Electronics > Beginners
A switching power supply in an oscilloscope?
rsjsouza:
Well, Bob Mammano designed the SG1524 during the 1970's and it was released in 1976. That is the staple of switching IC controllers, but it was probably too new (and too expensive) to be adopted in mainstream applications.
I had a 1976 TI30 calculator with a boost converter from 1.2V of its NiCd AA cell to the 9V. Terribly inneficient.
My 1980 TV set from Sharp had switching power supplies as well.
tggzzz:
--- Quote from: Martini on March 10, 2019, 11:35:20 am ---I'm currently reading Jobs's biography and it says they designed a switch mode power supply like those used in oscilloscopes for the Apple II.
Were scopes using these in the 70's!?
--- End quote ---
Yes.
Both to convert from mains voltages to the obvious low voltages, and also to get the high voltages (2.5kV to 20kV) for the CRT.
tggzzz:
--- Quote from: rsjsouza on March 10, 2019, 10:25:52 pm ---I had a 1976 TI30 calculator with a boost converter from 1.2V of its NiCd AA cell to the 9V. Terribly inneficient.
--- End quote ---
The earlier groundbreaking HP35 generated 8.2V [for the cathode LED driver], 6V [for the clock driver, the control & timing, the ROMs and the arithmetic registers] and -12V [for the clock driver, the control & timing, the ROMs and the arithmetic registers] from three NiCd cells.
http://home.citycable.ch/pierrefleur/Jacques-Laporte/HP35%20power%20unit.htm
There were many other calculators that had Panaplex displays needing >150V; some of them were portable.
tautech:
--- Quote from: Martini on March 10, 2019, 11:35:20 am ---I'm currently reading Jobs's biography and it says they designed a switch mode power supply like those used in oscilloscopes for the Apple II.
Were scopes using these in the 70's!?
--- End quote ---
While many were still using linear PSU's for the general circuitry voltages obtaining the higher EHT used on scopes from 70's onward a Colpitts Oscillator was often used on the primary side of EHT generation.
While they are not what we generally now consider as SMPS, they in essence perform the same task, switching a DC voltage to some form of AC to then be transformed to a higher voltage which then rectified becomes the DC EHT that CRO's need for CRT voltages.
In a CRO I had 30V was transformed in this way to -2750V for the CRT and also quintupled for the ~ +12 KV PDA voltages.
This scope was a UK D83 Telequipment which at that time in the early 70's was owned by Tek.
David Hess:
--- Quote from: tautech on March 10, 2019, 11:16:34 pm ---
--- Quote from: Martini on March 10, 2019, 11:35:20 am ---I'm currently reading Jobs's biography and it says they designed a switch mode power supply like those used in oscilloscopes for the Apple II.
Were scopes using these in the 70's!?
--- End quote ---
While many were still using linear PSU's for the general circuitry voltages obtaining the higher EHT used on scopes from 70's onward a Colpitts Oscillator was often used on the primary side of EHT generation.
While they are not what we generally now consider as SMPS, they in essence perform the same task, switching a DC voltage to some form of AC to then be transformed to a higher voltage which then rectified becomes the DC EHT that CRO's need for CRT voltages.
In a CRO I had 30V was transformed in this way to -2750V for the CRT and also quintupled for the ~ +12 KV PDA voltages.
This scope was a UK D83 Telequipment which at that time in the early 70's was owned by Tek.
--- End quote ---
I was actually surprised to see any oscilloscopes use a 50/60Hz transformer for the high voltages but this was still common with the lessor manufacturers. As far as I know, all Tektronix oscilloscopes which used a linear power supply after their first (511) one generated their high voltage as you describe with a separate high frequency inverter. The 511A used a 2kHz inverter for the high CRT voltages so Tektronix changed this immediately.
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