Direct current protection circuit

Claim 2

In combination: a first terminal at a point of reference potential: second and third terminals; a fourth terminal, this one for receiving an operating voltage; an inductor connected between said third and fourth terminals; a switch connected between said first and third terminals, whereby each time said switch closes, current flows through said inductor; energy storage means connected between said first and second terminals; asymmetrically conducting means connected between said second and third terminals in a sense to cause current flow between said energy storage means and said inductor, thereby to tend to charge said energy storage means, each time said switch opens; load circuit means; a second switch connected between said load circuit means and said second terminal for supplying the voltage at said second terminal to said load circuit means when said second switch is closed; and means coupled to said second switch and responsive to the voltage between said fourth and second terminals for maintaining said second switch closed in response to a value of said voltage of greater than a given magnitude and for opening said second switch at other times.

Claim 3

In the combination as set forth in claim 1, said second switch comprising a transistor having a conduction path and a control electrode, said conduction path connected between said second terminal and said load circuit and said control electrode connected to said fourth terminal.

Claim 4

In the combination as set forth in claim 2, said transistor comprising a MOS transistor connected at its source electrode to said second terminal.

Claim 5

In a circuit which includes liquid crystal between a pair of conductors, driver transistors for applying unipolarity voltages to these conductors and a direct current operating voltage source for providing the operating voltage for said driver transistors, and which also includes a relatively low voltage source, a direct current converter operated by said low voltage source and by direct current pulses for converting said relatively low voltage to a relatively higher direct current voltage, said direct current converter serving as said direct current operating voltage source and said relatively higher voltage as said operating voltage for said driver transistors, said converter including an inductor direct current coupled between said relatively low voltage source and said driver transistors, and an energy storage means which is periodically charged by said inductor, the improvement comprising: a switch having a conduction path, said path direct current coupled between said inductor and said driver transistors and operating to conduct the voltage produced by said converter to said driver transistors; and means responsive to the voltage difference between The voltage produced by said relatively low voltage source and that produced by the charge stored in said energy storage means for maintaining said switch closed when said voltage difference exceeds a given value and for opening said switch when said voltage difference drops to lower than said given value.

Claim 6

In a circuit which includes liquid crystal between a pair of conductors, driver transistors for applying unipolarity voltages to these conductors and a direct current operating voltage source for providing the operating voltage for said driver transistors, and which also includes a relatively low voltage source, a direct current converter operated by said low voltage source and by direct current pulses for converting said relatively low voltage to a relatively higher direct current voltage, said direct current converter serving as said direct current operating voltage source and said relatively higher voltage as said operating voltage for said driver transistors, said converter including an inductor direct current coupled between said relatively low voltage source and said driver transistors, and an energy storage means which is periodically charged by said inductor, the improvement comprising: a switch having a conduction path, said path direct current coupled between said inductor and said driver transistors and operating to conduct the voltage produced by said converter to said driver transistors; and means responsive to the voltage difference between The voltage produced by said relatively low voltage source and that produced by the charge stored in said energy storage means for maintaining said switch closed when said voltage difference exceeds a given value and for opening said switch when said voltage difference drops to lower than said given value.

Claim 7

In a circuit as set forth in claim 4, said switch comprising the conduction path of a field effect transistor, said path direct current coupled at its source electrode end to said inductor, and said means responsive to said voltage difference comprising the source-to-gate electrode input circuit of said transistor, said gate electrode being connected to the other end of said inductor, that is, to the end of said inductor coupled to said low voltage source.

Claim 8

In a circuit as set forth in claim 5, the direct current coupling of said source electrode to said inductor including a diode poled to conduct the conduction path current of said field effect transistor in the forward direction.