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Combining Frequency Jitter Function with Vcc Self Supply for Switch Mode Power Supply Controller

IP.com Disclosure Number: IPCOM000075575D
Original Publication Date: 2005-Mar-25
Included in the Prior Art Database: 2005-Mar-25
Document File: 5 page(s) / 110K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

In the following, a new multiple function for the Vcc (Voltage at the Common Collector) pin is proposed, where the Vcc voltage is self supplied by the internal current source and a random time delay is used for its regulation. In addition, this random time delay produces a random frequency jitter function in the internal oscillator. Up to now, the prevalent way to supply power to the controller of a switching mode power supply is based on the patent US6587357B1. Figure 1 shows the block diagram of this power supply solution, Figure 2 displays various waveforms associated with this self supply circuit. The main idea of this patent is to have one controllable current source for the power supply of the controller. The current source charges the Vcc capacitor until the Vcc voltage reaches the higher of two levels. It then stops charging and the Vcc capacitor is discharged by the controller until the voltage drops to the lower level when the charging of the Vcc capacitor begins anew. This solution is easy to implement, but it also has some disadvantages, namely there are high switching losses in the power source cell.

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Combining Frequency Jitter Function with Vcc Self Supply for Switch Mode Power Supply Controller

Idea: Dr. Gong Xiaowu

In the following, a new multiple function for the Vcc (Voltage at the Common Collector) pin is proposed, where the Vcc voltage is self supplied by the internal current source and a random time delay is used for its regulation. In addition, this random time delay produces a random frequency jitter function in the internal oscillator.

Up to now, the prevalent way to supply power to the controller of a switching mode power supply is based on the patent US6587357B1. Figure 1 shows the block diagram of this power supply solution, Figure 2 displays various waveforms associated with this self supply circuit. The main idea of this patent is to have one controllable current source for the power supply of the controller. The current source charges the Vcc capacitor until the Vcc voltage reaches the higher of two levels. It then stops charging and the Vcc capacitor is discharged by the controller until the voltage drops to the lower level when the charging of the Vcc capacitor begins anew. This solution is easy to implement, but it also has some disadvantages, namely there are high switching losses in the power source cell.

In the patent US5739658A1 it has been shown that by introducing a frequency jitter function, the EMI (Electromagnetic Interference) issue for switch mode power supply can be reduced. The frequency jitter waveform used in this patent is depicted in Figure 3. But there are still some difficulties with this solution. As can be seen from Fig. 3(c), it takes about 4ms for the frequency to ramp up and down, which is a very long period of time for an Integrated Circuit (IC). Therefore, it cannot be implemented inside the IC using analog methods, making the use of a big external capacitor necessary to generate this long time period signal.

In Figure 4 a new circuitry is proposed to solve the above-named problems wi...