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Linear Regulator Fundamentals

This overview discusses the fundamentals of NPN Quasi-LDO voltage regulators, which require an input voltage 0.9V to 1.5V above the output voltage. The Quasi-LDO features higher ground pin current compared to NPN-Darlington regulators, but lower than PNP-LDOs. While an output capacitor is necessary, it typically lacks stringent ESR requirements. Additionally, the document examines loss models and drive current for varying load requirements, providing insight into their operational characteristics and applications in electronic circuits.

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Linear Regulator Fundamentals

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  1. Linear Regulator Fundamentals 2.2 NPN

  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. NPN "Quasi-LDO" Voltage Regulator • The NPN-Quasi-LDO has the following Characteristics: • Requires the input voltage to be at least 0.9V to 1.5V higher than the output voltage • Has higher Ground pin current than the NPN-Darlington, but less than the PNP-LDO Voltage Regulators • Requires an output capacitor, but, generally, has no specific ESR requirement like the PNP-LDO

  4. Losses in the NPN "Quasi-LDO" Simple Model of Losses in the NPN "Quasi-LDO"

  5. Driving the NPN "Quasi-LDO" Pass Element

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

  7. Summary • The NPN-Quasi-LDO has the following Characteristics: • Requires the input voltage to be at least 0.9V to 1.5V higher than the output voltage • Has higher Ground pin current than the NPN-Darlington, but less than the PNP-LDO Voltage Regulators • Requires an output capacitor, but, generally, has no specific ESR requirement like the PNP-LDO

  8. Thank you!

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