[SOLVED] Help with project

[GH Crash]

I need help in determining the best approach for a lithium ion capacitor, LIC, (also know as a hybrid capacitor) low-voltage protection circuit. Can you suggest an approach, or a simple circuit design to address the requirement of this circuit?

Background: Hybrid (lithium ion) capacitors have a minimum voltage limit. Discharging them beyond that point, or storing them below their minimum voltage will damage or destroy the capacitor. The circuit (device) needed would be placed between the capacitor and the load and would interrupt the current flow when the capacitor voltage dropped to its minimum allowable voltage. The circuit will be used in environments where size and weight are a major concern.

Circuit requirements

1. The circuit shall not reduce the maximum voltage and/or amperage available at the load.
2. The circuit must be capable of handling currents up to 3 amps.
3. The circuit should operate satisfactorily at input voltages between one and six volts DC.
4. The completed circuit board needs to be small, preferably under 15mm by 15mm square.
5. The completed circuit must be light, Under 0.75 grams max weight, under 0.5gshould be the goal.
6. Items, or conditions, not directly mentioned in the requirements are left up to the designer's discretion.

Additional information (information that may be helpful in designing a solution.):

1. The LIC typically used will be between 10F and 100F capacitance and 5.0 max volts.
2. The load will typically be a DC coreless motor of under ten watts and 3.7 volts.
3. It is desirable that there be absolutely no current flow once the LIC reaches its minimum voltage limit but quiescent current flow through circuit components may be unavoidable.
   

I would appreciate any help you can give. A simple circuit diagram may be the best way to explain your thinking. I try to answer any and all questions concerning this circuit design request.

George

 

[danadakk]

Hysteresis calculator for an OpAmp or Comparator -

Comparator circuits with Hysteresis Design Tool

https://www.utmel.com/tools/comparator-hysteresis-calculator?id=39

Regards, Dana.

 

[D.A.(Tony)Stewart]

I came now, late to the game.

The LIC is a hybrid between LiPo and EDLC, Polymer Caps. So low ESR for higher power density and wider discharge voltage range than a battery but lower range energy capacity.

The under-voltage UVP protection threshold depends on your life cycle expectations, so choose conservatively or wisely as short-term energy gains cost dearly in the long run. That same is true for Lithium batteries so you could get 10x the lifetime Wh use if you only used 50% capacity each charge by reducing time over 3.7V and cutout at a higher voltage. Your choice of cutoff hysteresis value must exceed that of the ESR*I range of the storage cap/battery to prevent rapid oscillation This can be improved by a slow cutoff..

A low-side Nch power switch with a stable Vref is a minimal solution for a "hard" cutout which is the DO discharge output side of the battery protect IC. If you prefer a "soft cutout" that slows down before shutting off then a PWM-controlled DO-like switch comparing Vout to Vref cutout range could be designed,

All it takes is more specific design specs. with special attention to the resistance of every part of the design.

 

[GH Crash]

Hi,

it´s on you to press the [mark as solved] button.

Klaus

I must be a babe in diapers with regards to this forum. I can't find the "[mark as solved] button".

Where is it?

 

[KlausST]

Hi,

if I do a browser search for "mark as solved" ... it finds it immediately.
Hint: top, right, green

Klaus

 

[GH Crash]

All it takes is more specific design specs. with special attention to the resistance of every part of the design.

So true.

Unfortunately that is beyond my abilities. I'm just an electronics hacker. I do pretty well assembling a circuit once I know what parts are needed. I lack the knowledge to take theoretical or general knowledge and turn it into a solution to a problem.

Several people have tried to help me but I still couldn't come up with what component to stick where to solve the problem. Makes me feel like a kindergarten student attending a college course.

George Harris