PMOS Switching Regulator Reverse Current Protection
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Solution Overview
Problem
Existing power supply circuits using PMOS transistors suffer from reverse direction current flow when the input voltage is disconnected or lower than the output voltage, leading to efficiency degradation and potential circuit malfunctions, and existing solutions like diodes result in power loss due to forward voltage drops.
Innovation Solution
A switching regulator design that uses a PMOS transistor with a selection circuit controlling the substrate gate connection between the source and drain based on input and output voltage levels, preventing reverse current flow without relying on dedicated diodes, thereby maintaining efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a diode is inserted to prevent reverse direction flow, then reverse current protection is achieved, but power loss increases due to forward voltage drop
Solution Approach 1:
The invention extracts the reverse current protection function from the traditional diode and implements it using the parasitic diode D2 of the PMOS transistor itself. By controlling the substrate gate voltage, the parasitic diode is activated to block reverse current, eliminating the need for a separate protection diode and its associated forward voltage drop.
Solution Approach 2:
The PMOS transistor's own parasitic diode D2 is utilized to provide reverse current protection. The substrate gate control circuit activates this inherent protective element within the transistor structure, allowing the device to protect itself without requiring external protection components.
2Reliability
If an NMOS transistor is used as switching element, then reverse direction flow is prevented, but gate voltage requirement increases and circuit complexity rises
Solution Approach 1:
The PMOS transistor is made multi-functional by enabling it to perform both its primary switching function and reverse current protection function. Through substrate gate voltage control, the same PMOS transistor that switches the main current also activates its parasitic diode to block reverse current, eliminating the need for separate NMOS transistors or protection circuits.
Solution Approach 2:
The invention changes the voltage parameter of the substrate gate to control the activation state of the parasitic diode. By adjusting the substrate gate voltage relative to the drain voltage, the parasitic diode is selectively activated or deactivated, enabling reverse current protection without changing the transistor type or adding complex control circuits.
3Ease of operation
If substrate gate is connected to source to short parasitic diode D1, then normal operation is achieved, but reverse direction current flow occurs when input voltage is disconnected
Solution Approach 1:
The substrate gate connection is made dynamic rather than fixed. The substrate gate voltage is controlled based on the operational state: connected to source during normal operation to short parasitic diode D1, and connected to drain when reverse current protection is needed to activate parasitic diode D2. This dynamic switching of connection states allows the circuit to adapt to different operational requirements.
Solution Approach 2:
The control circuit monitors the input voltage status and preliminarily activates the substrate gate connection to drain before reverse current can flow. When input voltage disconnection or undervoltage is detected, the substrate gate is switched to drain connection in advance, activating the parasitic diode D2 to block potential reverse current before it can degrade the circuit.
Data Source
AI summary
A switching regulator is disclosed that is able to prevent reverse direction current flow without using a dedicated diode even when a PMOS transistor is used as a switching transistor of a step-down switching regulator. A selection circuit is provided to control connection of the substrate gate of the switching transistor, and a control circuit controls the selection circuit to connect the substrate gate to the drain of the switching transistor when the voltage on an input terminal of the switching regulator is less than or equal to the voltage on the output terminal of the switching regulator, and connect the substrate gate to the source of the switching transistor when the voltage on the input terminal is greater than the voltage on the output terminal.