Why don't SMPS CRT TV's have huge HV caps like in old CRT TVs or microwaves ? - Page 1
Forum section: electronics / beginners

author: lordvader88
author_rank: Frequent Contributor
timestamp: March 26, 2018, 04:02:01 am
content: Or is it built into the HV transformer ? Or just a little non-electrolytic, or is there none.

author: Richard Crowley
author_rank: Super Contributor
timestamp: March 26, 2018, 04:08:34 am
content: What do you mean by "SMPS TV"?Modern, flat-screen TVs do not require high voltages like CRTs did.So low-voltage electrolytic capacitors used in modern switch-mode power supplies are physically quite small.

author: Brumby
author_rank: Unknown
timestamp: March 26, 2018, 04:23:39 am
content: The highest voltage you're going to get in any LED TV is the supply voltage for the string of backlight LEDs. The last one I poked around had a string of 45 LEDs with an operating voltage of around 160V, which is easy to do.

author: james_s
author_rank: Super Contributor
timestamp: March 26, 2018, 04:42:10 am
content: CRT TVs didn't have much in the way of big capacitors either, the CRT itself doubles as the capacitor on the EHT. Conventional microwave ovens use a 50/60Hz transformer, TVs run around 15kHz so the capacitor can be much smaller.

author: paulca
author_rank: Super Contributor
timestamp: March 26, 2018, 07:02:53 am
content: So modern TVs even run on wall warts or DC bricks now. My 34" UHD monitor runs on a 35V 130W DC brick.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 26, 2018, 07:09:52 am
content: Quote from: james_s on March 26, 2018, 04:42:10 amMicrowaves don't need a smooth supply as it's just making heat. the cap needed to smooth a microwave supply would be a bit trerrifying.

author: lordvader88
author_rank: Frequent Contributor
timestamp: March 26, 2018, 07:17:14 am
content: I'm talking about modern CRT TVs with SMPS in them

author: lordvader88
author_rank: Frequent Contributor
timestamp: March 26, 2018, 07:19:31 am
content: Quote from: james_s on March 26, 2018, 04:42:10 amWhy do old CRT oscilloscopes have them ?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 26, 2018, 07:26:06 am
content: Quote from: lordvader88 on March 26, 2018, 07:19:31 amOn a TV, the EHT is derived from the line scan, so any ripple is synchronous with the line scan, so won't produce any moving visible artifacts.A scope needs a stable EHT supply as any variation will affect the deflection. A scope also has a smaller tube, which will have less self-capacitance.

author: tooki
author_rank: Super Contributor
timestamp: March 26, 2018, 08:06:01 am
content: Quote from: lordvader88 on March 26, 2018, 07:17:14 amIsn’t that an oxymoron? Who makes such things?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 26, 2018, 08:08:29 am
content: Quote from: tooki on March 26, 2018, 08:06:01 amNo. "modern" is relative. Though CRT TVs have had switching PSUs for such a long part of their lifetime than anything else is an antique

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 26, 2018, 08:35:50 am
content: Quote from: tooki on March 26, 2018, 08:06:01 amjumping to a bad conclusion is not nice. here is the last of my crt tv board that i stripped apart 7 years ago iirc. notice the smps on top left? obviously LCD/LED technology is more "modern" than smps... fwiw.

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: March 26, 2018, 12:29:57 pm
content: https://patents.google.com/patent/US6459350B1/enUses a 'diode split transformer' in which successive layers of the secondary winding are separated by diodes. The interwinding capacitance serves as the reservoir cap. So, the output of the transformer is actually DC. The glass wall of the CRT serves as a smoothing cap, Leyden jar style.Earlier designs used what was basically a Tesla coil, in which the secondary was tuned to the third or fifth harmonic of the primary resonance. That, and a voltage tripling rectifier often followed it. Such arrangements suffered corona discharge and were thus not all that reliable. The diode split transformer was a quantum leap in reliability.

