Open source-MC34063 switching power supply-step-down-series (small current application)

MC34063 switching power supply - step-down - series (low current application), this is the most commonly used method of using 34063. Generally, the application current is 1A. The oscillation frequency of 34063 can reach up to 100KHZ, so the external inductor should be as large as possible. , so that the current and power will be sufficient. Since the 34063 uses a triode internally, the maximum switching current is limited to 1A. In addition, the front stage requires a current detection resistor to control the on and off of the switch tube, the switch tube and the detection current resistor. The power consumption will affect the efficiency of the entire circuit, so no one is willing to use 34063, but it is cheap at 2 cents each. Add a CD127 chip inductor and several chip capacitors, and the cost will not exceed 1 yuan. The main reason is that the circuit size limits its range of use. I will try my best to present various usage methods of 34063 in subsequent open source projects! I will try to make 34063 as efficient as possible. The principle of the buck circuit: VIN1, C1, and C2 form the input filter capacitor. R1 is the resistor for detecting the switching current. D1, L1, and U1 are the focus of the circuit. C4 is the oscillation capacitor. When using 100PF, the frequency is 100KHZ, C5, and C6. C7 and VOUT-1A are the output filter circuit. R2, R3 and R4 form the output voltage sampling circuit except R2 and R4, which use 1% precision resistors. The working principle of 34063 is that after the input voltage reaches U1 through capacitor filtering, the IC oscillator works to drive the internal power transistor to conduct, passing through the inductor, output capacitor and external load. When charging starts, the capacitor is in a short-circuit state, and the resistor that detects the current When the voltage is greater than 0.3V, the internal power transistor is turned off. Then all the current is converted into a magnetic field and stored in the inductor. However, the current in the inductor cannot mutate. Then the internal magnetic field is converted into current and continues to charge the capacitor and external circuit. Based on V=I*R, the voltage is stable in a short period of time. The magnetic field in the inductor is limited. When the internal magnetic field cannot maintain a constant output current, the output voltage drops. When the voltage detection pin of U1 drops below 1.25V, the internal power The transistor turns on again and repeats the previous action over and over again.