CC mode problem with TOP248 for Battery Charger
I've designed 12V/6A Battery charger based on TOP248 as per design note as per DI-12 design idea. The circuit image is attached herewith. Now, I'm facing problem that the CC mode setting is highly difficult.
Resistors R23, R24 & Q1 controls the current through LED which will control the duty cycle. If I'm reducing R16, the CC mode tunes upto 4.2A for 0.1R shunt. So, I'm facing lot of problem in production.
Plz suggest solution.
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Comments
Ok.
The complete schematics is attached herewith.
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My power supply is of 14.3V/6A. So in CC mode my supply should work for 6A for any load applied.
The transistor Q1 is used to sink the current from LED of U1. The problem is to set the exact amount of current sinking through Q1. and obviously, it depends on base voltage (Vshunt), R16, (R23+R24). If (R23+R24) is low then CC mode work on 4A to 5A. If (R23+R24) is high (i.e. > 130 ohm) then CC mode jumps directly to 9A. So, I couldn't make out the exact point.
Also, I think the current control is just a P control i.e. Ic = (Vshunt/R16) * Beta of Q1. There is no I term in it so it will retain the offset in the controller and I hope this may be one of the reason.
Another solution which I can think to use TL431 as control element (i.e. current sink for CC mode). So a OPAMP can be used to amplify the Vshunt to 2.5V and once the Vshunt * Gain > 2.5V then TL431 will conduct and sink the current.
To maintain the stability, the bias resistor for TL431 (CC mode) should be exactly equal to (or less than) the bias resistor (R11+R12) of TL431 (CV mode).
I've done the simulation of same but couldn't tested on circuit. So, before going ahead can you plz understand and check from your side?
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Hi,
What exactly is R23 and R24 for? Note that this is not in DI-12 design.
If you need CC operation, the current limit will be set by voltage drop across R20. the I term will be provided by C15.
What is the performance of your circuit if R23 and R24 are removed from the circuit?
Regards
PI-Sarek
Ya, Initially I followed same i.e. no R23 and R24. I found that the CC mode is operating from 2A to 4.5A based on the tolerance of shunt resistor. i.e. CC mode is behaving in slope instead of full straight line (V vs I curve) as Q1 is in active mode even when Vshunt < 0.6V. So, it will reduces the duty and hence the output voltage.
There is around 10% tolerance in shunt. I cannot afford high precision shunt due to tight costing of the circuit.
Hence, I put the collector resistor to limit the current through LED at 6A. I can do it in some boards successfully but It gives difficulties in other boards. I hope it due to variations in beta of Q1. So, I'm trying different circuit which will give exactly straight line in CC mode. I've attached my concept in simulation here. Plz check it and reply me back.
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Dear PI-Sarek,
Any update over my previous comment? I'm going to place 1k pieces of TOP248Y for this circuit. Plz support. it is urgent
Hi,
Conceptually what you are trying to accomplish looks fine though I am not sure how you plan to combine it with the rest of your circuit.
I would strongly recommend reviewing the attached design note for more ideas and a possible use of an operational amplifier for a precision cc-mode.
For additional support you may contact one of our field offices in your country. Our field applications engineer can help you with any finetuning of the circuit.
Regards
PI-Sarek
Dear PI-Sarek,
Plz find the attached CC mode schematics with TL431. Check from your side if possible. My question for the CC mode with LM358 is,
in CC mode the Vo is decreased such that current will be constant. We are driving the LM358 with the same supply so, LM358 and TL431 will stop working below 4V (2.5V setpoint for TL431 and 1.5V taking by LM358 as it is not rail-to-rail OPAMP). So what will happen in that case?
Plz check and explain.
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Please sontact our field office in your country for further support.
Please use the link below to locate the closest office. One of our field applications engineers will be able to help you.
http://www.powerint.com/en/company/sales-information/worldwide-sales-support-locations
Regards
PI-Sarek
Hi,
Please provide us a copy of the complete schematic of your power supply. It will be very helpful if the copy has a better resolution so that we can clearly read the component designators and component values.
What exzctly are the specifications for your design and how much variation are you measuring in production?
Regards
PI-Sarek