L4960 adjustable output switching power supply

L4960 integrated circuit

L4960 is a step-down DC/DC converter integrated circuit. Its package and pin arrangement are shown in Figure 1. The functions of each pin are shown in the attached table.

       Schedule

5～15V continuously adjustable regulated power supply circuit

The 5~15V continuously adjustable regulated power supply circuit is shown in Figure 2. The DC voltage obtained after the mains power is stepped down by transformer T, rectified by Dl~D4 diodes, and filtered by Cl capacitor is input to pin ① of L4960. ②The pin is connected to the midpoint of the voltage divider composed of W1 and R3 to feedback the changes in the output voltage. The resistor values ​​of W1 and R3 determine the output voltage. The relationship between the output voltage Vout and W1 and R3 is VoUY, (1 + W1/R3).5.1V, where 5.1V is the internal reference voltage of the L4960. ⑧Pin is connected to C4, R2 and C5 for frequency compensation. ④The pin is grounded. ⑦Pin is connected to the parallel circuit of C3 and R1, which determines the operating frequency of the oscillator. ⑥Connect the pin to capacitor C2 to make the power supply have soft-start function. ⑦Pin is the output terminal.

Fixed output circuit

If W1 is changed to resistor R4, a fixed output regulated power supply can be formed. The resistance value can be determined according to the value of the output voltage Vout. After the output voltage is determined, the resistance of R4 can be calculated by the formula Vout=(1+R4/R3) ^. 5.1V, where R3 can be 4.7kΩ.

Component selection

D1~D4 can use rectifier diodes with an operating current of 3A, or 3A/50V full-bridge devices. D5 must use a Schottky diode with an operating current of 5A. The saturation current of the inductor L should be greater than 5A, and the operating frequency should be greater than 100kHz. C6 and C7 should use high-quality electrolytic capacitors with small equivalent series resistance. The equivalent resistance not only affects the conversion efficiency, but also affects the output ripple voltage. Potentiometer Wl is best to use a multi-turn potentiometer, or use a 10kΩ single-turn potentiometer and a 100Ω single-turn potentiometer in series instead. The 10kΩ potentiometer is used for coarse adjustment, and the 100Ω potentiometer is used for fine adjustment. Other components can be selected according to the parameters marked in the figure. L4960 needs to add a heat sink with a size of about 2x30x50mm or a corresponding profile heat sink.

When designing the printed circuit board, it should be noted that the thick lines in the picture are large circuit traces, and their width should be no less than 3mm (preferably 4 to 5mm). D5, D6, and C7 should be welded on thick wires.