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Diffstat (limited to 'content/blog/multichannel-led-driver')
| -rw-r--r-- | content/blog/multichannel-led-driver/index.rst | 28 |
1 files changed, 14 insertions, 14 deletions
diff --git a/content/blog/multichannel-led-driver/index.rst b/content/blog/multichannel-led-driver/index.rst index 86fab72..c4e17b8 100644 --- a/content/blog/multichannel-led-driver/index.rst +++ b/content/blog/multichannel-led-driver/index.rst @@ -40,7 +40,7 @@ good timing. .. raw:: html - <figure> + <figure data-pagefind-ignore> <img src="images/pwm_schema.jpg" alt="A visualization of PWM at different duty cycles."> <figcaption>Waveforms of two PWM cycles at different duty cycles.</figcaption> </figure> @@ -96,7 +96,7 @@ on. .. raw:: html - <figure> + <figure data-pagefind-ignore> <img src="images/bcm_schema.jpg" alt="A visualization of BCM at different duty cycles."> <figcaption>Waveforms of a single 4-bit BCM cycle at different duty cycles. This BCM can produce 16 different levels.</figcaption> @@ -144,7 +144,7 @@ period, one pulse will reset the shift register and one will strobe the freshly- .. raw:: html - <figure> + <figure data-pagefind-ignore> <img src="images/olsndot_output_schematic.jpg" alt="From left to right, we see the STM32, one of the shift registers, and the LEDs and MOSFETs. The LED tape is driven to ground by the MOSFETs, which are in turn directly driven from the shift register outputs. The shift register is wired up to the STM32 with its clock and data @@ -199,7 +199,7 @@ voltrage we saw on our oscilloscope on the LED tape. .. raw:: html - <figure> + <figure data-pagefind-ignore> <img src="images/driver_ringing_strong.jpg" alt="Strong ringing on the LED voltage waveform edge at about 100% overshoot during about 70% of the cycle time."> <figcaption>Bad ringing on the LED output voltage caused by wiring inductance. Note that the effect on the @@ -215,7 +215,7 @@ likely culprit. The figure below is the schematic used for the simulations. .. raw:: html - <figure> + <figure data-pagefind-ignore> <img src="images/driver_output_ltspice_schematic.jpg" alt="The LTSpice schematic of one output of the driver, taking into account the shift register's output ESR and the wiring ESL."> <figcaption>The schematic of the simulation in LTSpice</figcaption> @@ -228,7 +228,7 @@ driver. .. raw:: html - <figure> + <figure data-pagefind-ignore> <img src="images/overshoot_sim_r0.svg" alt="The result of the LTSpice simulation of our driver output. The LED current shows similar ringing to what we measured using the oscilloscope. Interestingly, the gate voltage shows strong ringing, too."> @@ -246,7 +246,7 @@ since the estimated ESL and stray capacitance of the wiring is probably way off. .. raw:: html - <figure> + <figure data-pagefind-ignore> <img src="images/driver_ringing_weak.jpg" alt="Weak ringing on the LED voltage waveform edge at about 30% overshoot during about 20% of the cycle time."> <figcaption>Adding a resistor in front of the MOSFET gate to slow the transition damped the ringing somewhat, @@ -257,7 +257,7 @@ since the estimated ESL and stray capacitance of the wiring is probably way off. .. raw:: html - <figure> + <figure data-pagefind-ignore> <img src="images/overshoot_sim_r100.svg" alt="The result of the LTSpice simulation of our driver output with an extra 100 Ohms between shift register output and MOSFET gate. Similar to the oscilloscope measurement the ringing is much reduced in its amplitude."> @@ -273,7 +273,7 @@ cycle of the LED current is not at all equal to the 50% duty cycle of the excita .. raw:: html - <figure> + <figure data-pagefind-ignore> <img src="images/asymmetric_iled.svg" alt="The result of an LTSpice simulation of the LED duty cycle without and with damping. Dampening widens the LED current waveform from 50% duty cycle with sharp edges to about 80% duty cycle with soft edges."> @@ -283,7 +283,7 @@ cycle of the LED current is not at all equal to the 50% duty cycle of the excita .. raw:: html - <figure> + <figure data-pagefind-ignore> <img src="images/asymmetric_vgate.svg" alt="The gate voltages in the spice simulation above. The undamped response shows sharp edges with the miller plateau being a barely noticeable step, but with strong ringing on the trailing edge. The damped response shows RC-like slow-edges, but has wide miller plateaus on both edges @@ -327,7 +327,7 @@ sensitive owing to their physically large die area. .. raw:: html - <figure> + <figure data-pagefind-ignore> <img src="images/linearization_setup.jpg" alt="The led measurement setup consists of several PCBs and a breadboard linked with a bunch of wires and a big tin can to shield the LEDs and the photodiode. A large sub-D connector is put into the top of the tin can as a feed-through for the LED tape's control signals and the @@ -356,7 +356,7 @@ photocurrents for a certain BCM setpoint just as our retinas would do. .. raw:: html - <figure> + <figure data-pagefind-ignore> <img src="images/driver_linearity_raw.svg" alt=""> <figcaption> A plot of the measured brightness of our LED tape for each BCM period. The brightness values are normalized @@ -376,7 +376,7 @@ the resulting brightness curve below. .. raw:: html - <div class="subfigure"> + <div class="subfigure" data-pagefind-ignore> <figure> <img src="images/uncorrected_brightness_sim.svg" alt=""> <figcaption> @@ -432,7 +432,7 @@ Conclusion .. raw:: html - <div class="subfigure"> + <div class="subfigure" data-pagefind-ignore> <figure> <a href="images/olsndot_schematic.png"> <img src="images/olsndot_schematic.png" alt="A picture of the LED driver schematic"> |