Honda Giken Kogyo Kabushiki Kaisha

Mitsuba Corporation

Shinichi Kubozuka

John W Vilkinofsky

Kiyohumi Nakayama

Yasunobu Onozato

A protection circuit protects from overheating a switching transistor that delivers current from a power source to a daytime running light on a vehicle. The protection circuit of the present invention open-circuits the switching transistor from the power source when the temperature at the switching transistor is sensed to be above a predetermined temperature. In this manner, excessive current is prevented from flowing through the switching transistor. In contrast, prior art protection circuits control only the gate of a MOSFET or base of a BJT switching transistor. In that case, if damage to the transistor results in an effective resistance, constant flow of current through such an effective resistance results in excessive overheating or even a fire. The protection circuit of the present invention open-circuits the conductive path from the power source through the effective resistance such that current does not flow through the effective resistance. Furthermore, a latching circuit in the protection circuit of the present invention maintains the switching transistor to be open-circuited from the power source once the temperature at the switching transistor reaches the predetermined temperature. Thus, the traffic hazard or degradation of the switching transistor, which may result from the daytime running light flashing on and off, are also avoided with the protection circuit of the present invention.

Protection from overheating of a switching transistor that delivers

A protection circuit prevents, from a short load, excessive current flow through a field effect transistor that delivers current to a daytime running light on a vehicle. The present invention uses commonly available devices, such as resistors and transistors, and a low number of such devices for low cost. Furthermore, the present invention includes a latching circuit for maintaining the switching transistor to be turned off once the current level through the switching transistor reaches an excessive level to prevent the daytime running light from flashing on and off. A voltage, which develops across a resistor that is coupled to the field effect transistor, is an indication of the current level through the field effect transistor. This voltage turns on a first transistor which couples the gate of the field effect transistor to a ground node when the current level through the field effect transistor is greater than a predetermined level. The field effect transistor turns off when the gate of the field effect transistor is coupled to the ground node to prevent excessive current flow through the field effect transistor. A second transistor is configured in a latching configuration with the first transistor to maintain the first transistor to be turned on once the current level through the field effect transistor is greater than a predetermined level and until the power source is reapplied to the field effect transistor.

Growing community of inventors

Ota, Japan

Shinichi Kubozuka