HV Flyback Protection Circuit for 800 V Fault Disconnect
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Solution Overview
Problem
Existing high voltage isolated DC/DC flyback switching power supplies face challenges in protecting against overcurrent and overvoltage, particularly in 800 V HV systems, where conventional fuses and resettable electronic fuses are either unsuitable or excessively expensive.
Innovation Solution
A protection circuit is introduced for the HV DC/DC flyback switching power supply, comprising a protection circuit transistor, a primary inductor, a switching transistor, and a sensing block. This circuit is powered by HV peaks produced during switching, allowing for overcurrent and overvoltage protection without the need for additional power supplies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fuses are used for overcurrent protection, then protection function is provided, but they are unsuitable for 800V HV systems and cannot provide resettable protection
Solution Approach 1:
The patent replaces conventional mechanical fuses with an electronic protection circuit that uses a MOSFET transistor (Q1) as an electronic switch, controlled by voltage-divider resistors (R1-R4) and Zener diodes (D1-D2) to detect overcurrent conditions and trigger protective action, enabling resettable protection suitable for high-voltage systems
Solution Approach 2:
The patent changes the protection mechanism from passive fuse melting to active electronic control by monitoring voltage parameters across the MOSFET and using Zener diodes to detect parameter thresholds, enabling the system to distinguish between normal and fault conditions and provide appropriate protective responses
2Reliability
If resettable electronic fuses are used for overcurrent protection, then protection function and reset capability are provided, but they are excessively expensive
Solution Approach 1:
The patent segments the protection function into discrete, inexpensive components: a MOSFET transistor for switching, voltage-divider resistors for sensing, Zener diodes for threshold detection, and a capacitor for timing, replacing the need for an expensive integrated resettable electronic fuse while achieving the same protective function
Solution Approach 2:
The patent uses inexpensive discrete electronic components that can be individually replaced if needed, rather than requiring an expensive resettable electronic fuse, making the protection system cost-effective for automotive applications
3Reliability
If separate low-voltage power supply is used for protection circuit, then protection circuit operation is ensured, but system complexity and cost increase
Solution Approach 1:
The protection circuit is designed to operate directly from the high-voltage battery power source through a voltage-divider network (R1-R4), allowing the same circuit to provide both power conversion and protection functions without requiring a separate low-voltage power supply system
Solution Approach 2:
The patent introduces voltage-divider resistors (R1-R4) as intermediary elements that step down the high voltage to usable levels for the protection circuit components, eliminating the need for complex power conversion circuitry while ensuring reliable operation of the protection system
4Reliability
If overcurrent protection is provided, then circuit safety is improved, but response time may be delayed compared to immediate disconnection
Solution Approach 1:
The patent implements continuous feedback monitoring of the voltage across the MOSFET transistor through the voltage-divider network, enabling the protection circuit to detect overcurrent conditions in real-time and immediately trigger protective action by disabling the MOSFET gate drive when fault thresholds are exceeded
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 solution provides effective overcurrent and overvoltage protection, capable of immediately disconnecting the circuit from the HV cellstack in case of electrical failure, thus preventing damage and ensuring system reliability. Additionally, it is cost-effective and does not require a separate low-voltage power supply.
Implementation Method 1
a rectifying diode in the connection between the switching node and the gate of the protection circuit transistor, wherein the rectifying diode is configured for rectifying voltage peaks caused by the inductance of the primary inductor to power the protection circuit
Implementation Method 2
at least one sensing block configured to detect an electrical failure on the HV input side
Data Source
Figure 1
Figure 2
AI summary
The present disclosure refers to the field of isolated high voltage, HV, DC/DC flyback switching power supplies. In particular, the present disclosure relates to a HV side based overcurrent and overvoltage protection circuit (30) for a HV DC/DC flyback switching power supply, which is powered from the HV peaks produced by the switching of the HV DC/DC flyback switching power supply. According to one aspect of the present disclosure, the protection circuit (30) comprises a protection circuit transistor (Mprot) on the HV input side (10) of the HV DC/DC flyback switching power supply; a rectifying diode (Drect), wherein the rectifying diode (Drect) is configured for rectifying voltage peaks caused by the inductance of a primary inductor (Lp) on the HV input side (10) to power the protection circuit (30); and a sensing block (32, 34) configured to detect an electrical failure on the HV input side (10).