Half-bridge SMPS special  - Diode Gone Wild (and cat) pass 100k subscribers - Page 1
Forum section: electronics / beginners

author: Cliff Matthews
author_rank: Unknown
timestamp: January 19, 2019, 07:26:20 pm
content: This has to be one of the most practical SMPS videos around (even for many beginners). Also, there's something about theup-close format and rustic natureof his material that make this electronics channel a winner! Congrats on the 100K!I worry about the cat.. Maybe one day if it no longer appears on the bench, we'll be able to say it got licked?Enjoy!It's hard to believe, but it's been over a year since I started promoting this guy on our YouTubers list. I got PicoScope UK interested in send him a scope for his channel, but maybe there was something not allowing it to be sent to the Czech Republic? His Russian scope seems to be 'doing the business' just fine though..

author: Cliff Matthews
author_rank: Unknown
timestamp: January 20, 2019, 08:49:03 pm
content: Any clue's about how he was able to fish a wire through the PCB mount transformer?https://youtu.be/KIilQrgJ-gg?t=795Certainly it's good way to avoid buying $500 active probe..

author: wraper
author_rank: Unknown
timestamp: January 20, 2019, 08:57:50 pm
content: Quote from: Cliff Matthews on January 20, 2019, 08:49:03 pmIt's not that difficult. Bent end of wire as half circle and push it through. You may need some help with tweezers on the opposite side to guide it properly.I wonder why he used thermal paste on sil-pads. It's completely useless, especially considering the strong tightening method used in this PSU.

author: Yansi
author_rank: Super Contributor
timestamp: January 20, 2019, 09:02:34 pm
content: I think that thermal paste should also NOT be used on silicone pads. It can harden them and eat them till they fail. (seen dried damaged silpads numerous times, probably due to using such paste on them).

author: Cliff Matthews
author_rank: Unknown
timestamp: February 11, 2019, 09:01:47 pm
content: Second part in the series.Again really good material for those less familiar with SMPS concepts.

author: Yansi
author_rank: Super Contributor
timestamp: February 11, 2019, 09:11:58 pm
content: A diode is probably missing in the center tap of the NPN driving transformer. Without it the current ca get partially shunted back to the power supply. Not sure if mistake when the schematic was drawn or intention to shave every cent possible from the BOM.Edit:I see two more mistakes (either be it schematic drawing, or the chinese designer guy was smoked):The base-to-ground resistors of the C1815 driving transistors are conneted a bit weirdly and,the auxiliary power winding should in fact be referenced with the center tap AFTER the current sense shunt.The schematic also contains some other interesting circuit nuances I'd consider at least strange and not much reason for them (for example the parallel RC in the pin 16 of the TL494).Also, Danyk's explanation of the current limit feedback loop I find kind of strange, as he probably? didn't get the point how that works. The current is not sensed by pin 16, that's just GND reference. In fact it is sensed in the node on the pin 15, where the reference current (5V ref divided by the 100k resistor) should equalize the node voltage to that of GND potential with the current flowing out of the node through the 1k resistor, towards the shunt - yes, the current is sensed as a negative voltage with respect to circuit GND.(That is because this way the burden voltage is compensated for in the voltage feedback loop, as the 5V reference is referenced to control circuit GND, which happens to be the output V- terminal).But otherwise very well executed explanation, at least for beginners or those who are looking for more circuit specifics of these power supplies.

