AN896 Datasheet PDF

AN896 APPLICATION NOTE A BATTERY CHARGER USING THE TSM101 by S. LAFFONT This technical note shows how to use the TSM101 integrated circuit with a switching mode power supply (SMPS) to realize a battery charger. An example of realization of a 12V Nickel-cadmium battery charger is given. 1 - TSM101 PRESENTATION The TSM101 integrated circuit incorporates a high stability series band gap voltage reference, two ORed operational amplifiers and a current source (Figure 1) Figure 1 : TSM101 Schematic Diagram 1 2 3 4 Vref 8 7 6 5 A great majority of low or medium end power supplies is voltage regulated by using shunt programmable voltage references like the TL431 (Figure 2). The galvanic insulation of the control information is done by using an opto-coupler in linear mode with a variable photo current depending on the difference between the actual output voltage and the desired one. A current limitation is used to protect the power supply against short circuits, but lacks precision. This limitation is generally realized by sensing the current of the power transistor, in the primary side of the SMPS.