Switching vs. Linear power supply

Lately i heard of a 2x 5000W power amplifier... in a 1 HE 19" unit!!! :shock:
(Awfully expensive...)
Possible without a switching psu? I don't think so. :grin:

Quasi-resonant mode halps a lot.

some of these big amps don't have power supplies in that normal sense

think of them more as dimmers, than power supples

[quote author="dale116dot7"]One thing about a switcher - if a feedback loop part breaks, it wil put out basically as much power as it can, frying everything in sight. If a linear regulator breaks, it is likely the series pass transistor, and if it shorts it will also blow up your board. The stressed part on a linear regulator is also its worst failure mode. A switcher's most stressed parts (diodes and power transistors) tend to cause a blown fuse on a blow-up, and your circuit just stops working.

[/quote]

ANY supply in an important part of a system should have an over-volt protection circuit. The linear supply companies sell "OVP" modules which are "crowbars".

Bri

just found this thread by searching this topic. thought i ask here before starting an new thread over.
meanwhile a lot of pro-audio products incorporate a sw psu. so is it still a no-go in diy-builds?  ???
are those modern sw-psu still struggling with hf noise? any thoughts and advices appreciated...
thanks, alex

I am not a switch mode designer and it has always been a field far away to me. However recently I started involving in more and  I am hoping to bring it to diy. I am working with a friend whom is a switching designer to develop a step down switching unit to eliminate the transformer. After that it is a matter of regulating using linear. According to him  if we (he really) spent some serious time on it we would not need the linear bit either but I am just being realistic and concentrating on the step down bit at the moment. A lot more safety issues involved though.

If I am not mistaking JDB also said he would design something.

sahib said:

If I am not mistaking JDB also said he would design something.

Click to expand...

I am, but work's getting in the way.

The general idea is to start with an off-the-shelf switching AC-DC converter, and add an RLC filter to get rid of the HF junk, and then a low dropout regulator inspired by Walt Jung's work to provide LF-MF smoothing and DC regulation. The thing that's still bugging me is the current limiter, as the Jung design isn't short circuit proof. I'm thinking hiccup limiter plus a fuse (and the fuse can be part of the RLC filter).

sahib said:

According to him  if we (he really) spent some serious time on it we would not need the linear bit either but I am just being realistic and concentrating on the step down bit at the moment. A lot more safety issues involved though.

Click to expand...

As always, there's a lot that's possible but not everything's worthwhile. Switchers can be quite eager to go boom due to the high amount of power per unit volume, and several required parts (in particular transformers) are hard to get and not easy to DIY.

I suspect that a traditional power transformer-bridge rectifier-reservoir cap setup combined with a couple of DC-DC switchers might make a good topology for a DIY PSU, but I haven't done all of the math yet. Not a good way to get rid of the bulk of a power toroid, but much more efficient (and thus cool) than a linear equivalent, and safer than something directly attached to mains voltages.

JDB.

+1 to the "eager to go boom" or poof.

Absolutely needs current limiting and maybe a few extra fuse resistors on power devices JIC. The small resistors might hurt efficiency a little but save more expensive active devices during fault conditions.

I wouldn't bother for hobby use, unless there is compelling advantage (like for higher power).

The good news for hobby is you can probably slide on interference regulations, unless you screw with your whole apartment building's TV reception.

Anything dealing with mains voltage needs to be well executed for safety concerns. I always worried about this when I ran my kit business.

JR

A trick that I did in a product back in the '80s that needed both a high current 5V supply (for digital display and circuitry), and +/- 15V for audio was to add an active switch device to disconnect a second, lower voltage unregulated supply reservoir cap from the transformer secondary winding at an appropriate lower voltage, before it rose to it's full peak voltage. This also delivered an efficiency improvement, without the complexity of a full switcher, which wasn't as "off the shelf" mature technology** back then as it is now.

The standard transformer I used in several products, didn't have enough power output to support scrubbing off all the excess voltage with a 5V pass regulator from the full unregulated voltage, not to mention the heat that would generate. Instead I dialed in the low voltage unregulated voltage to around 8V to power a typical 3 terminal 5V regulator of the day, with my disconnect switch operating at the mains frequency rate. The noise from this is similar to the noise from normal rectification, while I have seen some strange inductive kicks from wall wart transformers using this approach. Somebody more clever than I might harness this inductive kick to make a third low current supply, but that was too much complexity for my taste.

Of course a full switcher is most efficient, but my low tech approach (perhaps a variant on synchronous rectification?) worked well and was very reliable in production. Note: I added some hysteresis to the switch so it would switch cleanly but it was a simple maybe two transistor and one more reservoir cap add to the basic pass regulator design.

JR

PS: The nice thing about switchers for audio, is you can generate low current +48V phantom supply pretty easily from lower voltage rails.

** Coincidentally my first technician job was working on a switching regulator project (for a Navy submersible) back in the late 60's. The switchers back then were definitely new technology, and the one I worked on was built around tricking a linear regulator IC (LM100) to switch.   

I have around 20 of these Philips switched supplies.
They are huge like a brick. Were used around the clock in a broadcast station, for audio purposes gentlemen.




anyone interested in a few of these ?