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Linear Regulator Fundamentals

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. V. V. IN. OUT. PASS TRANSISTOR. R1. ERROR. C. AMP. C. IN. R. OUT. LOAD. R2. V.

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Linear Regulator Fundamentals

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  1. Linear Regulator Fundamentals 2.3 PNP

  2. Linear-Regulator Operation • Voltage feedback samples the outputR1 and R2 may be internal or external • Feedback controls pass transistor’s current to the load V V IN OUT PASS TRANSISTOR R1 ERROR C AMP C IN R OUT LOAD R2 V REF

  3. PNP-LDO Linear Regulator • Low drop-out voltage (VSAT of PNP) • Higher ground pin current (load dependent) • Requires output capacitor

  4. Simple Model of Losses in the PNP LDO Regulator

  5. The drive current for a load current requirement of 5mA Drive Current vs. Low/High Load Current Increasing the load current requirement to 500mA

  6. 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

  7. Thank you!

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