Mc34063 MP3 Switching Charger

The MP3 charger in Figure 1 uses only one switching regulator integrated circuit (MC34063) and a few external components. When outputting +5V voltage, the current can reach 500mA and the power consumption is less than 5W.

1. Working Principle

When the circuit is working, first add 9~15V DC voltage to IC1 through D2 and power switch S1. D2 is used for input voltage polarity protection, D3 is a transient clamping diode to suppress the possible spike voltage from the input power supply, and capacitor C1 (470uF) is used for filtering.

A 1Ω resistor is connected in parallel between pins ⑥ and ⑦ of IC1. It is used to monitor the current flowing through L1. When the current is 1A, the voltage of pin ⑦ is about 300mV, which is lower than the voltage of pin ⑥. At this time, the internal transistor Q1 of IC1 is turned off, and the energy stored in L1 is discharged through the load. Capacitor C1 and Schottky diode D1 (freewheeling function) are discharged, and C2 (1000uF) completes the filtering function.

The adjustable VR1 and the 560Ω resistor in Figure 1 form a voltage divider, and its voltage dividing point B is connected to the ⑤ foot of IC1. By adjusting VR1, the output voltage can be +5V. If the output voltage overshoots due to a sudden decrease in load, the voltage regulator ZD1 connected in parallel to the output has a clamping function, which prevents the output voltage from overshooting. In addition, the voltage rise inside IC1 is also stopped at this time to limit the current supplied to L1, so that the output voltage returns to +5V.

Under normal environmental conditions, as long as the input voltage is higher than +5V, ZD1 will be turned on. In order to limit the current flowing through ZD1, it is recommended that the output voltage of the switching power supply should not exceed +6.5V (adjust VR1). When the output voltage is adjusted to 6.5V, the current flowing through ZD1 and the resistor is 140mA.

As shown in Figure 1, if VR1 is adjusted to make the output voltage +5V, ZD1 will produce a transient clamping effect as long as the output voltage is higher than +5V.

If the output terminal is short-circuited, the fault current will be automatically limited to 0 to 120mA (determined by the resistance value between pins (6) and (7) of IC1).

During debugging, add +9~+15V DC voltage to the input end of the circuit in Figure 1, turn VR1 counterclockwise to the minimum output voltage, use a digital voltmeter to test the output voltage of Figure 1, and turn VR1 to +5V. At this time, the MP3 can be charged and put into use. The technical characteristics of MC34063 are shown in the attached table.