Transformerless 85-260V-AC to 12V-DC Power Supply - Page 1
Forum section: electronics / general

author: hesam.moshiri
author_rank: Regular Contributor
timestamp: August 29, 2024, 11:17:36 am
content: Whenever you hear the transformerless (ac to dc converter without transformer) supply term, you initially imagine the capacitor-based solution: a high-voltage non-polarized capacitor in series with the mains line, a bridge rectifier, a Zener diode, and a filtering electrolytic capacitor. Such a circuit is not only unable to deliver sufficient current for many applications, it is also not a reliable solution for the industry. However, you might see such circuits in some cheap products. This design uses a different method.CAD: Altium Designer, Altium-365PCB Fabrication: PCBX.comTools: Siglent SDL1020 DC Load, Siglent SDS1104X-E Oscilloscope, VEVOR SC240M Thermal Camera

author: hesam.moshiri
author_rank: Regular Contributor
timestamp: August 31, 2024, 10:26:15 am
content: [PCB Update] AC to DC Transformerless Power Supply

author: temperance
author_rank: Super Contributor
timestamp: August 31, 2024, 10:36:05 am
content: That's nothing new.Regarding a cap dropper you state:QuoteHow did you conclude they are not reliable?

author: hesam.moshiri
author_rank: Regular Contributor
timestamp: August 31, 2024, 02:41:11 pm
content: QuoteThe clearance between the bottom polygon and capacitor pins was low. I increased it to 1.8mm

author: temperance
author_rank: Super Contributor
timestamp: August 31, 2024, 09:18:18 pm
content: QuoteI'm referring to the bolt part of your statement.

author: Psi
author_rank: Super Contributor
timestamp: August 31, 2024, 09:58:34 pm
content: Nothing wrong with a capacitive dropper psu for consumer products.It just has to be designed and used safely.But it is true that they are low current, under 50mA. However since the voltage is only set by a zener if you want you can have your 50mA at 48V and then have a little DCDC to get 500mA at 3.3V

author: DavidAlfa
author_rank: Super Contributor
timestamp: September 01, 2024, 12:12:03 am
content: QuoteHah! Capacitor droppers are EVERYWHERE in commercial products.

author: temperance
author_rank: Super Contributor
timestamp: September 01, 2024, 01:48:01 am
content: QuoteAnd also industrial products. They are reliable when properly designed. That is: correct type of capacitor with proper surge and transient protection.But what I wonder is why the OP must list the CAD and PCB supplier used for this project... As if mentioning those made any improvement to the power supply. Oh, I see, it is all about promoting your video blog and your sponsors who seem to be happy with the things you present.I watched a few of your videos and they contain a lot of mistakes.

author: boB
author_rank: Frequent Contributor
timestamp: September 01, 2024, 02:04:36 am
content: When I think about a transformer-less (non-isolated) converter, I normally think of a buck converter for an application like this.Quite a range but can be done. Probably better to use a transformer. You could use a flyback which is not technically a transformer.boB

author: Xena E
author_rank: Frequent Contributor
timestamp: September 02, 2024, 07:41:39 pm
content: Quote from: Psi on August 31, 2024, 09:58:34 pmWhy limited to 50mA ?

author: temperance
author_rank: Super Contributor
timestamp: September 02, 2024, 07:53:49 pm
content: The OP is only abusing this forum for promoting his crappy video blog.

author: Psi
author_rank: Super Contributor
timestamp: September 03, 2024, 01:37:01 am
content: Quote from: Xena E on September 02, 2024, 07:41:39 pmThere's no hard limit, it's more a practicality limit in most application.Normally devices that use capacitive dropper power supplies do so because they are physical size constrained.The higher max current you need the bigger the capacitor becomes. Once you get to around 50mA the X2 mains film capacitor is so big that you have enough room to use a different/better power supply type.Also capacitive droppers are shit in terms of efficiency. If your circuit needs up to 50mA periodically (like for a relay) but normally only needs 1mA to run a MCU you must design your capacitive dropper so it can produce 50mA. However that means it's always drawing 50mA 24/7 whether you need it or not. Either the 50mA goes into your circuit or, if not, the remainder is all burnt off as heat in the zeners and you have to deal with the heat dissipation, which gets worse at higher currents.

author: Xena E
author_rank: Frequent Contributor
timestamp: September 03, 2024, 05:10:02 am
content: Quote from: Psi on September 03, 2024, 01:37:01 amThanks.I just commented as I've just done one for 1 amp on a 50Hz supply! It's for an approximate constant current in a device that has to have no magnetic radiated fields: it's dopper capacitor is 15μF.The design is customer led so inevitable it would be quirky but works it does!Regards,X

author: ArdWar
author_rank: Frequent Contributor
timestamp: September 03, 2024, 05:58:22 am
content: Quote from: boB on September 01, 2024, 02:04:36 amTransformers are neat way to keep duty cycle within sane value.You can also use tapped inductor (a.k.a. autotransformer) to do that, which I guess even closer to "not a transformer" than a flyback. Depending on if you're function purist or construction purist.