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Battery Management - Chargers Forum
UC3906 LED Indicator Problem
I am using UC3906 to charging my SLA battery 6V 4.5Ah, the following are the specification:
Voc=7.45V V12=7.08V Vf=6.9V V31=6.21V Vin=12V Imax=500mA
R2=0.51Ω R7=82KΩ R12=10KΩ R13= 39kΩ R8=220Ω R6=390KΩ
other the resistor value are same as below circuit.
My input is connected with an adapter 12V 1A.
The problem i facing is that when i on the power, my led float(green) and bulk(orange) are on without connect to the battery.May i know it that my resistor calculation are wrong or anyway i can check the problem that i facing.
Thank You .
Hope can get the reply as soon as poosible.
Your voltages looks right to me, but for the resistor values, I can not see the attached circuit, can you please send it again? You can use the design procedure on page 5 in the datasheet.
I deleted the second post, it is the same question.
This is the circuit i use but the problem i facing is the bulk and float led is on at the same time when power is on.
The resistor values are correct, the only thing I can see may cause the issue is on the comparators (U1) and the values of R3 and R5.
Thank for your reply,
Did you got any way that i can indicate the float and the bulk or calculate the value of R3 and R5???
measure the voltage on the comparator pins. From the schematic, the reference is the portion of the input voltage (I can not read the values of R3 and R5). Then compare that to the pin 10 of the charger, you will have a better understanding on what is going on in the circuit.
Send me some scope plots to look at.
I had measure the input voltage for between R3 and R5 is 0.84V.
I found that when float led is on the voltage at pin 10 of the charger is 2.2V.
when the bulk led is on the voltage at pin 10 of the charger will drop until 11.8mV.
For the scope plot,which scope should i need to take???
This makes sense, when you have 2.2V at pin 10, which means the V- of the comparator is higher than V+, thus the output (7) drives low and the LED turn on. Can you tell me what the battery voltage is at this time? Why do you use pin 10 instead of pin 13?
Bulk LED, do you mean D1 or D2?
The voltage from the battery is around 7.04 when connect to with the charger, if i unplug without the chager and measurethe battery voltage is around 6.83V. I though the pin 10 is to indicate the battery whether is float charge or not.
For the circuit,
D1- bulk charge( taken from pin 7)
D2-overcharge( taken from pin 9)
D3-float charge(taken from pin 10)
Please see figure 2 and figure 3 in page 5 in the datasheet to understand the functionality of the pins and typical charge cycle.
I had see the datasheet for few times already.I found out that the pin 7 is power indicate(prevent the divider resistor from discharching the battery when the input is removed), so i can't using the pin7 as my bulk charge indicator.Correct me if i wrong. Got any other way i can indicate my bulk charge.
Which pin of UC3906,scope can take to make sure that my battery charger is working correctly???
Use a ground instead of pin7, pin 7 is not ground when there is no power to the charger. Your circuit does not have ground.
Pin 9 is for over charge indication, not for charge indication. As shown in the datasheet, it goes low when the battery voltage exceeds V12.
Use figure 3 as a ref to verify that the charger is working as expected.
You can also use bq24105 with the app note SLUA425.
Izit i need to put a ground to pin7???
This is taking so long over e2e, let's set a conference call and discuss this issue over the phone.
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