Patent ID: 7847438

Claim:
A power transmission device included in a non-contact power transmission system that transmits power to a power reception device by electromagnetically coupling a primary coil and a secondary coil to transmit power to a load of the power reception device, the power transmission device comprising: a waveform monitoring circuit that includes a first rectifier circuit and generates and outputs a waveform-monitoring induced voltage signal based on a coil end signal of the primary coil; and a power transmission control device that controls a power transmission driver that drives the primary coil, the power transmission control device receiving the waveform-monitoring induced voltage signal and detecting a waveform of the induced voltage signal to detect a power-reception-side load state, the first rectifier circuit including: a first resistor that is a current-limiting resistor provided between a coil end node where the coil end signal of the primary coil is generated and a first monitoring node where a first induced voltage signal that is the waveform-monitoring induced voltage signal is generated; a first diode provided between the first monitoring node and a high-potential-side power supply node, a forward direction of the first diode being a direction from the first monitoring node to the high-potential-side power supply node; and a second diode provided between the first monitoring node and a low-potential-side power supply node, a forward direction of the second diode being a direction from the low-potential-side power supply node to the first monitoring node.