Conduction limit protection arrangement for power transistor switch

A conduction limit protective arrangement for a power transistor switch regulated by a succession of control pulses which changes the conduction limit as a function of switch operating conditions comprising, in combination,

• an RC integrator circuit including a timing capacitor in series with a resistance connected across said power transistor switch so that said timing capacitor is charged with the voltage from across said power transistor switch through said resistance during said control pulses to a voltage which is the time integral of the voltage across said power transistor switch,
• a comparator for comparing said voltage across said timing capacitor to a threshold voltage and for providing an output signal when the former becomes equal to the latter,
• means for discharging said timing capacitor to a predetermined voltage after the termination of each control pulse, and
• means responsive to said output signal from said comparator for removing said control pulses from said power transistor switch, whereby, if said power transistor switch experiences high on-voltages, it is turned off after a time interval which is a function of the time integral of the voltage drop thereacross.

A conduction limit protective arrangement for a power transistor switch regulated by a succession of control pulses which changes the conduction limit as a function of switch operating conditions and permits it to carry maximum current while being fully protected at all times comprising, in combination,

• an RC integrator circuit including the serial arrangement of a first resistance, a second resistance, and a timing capacitor connected across said power transistor switch so that said timing capacitor is charged with the voltage from across said power transistor switch through said first resistance and said second resistance during said control pulses,
• a comparator for comparing the voltage across the serial arrangement of said timing capacitor and said second resistance to a threshold voltage and for providing an output signal when the former becomes equal to the latter,
• means for discharging said timing capacitor to a predetermined voltage after the termination of each said control pulse, and
• means responsive to said output signal from said comparator for removing said control pulses from said power transistor switch, whereby, if said power transistor switch experiences high on-voltages, it is turned off after a time interval which is a function of the time integral of the voltage drop thereacross and it is turned off immediately if said on-voltages are abnormally high.

A conduction limit protective arrangement for a power transistor switch regulated by a succession of control pulses which changes the conduction limit as a function of switch operating conditions and permits it to carry maximum current while being fully protected at all times comprising, in combination,

• RC integrator means including a timing capacitor in series with a resistance connected across said power transistor switch for charging said timing capacitor with the voltage from across said power transistor switch through said resistance during said control pulses to derive a potential which increases in magnitude as a function of the time integral of said voltage across said power switch,
• a comparator for comparing said potential to a threshold voltage and for providing an output signal when the former becomes equal to the latter,
• means for discharging said timing capacitor to a predetermined voltage after the termination of each said control pulse,
• means responsive to said output signal from said comparator for removing said control pulses from said power transistor switch, whereby, if said power transistor switch experiences high on-voltages, it is turned off after a time interval which is a function of the magnitude of the voltage drop thereacross,
• a first monostable multivibrator (MONO 1) which is triggered adjacent the leading edge of each said control pulse, and wherein said timing capacitor discharge means (CDT) is actuated when said first multivibrator is triggered, and a second monostable multivibrator (MONO 2) having a longer period than said first multivibrator which is triggered at the end of the period of the first multivibrator and locks out the first multivibrator, and means (NAND 1, D2) for turning said power transistor switch off when said first multivibrator is triggered and for turning it on at the end of the period of said first multivibrator, whereby high frequency conduction limit mode oscillations are prevented.

A conduction limit protection arrangement for a power transistor switch (PS1-PS7 FIG. 3) regulated by a succession of control pulses and which changes the conduction limit as a function of switch operating conditions comprising, in combination,

• an RC integrator circuit including a timing resistance (R7) in series with a timing capacitor (C1) connected across said power transistor switch so that said timing capacitor is charged with the voltage from across said power transistor switch through said timing resistance during said control pulses to a voltage which is the time integral of the voltage across said power switch,
• means for discharging said timing capacitor (C1) to a predetermined voltage after the termination of each control pulse,
• a base current drain transistor (Q5) having its emitter-collector path in shunt to the base-emitter junction of said power switch, and
• means including a comparator transistor (Q3) having its base-emitter junction connected in series with the base-emitter junction of said base current drain transistor for comparing the voltage across said timing capacitor to a threshold voltage established by said series arrangement of the base-emitter junctions of said comparator and base current drain transistors, whereby said comparator and base current drain transistors will turn on, if said power switch comes out of saturation, after a time interval which is a function of the time integral of the voltage drop across the power switch.