Solid state power controller

Claim 2

A solid state controller for controlling current through a wire to a load by means of a solid state switch through an input line comprising: solid state switch means serially connected to the load through a wire, a shunt resistor serially connected to the switch means and the wire, means for generating a first electrical signal proportional to the voltage drop across the shunt resistor, means for squaring the said first electrical signal to produce a second electrical signal proportional to the power being dissipated in the wire, RC network means coupled to the means for squaring the said second electrical signal and being charged thereby to integrate the second electrical signal as a function of time, means for comparing the voltage across the RC network indicative of the temperature rise of the wire with a reference and when the RC network voltage is greater than the reference for providing an electrical trip signal for turning off the solid state switch means and latch means for maintaining the controller in a trip condition once it is tripped until reset by an input signal.

Claim 3

A solid state controller according to claim 1 in which the first electrical signal is a current.

Claim 4

A solid state controller according to claim 1 in which the solid state switch means comprise at least one MOSFET.

Claim 5

A solid state controller according to claim 1 including means for providing a signal indicative of whether the voltage at a load terminal exceeds a predetermined level.

Claim 6

A solid state controller according to claim 1 including means for providing a signal indicative of whether the load current exceeds a predetermined level.

Claim 7

A solid state controller according to claim 1 further including thermal memory means in which the voltage across the RC network means is allowed to decay in proportion to the cooling of the wire when the solid state switch means is turned off.

Claim 8

Apparatus for providing an electrical trip signal representative of a selected temperature rise of a wire which has been reached due to power dissipated from load current flowing therethrough comprising: a shunt resistor serially connected to the wire, first and second current paths coupled together through a first current mirror, the first current path coupled to the shunt resistor and being adapted to conduct current in response to the voltage across the shunt resistor, current squaring means, a third current path coupled to the second current path through the current squaring means, the third current path coupled to a fourth current path through a second current mirror, the fourth current path coupled to an RC network to charge the network which is adapted to provide a voltage representative of the temperature rise of the wire, and voltage responsive means having a threshold level coupled to the RC network for comparing the voltage across the network to a reference voltage to provide a trip signal when the voltage across the network reaches the threshold level.

Claim 9

Apparatus for providing an electrical trip signal representative of a selected temperature rise of a wire which has been reached due to power dissipated from load current flowing therethrough comprising: a shunt resistor serially connected to the wire, first and second current paths coupled together through a first current mirror, the first current path coupled to the shunt resistor and being adapted to conduct current in response to the voltage across the shunt resistor, current squaring means, a third current path coupled to the second current path through the current squaring means, the third current path coupled to a fourth current path through a second current mirror, the fourth current path coupled to an RC network to charge the network which is adapted to provide a voltage representative of the temperature rise of the wire, and voltage responsive means having a threshold level coupled to the RC network for comparing the voltage across the network to a reference voltage to provide a trip signal when the voltage across the network reaches the threshold level.

Claim 10

A solid state controller according to claim 7 in which the current squaring means comprises first and second diode connected transistors, current to be squared being fed through the first and second transistors, a third transistor and a fourth diode connected transistor, a relatively large current source connected to the fourth transistor creating a relatively constant base emitter voltage, V be , thereby imposing the change in the two V be drops built-up across the first and second transistors across the base emitter of the third transistor.

Claim 11

Apparatus according to claim 7 further including first and second calibration resistors respectively tied to the first and second current paths the first and second resistors selected to adjust the load current level relative to the threshold level of the voltage responsive means.

Claim 12

Apparatus according to claim 9 further including an operational amplifier having a feedback circuit, the first current path coupled to the shunt resistor through the operational amplifier and a feedback resistor being connected to the feedback circuit of the operational amplifier whereby the first current is produced proportional to the voltage across the shunt resistor and wherein the trip signal is produced approximately according to the formula: ##EQU6## where Y=(R s R t 1/(R iv R t 2))2/I ref ______________________________________ and R.sub.s = shunt resistor V.sub.w (t) = trip signal R.sub.1 = resistor of RC network I.sub.w = current through the wire C.sub.i = capacitor of RC network I.sub.ref = current source R.sub.t 1 = first resistor R.sub.t 2 = second resistor R.sub.iv = feedback resistor ______________________________________

Claim 13

Apparatus according to claim 7 further including a diode to allow selected decay of the RC network voltage to provide thermal memory.

Claim 14

Apparatus according to claim 11 in which the trip signal is produced to conform to a selected trip time vs load current curve having the following component values: ______________________________________ R.sub.s 10 m ohm (10.0 amp rated load current) R.sub.iv 15.8K ohm C.sub.i 1 uF R.sub.i 15.1 M ohm R.sub.t 1 and R.sub.t 2 adjusted to set nominal "ultimate trip" load current percentage (126.5% of rated current) - approximate value is 20K OHM each. ______________________________________

Claim 15

A solid state controller for controlling load current through a wire by means of a solid state switch through an input line comprising solid state switch means serially connected to the load through a wire, a shunt resistor serially connected to the switch means and the wire, means for measuring the voltage drop across the shunt resistor to generate a first electrical signal proportional to the voltage drop across the shunt resistor, means for squaring the first electrical signal to produce a second electrical signal proportional to the power dissipated in the wire, the means for squaring the first electrical signal including first and second diode connected transistors, current to be squared being fed through the first and second transistors, a third transistor and a fourth diode connected transistor, a relatively large current source connected to the fourth transistor creating a relatively constant base emitter voltage, V be , thereby imposing the change in the two V be drops built-up across the first and second transistors across the base emitter of the third transistor means for integrating the second electrical signal as a function of time providing a third electrical signal proportional to the temperature rise of the wire, and means for comparing the third electrical signal with a reference representing the maximum allowable temperature rise of the wire and for developing a trip signal when the third electrical signal exceeds the reference.

Claim 16

A solid state controller for controlling load current through a wire by means of a solid state switch through an input line comprising solid state switch means serially connected to the load through a wire, a shunt resistor serially connected to the switch means and the wire, means for measuring the voltage drop across the shunt resistor to generate a first electrical signal proportional to the voltage drop across the shunt resistor, means for squaring the first electrical signal to produce a second electrical signal proportional to the power dissipated in the wire, the means for squaring the first electrical signal including first and second diode connected transistors, current to be squared being fed through the first and second transistors, a third transistor and a fourth diode connected transistor, a relatively large current source connected to the fourth transistor creating a relatively constant base emitter voltage, V be , thereby imposing the change in the two V be drops built-up across the first and second transistors across the base emitter of the third transistor means for integrating the second electrical signal as a function of time providing a third electrical signal proportional to the temperature rise of the wire, and means for comparing the third electrical signal with a reference representing the maximum allowable temperature rise of the wire and for developing a trip signal when the third electrical signal exceeds the reference.

Claim 17

A solid state controller according to claim 13 in which the means for integrating the second electrical signal comprises an RC network.

Claim 18

A solid state controller according to claim 14 further including thermal memory means in which the voltage across the RC network is allowed to decay naturally in proportion to the cooling of the wire when the solid state switch means is turned off.

Claim 19

A solid state controller according to claim 15 in which the thermal memory means includes a diode connected to the RC network.