Active Clamp Transistor Feedback Path for Low-Temperature Protection
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Solution Overview
Problem
Conventional active clamped transistor circuits fail to operate reliably at low temperatures, such as below -40 degrees Celsius, leading to failures in AC solid state power controllers due to delayed current flow in the feedback path, which can result in transistor damage.
Innovation Solution
The active clamped transistor circuit is improved by incorporating a capacitor in parallel with the rectifier diode or replacing the rectifier diode with a Schottky diode, ensuring immediate current flow and preventing excessive voltages by enhancing the response time of the feedback path, thereby avoiding transistor damage at low temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional active clamp circuit with a rectifier diode is used, then the circuit can block reverse current when the transistor is turned on, but the response time of the feedback path is delayed at low temperatures, causing the transistor to enter avalanche breakdown state and suffer damage
Solution Approach 1:
A capacitor is introduced as an intermediary component connected in parallel with the rectifier diode. This capacitor acts as a mediator that provides an alternative current path during overvoltage events, allowing the feedback signal to reach the transistor gate faster than the rectifier diode alone could provide, thereby preventing avalanche breakdown while maintaining the diode's reverse current blocking function
Solution Approach 2:
The electrical parameters of the feedback path are changed by adding the capacitor in parallel with the rectifier diode. This modification alters the time constant and frequency response of the feedback circuit, enabling it to respond faster to overvoltage conditions at low temperatures without affecting the steady-state blocking function of the diode
2Speed
If the rectifier diode is replaced with a Schottky diode, then the response time of the feedback path is improved at low temperatures, but the device complexity and component selection requirements increase
Solution Approach 1:
The rectifier diode is replaced with a Schottky diode, which has fundamentally different electrical parameters including lower forward voltage drop and faster switching characteristics. This parameter change enables the feedback path to respond faster to overvoltage conditions at low temperatures while maintaining the same circuit topology and functionality
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 modifications ensure that the feedback path responds faster than the transistor can enter an avalanche breakdown state, even at low temperatures, effectively preventing damage and maintaining reliable operation down to -60 degrees Celsius.
Implementation Method 1
A capacitor is connected parallel to the rectifier diode
Implementation Method 2
The Zener diode or TVS diode allows current to pass when the voltage exceeds the breakdown voltage of the Zener or TVS diode
Implementation Method 3
replacing the rectifier diode with a Schottky diode, ensuring immediate current flow and preventing excessive voltages by enhancing the response time of the feedback path
Data Source
Figure 1a~1b
Figure 2~3
Figure 4a~4b
AI summary
An active clamped transistor circuit includes a feedback path comprising any of: (a) a serial connection of (i) at least one Zener diode (Z1, Zn) and/or at least one unidirectional transient voltage suppressor (TVS) diode, connected in blocking direction, and (ii) at least one rectifier diode (D) connected in flow direction, and a capacitor (C) connected parallel to the rectifier diode (D); (b) a serial connection of (i) at least one Zener diode (Z1, Zn) and/or at least one unidirectional transient voltage suppressor (TVS) diode, connected in blocking direction, and (ii) at least one Schottky diode (SD) connected in flow direction; or (c) a serial connection of (i) at least one Zener diode (Z1, Zn) and/or at least one unidirectional transient voltage suppressor (TVS) diode, connected in blocking direction, and (ii), instead of a conventional rectifier diode connected in flow direction, an unidirectional transient voltage suppressor (TVS) diode connected in flow direction; or (d) a bidirectional transient voltage suppressor (TVS) diode connected between the control node (116) and the first output node (112) of said transistor (110); all directions with respect to the direction of current from the first output node (112) to the control node (116).