A method and switching circuit for connecting and disconnecting current to a load having inductance

Abstract

The invention relates to a method and a switching circuit for connecting and disconnecting current to a load having inductance, particularly relates to a switching circuit. The switching circuit has a primary MOSFET switch (10) connected between first and second terminals (T1, T2) which are connected to a power line (P) and a load represented as a resistance (R1) and inductance (LI). The primary switch is operable by primary control commands to assume a conductive or non-conductive state. Four protection branches (B1-B4) are connected in parallel with the primary switch, each having a series connected resistive element (RB1-RB4) and a secondary MOSFET switch (S1-S4) operable by branch control commands received at branch command terminals (12B1, 12B2, 12B3, 12B4) to assume a conductive or non-conductive state. A timing circuit (13') applies branch turn off control commands in sequence to the branch command terminals, each delayed by a different predetermined time interval relative to when a primary turn off control command is applied to the primary switch.

Description

technical field [0001] The present disclosure relates to a method and switching circuit for connecting and disconnecting a power line supplying current to a load having an inductance, particularly when solid state switches are used to effectuate the connection and disconnection. Background technique [0002] When a power line supplies current to a load, if a short circuit occurs in the load, the current flow to the load must be disconnected quickly to avoid dangerously high current flow. Typically, solid state switches such as MOSFETs or IGBTs are used to connect and disconnect the power line to the load due to their fast switching times. They can be arranged individually or in multiples in parallel in the circuit. [0003] Many loads have an inductance (L) associated with them. Although the inductance is usually quite small, when the supplied current (I) is high, there may also be a large amount of energy (E) associated with this inductance when it is turned off (E=1 / 1.L....

AI Technical Summary

Problems solved by technology

First, the negative voltage across coil L1 causes the voltage across MOSFETs M1-M4 to increase

Because the MOSFETs M1-M4 are not exactly equal due to device-to-device variation, current will preferentially flow through one MOSFET and the voltage across it may exceed the breakdown voltage causing an avalanche and then that MOSFET may fail

Second, MOSFETs M1-M4 cannot withstand the energy that must be dissipated from coil L1, and the MOSFETs may fail

In either case, there is the possibility of a soft short, and the MOSFET may not turn on properly, causing safety issues

[0011] At present, when supplying higher currents, a single MOSFET cannot withstand the above-mentioned disconnection, and even MOSFETs connected in parallel cannot be used for the reasons mentioned above

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