Performance Analysis of Inductive L1 for Selection of Main Components of Switching Power Supply

Click on the blue font above, pay attention to us 15 Main partial selection Inductance plays an important role in the switching power supply, this article Rohm Jun will introduce the selection method of inductance. Inductance: L1 Inductive L1 is composed of an output capacitor C5 and an LC filter as shown in the circuit diagram. The setting of the L1 inductance value is to operate the device in discontinuous mode. This is because if the reverse current of the diode is operated in a continuous mode, the reverse current of the TRR causes the diode loss to increase, and the reverse current will also become the peak current at the MOSFET, so the MOSFET is also Will add it. In order to avoid this problem, the discontinuous mode is selected. Details can scan the two-dimensional code at the bottom of the article, see the introduction in the "Basic Work and Unconstallless Mode and Continuous Mode" in TechWeb. Inspiration value First calculate the inductance value. Sets VIN to 101V. Assuming 90VAC conditions, the peak voltage is 1.41 times, and the margin is 20%. Set VIN = 90VAC × 1.41 × 0.8 = 101V, then: IOMAX takes about 20% of the margin to draw: IOMAX = 0.2a × 1.2 = 0.24A. Set up a critical point (peak) IP = iomax × 2 = 0.48A, then: According to the calculation result, the standard value is selected for 470μH. Calculation of inductor current Next, the inductor current is calculated to determine the allowable current of the inductor. When the input voltage is maximum, the inductor current is the largest. When the maximum input voltage is 264VAC, the power supply IC switch (MOSFET) is on the minimum turn-on time of the IC. The minimum conduction time is about 0.6 to 1.5 μs depending on the conditions such as the inductance value of the output voltage and inductance. Assume that the minimum on-time at 264VAC is 1μs, then: Therefore, the inductance of the inductor value of 470μH and the inductor current is 0.8a should be selected. It must be noted that it is necessary to confirm the inductor current by actual installation to ensure that it is unsaturated inductance. Rohm's key time Considering everyone's time is precious, Rohm Jun's focus on this section is as follows, take it, not thank you ~ • The setting of the inductor is to make the device work in discontinuous mode. The inductance value is calculated based on the minimum value of VIN and the maximum value of TON. · Inductor current calculates according to VIN's maximum and minimum conduction time. Read more

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