author: tooki
author_rank: Super Contributor
timestamp: March 26, 2018, 12:33:57 pm
content: Quote from: Mechatrommer on March 26, 2018, 08:35:50 amWell what I mean is... no CRT TV is modern. I have no doubt that the later CRT TV models used SMPSs. But literally, does anyone even make CRT TVs any more? I know they were making smallish ones for emerging markets a bit longer than for most of the world, but even that was years ago.So yeah, my entire gripe was that I don’t thinkanyCRT TV can be called “modern”.

author: lordvader88
author_rank: Frequent Contributor
timestamp: March 26, 2018, 03:00:14 pm
content: Quote from: mikeselectricstuff on March 26, 2018, 08:08:29 amModern as in uses IC's and in the 80/90s when they went to SMPS.I scrapped a 1970's zenith chromacolor 2, with 2 or 3 transformers/inductors used over all for its HV and I think a multiplier. IDK if it was switching supply or what tho (wish I had the space to keep it intact and repair it) Can't find a 1970s schematic yet, need to look harder. It had a large HV cap aswell, like in my vacuum tube CRT and like a microwave.

author: schmitt trigger
author_rank: Super Contributor
timestamp: March 26, 2018, 03:08:51 pm
content: Short answer:The CRT's exterior aquadag layer and the internal aluminum metalization, coupled to the glass dielectric, form the actual HV capacitor.https://en.wikipedia.org/wiki/Aquadag

author: paulca
author_rank: Super Contributor
timestamp: March 26, 2018, 03:56:22 pm
content: I bumped into a group of teenagers slagging off "old" CRT computer monitors.I had to point out to them that before this flat panel LCD stuff and this standardised "HD" resolution stuff I was enjoying a 21" CRT with a resolution about 3 times that of "HD".LCDs have more or less caught up today though. However 1920x1080 is not a high resolution in comparison to high end CRTs of the 1990s and early 2000s.

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 26, 2018, 04:39:16 pm
content: Quote from: paulca on March 26, 2018, 03:56:22 pmwhy dont you tell them CRT has 180deg viewing angle with almost zero color/brightness/hue change. and ask them to poke the LCD and CRT screen with a pen and see what happen. i have seen numerous damages to LCD screen including my own of at least 2 units. i've never seen such happening to CRT except brutally tortured in a dumpster. these features are to be remembered of how the LCD is not something to be too fascinated at,except its weight and size.

author: james_s
author_rank: Super Contributor
timestamp: March 26, 2018, 04:43:10 pm
content: Quote from: tooki on March 26, 2018, 12:33:57 pmAs has been said, "modern" is relative. Compared to a TV made in 1955, a TV made in 1995 is quite modern. CRT TVs made in the final generation of CRT technology will always be modern in that sense, they were the most modern that tech ever got.

author: james_s
author_rank: Super Contributor
timestamp: March 26, 2018, 04:44:17 pm
content: Quote from: mikeselectricstuff on March 26, 2018, 07:09:52 amNo, but the capacitor used in the voltage doubler is large for the same reason. I don't think inverter microwaves use a voltage doubler like the iron transformer type but if they did, the capacitor(s) could be correspondingly smaller.

author: Jwillis
author_rank: Super Contributor
timestamp: March 26, 2018, 11:14:24 pm
content: Very old CRT televisions around pre 80's still used linear type power supplies.Caps were bigger,transformers were bigger and so on.With the onset of SMP's becoming more popular because they started costing less to produce and could deliver equal or greater power in a smaller package.Switch mode power supplies work on the principle that if you increase the frequency of the input power you can decrease the size of the transformer.That's a significant cost saver there because of less materials.Also SMPs tend to much more efficient than than linear so smaller power caps can be used for the equivalent loads.Even though SMPs can be very complex with the extra filtering ,the reduction in material still brought costs down.

author: Bassman59
author_rank: Super Contributor
timestamp: March 26, 2018, 11:32:34 pm
content: Quote from: Mechatrommer on March 26, 2018, 04:39:16 pmYou used to be able to bang your forehead on a CRT monitor. Try that with an LCD monitor. Ouch!

author: Circlotron
author_rank: Super Contributor
timestamp: March 27, 2018, 12:01:24 am
content: It was such good fun to drag home a discarded 50s or 60s vacuum tube TV set back in the day and open it up and see just what sort of 300VA power transformer it had lurking inside that you could use for any number of big amplifier projects. Those days are gone.

