MT3608 ENable PIN ... does it work as supposed or i miss something? - Page 1
Forum section: electronics / projects

author: soubitos
author_rank: Frequent Contributor
timestamp: January 18, 2018, 01:50:25 am
content: I use MT3608https://tinyurl.com/yd5xsyh7from AEROSEMI a lot in my projects but until now, i was simply connecting the EN pin to the IN power line for permanent active configuration.I am now attempting to configure it with the EN pin either connected to IN power via jumper on the pcb or removing the jumper and connecting a cable to a logic drive (some sensor, arduino or avr etc).I was expecting that the EN pin forced to the ground would deactivate the booster (which it does) AND bring the output to 0.. As i see though, it does stop the booster but VIN goes straight to VOUT ... so there is always voltage in the output, simply not boosted when EN is forced to ground...Is this normal or am i doing something wrong? Is there a way to disable the chip so that the output goes to zero? (besides the obvious, switch relay etc)

author: floobydust
author_rank: Super Contributor
timestamp: January 18, 2018, 02:54:00 am
content: If the boost-converter IC is disabled, current flows (around the IC) through the inductor and output diode. This is how the boost configuration works.So it stops boosting but Vout = Vin-0.3VI had no luck with MT3608 boost converter pcbs from china, lots of youtube videos where they smoke and burn.Most just sit there dead, and output is Vin-0.3V

author: ArdWar
author_rank: Frequent Contributor
timestamp: January 18, 2018, 06:06:05 am
content: That is the expected behavior of most (if not all) boost converter. As it should be obvious from the schematic, when there's no switching happening, the supply current just flow through the inductor and high-side switch/diode to the load.If you need to disable the output completely just add one pass transistor as switch, or use some non-direct topology (4-switch buck-boost/SEPIC/Cuk, I dunno if that warrant the additional complexity if you don't need buck-boost in the first place)Some boost controller can be used in SEPIC configuration, some are not. My cursory google-fu showed there's some Russian guy making SEPIC 3608.

author: soubitos
author_rank: Frequent Contributor
timestamp: January 19, 2018, 01:37:23 am
content: Quote from: floobydust on January 18, 2018, 02:54:00 amI figured out this was normal i just didnt get the functionality of the EN pin.. in my project, it will only save some battery life which is good but other than that, nothing else.... well, saving battery life is not bad for an extra jumper or switch on the board LOL!I dont use ready made booster modules, i make my own stuff with it and so far, it works very well.... i did fry a few over time but only testing/abusing them.... or by human error...The one thing one needs to make sure with them is the voltage divider resistors... if not selected carefully, it is easy to drive the ic to overshoot and it will die almost in split second (done that!)

author: soubitos
author_rank: Frequent Contributor
timestamp: January 19, 2018, 02:01:18 am
content: Quote from: ArdWar on January 18, 2018, 06:06:05 amI will add something to isolate the output when chip is in disable mode in my future version of the projects i use them, i definitely dont need to make things more complicated, i might go with another booster chip in my next prototype though, not because MT3608 is disappointing but because i think i found a couple alternatives that suit my designs better..

author: soubitos
author_rank: Frequent Contributor
timestamp: March 03, 2018, 09:21:06 pm
content: Quote from: ArdWar on January 18, 2018, 06:06:05 amI did some research about the russian SEPIC conversion on chinese MT3608 modules and its interesting.I am really very confused right now as i cannot find a ready made IC to fit my design demands...The problem is this... i have a 8-25V input and a 1-2S (or 2-3S) lithium pack which means 3/4.2-6/8.4 or 6/8.4-9/12.6V ... i need to make a "power supply" out of these two sources so, generate 0 or more realistically say something over 1V and up to 12-15 or more V and min 1A hopefully 2-3