LDO Control Circuit for Parasitic Diode Backflow Prevention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional low dropout linear regulators (LDOs) face issues with parasitic diodes turning on under forward voltage conditions, leading to current backflow and potential damage to the power transistor, especially when output voltage exceeds input voltage, which affects reliability.
Innovation Solution
A control circuit with a backflow prevention mechanism that compares input and output voltages to switch the substrate voltage and control terminal voltage of the power transistor to the higher of the two, incorporating a switch circuit to prevent current backflow and a clamp circuit to protect against excessive feedback voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the LDO is used for voltage reduction with input voltage greater than output voltage, then the parasitic diode is turned off and normal operation is maintained, but when output voltage exceeds input voltage or input is short-circuited, the parasitic diode turns on causing current backflow and potential damage
Solution Approach 1:
The patent applies preliminary anti-action by introducing a backflow prevention circuit that proactively detects voltage reversal conditions and activates protective measures before current backflow can damage the power transistor. The circuit compares input and output voltages and preemptively switches the substrate connection when backflow is detected, preventing harm before it occurs.
Solution Approach 2:
The patent uses an intermediary substrate switching mechanism that mediates between the power transistor and the harmful backflow current. By dynamically switching the substrate connection based on voltage comparison, the circuit acts as an intermediary protective layer that isolates the power transistor from damaging conditions while maintaining normal operation during standard voltage regulation.
2Reliability
If a backflow prevention circuit is added to protect against current backflow, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent merges the backflow prevention function with the existing error amplifier and control circuitry of the LDO. The substrate switching control is integrated into the existing feedback loop, combining multiple functions (voltage regulation and backflow protection) into a unified control mechanism, thereby reducing the increase in device complexity.
Solution Approach 2:
The error amplifier and control circuit are designed to serve multiple functions: both voltage regulation and backflow prevention. By making the control circuit universal, the patent avoids adding separate dedicated protection circuits, thus improving reliability while minimizing the increase in device complexity.
Data Source
AI summary
Disclosed is a low dropout linear voltage regulator and a control circuit thereof. The control circuit includes an error amplifier and a backflow prevention circuit, which compares an input voltage with an output voltage, to switch a substrate voltage and a voltage at a control terminal of the power transistor to a higher one of the input voltage and the output voltage, thus the power transistor and its parasitic diode can be turned off in time when the output voltage is greater than the input voltage, so as to prevent the power transistor from being damaged by current backflow and improve reliability of the low dropout linear regulator.