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Old 6th Sep 2017, 8:05 pm   #1
Panrock
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Default Vintage switched mode power supplies

Not sure whether this topic belongs here or in the modern technology section.

How far back does the switched mode power supply go? How has the technique developed? Were there any in the valve era? Was the first SMPS really the Induction Coil perhaps?

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Old 6th Sep 2017, 8:54 pm   #2
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Default Re: Vintage switched mode power supplies

My first experience was with some Sony hi fi amplifiers in possibly the 1970s. They were built in heavy diecast boxes within the amp to stop the stray high frequencies getting into the amp and also act as a heatsink fit the power devices. Not easy to work on.
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Old 6th Sep 2017, 8:55 pm   #3
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Default Re: Vintage switched mode power supplies

Definitely 1970s. Tektronix started using them then in the 7000 series. I suspect this happened when truly rugged silicon power transistors made an appearance.
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Old 6th Sep 2017, 10:47 pm   #4
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Default Re: Vintage switched mode power supplies

The induction coil, the standard petrol engine ignition system, and most TV line output stages are close to being switch-mode PSUs, so the idea goes back a long way.

As to things that are used as 'power supplies', in the early 1970s (if not before), many manufacturers (DEC, HP) made PSUs that had a normal mains transformer, the outputs of which were rectified and smoothed and then fed switch-mode regulators (transistor, flyback diode, inductor circuits). Many PDP11s had a power supply that consisted of a large mains transformer with 30V secondary windings each feeding what was commonly called a 'DEC power brick', a switching regulator giving perhaps 5V at 25A.
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Old 6th Sep 2017, 11:51 pm   #5
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Default Re: Vintage switched mode power supplies

Philips used a buck converter type supply in their 1972 K9 colour TV design. Not the first but definitely vintage. Very similar buck converters were used in almost all mains coupled or partially mains coupled Philips TV sets up until the last one some 25 years later.
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Old 7th Sep 2017, 12:12 am   #6
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Default Re: Vintage switched mode power supplies

Depends how you define SMPS, really.

Switch Mode Power Supplies basically use switching (hard on, or completely off) techniques to regulate outputs, thus offering high efficiency. Regulation is achieved by altering the 'on' and 'off' times.

The flyback-derived step-up EHT of televisions, I'd probably exclude, because there's no regulation. Similarly, the step-down of the 4V 3W exciter lamp supply of the Bell and Howell projector amplifier, using an oscillating 6V6 driving a step-down transformer, I'd exclude because it's largely sinewave, so not dissipationless.

Ignition coils etc I'd exclude, again there is no regulation.

Really, switchers started becoming mainstream in the 1970's. First ones used a 50Hz step-down transformer, diodes, and a reservoir capacitor to give a raw DC supply at high efficiency, albeit unregulated. Then, a buck regulator using PWM regulated this, giving overall fairly high efficiency, even though the thing was still bulky and heavy (but not so heavy as a linear regulator and loads of heat sinks). A bit later, with the advent of high-voltage switching transistors, the direct-off-line switcher became possible, eliminating the 50Hz transformer. I have a pre-production Coutant SOL40/5 dating from about 1976.
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Old 7th Sep 2017, 12:37 am   #7
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Default Re: Vintage switched mode power supplies

The Royer oscillator (push pull switchmode DC-DC converter) made its appearance in the mid to late 1950's as soon a germanium power transistors became available.

General motors were experimenting with CDI units at this time and used this design. Also by the early 60's these supplies were ubiquitous in cars to acquire HT for tube transceiver equipment. But as pointed out, supplies like this are not regulated , nor is the classic TV line output stage (with energy recovery diode) in most cases, the fundamental design of which goes back to the early work by Blumlein.

Modern architecture switchmode psu's , like those we have in modern computers, I think did make their debut in the 1970's. They were very common in the 1980's, I have a 1984 vintage IBM 5155 computer which uses a classic switchmode psu that really is identical to the ones we have today.

A big part of the notions that are now common knowledge in the design of switchmode psu's involve the recovery of stored magnetic energy and returning that to the power supply during part of the operating cycle, instead of wasting it as heat. The idea of this appears to belong to Blumlein. RCA did extensive experiments in the early 1940's. (I have their research papers on the topic) and investigated energy recovery diodes for TV line scanning work. By the immediate post war period they had solidified their ideas and all post war American TV's had energy recovery line scanning. They made a reference to Blumlein's original patent in their work.

I noticed that the energy recovery diode was not covered as a single topic as it related to TV scanning, so I did up a brief article on it in the past, its here if it is of any interest, it explains how we ended up with the type of circuit configuration shown in figure 9B in the article, which is certainly not intuitive unless one knows the evolution of the circuits:

http://www.worldphaco.com/uploads/TE...R_DIODE_OR.pdf
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Old 7th Sep 2017, 1:45 am   #8
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Default Re: Vintage switched mode power supplies

What about the vibrating contact regulators on classic cars that had dynamos on them?
My clatterbox had an alternator with a vibrating contact. It was a horrid car.
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Old 7th Sep 2017, 3:18 am   #9
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Default Re: Vintage switched mode power supplies

Quote:
Originally Posted by Refugee View Post
What about the vibrating contact regulators on classic cars that had dynamos on them?
Yes these were the electro-mechanical version of the Royer Oscillator that switched basic square waves to a transformer primary. Actually, if they are in good order and set up properly the efficiency is reasonable at around 65 to 70% for small supplies. The trouble is they don't last well due to contact wear, arcing and oxidation issues.
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Old 7th Sep 2017, 7:02 am   #10
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Default Re: Vintage switched mode power supplies

I think refugee was referring to the field controller for the dynamo. The vibrating contact varied its mark/space ratio to control the field current to regulate the battery voltage. There was no Royer oscillator or transformer involved. Those would have been found in a radio with either a vibrator HT generator, or a transistorised one and they usually weren't regulated.

