OLED Power via internal charge pump?

Thread Starter

Okito

Joined Jan 10, 2019
6
Hi,

I'm looking for some advise on powering an OLED display!

I have not ordered the display yet but after much searching I selected this (based on size, interface(I2C) and cable type/length)

ali-link (https://www.aliexpress.com/item/1000005361020.html?spm=a2g0o.detail.1000023.22.76ae6c78YN65tv)

The information on that page is limited but after some searching I found what I think is the correct(complete) technical drawing for the screen
GLO091-D-M2018.jpg

I have visually identified the screen the screen as an GLO091-D-M2018 from the chart shown on this page, the data on this chart suggests that the display can be powered by 3.3~4.2V using the internal charge pump or with an external 9V source (for VCC)
https://www.alibaba.com/product-detail/0-91-Mono-128x32-SSD1306-OLED_60504702565.html

I would like if possible to use the internal charge pump, but don't really understand how, as with any other OLED to use the internal pump you need to add capacitors on C1/C2 lines and power to the VBAT line - these are not present on this connector.

I also found this page with a slightly different cable, the page has a suggested schematic that shows the screen being powered externally with 9V (the 9V is mentioned in the notes)
https://www.alibaba.com/product-detail/0-69-inch-0-69-OLED_60703608825.html

And then this - from someone having issues getting one to work (he never says if/how he fixed his issue but it may be related to the power or reset)
He seems to be just using 3.3V with VCC connected to ground via a cap (as in previous diagram - but no mention of suppling VCC)
https://github.com/olikraus/u8g2/issues/994

So how do I use the internal pump... Do I just connect VCC to ground or must I supply the 9V?
Also I if I have to or wanted to provide the 9V what would be the best (best = low price & PCB space) way to provide 9V for this? (I have 3.3V & 5V available, and mains power so efficiency is not much of an issue).


Thanks All.
 

Thread Starter

Okito

Joined Jan 10, 2019
6
Hi Keith, Thanks for your reply.

From the schematic in the linked page your module uses a slightly different display with a 14Pin cable with the usual connections for using the internal charge pump.
From the schematic you can see the capacitors and VBAT pins are connected on the modules board enabling you to use the internal charge pump and hence just supply the one 3.3~5V power line.

I would just order up the stuff to test out just connewcting VCC to GND, but the lead times for everything are just to long, so since I have space on the board I'm thinking that I will just include the 9V(VCC) circuit, should it not be required then I could just not mount the components.

That would still leave the issue of getting 9V out of my 3.3 & 5V supplies - could anyone suggest the best method for doing this? - I was thinking switched-capacitor charge pump, but I'm having trouble selecting a ideal device.

Thanks,
 

Thread Starter

Okito

Joined Jan 10, 2019
6
Cheers....

I had looked at charge pumps - and that one in particular, however when I 'perused' the data sheet i seen that it had a 170uH inductor, when I searched for suitable 170uH inductors and seeing the price/size of them ruled them out as both too big and expensive *I had not got as far as actually calculating what value I would need.

I see from your schematic you are using a 46uH inductor that seems to be available in much smaller packages and much cheaper - if this would be suitable - *UPDATED LINK
https://www.mouser.co.uk/ProductDetail/Murata-Electronics/LQM21DH470M70L?qs=17u8i/zlE89KtbI%2Bu6wV5Q==

I'm still thinking this seems like a lot to add just to get my 9V, with a capacitor charge pump type circuit only requiring 3 components (If I could find a suitable device)

Thanks again!
 
Last edited:

Thread Starter

Okito

Joined Jan 10, 2019
6
Thanks,

The inductor you linked is much more reasonable than the ones I found on Mouser, I widened my search ans found many more suitable possibilities :)

Size... basically as small as I can hand solder without to much pain, the area available is around 15x15mm(two layers, one component side), height available is ~5mm

Thanks... so decision made, I'll use the suggested 9V solution!
 

Thread Starter

Okito

Joined Jan 10, 2019
6
Change of plans...
So i calculated the component values for 5 to 9V and selected suitable parts.

The completed circuit uses around 12x25mm - I guess I have space for this with some moving around, the total price would be around UK£2 for the components (very rough guess).

That said if I weigh up the extra complexity and cost of using the display I originally selected (for the benefit of having a extra 5mm cable length and a ZIF / not soldered cable) I think I'm probably better off using another display that supports lower voltages, this will introduce some assembly issues, but I'll deal with them later.... I think!!!

I will still order some of the original display to see if they will work at lower voltages - as they might be useful going forward.

Nothing's ever simple!
 
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