LDO Pre-Regulator With Bypass Switching for Wide Input Voltage
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Solution Overview
Problem
Designing electronic devices like smoke detectors that require a wide input voltage range poses challenges due to the need for high voltage devices, which are unsuitable for low current, high-speed applications and result in inefficiencies and increased power consumption when using LDO regulators or DC-DC converters to step down voltages.
Innovation Solution
A pre-regulator circuit that uses a simple clamp diode on the gate of a pass transistor to regulate upper supply voltages above a threshold and a bypass switch to avoid regulation for lower voltages, allowing an LDO's input voltage to be extended without requiring high voltage devices, thereby maintaining reliability and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If high voltage devices are used to handle wide input voltage range, then the device can operate from 15V AC/DC supply, but it increases power consumption and is unsuitable for low current applications
Solution Approach 1:
The voltage regulation system is divided into two segments: a pre-regulator circuit that handles high voltage input (up to 15V) and an LDO regulator that operates at lower voltage. The pre-regulator uses a high-voltage NFET and clamp diode to initially step down the voltage, then the LDO provides precise regulation. This segmentation allows each component to operate in its optimal voltage range, reducing overall power consumption while maintaining wide input voltage compatibility.
2Reliability
If voltage regulation is always applied, then output voltage is protected from harming downstream circuits, but it increases current consumption when input voltage is already within acceptable range
Solution Approach 1:
The pre-regulator circuit incorporates dynamic control through a bypass switch (PFET) that is controlled by a comparison circuit. When the input voltage exceeds the regulation threshold (e.g., 4.0V), the bypass switch turns off and the pre-regulator activates to clamp the output voltage. When input voltage is below the threshold, the bypass switch turns on and directly connects input to output, eliminating unnecessary regulation overhead and reducing current consumption while still protecting downstream circuits when needed.
3Device complexity
If LDO regulator is used directly with wide voltage range, then circuit simplicity is maintained, but it requires high voltage devices that reduce efficiency
Solution Approach 1:
The regulation function is segmented into two stages: the pre-regulator handles the coarse voltage reduction from high input voltage to a intermediate level using a simple NFET and clamp diode configuration, and the LDO regulator handles the fine adjustment to the final output voltage. This segmentation allows the LDO to operate efficiently at lower voltages without requiring high-voltage-rated devices, improving overall efficiency while adding only moderate complexity to the circuit.
Solution Approach 2:
The pre-regulator circuit acts as an intermediary between the high-voltage input source and the LDO regulator. It conditions the input voltage by performing initial regulation and voltage clamping, presenting a more manageable voltage level to the LDO. This intermediary function protects the LDO from high voltage stress and allows it to operate in its optimal efficiency range, reducing energy loss in the overall system.
Data Source
AI summary
An electronic device includes a voltage regulator circuit having a power NFET coupled between an upper supply voltage and a pre-regulator output node and a current source coupled in series with a diode element between the upper supply voltage and a lower supply voltage. A gate of the power NFET is coupled to a first node between the current source and a diode element. A bypass circuit includes a power PFET coupled between the upper supply voltage and the pre-regulator output node. A comparison circuit is coupled to turn the bypass circuit off when the upper supply voltage is greater than a regulation threshold voltage.