High pitch noise from Li Poly Charging circuit

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Hi All, Happy Christmas

 

I have another post where I am discussing charging a Li-Poly with a solar panel. I did not want to post this question on the same topic to avoid any confusion. This issue was noticed while experimenting while charging with both benchtop power supplies as well.

 

My boards all use a simple ST4054 charger ic. The charge current is set to a max 0.66A, and Input Voltage is set to 5.5V.

 

If I were to limit the current on the power supply to 0.25A or less, I noticed a high pitch noise from the charger IC.

 

When the ST4054 charger has less current than required, the VIN drops to a little above the battery voltage but continues charging the battery.

 

This noise will not really have to affect anyone's ears as it is kept in an enclosure and placed outside, but can this have any damage to the IC?

 

Thanks

 

 

 

 

 

 

 

This topic has a solution.

Thanks

Regards

DJ

Last Edited: Thu. Dec 24, 2020 - 09:29 PM
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djoshi wrote:
... but can this have any damage to the IC?
Potentially yes in the long term.

800 mA standalone linear Li-Ion battery charger with thermal regulation (ST AN2370)

[page 6]

2 Stability considerations

via STC4054 - 800mA Standalone linear Li-Ion battery charger with thermal regulation - STMicroelectronics

 

"Dare to be naïve." - Buckminster Fuller

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First, I would ask, do you mean STC4054?

 

Next, I would say "maybe damage". One has to look at WHERE that sound is coming from. Its a linear regulator, not a switcher, so there is no inductor and things like low power "burst mode" are not there. So, WHERE is the sound coming from? The battery, maybe? Until that is known, we cannot answer your question. Do you have the required series resistor and a 4.7uF cap across the battery for light load stability?

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

This reply has been marked as the solution. 
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If I were to limit the current on the power supply to 0.25A or less, I noticed a high pitch noise from the charger IC.

Well, of course it is not proper for you to do so.  You must not artificially limit the current supplied to the chip (below its configured setting), unless that is for a severe event failsafe, intended to bring the entire charger to a halt. 

If you artificially limit the current below what is needed, you have starved or choked the chip circuitry, so it is gasping for power & its voltage will fall to zero & it will stop operating properly.   

 

Of course when it quits working, the current draw falls to nothing which causes the voltage to rise back up...which causes it to restart and draw current...which hits your current limit and causes the voltage to fall & it will stop operating properly.   Of course when it quits working the current draw falls to nothing which causes the voltage to rise back up...which causes it to restart and draw current...which hits your current limit and causes the voltage to fall & it will stop operating properly.   Of course when it quits working the current draw falls to nothing which causes the voltage to rise back up...which causes it to restart and draw current....which hits your current limit and causes the voltage to falls  & it will stop operating properly.   Of course when it quits working the current draw falls to nothing which causes the voltage to rise back up...which causes it to restart and draw current.  I think you see a pattern...DON'T SUPPLY a LOW CURRENT LIMIT...let the chip do that.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Thu. Dec 24, 2020 - 07:35 PM
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ka7ehk wrote:

First, I would ask, do you mean STC4054?

 

Next, I would say "maybe damage". One has to look at WHERE that sound is coming from. Its a linear regulator, not a switcher, so there is no inductor and things like low power "burst mode" are not there. So, WHERE is the sound coming from? The battery, maybe? Until that is known, we cannot answer your question. Do you have the required series resistor and a 4.7uF cap across the battery for light load stability?

 

Jim

 

Yes, sorry I meant STC4054. Yes I have got the  4.7uF.

 

Its hard to tell if the noise is from the IC or a capacitor. 

 

 

 

 

Thanks

Regards

DJ

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Its hard to tell if the noise is from the IC or a capacitor. 

Why is it hard to tell? If you read #4 you will see the source of the oscillation.   You cannot starve the chip & cause it to choke off.

 

What would happen if you had a LM555 and were blinking an LED with 50ma, then set your power supply, so it could only deliver 30ma?  Very odd things would happen at the 555 when it turned on the LED!!   The V+ to the 555 would collapse until some balancing point was reached & maybe it would restart a new timing interval.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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avrcandies wrote:

Its hard to tell if the noise is from the IC or a capacitor. 

Why is it hard to tell? If you read #4 you will see the source of the oscillation.   You cannot starve the chip & cause it to choke off.

 

What would happen if you had a LM555 and were blinking an LED with 50ma, then set your power supply, so it could only deliver 30ma?  Very odd things would happen at the 555 when it turned on the LED!!   The V+ to the 555 would collapse until some balancing point was reached & maybe it would restart a new timing interval.

