Temperature sensors

A circuit, comprising:

• a first current source having first and second current source terminals, wherein the first current source terminal is coupled to a voltage source terminal;
• a resistor coupled to the second current source terminal;
• a second current source coupled to the resistor and coupled to a ground terminal;
• a Schmitt trigger having an input coupled to the second current source and a power terminal coupled to the voltage source terminal;
• and
• a bipolar transistor including:
• an emitter including an n-doped region and an emitter contact coupled to the n- doped region, the emitter contact coupled to the resistor, the second current source, and the Schmitt trigger;
• a base including a p-doped epitaxial layer, a p-doped buried layer, a p-doped well positioned in the p-doped epitaxial layer, and a base contact coupled to the p-doped well, wherein the base contact is coupled to the first current source and the resistor;
• a collector separated from the emitter by the base, the collector including an n-doped buried layer, a first n-doped well, and a collector contact coupled to the first n-doped well, the collector contact coupled to the voltage source terminal;
• and
• a substrate layer abutting the n-doped buried layer.

A system, comprising:

• a thermal protection device;
• a switching power circuit coupled to the thermal protection device;
• and
• a temperature sensing circuit positioned inside the switching power circuit, the temperature sensing circuit including:
• a bipolar transistor having a base, an emitter, and a collector, the collector coupled to a voltage source terminal;
• a first current source coupled to the base and coupled to the voltage source terminal;
• first and second resistors coupled to the base;
• a Schmitt trigger coupled to the emitter and to an inverter;
• a transistor having a transistor gate, a transistor drain, and a transistor source, the transistor gate coupled to the inverter, the transistor drain coupled to the first and second resistors, the transistor source coupled to the second resistor and the emitter;
• a current mirror coupled to the second resistor, the emitter, and the transistor source, the current mirror coupled to a ground terminal;
• and
• a second current source coupled to the current mirror and coupled to the voltage source terminal.