Help with troubleshooting boost converter for eInk display - Page 1
Forum section: electronics / beginners

author: OrlandoBlyat
author_rank: Newbie
timestamp: November 26, 2024, 06:21:24 pm
content: I have a project I made that uses an eInk display. While prototyping I used this module:https://www.aliexpress.com/item/1005004644515880.html?spm=a2g0o.order_list.order_list_main.162.13df1802Q231REfrom weActStudio. For my custom PCB I just copied the driver circuit from the module:https://github.com/WeActStudio/WeActStudio.EpaperModule/blob/master/Hardware/WeAct-EpaperModule%20SchDoc.pdfThis is my layout in KiCad:The inductor and mosfet are different from the original but still work, which I tested by swapping the original components with mine. I managed to get the same diodes as on the weAct module.I suspect that somehow my layout is at fault:I have broken out the VGL, VGH, GDR and RESR signals. When connecting the display to the board, plugging a microcontroller in then attempting to update the display. The VGL stands at a still 0V and VGH at 3.3V.The working module produces +-15V. I am a begginner in electronics. I have a brief understanding of boost converters. This specific variant is foreign to me. I did a check over the connections and found nothing wrong. I need some basic troubleshooting steps from someone who is more experienced.

author: jwet
author_rank: Frequent Contributor
timestamp: November 27, 2024, 02:26:17 am
content: The layout isn't great but it should work. The trick to switchers is to keep the loop of the drain of the FET (pin 3), the inductor and C15 tight. With a 47 uH inductor, this isn't quite as critical. This is a relatively low power boost and looks ok.Troubleshooting- you need a O'Scope of some kind- pretty basic.E_VGH will be Vin minus a diode drop if the transistor isn't getting switched on and off. There should be a strong square wave signal on E_GDR that turns the FET on and off hard. The source E_RESR is sensing the fet current. When the FET gets turned on, it will pull its drain down low, almost to ground. The current in the inductor will rise linearly and is sensed at the 2.2 ohm resistor. The gate drive will turn off when this voltage rises to probably .5V- its specific to the boost converter. If the gate isn't pulsing, remove the FET and see if the gate runs without it. If so, FET gate is shorted, replace FET. Once you get FET switching, things should just work.Good Luck.

author: BennoG
author_rank: Frequent Contributor
timestamp: November 27, 2024, 06:32:37 am
content: Most gnd connections are single via, and some can carry high pulsed currents. (especially D4 and D5)The GND path from R10 to D5 is long and involves 2 via'sYou also left C16 out, that is used to boost the start current in the inductor.Benno

author: OrlandoBlyat
author_rank: Newbie
timestamp: November 27, 2024, 12:50:14 pm
content: This is extremely informative, thank you!

author: OrlandoBlyat
author_rank: Newbie
timestamp: January 19, 2025, 04:00:44 pm
content: After almost two months of school and work, I finally managed to get ahold of a cheap chinese osciloscope.After checking the working module's FET gate I saw a nice somewhat square wave, every time the display updated:When checking the same on my module I getnothing.I double checked all the connections to the module, there are SCL, SDA signals going to the display.I'm pretty sure that the module isn't communicating with the microcontroller properly. Again as I am out of my depth I don't have a clue how to properly troubleshoot this.