MOSFET Current Limiting Circuit for Fast Pulse Current Shutdown
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Solution Overview
Problem
Existing current limiting circuits struggle to quickly control a MOSFET to an off state when faced with pulse currents having excessive current values, particularly at high frequencies, leading to potential device failure due to uncontrolled current flow.
Innovation Solution
A current limiting circuit incorporating a MOSFET, a series circuit with a resistor and inductor, and a control element driven by a voltage-generated state to instantly control the MOSFET to an off state through a pulse current conduction circuit with a capacitor, allowing instantaneous voltage decrease between the gate and source to interrupt pulse current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional current limiting circuit using a transistor and resistor is used, then the circuit can limit current under normal operating conditions, but it cannot quickly respond to and limit high-frequency pulse currents exceeding the pre-specified current value
Solution Approach 1:
The invention segments the current limiting function into two distinct paths: a normal current limiting path using the transistor Q1 and resistor R3 for continuous current control, and a pulse current limiting path using the capacitor C1 and resistor R4 for high-frequency pulse current control. This segmentation allows each path to be optimized for its specific function, resolving the contradiction between reliable current limiting and fast response to pulse currents.
Solution Approach 2:
The capacitor C1 acts as an intermediary element that detects voltage changes across the MOSFET and rapidly activates the pulse current limiting path. When a pulse current causes a voltage change, the capacitor quickly charges or discharges through the resistor R4, generating a rapid gate voltage change that forces the MOSFET into the off state, thereby achieving fast response to pulse currents while maintaining reliable current limiting through the conventional path.
2Ease of operation
If the transistor Q1X is used to control the MOSFET gate voltage, then the circuit can control current flow, but it cannot rapidly decrease the gate voltage to control the MOSFET to an off state when pulse current flows
Solution Approach 1:
The capacitor C1 is pre-charged to a voltage equal to the gate-source voltage of the MOSFET during normal operation. When a pulse current occurs, the capacitor can immediately discharge through the resistor R4, providing a pre-prepared charge path that rapidly decreases the gate voltage and forces the MOSFET into the off state, eliminating the time delay associated with transistor response.
Solution Approach 2:
The capacitor C1 periodically charges and discharges in response to voltage changes across the MOSFET. During normal operation, it maintains a charge that corresponds to the MOSFET's on state. When a pulse current causes a voltage change, the capacitor rapidly discharges, creating a periodic action that quickly transitions the MOSFET to the off state, thereby reducing the time loss.
3Reliability
If the circuit allows passage of pulse current through the resistor R2X, then the voltage difference increases and the transistor should turn on, but at high frequencies the transistor cannot turn on rapidly enough
Solution Approach 1:
The invention changes the operational parameters of the circuit by introducing the capacitor C1 and resistor R4 in parallel with the transistor Q1. This creates a separate pulse current limiting path with different time constants and frequency characteristics, allowing the circuit to handle high-frequency pulse currents effectively while maintaining overcurrent protection through the conventional transistor path for lower frequencies.
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 circuit enables rapid control of the MOSFET to an off state, effectively protecting connected devices from overcurrent by instantly interrupting pulse current flow and preventing device failure.
Implementation Method 1
a pulse current conduction circuit including a capacitor and allowing conduction of a pulse current from the control terminal toward the output end of the MOSFET
Implementation Method 2
a series circuit of a second resistor and an inductor connected between the current output terminal of the MOSFET and the output end
Data Source
Figure 1
Figure 2
AI summary
When a pulse current is input, a current interrupting MOSFET is quickly brought into an off state. A current limiting circuit 1 includes: a MOSFET M1 connected between an input terminal T1 and an output terminal T2 to allow and interrupt passage of a current I1; a series circuit SC1 connected between a source of the MOSFET M1 and the output terminal T2; and a transistor Q1 having a base connected to a connection point between one end of the series circuit SC1 and the source of the MOSFET M1 via a resistor R3, a collector connected to a gate of the MOSFET M1 via a resistor R1, and an emitter connected to the other end of the series circuit SC1, in which when supplied with the current I1 exceeding a pre-specified current value, the transistor Q1 is driven at a voltage generated at the one end of the series circuit SC1 to limit a current value of the current I1 passing through the MOSFET M1, and the current limiting circuit 1 includes a series circuit SC2 that allows conduction of a current I3 from the gate of the MOSFET M1 toward the output terminal T2.