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UC3800G-S08-R 데이터시트(PDF) 6 Page - Unisonic Technologies |
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UC3800G-S08-R 데이터시트(HTML) 6 Page - Unisonic Technologies |
6 / 10 page UC3800 Preliminary LINEAR INTEGRATED CIRCUIT UNISONICTECHNOLOGIESCO.,LTD 6 of 10 www.unisonic.com.tw QW-R103-083.a OPERATION DESCRIPTION The UTC UC3800 devices integrate many useful designs into one controller for low-power switch-mode power supplies. The following descriptions highlight some of the features of the UTC UC3800 series. HV Start-up UTC UC3800 integrated HV start circuit, and provide about 1mA current to charge VDD pin during power on state from HV pin. When VDD cap voltage is higher than UVLO (OFF), the charge current is switched off. At this moment, the VDD capacitor provides current to UTC UC3800 until the auxiliary winding of the main transformer starts to provide the operation current. Power-Saving Mode Operation The proprietary Power-Saving Mode function provides linearly decreasing the switching frequency under light-load conditions for higher efficiency. The feedback voltage, which is sampled from the voltage feedback loop, is taken as the reference. Once the feedback voltage dropped below the threshold voltage, the switching frequency starts to decrease. This Power-Saving Mode function dramatically reduces power consumption under light-load conditions. The 22KHz minimum frequency control also eliminates the audio noise at any loading conditions. At zero load condition, the magnitude of power loss is in proportion to the number of switching events within a fixed period of time. Reducing switching events leads to the reduction on the power loss and thus conserves the energy. The UTC UC3800 enter burst mode at standby condition to minimize the switching loss and reduces the standby power consumption. Power supplies using the UTC UC3800 can easily meet even the strictest regulations regarding standby power consumption. Switch Frequency Set The maximum switch frequency is fixed to 65KHz. Switch frequency is modulated by output power POUT during IC operating. At no load or light load condition, most of the power dissipation in a switching mode power supply is from switching loss on the MOSFET transistor, the core loss of the transformer and the loss on the snubber circuit. The magnitude of power loss is in proportion to the number of switching events within a fixed period of time. So lower switch frequency at lower load, which more and more improve IC’s efficiency at light load. At from no load to light load condition, The IC will operate at from Burst mode to Reducing Frequency Mode. The relation curve between fSW and POUT/POUT (MAX) as followed Fig.1. Fig.1 The relation curve between fSW and relative output power POUT/ POUT (MAX) |
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