author: westfw
author_rank: Super Contributor
timestamp: March 27, 2018, 05:32:58 am
content: For the same reason (ie PHYSICS) that higher frequencies let you use smaller inductors in a SMPS, you also get to use smaller capacitors.IIRC, most "older" CRT TVs would directly rectify the mains (60Hz or so), to get their B+ voltages (that was for tubes. Perhaps you didn't mean THAT old?)(I guess you could be talking about different "big capacitors? TVs never had the huge caps that were present in supplies for digital logic (minicomputers and the like.))

author: james_s
author_rank: Super Contributor
timestamp: March 27, 2018, 04:51:32 pm
content: Up into the early 80s it was still common to get B+ from a linear regulator, but most of the other voltages used came from the flyback transformer, so technically a SMPS.

author: tooki
author_rank: Super Contributor
timestamp: March 27, 2018, 10:02:56 pm
content: Quote from: james_s on March 26, 2018, 04:43:10 pmExcept that, not including specific areas like history and art where it has a specific, nontrivial meaning, the word “modern” is actuallynotrelative. It means “recent compared to now”, not “late within an arbitrary timeframe”. It may be nonspecific, but it’s not relative. Given that CRT TVs haven’t been made for years, and no LCD or plasma TV from the era of the last CRTs would be called a “modern TV”, I don’t think one can call any CRT TV “modern”. How about “late model” instead?

author: westfw
author_rank: Super Contributor
timestamp: March 28, 2018, 01:20:48 am
content: They still make CRT monitors... In fact, gamers have a preference for analog CRT TVs (with direct video inputs.) Apparently there can be enough "lag" in between the inputs of a modern LCD TV/Monitor and the actual display to interfere with gameplay. (Especially (?) on the "legacy" inputs.)

author: james_s
author_rank: Super Contributor
timestamp: March 28, 2018, 01:33:25 am
content: If someone is still making CRT monitors I'd love to know where. In the vintage arcade collecting circles monitor supplies have dried up and the occasional NOS monitor that pops up tends to fetch $500+.For retro console games a CRT TV is essential too, the light guns won't work on any other type of display.

author: westfw
author_rank: Super Contributor
timestamp: March 28, 2018, 01:53:40 am
content: QuoteWow. Ok, I expected that CRT monitors would still be available, but I'm not finding any either...

author: Jwillis
author_rank: Super Contributor
timestamp: March 28, 2018, 05:47:44 am
content: Theirs still a few refurbished ones on amazon.But I imagine that the same thing will happen as when turntables disappeared off the market.Eventually niche markets will pick up the demand for CRT monitors again.

author: janekm
author_rank: Unknown
timestamp: March 28, 2018, 06:42:43 am
content: Quote from: Jwillis on March 28, 2018, 05:47:44 amSetting up a production line for CRT monitors may just be a tad more involved than for a turntable though...

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 28, 2018, 08:20:41 am
content: Quote from: janekm on March 28, 2018, 06:42:43 amDitto Nixie tubes

author: tooki
author_rank: Super Contributor
timestamp: March 28, 2018, 04:37:12 pm
content: Quote from: westfw on March 28, 2018, 01:53:40 amYou can still special-order broadcast 19" HD CRTs from Ikegami, at least theoretically — starting at $8500.No, I didn't accidentally add an extra zero there.But yeah, googling for "last CRT computer monitor" seems to indicate 2012 as when people were already asking this questionin the past tense.Sony, who arguably made the very best CRTs ever made, shut down the Trinitron production lines in 2008.There are still some CRT TVs (14-19") made in and for emerging markets, if alibaba is to be believed, but I think even they must be living on borrowed time, given how cheap large LCD panels have gotten. But unlike TVs, I don't think that emerging markets continued with CRT computer displays any longer than developed countries.Quote from: Jwillis on March 28, 2018, 05:47:44 amArcade game refurbishers were the very last source of demand for large CRTs, and they lost that battle, having totally depleted stocks of some sizes a few years ago. I think they're basically doing LCD retrofits wherever possible, and saving the CRTs for games with light guns that simply cannot operate with any other display type.I honestly don't think these things will make a comeback. The image quality advantages of CRTs can likely be matched or exceeded by newer technologies (I'm lookin' at you, OLED!), and I suspect that for applications that require the specific properties of CRTs (like light pens/guns), it may even be possible to make retrofit OLEDs that mimic those properties. (For example, is there any reason you couldn't simulate the line-by-line painting on an OLED panel, given beefy enough drive electronics?) Given that the expertise in making quality CRTs is in retirement right now, and will soon die off, resuming CRT production would require enormous investment that almost certainly will never be worth the effort.Quote from: mikeselectricstuff on March 28, 2018, 08:20:41 amHonestly, I think that Nixie tubes are positivelytrivialto make compared to color CRTs. So many more parts, and they all must be in perfect alignment.

