UC3906 LED Indicator Problem

Hi,

 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.

 -Tahar

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.

Hi,

 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.

 -Tahar  

Hello,

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???

thank you

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.  

Hi,

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???

Thank You

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?

 -Tahar

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)

Thank You

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???

Thank You

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.

 -Tahar  

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.

 -Tahar