Liquid crystal writing device with slow discharge erase

A cholesteric liquid crystal eWriter that forms an image by applying pressure to a writing/drawing surface comprising a liquid crystal layer including a dispersion of cholesteric liquid crystal material and polymer, and electrically conductive layers between which said liquid crystal layer is disposed, wherein electronics of said eWriter are adapted to apply an erase voltage waveform across said electrically conductive layers that forms a focal conic texture and erases the image, said erase voltage waveform including an erase portion and a slow discharge portion, said electronics comprising:

• a regulated power source or a battery having a voltage VDD;
• a controller including a voltage VDD input, a switch SW input, an enable EN output, a boost BST output, a feedback FB input and an optional discharge DCHG output;
• a transistor Q3 acting as a switch controlled by an enable signal from said enable EN output of said controller;
• a boost converter circuit including:
• a transistor Q1 acting as a switch controlled by a boost signal from said BST output of said controller, a diode, an inductor located between said switch Q3 and said diode, and a capacitor C1 in parallel with said writing/drawing surface;
• said boost converter circuit including a feedback circuit configured to provide feedback to said FB input of said controller based on a boost converter output voltage from said boost converter circuit;
• a discharge circuit optionally under control of a discharge signal from said DCHG output of said controller;
• wherein in response to a control signal instructing erase of the image applied to said switch SW input, said controller turns on said transistor Q3 applying said voltage VDD to said boost converter circuit, said feedback circuit indicates to said controller via said feedback FB input when said boost converter output voltage is below a set level, resulting in said controller enabling said signal from said output BST that turns on said transistor Q1 and causes energy to be stored in said inductor, wherein when said controller subsequently turns off said transistor Q1, said energy stored in said inductor is discharged through said diode increasing said erase voltage on said capacitor C1 and increasing said erase voltage in said parallel writing/drawing surface forming said erase portion of said erase voltage waveform, and said discharge circuit produces said slow discharge portion of said erase voltage waveform.

A cholesteric liquid crystal eWriter that forms an image by applying pressure to a writing/drawing surface comprising a liquid crystal layer including a dispersion of cholesteric liquid crystal material and polymer, and electrically conductive layers between which said liquid crystal layer is disposed, wherein electronics of said eWriter are adapted to apply an erase voltage waveform across said electrically conductive layers that forms a focal conic texture and erases the image, said erase voltage waveform including an erase portion and a slow discharge portion, said electronics comprising:

• a regulated power source or a battery having a voltage VDD;
• a controller including a voltage VDD input, a switch SW input, an enable EN output, a boost BST output, and a feedback FB input;
• a transistor Q2 acting as a low-side switch controlled by an enable signal from said EN output of said controller and referenced to ground;
• a boost converter circuit including a transistor Q1 acting as a switch controlled by a boost signal from said BST output of said controller, an inductor, a diode D2, a capacitor C1 electrically connected to the cathode of diode D2 and to a first one of said electrically conductive layers,
• a voltage on said capacitor C1 being an output from said boost converter circuit;
• said boost converter circuit including a feedback circuit configured to provide feedback to said FB input of said controller;
• an optional current limiting resistor located in a path between a second of said electrically conductive layers and said transistor Q2;
• a discharge resistor R6 connected across said electrically conductive layers;
• wherein in response to a control signal instructing erase of the image said controller turns on said transistor Q2 providing the ground reference to said boost converter circuit, said feedback circuit being configured to indicate to said controller when a boost converter voltage appearing on said capacitor C1 output from said boost converter circuit is below a set level, resulting in said controller enabling said boost signal that turns ON said transistor Q1 and causes energy to be stored in said inductor, wherein when said controller subsequently turns OFF said transistor Q1, said energy stored in said inductor is discharged through said diode D2 increasing voltage on said capacitor C1 and increasing said erase voltage across said writing/drawing surface to form said erase portion of said erase voltage waveform, and said discharge resistor R6 produces said slow discharge portion of said erase voltage waveform.