Power Supply Spike Absorption Circuit for Switch Protection
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Solution Overview
Problem
Power supply devices face the risk of avalanche breakage of current shutdown switches due to kickback voltages when cutting off large currents, especially when connected to inductive loads or long wires, which can lead to safety issues and device failure.
Innovation Solution
A power supply device design that includes a spike absorption circuit with a series connection of a semiconductor protection switch and a diode, along with a delay circuit to maintain the protection switch in an ON state after the current shutdown switch is turned OFF, effectively damping kickback voltages and preventing avalanche breakage, while also preventing overcurrents during reverse charger connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current shutdown switch is used to cut off load current, then overcharge and over-discharge are suppressed, but avalanche breakage occurs due to kickback voltage when large current is cut off
Solution Approach 1:
A protection switch is introduced as an intermediary component between the current shutdown switch and the load. When kickback voltage exceeds the protection switch's threshold, it activates to short-circuit the voltage, preventing avalanche breakage of the current shutdown switch while maintaining battery protection functionality
Solution Approach 2:
The protection switch is configured to activate beforehand when kickback voltage reaches a certain level, cushioning the voltage spike before it can cause avalanche breakage. This preemptive action protects the current shutdown switch from damage while allowing normal operation
2Object-affected harmful factors
If a diode is connected in reverse direction to absorb kickback voltage, then avalanche breakage is suppressed, but large short-circuit current flows when charger is reversely connected
Solution Approach 1:
The protection switch dynamically changes its state based on operating conditions. It remains off during normal charging to prevent short-circuit current, and activates only when kickback voltage exceeds its threshold, thus suppressing avalanche breakage without allowing dangerous short-circuit current during reverse connection
3Object-affected harmful factors
If a fuse or PTC device is connected in series to the diode to prevent short-circuit current, then safety is improved, but kickback voltage suppression becomes ineffective after fuse blows or PTC trips
Solution Approach 1:
The protection switch serves multiple functions: it suppresses kickback voltage during normal operation, prevents short-circuit current during reverse connection, and remains reusable unlike fuses or PTC devices. This single component achieves both protection goals without the limitations of passive protective devices
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 solution reliably suppresses avalanche breakage of the current shutdown switch and ensures safety by limiting the spike voltage across the diodes, preventing overcurrents during reverse connections, and effectively managing kickback energies in various applications, including those with high inductance loads or long wires.
Implementation Method 1
a kickback voltage appears in response to a variation in a current flowing through inductance contained in the load. The kickback voltage is expressed by the following theoretical formula: (kickback voltage)=(inductance of load)×di/dt
Implementation Method 2
By connecting a diode in the reverse direction to an output side of a current shutdown switch, an avalanche breakage of the current shutdown switch due to a kickback voltage can be absorbed
Data Source
AI summary
A power supply device includes a spike absorption circuit that suppresses an avalanche breakage of a current shutdown switch due to a kickback voltage that may appear in response to the cut-off of a load current. The current shutdown switch is connected to secondary batteries. The spike absorption circuit is a series circuit of a protection switch, formed of a semiconductor element, and a diode. The power supply device further includes: a small-signal switch that controls turn-on and turn-off of the protection switch; and a delay circuit that maintains the small-signal switch in an ON state over a setup time after a current shutdown timing of the current shutdown switch. The delay circuit maintains the small-signal switch in the ON state over the setup time (T), and the small-signal switch thereby causes the protection switch to the ON state. Then, the spike absorption circuit damps the kickback voltage.