Complementary Cascode Switch for Radiation-Tolerant Power Control
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Solution Overview
Problem
Conventional power switching circuits using non-radiation hardened FETs fail in radiation environments due to shifting gate threshold voltages, leading to uncontrollable device operation and high costs associated with radiation hardened components.
Innovation Solution
A power switching circuit design utilizing a high voltage non-radiation hardened N-channel FET controlled by a low voltage non-radiation hardened P-channel FET, where the P-FET is driven with a sufficiently high gate drive voltage to maintain radiation tolerance, and a zener diode is used to protect against transients, allowing the circuit to function controllably in radiation environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If non-radiation hardened N-channel FET is used for power switching, then lower ON resistance is achieved for any given die size, but the device fails at relatively low radiation levels due to gate threshold voltage shifting
Solution Approach 1:
The power switching circuit is segmented into two separate FETs: a high-voltage N-channel FET for power switching and a low-voltage P-channel FET for control. This segmentation allows each device to be optimized for its specific function while using non-radiation hardened components.
Solution Approach 2:
The low-voltage P-channel FET acts as an intermediary control device that drives the high-voltage N-channel FET. This intermediary approach allows the control circuit to operate at lower voltages while maintaining control over the power switching device, and the P-FET's negative threshold voltage provides inherent radiation tolerance.
2Reliability
If radiation hardened FETs are used in radiation environments, then gate threshold voltage stability is improved, but cost and production lead times increase due to limited supply
Solution Approach 1:
The invention uses inexpensive, commercially available non-radiation hardened FETs instead of expensive radiation hardened components. The circuit design compensates for the radiation sensitivity of these cheap components through the complementary FET configuration and drive circuitry.
Solution Approach 2:
The invention changes the operating parameters of the FETs by using complementary N-channel and P-channel devices with opposite polarity threshold voltages. This parameter change allows the circuit to maintain control functionality even as individual device characteristics shift due to radiation exposure.
3Ease of manufacture
If non-radiation hardened FETs are used in radiation environments, then cost is reduced, but the devices become uncontrollable due to gate threshold voltage shifting through zero to negative voltage
Solution Approach 1:
The invention inverts the conventional approach by using a P-channel FET with negative threshold voltage to control the N-channel power FET. The P-FET's threshold voltage shifts in the opposite direction (more negative) under radiation, which actually improves its control characteristics rather than degrading them.
Solution Approach 2:
The circuit uses a composite configuration of N-channel and P-channel FETs with complementary characteristics. This composite approach combines the low ON resistance of the N-FET with the radiation-tolerant control characteristics of the P-FET, creating a system that is more robust than either device alone.
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 operates effectively in radiation environments, maintaining control over a wide range of ionizing radiation doses without significant increase in conduction losses, reducing the need for expensive radiation hardened components and minimizing production delays.
Implementation Method 1
An enhancement mode FET is normally non-conducting. However, when a gate voltage above a threshold value is applied, the enhancement mode FET becomes conducting.
Implementation Method 2
a zener diode is used to protect the P-FET from radiation-induced damage
Implementation Method 3
The circuit operates effectively in radiation environments, maintaining control over a wide range of ionizing radiation doses
Data Source
AI summary
A power switching circuit designed for operating in a radiation environment using non-radiation hardened components is provided. The power switching circuit provides a high-voltage rated, non-radiation hardened N-channel FET (N-FET) controlled by a relatively small, low-voltage, non-radiation hardened P-channel FET (P-FET), while both devices are operating in a radiation environment. The P-FET device is drive by a sufficiently high drive voltage in order to overcome gate threshold shifts resulting from accumulated radiation damage.