Abstract: A PTC planar heater according to the present invention is produced by bonding one or a plurality of PTC ceramic sheets, each having a pair of electrodes formed on the surface thereof, to an insulator. The electrode pairs are electrically connected in parallel by lead wires. An insulating elastic layer covers the electrodes to prevent warpage, electrical leaks, and shorting. A thickness of the PTC ceramic sheets equal to or greater than 0.5 mm prevents warpage. Resistance is adjusted by cutting conductive paths in the electrodes or by connecting predetermined portions of the electrodes. Further, in a PTC planar unit according to the present invention, a PTC thermistor element having a pair of electrodes formed thereon is in direct contact with one side of an insulation substrate, and a insulation substrate is mounted to the other side thereof.

Abstract: A panel heater comprising, on an upper surface of a metallic sheet (2) provided with PTC ceramics (1) on the back side thereof, a highly insulating material or an open space (4) at the portion corresponding to the back side portion to which the PTC ceramics are provided, with a material (3) for conducting heat from the metallic sheet being thus provided to the rest of the surface side of said metallic sheet, and a finishing sheet (5) being established on the upper surface of the whole structure. More preferably, the metallic sheet (2) is provided with equally spaced concave grooves with PTC ceramics (1) on the back plane of said grooves and a highly insulating material or an open space (4) inside said grooves, and a finishing sheet (5) established thereon. Accordingly, a simply structured panel heater resistant to heavy loads yet free from local overheating is provided.