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MC34262DR2G Datasheet(PDF) 9 Page - ON Semiconductor |
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MC34262DR2G Datasheet(HTML) 9 Page - ON Semiconductor |
9 / 19 page MC34262, MC33262 http://onsemi.com 9 A Quickstart circuit has been incorporated to optimize converter startup. During initial startup, compensation capacitor C1 will be discharged, holding the error amp output below the Multiplier threshold. This will prevent Drive Output switching and delay bootstrapping of capacitor C4 by diode D6. If Pin 2 does not reach the multiplier threshold before C4 discharges below the lower UVLO threshold, the converter will “hiccup” and experience a significant startup delay. The Quickstart circuit is designed to precharge C1 to 1.7 V, Figure 7. This level is slightly below the Pin 2 Multiplier threshold, allowing immediate Drive Output switching and bootstrap operation when C4 crosses the upper UVLO threshold. Drive Output The MC34262/MC33262 contain a single totem−pole output stage specifically designed for direct drive of power MOSFETs. The Drive Output is capable of up to ±500 mA peak current with a typical rise and fall time of 50 ns with a 1.0 nF load. Additional internal circuitry has been added to keep the Drive Output in a sinking mode whenever the Undervoltage Lockout is active. This characteristic eliminates the need for an external gate pulldown resistor. The totem−pole output has been optimized to minimize cross−conduction current during high speed operation. The addition of two 10 W resistors, one in series with the source output transistor and one in series with the sink output transistor, helps to reduce the cross−conduction current and radiated noise by limiting the output rise and fall time. A 16 V clamp has been incorporated into the output stage to limit the high state VOH. This prevents rupture of the MOSFET gate when VCC exceeds 20 V. APPLICATIONS INFORMATION The application circuits shown in Figures 19, 20 and 21 reveal that few external components are required for a complete power factor preconverter. Each circuit is a peak detecting current−mode boost converter that operates in critical conduction mode with a fixed on−time and variable off−time. A major benefit of critical conduction operation is that the current loop is inherently stable, thus eliminating the need for ramp compensation. The application in Figure 19 operates over an input voltage range of 90 Vac to 138 Vac and provides an output power of 80 W (230 V at 350 mA) with an associated power factor of approximately 0.998 at nominal line. Figures 20 and 21 are universal input preconverter examples that operate over a continuous input voltage range of 90 Vac to 268 Vac. Figure 20 provides an output power of 175 W (400 V at 440 mA) while Figure 21 provides 450 W (400 V at 1.125 A). Both circuits have an observed worst−case power factor of approximately 0.989. The input current and voltage waveforms of Figure 20 are shown in Figure 22 with operation at 115 Vac and 230 Vac. The data for each of the applications was generated with the test set−up shown in Figure 24. |
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