author: james_s
author_rank: Super Contributor
timestamp: March 28, 2018, 05:33:52 pm
content: Yeah a nixie tube is going to be easy even compared to a small B&W CRT, and color CRTs are enormously more complex. It's absolutely amazing that they got the process refined to the degree they did, early color sets were hugely expensive and building them was extremely labor intensive. When they're gone, they're gone, that tech is never coming back unless something like the Star Trek replicator becomes reality.One of the last hopes is that a museum in Ohio has the equipment from the last CRT rebuilder in the US that shut down a number of years ago. They have it set up and are working on getting everything operational to rebuild antique TV CRTs, it's not possible to re-phosphor color tubes though so if the phosphor is burned as is common with arcade games, the tube is done.

author: westfw
author_rank: Super Contributor
timestamp: March 29, 2018, 07:35:12 am
content: Sorta like tungsten filament light-bulbs. They SEEM really simple compared to an LED light bulb, and then you start wondering just how one goes about manufacturing tungsten filaments, given that it's very hard and has a very high melting point. (https://www.tungsten.com/tips/how-tungsten-wire-is-made/)

author: tooki
author_rank: Super Contributor
timestamp: March 29, 2018, 02:29:02 pm
content: Quote from: james_s on March 28, 2018, 05:33:52 pmBy pure chance, do you have any knowledge of (or links to) how the color phosphors were applied? I've seen how it's done on monochrome CRTs (it's fairly trivial), but have never come across a detailed description of the process for color.

author: tooki
author_rank: Super Contributor
timestamp: March 29, 2018, 02:35:02 pm
content: Random thought: Isn't it sad that the knowledge for how to make things gets lost? Like, not even including the knowledge that exists only in the heads of people, even just the documentation is often lost, since the processes are developed by companies who guard that information as trade secrets. What happens when they eventually go out of business? Or if some bean counter simply decides the company archives aren't worth the storage costs?An example from my own world: Apple's old Tech Info Library. Tons and tons of info on how the old Mac hardware and software worked, release notes, etc. From one day to the next, wiped from apple.com -- and not backed up fully by archive.org due to the flags set.Or what about how companies used to publish on their development processes (for example, in the HP Journal), release schematics in service manuals, etc. Also all gone.I kinda wish I'd been born a few decades earlier, when we didn't have quite the corporate secrecy we have now. (On the other hand, then I wouldn't have the Internet... sigh...)

author: james_s
author_rank: Super Contributor
timestamp: March 29, 2018, 04:16:11 pm
content: Quote from: tooki on March 29, 2018, 02:29:02 pmBy pure chance, do you have any knowledge of (or links to) how the color phosphors were applied? I've seen how it's done on monochrome CRTs (it's fairly trivial), but have never come across a detailed description of the process for color.They used a photographic process. The phosphor compounds were mixed with a photo sensitive binder, the tube face was coated fully with one, then the shadow mask installed and the assembly exposed under a light source positioned precisely where the electron gun for that color will be. Then the non-exposed phosphor is washed off and the process repeated for the other two colors. The shadow mask used for this process is permanently paired with that tube and used for all three exposures. After that process is complete the bell and the face are joined.