I've been assigned the task of designing the charging circuit for my senior design project. I've chosen the UC3906 to charge the two 12 V SLA batteries that I've put in series. I've read over the spec sheet and U-104 application notes numerous times and set up my circuit using Figure 13 of the U-104 application notes as a reference. I used the design equations from the spec sheets to obtain the resistor values needed to set up the dual level float charger. I set my over-charge voltage at 29.1 V, the floating voltage at 27.3 V and my turn on voltage at 20.4 V. Below is the schematic for my design.
I am not getting the correct maximum current into the battery during operation. Using the .470 Ω resistor, the maximum charging current should be around 530 mA. I am getting double that, around 1.1 A, into the battery during charging. Could it possibly have something to do with ∆V across the TIP32B? Any help with this problem would be greatly appreciated.
