15 Oct
2025
15 Oct
'25
9:30 p.m.
On Wed, Oct 15, 2025 at 12:47 AM Rob Jarratt via cctalk <
cctalk(a)classiccmp.org> wrote:
TI is one of the worst for this.Especially if the chip implements an
industry standard or is compatible with some other chip. In those cases,
you barely get enough to understand. I've had to many times in the past
hunt down an industry standard or get the datasheet for the part it's
compatible with.
DEC was really paranoid about single sourced parts, so just about
everything is something that's widely used in the industry, and so has many
suppliers... You might try that if you're having trouble understanding the
datasheet for the exact part.
Warner
behaviour as an op
-----Original Message-----
From: Brent Hilpert via cctalk <cctalk(a)classiccmp.org>
Sent: 14 October 2025 23:14
To: General Discussion: On-Topic and Off-Topic Posts (
cctalk(a)classiccmp.org)
<cctalk(a)classiccmp.org>
Cc: Brent Hilpert <bhilpert(a)shaw.ca>
Subject: [cctalk] Re: Rainbow H7842 PSU
On 2025Oct 14,, at 1:42 PM, Rob Jarratt <robert.jarratt(a)ntlworld.com>
wrote:
>> -----Original Message-----
>> From: Brent Hilpert via cctalk <cctalk(a)classiccmp.org>
>>
>> There’s some confusion here somewhere.
>> Those input V's would imply the comp. output should be loZ to
>> Vsupply– pin, around –12V; not hiZ, +7.5V.
>
> Oh my! I have clearly got my understanding the wrong way around, not
sure
how I did that because I read the datasheet
carefully. Somehow, I got
confused. I re-measured and found 1IN+=5.5V, 1IN-=9.4V, Power OK=6.7V,
but
GND (on the 393) is -13V. So as you say Power OK
should be -13V and AC OK
H would be asserted. I guess this must mean that the comparator itself is
faulty. I have some 393s, so I will replace it and see what happens.
I don’t think I’ve ever seen a comparator datasheet that explicitly laid
out the
input-to-output function - contrast with other
device datasheets with
detailed
truth tables galore.
I have a Texas Instruments datasheet that does explain it, but much
further down in the Application section. I have to say that many datasheets
assume you already know an awful lot about the devices and how they work,
which is definitely not the case for someone like me.
The comp. datasheets always seem to assume “everybody knows that”. You
can figure it out if you look at some of the example circuits or squint
closely at
just the right parameters in the specs and graphs
or trace the operation
through the internal schematic if present.
In the absence of that, a lot of people seem to (wrongly) assume that
“well, +
– would
be 1, so transistor ON”.
The other way of looking at it, is it’s the 'same direction' of
amp, but without the upper drive-high output
transistor.