A DC-DC converter includes a chip including an error amplifier, a pulse width modulator, and an inductor driven by said PWM in series with an output node, wherein a load current flows through the inductor. The provided two-dimensional sensory structure includes a substrate having plural first metal structures and second metal structures on a first surface thereof, a dot-like insulating layer located on the substrate and composed of plural insulating dots, and an electrode layer located on the dot-like insulating layer and composed of plural conductive traces. The retention mechanism allows the operation panel to be retained in the device main unit with either the front or back side of the operation panel being directed forwards or exposed. The key pad is disposed on the top surface of the frame part correspondingly. The circuit is configured to switch to holdup power when a predetermined threshold voltage difference between the power supply and a holdup capacitor is exceeded. The pad assembly may include three separate hollow core heat barrier units in hinged relationship with one another to provide a relatively shortened lengthwise dimension to the entire assembly when the end units are folded.