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Download Power Fundamentals: Linear Regulator Fundamentals
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Transcript
Linear Regulator Fundamentals 2.3 PNP Linear-Regulator Operation • Voltage feedback samples the output R1 and R2 may be internal or external • Feedback controls pass transistor’s current to the load VIN VOUT PASS TRANSISTOR R1 CIN ERROR AMP COUT R LOAD VREF R2 2 PNP-LDO Linear Regulator • Low drop-out voltage (VSAT of PNP) • Higher ground pin current (load dependent) • Requires output capacitor 3 Simple Model of Losses in the PNP LDO Regulator Driving the PNP LDO Pass Element 4 Drive Current vs. Low/High Load Current The drive current for a load current requirement of 5mA Increasing the load current requirement to 500mA 5 Summary • The NPN-Quasi-LDO has the following Characteristics: – Requires that the input voltage be only 100mV to 700mV higher than the output voltage – Has a higher Ground pin current than NPN type – Requires careful selection of the output capacitor value and ESR ratings 6 Thank you! 7
