Two levels of hysteresis

Thread Starter

Marus780

Joined Jan 11, 2023
18
Hi,
I have this schematics, with two comparators...
I want to make them work in the following way:
- when the input voltage V2 drops under a certain level (lets say 11V), both comp. switch to "high".
- when the input voltage V2 raise to Level 1 (lets say 11.5V), U3 switch to "low", U1 remains "high".
- when the input voltage V2 raise to Level 2 (lets say 12V), U1 switch to "low".
The main circuit is around U1. It's working priciple must ramain the same. But the rest (U3) can be anything that output a "low" level before U1 and "high" level in the same time with U1 (as I described above). It may not even be with an opamp.
Is such a thing possible ?

screenshot.2.png
 

ericgibbs

Joined Jan 29, 2010
16,803
Hi M,
Is this plot of V2 and the states of U1 U3 as you require.?
E

@crutschow
Carl, any ideas on the 'drift' on the PWL profile, two PC's the same. RefEG57_ 491.png this image.
 

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Thread Starter

Marus780

Joined Jan 11, 2023
18
@ericgibbs
Ok, this is the .asc file, but it uses a custom library and I think it's useless...
The plot is ok, but in the middle U1 must be low and U3 high.

@Ian0
If I use two separate opamps I cannot adjust the low level (11V) of both at once. This must be exactely the same.
In other words... both must go high under 11V and both must go low on 12V, but I want U1 to go low sooner.
 

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Ian0

Joined Aug 7, 2020
6,713
@Ian0
If I use two separate opamps I cannot adjust the low level (11V) of both at once. This must be exactely the same.
In other words... both must go high under 11V and both must go low on 12V, but I want U1 to go low sooner.
I see. The output of U1 has to force U2 high when it reaches 11V.
I’ll have to think about it, but I suspect that a diode from the output of U1 to the non-inverting input of U2 will do the trick.
 

ericgibbs

Joined Jan 29, 2010
16,803
Ok, this is the .asc file, but it uses a custom library and I think it's useless...
The plot is ok, but in the middle U1 must be low and U3 high.
Hi M.
This is what said in your opening post.
E
EG57_ 492.png
 

Thread Starter

Marus780

Joined Jan 11, 2023
18
Indeed, that plot is correct. I confused the opamps...

The way I see it, when both opamps are low, they should have the same reference on In+, so they go high at the same level.
And then the references must be different, so they can trigger at different levels...
 

Thread Starter

Marus780

Joined Jan 11, 2023
18
I think I did it ! :D
Indeed... a diode was the key. When I put the diode that way, I can have same low threshold but different high ones.
screenshot.3.png
 

ericgibbs

Joined Jan 29, 2010
16,803
Hi M,
This is my version of your circuit, is there anything special regarding your OPA's.?
E
I will modify the circuit as your last posting, see if I can match your result.

EG57_ 493.png
 

Ian0

Joined Aug 7, 2020
6,713
Careful with op-amp bias currents - there will be a slight difference between the two due to the voltage drops across RV2 and RV3. FET inputs will help, but the offset voltages might not be as good
This is what I was thinking of:
Screenshot at 2023-01-24 20-54-06.pngThe second comparator is set with thresholds of 12V and 10.5V. The diode overrides the 10.5V threshold and forces the output high as soon as the first comparator goes high.
(I've used a 5V supply as the reference to save time)
 

Thread Starter

Marus780

Joined Jan 11, 2023
18
I have a drop of 10uV and 100uV on those resistors. I use TLV1812...
I can't figure out right now if that could be a problem... until I buid the real circuit. In simulation they seems to trigger in the same time...
 

Ian0

Joined Aug 7, 2020
6,713
I have a drop of 10uV and 100uV on those resistors. I use TLV1812...
I can't figure out right now if that could be a problem... until I buid the real circuit. In simulation they seems to trigger in the same time...
That’s a good choice of comparator. At 150fA, bias current won’t be a problem, a lot better than the 3nA for an LM339, and offset isn’t too bad either. I might try it, but none of my usual suppliers stocks it.
 

Thread Starter

Marus780

Joined Jan 11, 2023
18
@LowQCab
It is part of the control board of a UPS that I want to build...
When the battery is discharging and drops under a certain level all the power must be cut off. When start charging again and the voltage rise a a little I want to power non-esential systems. And then, when the battery is almost full, all the system must be started.

@Ian0
I am from Europe and I buy it from a USA online store... So, imagine that... : ))
I have no choice since I want a verry low-power comparator, because it will be part of the stand-by circuit that runs from a battery.
 

Ian0

Joined Aug 7, 2020
6,713
I guessed it might be something to do with lead acid batteries!
I see they are in Mouser, but I don’t use Mouser very often.
 
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