Sinrace Power Supply Technology (Shenzhen) Co., Ltd.

Self-oscillating flyback converter. RCC (Ring Choke Converter),because of its simple circuit topology, the output and input voltage electric are isolated and without the output filter inductor, to efficiently provide multiple DC output voltage down range with small and widely used in power conversion applications, but also the capacity generally less than 50 W of power converters are frequently used. Is widely used in mobile phone chargers and laptop adapters and other devices. However, if the RCC circuit using discrete components, then the typical number of circuit elements by just over 50, so the design of an integrated power devices RCC has become a trend.

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Application circuit of RCC device

Typical RCC circuit takes about 50 discrete components, design and debugging very difficult, reliability is not high enough. To solve this problem, designed a RCC integrated device, Figure l is the typical application circuit. It can be seen from the figure, only 8 discrete input side of the discrete components, the output side there are two discrete components, if the 13001 transistor, diode VD2 and capacitor C4, then packaged into the device, discrete components will be reduced to 7 to improve integration, the RCC will be the most simple circuit.

Internal structure of RCC deivce

Device course of work

When the supply voltage VCC increases undervoltage lockout (UVL0) open circuit voltage, the circuit to work, the oscillator, the small duty cycle generating circuit, the duty cycle selection circuit, blanking circuit starts, then SW port hopping, back-up power-up, the FB pin charge, with the FB pin voltage rise, when the VCC voltage exceeds the diode VD8 turn, provide backup power to the VCC current. Oscillator provides a 12% duty cycle oscillation frequency of 40 kHz square wave, with the VCC voltage continues to rise, rise to the clamp circuit when the clamp voltage, the flyback switching power supply circuit will switch to the small total air ratio (4%) mode of operation, when the output voltage will drop, but will not immediately switch to the large duty cycle until the VCC voltage is below the over-voltage point, a large duty cycle will return to the state, At this frequency will be increased to avoid flyback switching power supply IC operates at frequencies below 20 kHz; when the flyback switching power supply circuit of the output load increases, the inductive flyback energy when not sufficient to provide the system output energy, VCC voltage will drop when the voltage drops to a flyback switching power supply circuit under-voltage point, the flyback switching power supply integrated circuit will be fully off, waiting for restart, when the system enters hiccup mode. If the flyback switching power supply IC operating temperature is too high, the flyback switching power supply IC over-temperature protection will shutdown the output SW, when VCC voltage will continue to fall until the voltage drops to under-voltage point, the anti- Flyback switching power supply circuit off and wait for reboot, flyback switching power supply IC will enter hiccup mode.

Experimental data and dispose

The application form according to Figure l circuit, a single lithium battery charger test data in Table l, Table 2. Figure 3 shows the transient characteristics of the current map.

Tables 1 and 2 through the data showed that the device meets the design standards for basic, but still the following problems: 1) The starting current is too large; 2) over-voltage voltage and the voltage is too close to the start; 3) operating frequency is too small, need through subsequent design improvements.

The typical number of components included in RCC is the same linear power supply 5 to 10 times, although most of the components are very cheap, but the absolute number of large, so the design and manufacturing costs are higher. The more number of components, PCB traces the more complex, the time required to optimize the layout of the longer component placement occurs when the higher the likelihood of error. Mount SMD components also require additional manufacturing steps, it will increase production time and costs. RCC's performance depends on the parasitic component values are difficult to control a large number of discrete components with a combination of the interaction between the tolerances in the manufacturing process requires continuous monitoring and adjustment to make the yield remained at acceptable levels, it must design a RCC integrated device, in order to effectively improve the RCC circuit has the advantage.

The design of the device including internal structure in order to connect the rectifier filter circuit, the converter and the output circuit, the rectifier filter circuit connected with the start circuit. Rectifier filter circuit, converter and start-up circuit, respectively, and flyback switching power supply integrated circuits connected. Device simulation and actual test. Test results show that although there is "the starting current is too large" and three issues, but basically the program to overcome the shortcomings of the program separate RCC, and efficiency greater than 65%, is the ideal one RCC switching power supply unit.