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NNTP-Posting-Date: Sat, 09 Mar 2024 23:14:44 +0000
From: John Larkin <jl@997PotHill.com>
Newsgroups: sci.electronics.design
Subject: Re: Motor Speed Control
Date: Sat, 09 Mar 2024 15:13:20 -0800
Organization: Highland Tech
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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:
>>> ...
>>>>>
>>>>> Not in 1970. Even after that time they did not possess any advantage 
>>>>> over DC motor drive with speed stabilization based on back-emf.
>>>>
>>>> Don't be silly. Back-emf depends on the strenght of the magnetic 
>>>> field generating the basck-emf, and that is temperature dependent.
>>>
>>> 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
>
>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.
>>>>>
>>>>> ICs were available to integrate that circuitry:
>>>>>
>>>>> eg https://www.precisionmicrodrives.com/ab-026
>>>>>
>>>>>>> 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.
>>>>>>
>>>>>> Which you could could buy in an integrated circuit. Most of mine 
>>>>>> were in a chunk of PROM.
>>>>>
>>>>> Not in 1970. Even by the late 70's a bipolar (P)ROM would use up all 
>>>>> your power budget.
>>>>
>>>> It didn't - and it wasn't bipolar.
>>>
>>> MOS EPROMS such as the 1702 were cumbersome to use with multiple 
>>> supplies required. 
>> 
>> It was one-time programmable, not an EPROM.
>
>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.