looking for a low size and cheap DC/DC negative inverter - Page 1
Forum section: electronics / projects

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: January 15, 2020, 07:44:20 am
content: Hi,I want to know if you know something for generating -12V from 5V like the jelly-bean MC34063 in SOT23 package,for powering op-amps, I need at most 100ma current. do we have chinese parts? I need it to be sub 0.1$

author: i_am_fubar
author_rank: Regular Contributor
timestamp: January 15, 2020, 07:48:52 am
content: I imagine a charge pump could do this for minimal cost as there's no inductor requirement.What sort of volume? Not going to get a single component solution for that cost in any low volume.

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: January 15, 2020, 09:10:08 am
content: Can a charge pump supply 100ma!?

author: Yansi
author_rank: Super Contributor
timestamp: January 15, 2020, 10:01:18 am
content: Charge pumps are the shittiest way of doing things.Use for example AOZ1282CI or any other cheap buck converter for it. There is a metric shit ton of these available. And yes, they are cheap.

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: January 16, 2020, 06:43:15 am
content: Thanks Yansi for the hint, I want to generate -10V, this part is a buck! how can it be done?

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: January 16, 2020, 11:09:30 am
content: Thanks blueskull, can it give 100ma? Also what's the size of the cap that couple into the reverse diode?

author: MagicSmoker
author_rank: Super Contributor
timestamp: January 16, 2020, 12:09:38 pm
content: Quote from: ali_asadzadeh on January 16, 2020, 11:09:30 amIt's safe to say you didn't even bother to download the MT3540 datasheet...

author: Yansi
author_rank: Super Contributor
timestamp: January 16, 2020, 12:53:56 pm
content: Blueskull: Wtf?Almost every buck converter can be used as an inverting converter. Because it doesn't matter, if it makes 3V from 5V, or -5V from 5V. Either way the output voltage is lower, that input one. (Input voltage is the Vin+Vout, output just Vout). So I have correctly suggested a AOZ1282 for the job.Just connect the input voltage to input +V terminal, the output V+ of the buck connect to input and output GND, then you get the negative voltage from the former GND of the buck converter. (In fact, this way the buck converter becomes wired as a textbook inverter).

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: January 16, 2020, 01:37:49 pm
content: QuoteI have and it's a boost cnvertor! I think blueskull has some points and i think it can be done in this way too.QuoteI do not get it fully, would you explain with a circuit diagram!?

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: January 16, 2020, 08:56:18 pm
content: Thanks

author: Yansi
author_rank: Super Contributor
timestamp: January 16, 2020, 09:07:51 pm
content: Quote from: blueskull on January 16, 2020, 03:08:19 pmI do not like this configuration and do not suggest using it. A lot of ICs do not like to switch into capacitive loads like this and will trip the OCP. Also I'd say this produces likely more EMI, due to higher di/dt in the charge pump circuit (no di/dt limiting element at transistor switch on). Output regulation is also worse (may not be an actual problem though).