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Old 7th Sep 2017, 8:17 am   #11
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Default Re: Vintage switched mode power supplies

By the middle 60's, valve line output stages did have a crude type of regulation, a VDR in a feedback loop.
Would that be sufficient to put into the "switched" class?
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Old 7th Sep 2017, 10:28 am   #12
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Default Re: Vintage switched mode power supplies

Switching regulators were becoming more mainstream in the early sixties when companies like TI were offering fast recovery diodes as standard production devices. I recall that National Semiconductor also offered dedicated integrated circuits for switch mode devices that included full voltage regulation. However, these devices were all intended for use with low input DC voltages (<60v) not like the current generation which use rectified mains input. The switching devices at that time did not have a high enough voltage capability, this invariably meant that a mains transformer was still required but the heatsinks were smaller!
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Old 7th Sep 2017, 10:30 am   #13
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Default Re: Vintage switched mode power supplies

First one I ever met was the Thorn 3000

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Old 7th Sep 2017, 11:47 am   #14
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Default Re: Vintage switched mode power supplies

It could be argued that electronic ballasts for fluorescent lamps are a type of SMPSU. These were certainly available in the 1970s, mainly for ELV input.

Philipps produced a range of transistor ballasts for 24/28 volt input mainly used for bus lighting. They were regulated to a degree and gave roughly constant light output over a wide range of input voltage.

They were very expensive, especially compared to incandescent bus bulbs that were pennies each if bought in bulk.
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Old 7th Sep 2017, 12:17 pm   #15
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Default Re: Vintage switched mode power supplies

I've seen a video of a valve SMPSU that used a mechanical vibrator on Utube, unfortunately it's on a patreon channel so can't be seen unless you cough up some cash. It must have dated from the mid fifties to early 60's.

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Old 7th Sep 2017, 1:10 pm   #16
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Default Re: Vintage switched mode power supplies

Quote:
Originally Posted by Radio Wrangler View Post
I think refugee was referring to the field controller for the dynamo. The vibrating contact varied its mark/space ratio to control the field current to regulate the battery voltage. There was no Royer oscillator or transformer involved.
True, although the field coil had a fair bit of inductance. So when the contact closed, the current ramped up; when the contact opened, the current ramped down. And the open and closed times were determined by a solenoid pull, with a carefully-adjusted return spring.

The inelegant bit was that when the contacts opened, there was no flywheel diode in parallel with the coil, to allow the current to continue (gently ramping down, of course). Instead, there was just a power resistor in parallel with the contacts, which meant the voltage shot up and the current ramped down (with lower limit determined by the resistor). So it wasn't dissipationless, although as copper-oxide rectifiers and selenium diodes existed, it could have been! (although it would also have been polarity sensitive, then).
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Old 7th Sep 2017, 1:30 pm   #17
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Default Re: Vintage switched mode power supplies

The Bell & Howell 640 16mm cine projector from around 1957 uses a push pull pair of UL84s run straight off the rectified 110v mains input to supply most of the amplifier, see attachment.

The predecessor 630 model had an extra mains transformer adding to the height and weight. The 40kHz supply in the 640 is used to drive the exciter, erase head, the main amplifier HT supply and preamp heaters.

A stunning piece of forward thinking design anticipating switched mode. It seems to have been a UK innovation, I've not seen a similar US B&H circuit.
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Old 7th Sep 2017, 2:13 pm   #18
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Default Re: Vintage switched mode power supplies

It could be argued that the early spark transmitters were a form of SWPS using the coil to generate the high voltages.
I'm currently reading the history of Marconi and there are several references to the development of transmitter coils and particularly innovations such as the disc discharger. This removed the problem of contact failure and allowed continuous operation.
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Old 7th Sep 2017, 3:06 pm   #19
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Default Re: Vintage switched mode power supplies

Hi
As far as TVs go the benchmark switch-mode PSU was generally regards to be the Siemens self-oscillating design from around 1975. While obviously not the first, it paved the way for high-voltage, low current supplies as used in many sets of the period and later. Of course most UK designs (G8, G11, Decca 80/100, Pye, Bush 823) carried on using thyristors much to the chagrin of the electricity boards. And Thorn were off doing something entirely different as they always did, only reluctantly accepting the design for the TX9 Mk3.
You always knew where you were with the TDA4600 and BU326!
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Old 7th Sep 2017, 3:35 pm   #20
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Default Re: Vintage switched mode power supplies

Bruel & Kjaer were early adopters of switch-mode supplies in their precision sound-level meters. Here's a section of the circuit of SLM type 2203 dating from 1960 and presumably developed in the early days of transistor circuits in the 1950s. It uses germanium transistors and a ferrite core transformer to generate +40V -40V amplifier supplies and the +200V condenser microphone polarizing voltage, all from three D cells.

It's remarkable that they managed to avoid induced PSU noise in some very low level circuitry capable of over 120dB dynamic range.

Martin
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