Switching power supply is used in almost all electronic equipment due to its high efficiency, small size and light weight. It is an indispensable power source for the rapid development of the electronic information industry. In the design of the switching power supply, the design of the parameters of the peripheral circuit of the switching power supply chip is a very important part of the stable and reliable operation of the switching power supply. The MC34063 is a current-sensing DC-DC converter chip with variable oscillation frequency. According to its specification, its peripheral circuit is designed. When the load is heavy, the output voltage often cannot be stabilized at the target voltage. In response to this problem, this paper improves the design method of circuit parameters, and verifies the rationality of the improved parameters through experiments. 1.1MC34063 basic characteristics The MC34063 is a monolithic bipolar linear integrated circuit dedicated to the DC-DC converter control section. The chip contains a temperature-compensated bandgap reference, a duty cycle control oscillator, a driver, and a high-current output switch that can output a 1.5A switching current. Through different peripheral circuit design, functions such as boost, buck, and voltage reversal can be realized. The basic characteristics are as follows: input voltage between 6~40V; short circuit current limit; low quiescent current; output switch current up to 1.5A (no external triode); adjustable output voltage; oscillating capacitor is 470pF, when the load is light Its working oscillation frequency is from 50KHz to 55KHz. When the load is heavy, its working frequency can reach 80KHz. The internal structure of the MC34063 is shown in Figure 1. The oscillator continuously charges and discharges the timing capacitor externally connected to the CT pin (pin 3) through the constant current source to generate an oscillating waveform. Both the charge and discharge currents are constant (when the load is constant) and the oscillation frequency depends only on the capacity of the external timing capacitor. In Figure 1, one end of the AND gate is connected to the oscillator output, and the oscillator output is flipped high when the oscillator is externally charged to a certain threshold level. The other end of the AND gate is connected to the output of the comparator. When the inverting input of the comparator is lower than 1.25V, the comparator outputs a high level. When the two inputs of the AND gate become high level, the flip-flop is set to high level, and the output switch tube is turned on. Otherwise, when the capacitor of the oscillator outputs low level during discharge, the flip-flop is reset, so that the output switch The tube is off. Figure 1 Internal structure of MC34063 The current limit is completed by detecting the voltage drop across the sampling resistor connected between VCC (6-pin) and 7-pin. When the voltage drop across the resistor is detected to be 300 mV, the current-limiting circuit energizes the charging process of the oscillator into a discharge process. , forcing the output of the oscillator to be low, resetting the flip-flop and turning off the output switch.
To satisfy high voltage application demands, allowing apm DC Source System to cover a voltage range from 0V to 800V,the switching power supply has low load regulation, which ensure stable output when the load is changing constantly. The smps power supply supports standard SCPI communication protocol, which is convenient for user`s secondary development.
Some features as below:
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