Best way to step up a voltage? - Page 1
Forum section: electronics / beginners

author: Sudo_apt-get_install_yum
author_rank: Regular Contributor
timestamp: October 29, 2018, 09:11:00 am
content: Hey all!This is a simple question but I guess it’s got a lot of answers!What is the best way to step up a voltage from 3.3v to 12v? The max current draw is only 7mA.I was thinking of using a capacitive charge pump driven by a PWM pin on my micro but I’m not sure if it’s the best practice for low power applications.Since the current draw is so small id want to avoid using a boost converter. There are some for low current applications but they cost ~5$.Any suggestions or design tips would be awesome!***EDIT***They datasheet says VCC-MAX = 12.5V but later says that VCC-MAX is 15V, so I guess I could use a voltage doubler and get 13.2V and still be within specs.The datasheet doesn’t specify max noise so I’m not really sure. The IC is a SSD1306.

author: stmdude
author_rank: Frequent Contributor
timestamp: October 29, 2018, 09:11:58 am
content: How clean your want your 12V to be would be relevant

author: Sudo_apt-get_install_yum
author_rank: Regular Contributor
timestamp: October 29, 2018, 09:34:16 am
content: I’m not 100% sure but a few mV should be within tolerance I think. Not crazy amount like 100mV!

author: Ian.M
author_rank: Super Contributor
timestamp: October 29, 2018, 09:45:56 am
content: If your MCU's PWM can be gated by an on-chip comparator, you can implement the control loop of a boost converter in hardware inside your MCU, only needing an external inductor, N-MOSFET, Schottky diode, smoothing cap and a potential divider for feedback. The feedback disables the PWM on a cycle by cycle basis if the output voltage is over the threshold thus regulating it.Set the on time so the inductor doesn't saturate starting fron zero flux and the off time slightly greater than the on time, to avoid flux walking during startup. If you need more output current, you can run a software control loop to reduce the off time in proportion to the output voltage.Excessive ripple is likely to cause display flicker so you'll probably need a LC filter or a capacitance multiplier after the point the feedback divider taps from.

author: pieroc91
author_rank: Contributor
timestamp: October 31, 2018, 01:29:34 pm
content: On a project i needed 12v from 7.2v, i just bought a kit based on a mt3608 that are less than $5 , tested to see how much stress could handle and overdrived an 12v motor from 3.3v, the motor suffered more than the booster, really happy on how easy to use it was

author: johnkenyon
author_rank: Regular Contributor
timestamp: October 31, 2018, 07:54:39 pm
content: Quote from: pieroc91 on October 31, 2018, 01:29:34 pmI would recommend looking at the following article when using MT3608 boards from eBay etc.https://www.eevblog.com/forum/other-blog-specific/is-youtuber-_simple-electronics_-here-re-mt3608-modules-catching-fire/TL;DR version - these boards release the magic smoke when Vin is greater than the Vout selected on the trimmer pot.

author: pieroc91
author_rank: Contributor
timestamp: October 31, 2018, 08:11:55 pm
content: i've bought like 7 of them... they were so cheap that i decided to sacrifice one or two to test how they worked and at first they did nothing, like the video, but after rotating the trim like 3 millions of spins they started to work and suprised me how good they worked i've even put them in over consumption making the poor coil whirr and heat up but the ic runned cool... i guess the key is to have luck and not end up with a fake one.Also if the OP is trying to drive a SSD1306 that is a very small current can limit the input current of the booster for added protection

author: Sudo_apt-get_install_yum
author_rank: Regular Contributor
timestamp: November 02, 2018, 08:08:40 am
content: Quote from: Ian.M on October 29, 2018, 09:45:56 amThis seems like the most suitable solution; problem is that I have the MCU go into sleep after each push so I can’t do this because the sleep mode I use disables the timers.Quote from: pieroc91 on October 31, 2018, 01:29:34 pmI would never touch these with a 10 foot pole; they aren’t suited for neither low power application nor high current application. By looking at the efficiency curve in the datasheet you’ll se that the peak efficiency is around 200mA way above any current draw ill need, it also quickly drops off. At 5v to 12v and a few mA it says that the efficiency is ~91% witch I highly doubt, maybe under ideal circumstances

author: MiDi
author_rank: Frequent Contributor
timestamp: November 02, 2018, 08:44:56 am
content: Is the SSD1306 part of own design for display or is it part of a module?I am not shure what you are planning to do with the 12V, only power SSD1306?Why I ask: if a display is needed for 3.3V, simply put in a display module with 3.3V without getting headaches.

author: Sudo_apt-get_install_yum
author_rank: Regular Contributor
timestamp: November 02, 2018, 09:15:48 am
content: Quote from: MiDi on November 02, 2018, 08:44:56 amYeah it’s a part of an own design.Most OLED that are 128x32/64 use the SSD1306 or SH1106 driver IC; this IC has 3v3 logic level for communication. It also requires a higher voltage to drive the pixels, some ware between 11-15v. There is a built in charge pump controller in the IC’s but according to the OLED manufacturers I should not use it and go for an externally supplied voltage.