 

Just read #4 now, seems browser needed to be refreshed. 

 

My low current issue, I guess be the worst-case scenario. Ideally for my application will have adequate current, but if my source becomes solar cells, then towards the evening before it completely shuts off i might have some low current.

 

Unfortunately, these boards are made with STC4054, I guess in the future its best to use an MPPT based IC that has control over current.

 

 

 

 

Thanks

Regards

DJ

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Not only MPPT but something that works down to low input voltages with current starved sources. LinearTech (now Analog Devices) has a number of chips designed to do exactly this.

 

For what ever it is worth, solar cells are ALWAYS current limited. As the light level drops, simultaneously, the voltage drops and the available short circuit current drops. Setting the current limit on a 5V supply is a REALLY long ways from a solar panel behavior.

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

Last Edited: Thu. Dec 24, 2020 - 09:55 PM
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So for my current setup with the STC4054, is there anything I could do ensure the IC does not get damaged when current reduces?

 

I am hoping that ultimately the battery will get fully charged and then the charge current will be less as then the battery will only need to be topped up rather than full charge. If I am correct as the battery gets charged up and voltage gets close to 4.2V the charge current requirement is also is reduced,

 

 

 

 

Thanks

Regards

DJ

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djoshi wrote:
is there anything I could do ensure the IC does not get damaged when current reduces?
Yes (reduce the bandwidth of the constant current control loop)

800 mA standalone linear Li-Ion battery charger with thermal regulation (ST AN2370)

[page 6]

2 Stability considerations

[last paragraph and Figure 8]

 

"Dare to be naïve." - Buckminster Fuller

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If you have a primary current limit, then you must always draw less than that limit, or accept that the voltage will drop drop drop.   If the voltage will plummet, then you should operate the chip from an independent supply (say 5V) and then let it control the solar charging path.  You can probably bootstrap it so the battery supplies the very little current & fixed voltage the chip itself requires to operate (so you need a chip with a separate Vcc from the charging voltage).

 

Or, you can set it so if the chip supply voltage starts to fall, then it backs off the charging current draw, to prevent the chip supply from drooping too low.  One way or another, you need to ensure the chip always has enough voltage to operate properly.  This is especially critical for li-ion, since they need precision charging to avoid explosion, fire, or other incidents.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Fri. Dec 25, 2020 - 01:53 AM
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Yes, it makes sense. The voltage drops, and the IC restarts and repeats the cycle. 

 

Well having a separate VCC IC will be an option for the next batch of PCB's.

 

If the battery is to low, the PCB shuts down. Every 10mins it will check that battery has at least reached 5% before powering the circuit.  So draw from battery will also be low.

Thanks

Regards

DJ

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Li batteries of all kinds have a minimum discharge voltage. lf you discharge below that, you damage the battery. Usually, for a single cell, that is in the range of 2V2 to 2V6 or so; it can be different for batteries from different manufacturers. Also, if the battery IS below that minimum, you have to be very careful when charging. The charging current has to be fairly low until it gets back up to that minimum.

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

Last Edited: Fri. Dec 25, 2020 - 06:11 PM
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Yes, I got a battery protection circuit.

 

I have also noticed if the battery is very low, the charge current is also very low, once it gets above a certain threshold it then increase the charge current. 

 

 

Thanks

Regards

DJ

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If you regularly see that, you are discharging the battery way too far, way too often. Recipe for short battery life.

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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ka7ehk wrote:

If you regularly see that, you are discharging the battery way too far, way too often. Recipe for short battery life.

 

Jim

 

The only time I have seen that is when the power lead has been removed from the PCB and the circuit has been draining for a few days.

 

I think I need to add some type of case, where if the battery reaches 1%, disable the systems and go into some type of sleep mode, till someone resets the system.

 

 

Thanks

Regards

DJ

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1% is way too low! Unless that is "percent available energy" relative to the cut-off point. The real question is 1% of what? 

 

a) Terminal voltage

 

b) Voltage above the cut-off

 

c) Available energy

 

d) ...

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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I am using GSM module the BG95, and it reports remaining capacity.  I guess it must be doing it by monitoring the voltage.

Thanks

Regards

DJ

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OK, with something "smart" like that, one would hope that the percentage is above the cut-off voltage. I looked for a real manual but could not find one.

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

Last Edited: Sun. Dec 27, 2020 - 07:38 PM