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ML4812IQ 数据表(PDF) 7 Page - Fairchild Semiconductor |
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ML4812IQ 数据表(HTML) 7 Page - Fairchild Semiconductor |
7 / 16 page ML4812 REV. 1.0 10/10/2000 7 ENABLE VREF VREF GEN. 9V INTERNAL BIAS 5V VREF VCC – + VCC (V) 0 30 20 40 10 25 20 15 10 5 0 25 20 15 10 5 0 TEMPERATURE (degrees) –60 20 60 140 100 –20 –40 40 80 120 0 OPERATING CURRENT STARTUP IREF (mA) 0 40 100 20 60 120 80 0 -4 -8 -12 -16 -20 -24 Figure 10. Reference Load Regulation Figure 8. Under-Voltage Lockout Block Diagram Figure 9a. Total Supply Current vs. Supply Voltage Figure 9b. Supply Current (ICC) vs. Temperature TYPICAL APPLICATIONS INPUT INDUCTOR (L1) SELECTION The central component in the regulator is the input boost inductor. The value of this inductor controls various critical operational aspects of the regulator. If the value is too low, the input current distortion will be high and will result in low power factor and increased noise at the input. This will require more input filtering. In addition, when the value of the inductor is low the inductor dries out (runs out of current) at low currents. Thus the power factor will decrease at lower power levels and/or higher line voltages. If the inductor value is too high, then for a given operating current the required size of the inductor core will be large and/or the required number of turns will be high. So a balance must be reached between distortion and core size. One more condition where the inductor can dry out is analyzed below where it is shown to be maximum duty cycle dependent. For the boost converter at steady state: (1) Where DON is the duty cycle [TON/(TON + TOFF)]. The input boost inductor will dry out when the following condition is satisfied: (2) or (3) VINDRY: voltage where the inductor dries out. VOUT: output DC voltage. Effectively, the above relationship shows that the resetting volt-seconds are more than setting volt-seconds. In energy transfer terms this means that less energy is stored in the inductor during the ON time than it is asked to deliver during the OFF time. The net result is that the inductor dries out. V V D OUT IN ON = - 1 (1) Where DON is the duty cycle [TON/(TON + TOFF)]. The input boost inductor will dry out when the following condition is satisfied: Vt V D IN OUT ON () ( ) <´ - 1 (2) or VD V INDRY ON OUT =- ´ [(max)] 1 (3) |
类似零件编号 - ML4812IQ |
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类似说明 - ML4812IQ |
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