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Power consumption of circuit
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raff5184:
Hi all,
I am trying to realize a low power voltage monitor with hysteresis.
I have a battery or capacitor, and I want to monitor its charge using a comparator (TLC3702). I set 2 thresholds for the comparator so that I have a hysterical type of comparator. The output of the comparator drives a solid state SPST relay (CPC1114N).

The tricky thing is that from the battery I derive and keep independently 3 things:
1) the supply of the comparator Vs
2) the reference voltage of the comparator Vref, that creates the 2 thresholds (voltage divider R4-R5)
3) the voltage across the battery that I want to monitor Vin, I scale it with the voltage divider R6-R7 so that I can compare it with Vref as I need.

To generate a Vsupply (Vs)  and the Vref both at 2.5V, but keeping them independently, I use two LM285LPE 3-2-5 (http://www.ti.com/lit/ds/symlink/lm285-2.5.pdf).
Functionally this works and it does what it is supposed to do.

Now, my problem is the power consumption of the whole circuit, I mean the current drawn from the battery. The comparator TLC3702 is supposed to draw current in the order of micro-amps. But my whole circuit nabsorbs 3-4 mA. I don't know which component is absorbing that much.
I thought it was the switch but very little changes if I remove it
Vovk_Z:
Are you talking about power consumption from B1? Then you should increase nominals of voltage dividers and ballast resistors (by an order). R1, R2, R6 etc.
Second (not used) comparator have to be set to some stable steady state - fully on or fully off, otherwise it can oscillate.
Chalcogenide:
R1 and R2 will each draw a current of (V(B1_pos) - 2.5 v) / 3.3k; then you will have the direct path to ground through R6 and R7.
Finally, have you left the second comparator in the TLC3702 with its inputs floating? That may also be a problem as it might be oscillating.
Prehistoricman:
Your schematic isn't nice to read. Ground is usually expected at the bottom and power at the top, with use of the ground symbols to make everything neat.
raff5184:

--- Quote from: Vovk_Z on March 27, 2020, 08:58:22 pm ---Are you talking about power consumption from B1?
--- End quote ---
Yes, exactly


--- Quote from: Vovk_Z on March 27, 2020, 08:58:22 pm ---Second (not used) comparator have to be set to some stable steady state - fully on or fully off, otherwise it can oscillate.

--- End quote ---
I want it fully off, how do I do it?


--- Quote from: Chalcogenide on March 27, 2020, 09:00:33 pm --- then you will have the direct path to ground through R6 and R7.

--- End quote ---
Is this an issue?


--- Quote from: Prehistoricman on March 27, 2020, 09:06:16 pm ---Your schematic isn't nice to read. Ground is usually expected at the bottom and power at the top, with use of the ground symbols to make everything neat.

--- End quote ---
I'll clean it and reupload

Anyways, I'll try different resistors and see what happens
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