each other to avoid ringing.
The Ground return path from C1 must be a low impedance path with the ground plane as large as possible
The LED current sense resistor (Rs) has to be placed as close as possible to the VIN and SET pins.
The majority of the conducted heat from the AL8860Q is through the GND pin 2. A maximum earth plane with thermal vias into a second
earth plane will minimise self-heatingTo reduce emissions via long leads on the supply input and LEDs, low RF impedance capacitors should be used at the point where the
wires are joined to the PC
Probable Upgrades
Add reverse polarity protection using PMOS transistor
Example Circuits
https://youtu.be/oFdsiRMZZWk?t=145
We could have led chasing LOL
Another example of a sequential led circuit
https://www.homemade-circuits.com/sequential-bar-graph-turn-light/
Rough Sample Nita made
There are some RC filters which delay the "ON" signal sent from power distribution, making the voltage on each of the nodes increase one after the other (you can see on the probes). The NMOS should be on each node but is just on one for illustration. the diode models an LED (which would be technically on another board - space might be constrained so we have separate boards for driver + LEDs)
Useful Resources
https://www.edn.com/overcome-the-challenges-of-driving-parallel-led-strings/
Relevant Confluence Pages