Why don't SMPS CRT TV's have huge HV caps like in old CRT TVs or microwaves ?

[lordvader88]

Or is it built into the HV transformer ? Or just a little non-electrolytic, or is there none.

[Richard Crowley]

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.

[Brumby]

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.

[james_s]

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.

[paulca]

So modern TVs even run on wall warts or DC bricks now.  My 34" UHD monitor runs on a 35V 130W DC brick.

[mikeselectricstuff]

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.

Microwaves 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.

[lordvader88]

I'm talking about modern CRT TVs with SMPS in them

[lordvader88]

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.

Why do old CRT oscilloscopes have them ?

[mikeselectricstuff]

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.

Why do old CRT oscilloscopes have them ?

On 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.

[tooki]

I'm talking about modern CRT TVs with SMPS in them

Isn’t that an oxymoron? Who makes such things?

[mikeselectricstuff]

I'm talking about modern CRT TVs with SMPS in them

Isn’t that an oxymoron?

No. "modern" is relative. Though CRT TVs have had switching PSUs for such a long part of their lifetime than anything else is an antique

[Mechatrommer]

I'm talking about modern CRT TVs with SMPS in them

Isn’t that an oxymoron? Who makes such things?

jumping 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.

[IanMacdonald]

https://patents.google.com/patent/US6459350B1/en

Uses 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.

[tooki]

I'm talking about modern CRT TVs with SMPS in them

Isn’t that an oxymoron? Who makes such things?

jumping 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.

Well 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 think any CRT TV can be called “modern”.

[lordvader88]

I'm talking about modern CRT TVs with SMPS in them

Isn’t that an oxymoron?

No. "modern" is relative. Though CRT TVs have had switching PSUs for such a long part of their lifetime than anything else is an antique

Modern 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.

[schmitt trigger]

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

[paulca]

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. 

[Mechatrommer]

I bumped into a group of teenagers slagging off "old" CRT computer monitors.
I had to point out to them that...

why 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.

[james_s]

Well 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 think any CRT TV can be called “modern”.

As 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.

[james_s]

Microwaves 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.

No, 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.

[Jwillis]

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.

[Bassman59]

I bumped into a group of teenagers slagging off "old" CRT computer monitors.
I had to point out to them that...

why 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.

You used to be able to bang your forehead on a CRT monitor. Try that with an LCD monitor. Ouch!

[Circlotron]

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.

[westfw]

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.))

[james_s]

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.