MOSFET Rectifier Circuit Reducing Reverse Recovery Time
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Solution Overview
Problem
Conventional diodes suffer from long reverse recovery times, which can lead to performance degradation and potential damage in circuits that require rapid transitions between forward and reverse biased states, especially in applications like high-side drivers where reverse current can be detrimental.
Innovation Solution
A rectifier circuit comprising a MOSFET and a Zener diode or Zener emulator, with specific on-resistance and Zener-voltage configurations, is used to minimize the stored charge in the body-diode, thereby reducing the reverse recovery time. This configuration ensures that the body-diode is not fully forward-biased, allowing current to flow primarily through the MOSFET's on-resistance, reducing the reverse recovery time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional diode is used to conduct current in forward direction and block current in reverse direction, then the rectification function is achieved, but the reverse recovery time is long causing performance degradation
Solution Approach 1:
The patent divides the rectifier function into two separate components: a MOSFET (M1) for primary current conduction and a Zener diode (D1) for voltage regulation and body-diode charge control. This segmentation allows each component to be optimized independently, with the MOSFET providing low on-resistance for forward conduction and the Zener diode limiting the forward voltage across the body-diode to reduce stored charge, thereby resolving the contradiction between reliable rectification and fast reverse recovery.
2Loss of time
If the stored charge in the body-diode is reduced to decrease reverse recovery time, then the reverse recovery performance is improved, but the forward current conduction capability may be affected
Solution Approach 1:
The patent changes the voltage parameter across the body-diode by introducing the Zener diode (D1) with a specific Zener voltage (e.g., 3V) that limits the forward voltage drop. This parameter change reduces the stored charge in the body-diode (Q = C × V) without significantly impacting forward current conduction, as the MOSFET's low on-resistance (e.g., 10mΩ) provides an efficient conduction path. The Zener voltage is carefully selected to balance charge reduction with maintaining adequate forward conduction capability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed rectifier circuit achieves a shorter reverse recovery time compared to conventional diodes, minimizing the risk of reverse current damage and enhancing the overall efficiency of high-side drivers by reducing the stored charge and leakage currents.
Implementation Method 1
The D1 defines an anode and a cathode of the D1. The cathode is connected to the input, the anode is connected to the source, and the D1 is characterized by a Zener-voltage. The Zener-voltage and the on-resistance are selected such that a stored-charge in the body-diode is less than a forward-charge-threshold
Implementation Method 2
The M1 defines a gate, a drain, a source, and a body-diode oriented to allow current to flow from the source to the drain of the M1. The M1 is characterized by an on-resistance.
Data Source
Figure 1
Figure 2
AI summary
A rectifier circuit (20) includes a MOSFET (M1 (30)), and a first Zener diode (D1 (34)) or a first Zener-emulator (E1 (50)) that emulates the D1 (34). The circuit (20) conducts current in a forward direction (22) from an input (24) to an output (26), and substantially blocks current in a reverse direction. The M1 (30) is characterized by an on-resistance (33). A cathode of the D1 or a cathode-contact (56) of the E1 (50) is connected to the input (24), and the anode of the D1 (34) or an anode-contact (54) of the E1 (50) are connected to the source. The E1 (50) includes a first small-Zener-diode (D11 (62)), a first resistor (R11 (64)) and a first transistor (M11 (66)) interconnected such that the E1 (50) emulates the D1 (34), and is characterized by a Zener-voltage (36). The Zener-voltage (36) and the on-resistance (33) are selected such that a stored-charge in the body-diode (32) is less than a forward-charge-threshold when current flows in the forward direction (22), whereby the reverse recover time of the body-diode (32) is reduced.