Lights Driver Board

Parts:

LEDs

Note: Lights Links should be double checked to give us the best binning possible (within reasonable price).

Drivers:

PWM:

There is a PWM generator in the first versions of the design. It uses a 555 timer and a potentiometer to vary the duty cycle of the PWM signal.

I believe it is based off of this page here: https://www.electroschematics.com/pulse-generator-with-555/

We should adjust the values of the resistors and the potentiometers in order to be able to adjust the current limit of the LED driver from 50mA to 500mA.

Heat sink:

See thermal calculations here: Lights Thermal Calculations

Mechanical:

NOTE: Some of the pictures of the mechanical lights layout are no longer valid, however this is to show that we are very constrained for our lights board layouts.

Open

Open

Design

Optimizing PCB thermal performance:
https://www.cree.com/led-components/media/documents/XLamp_PCB_Thermal.pdf

Prototype Rev 1:

3 LEDs in series with no additional parts. Lights were sufficiently bright and stable, but became very hot (around 80 C) very quickly.

Prototype Rev 2:

6 LEDs in series driven by a boost converter. PWM signal provided by 555 timer. Potentiometer included in 555 timer circuit to allow experimentation with duty cycles. LEDs and current sense resistors are kept on a separate board to account for the physical constraints of the car.

List of issues:

• Lack of decoupling capacitors

• Incorrect capacitor value for 555 timer (which set the incorrect frequency for the CTRL pin on the driver).

• Pins configured incorrectly

• Lack of ground pour for stability

• Inductor was not placed close enough to the potentiometer (no boost was measured).

Further Testing for Rev 2:

• Measure current at the connectors on startup to determine whether additional capacitors are required at the connectors.

Prototype Rev 3:

• Fixed the mistakes from Rev 2

• Separate LEDs from other components to preserve space

• A zener diode is placed parallel with each LED to prevent entire LED string from burning out

• LED board will have a heat sink

List of issues:

• Too many decoupling capacitors

• LEDs are not bright enough for some lamps - Rsense must be adjusted, or more LEDs must be added for those lamps.

Testing for Rev 3:

• Determine what resistor is required to replace the potentiometer and set the duty cycle of the PWM signal.

• Start looking into light dissipation (with mechanical team)

General Testing for Lights:

• Measure brightness of the LEDs.

• Ensure that the driver is boosting the voltage properly.

• Ensure that temperature is within safe limits (<100 C).

• Measure the stability of the LEDs by using a varying voltage.

• Measure the current and voltage on startup at the connectors.