Patent ID: 7301745
Filing Date: 2007-11-27
Classification: H03K

Abstract:
1. A temperature dependent switching circuit comprising: a first transistor with a threshold voltage Vth having a negative temperature coefficient; a diode having a forward voltage drop with a negative temperature coefficient coupled with its anode connected to the drain of the first transistor and its cathode connected to the gate of the first transistor; a power supply terminal; a first resistor coupled between the power supply terminal and the drain of the first transistor; a low voltage supply terminal connected to the source of the first transistor; a second resistor coupled between the gate of the first transistor and the low voltage supply terminal; and a switching transistor with its source connected to the low voltage supply terminal and its gate coupled to the drain of the first transistor; wherein the drain of the first transistor provides a voltage with a negative temperature coefficient equal to the sum of the forward voltage drop across the diode and the threshold voltage of the first transistor, such that as the temperature in the circuit rises to a predetermined temperature the voltage at the gate of the switching transistor drops below the threshold voltage for the switching transistor turning off the current flowing from the drain to the source of the switching transistor.