Re: Motor Speed Control

On Sat, 9 Mar 2024 14:56:43 -0800, KevinJ93 <kevin_es@whitedigs.com>
wrote:

On 3/8/24 8:42 PM, Bill Sloman wrote:

On 9/03/2024 5:49 am, KevinJ93 wrote:

On 3/7/24 8:48 PM, Bill Sloman wrote:

On 8/03/2024 7:13 am, KevinJ93 wrote:

...

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Not in 1970. Even after that time they did not possess any advantage over DC motor drive with speed stabilization based on back-emf.

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Don't be silly. Back-emf depends on the strenght of the magnetic field generating the basck-emf, and that is temperature dependent.

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At about 0.2% per deg the magnetic field strength stability was adequate for the speed accuracy required under the required environmental conditions.

 Motors run hotter than their environment

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With only 50-100mW being consumed by the motor (10's of mA at 3-6V) the temperature differential was small.
>

Synchronous motors rotate at a rate that reflects the stability of the frequency source that determines the drive frequency, and reasonably stable frequency source - watch crystals have been around for ages.

>

Even for AC powered units where power was not an issue stepper motors were never used. Synchronous motors with synthesized drive were occasionally a feature but many/most used back-emf stabilization with DC motors.
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ICs were available to integrate that circuitry:
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eg https://www.precisionmicrodrives.com/ab-026
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Even implementing the discrete drive electronics would be more costly than necessary at a time where individual transistors were a significant cost; Philips' solution used two transistors - creating a divide by 4 plus driver transistors plus an oscillator would probably require about ten transistors plus numerous other components.

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Which you could could buy in an integrated circuit. Most of mine were in a chunk of PROM.

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Not in 1970. Even by the late 70's a bipolar (P)ROM would use up all your power budget.

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It didn't - and it wasn't bipolar.

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MOS EPROMS such as the 1702 were cumbersome to use with multiple supplies required.

 It was one-time programmable, not an EPROM.

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If it was NMOS it was almost certainly an EPROM in a cheaper package without the quartz window.

1702 was a p-mos UV-erase part. It was called an eprom.