author: Cliff Matthews
author_rank: Unknown
timestamp: February 13, 2019, 12:33:17 am
content: Quote from: Yansi on February 11, 2019, 09:11:58 pmWell as much as I want to dig-in at the level of you and DanyK, I'll probably hold off until his series finishes. I don't know why he's not on the forum (100K subs or a day job might be a reason) but he replied explaining a bit more:The diode in the centre tap is really not there. (I know that this diode is present in AT/ATX power supplies, but they also use the auxiliary transformer for current sensing.) But it works anyway. The current from the auxiliary transformer probably backfeeds into the auxiliary power supply, but it doesn't seem to be a problem. It may actually help to power the chip. ... The base to ground resistors of the C1815s are really connected this way (each of them a different way), no matter how odd it looks. It's not my drawing mistake. I was also surprised by this and I triple checked it. Maybe this gives the circuit a starting position on power up. ... The current sensing shunt drops only less than 50mV, so it's not that important where the control circuitry ground is connected. But you're right, the ripple of the shunt goes into the auxiliary power. I was also a bit surprised by this. Maybe it's done like this so the transformer has one pin less. The center taps of the main and auxiliary secondaries are on the same pin. Maybe the auxiliary winding is actually not a winding, but only taps on the main secondary! This may be the explanation. ... The RC on the pin 16 is there for a good reason. Both inputs of an OpAmp should be connected via the same resistance (here it is 1k). This is a common practice with OpAmps. Using the same resistance in both inputs helps to cancel the voltage drop on the resistors caused by the leakage current of the inputs. Ideally the inputs draw or supply no current, but in real life there's always some tiny current. ... Where the current is sensed on the shunt, depends on the perspective. It depends whether your reference point is before or after the shunt. You're in fact right, but it was easier to explain it saying that the voltage of the shunt is compared with a 50mV reference voltage. This is true if our reference point is before the shunt. Of course, the GND of the chip is connected after the shunt, but this doesn't change the behavior of the OpAmp.﻿Note: When the series finishes, I'll stop adding on this thread and just link to it from sticky "Electronics primers, course material and books" (I wish I had done that for his 3-part series we had last year.. he makes SMPS look so easy)

author: Yansi
author_rank: Super Contributor
timestamp: February 13, 2019, 12:55:43 am
content: Well I don't doubt his knowledge at all, he was one of my mentors in my early electronics diy age - he is just a bit older than me and we know each other I'd say quite wellI just can't stand his English pronunciation. Mine is not probably much better either (I have none practice speaking), but it sounds reallyweird. I would say he might even do that on purpose, it is just impossible to talk like thisI just wanted to point out some interesting parts of the circuit that look suspicious. His further explanation I think is completely valid, however that does not change anything on the fact, that some parts of the circuit may be done a bit differently - each engineer can have a bit different point of view, based on his knowledge and/or experience.He is true that I have completely missed the point of the resistor in the opamp input - to lower offset voltage. However, looking in the datasheet of TL494, the input bias is typical 200nA or 1uA maximum. With the impedances the circuit is working with, this could create an error of 1mV maximum. Compared to the maximum of 10mV input offset voltage and the accuracy of the surrounding resistors, makes this effort likely void anyway.In no way I am saying his explanations are wrong, the effort put into this is just stunning. This is some real practical engineering, not a popularized electronics youtube channel, where the author has close to no clue what he is talking about, but he got a shiny camera pointed at him... (which, unfortunately, is the way most youtubers are set up).

author: Cliff Matthews
author_rank: Unknown
timestamp: February 13, 2019, 03:41:23 am
content: I've worked 5+ years in Spanish countries and had to adapt to the oddities of 'sing-song speech' so I found his 'slowly gliding tonal inflections' easy to accommodate. With all his animal friends, I wonder if he speaks to them (and us) in this way as a 'secret sauce' to his unique channel?IMO, It's rather relaxing for me to see placid, calm animals (I have none of my own) walking calmly nearby as he continues unaffected, while teaching on some pretty detailed topics. Calm animals seem to lift tension in some therapeutic sense.

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: February 13, 2019, 11:43:35 am
content: I like the way he puts up video´s on post USSR hospital elevator systems.

author: Yansi
author_rank: Super Contributor
timestamp: February 13, 2019, 01:54:30 pm
content: Quote from: Cliff Matthews on February 13, 2019, 03:41:23 amI am also in desperate need of cat cuddles - I even take both the two or four legged versions!

author: schmitt trigger
author_rank: Super Contributor
timestamp: February 13, 2019, 05:09:17 pm
content: Quote from: Cliff Matthews on January 19, 2019, 07:26:20 pmA cat’s paws are CAT I rated. The whiskers are CAT II rated. (See what I did here?)Since cat’s have 9 lives, they can sustain significant overload conditions before suffering an irreversible EOS condition.

author: Cliff Matthews
author_rank: Unknown
timestamp: February 13, 2019, 05:28:16 pm
content: Fat cats won't let you tin their whiskers..Unless you really want to see the paws in action (See what I did?)

author: DMartens
author_rank: Contributor
timestamp: May 02, 2020, 10:25:30 am
content: This video (along with similar ones he made) are indeed amazing to get familiar with the practical side of SMPS. Just wondering if people here can recommend some good book about SMPS. Preferably about ATX power supplies in particular, as I am not really looking for anything about 1kW or so. Thanks.