Low voltage thermostat circuit

US6622927B2 · kind B2 · utility

Inventors

• Ion Opris · San Jose, US
• Jay Friedman · Monte Sereno, US

Key dates

• Filing date: May 8, 2001
• Grant date: Sep 23, 2003
• Expiry date: Jul 18, 2021

Classification

• Technology area (CPC G): Physics
• CPC primary: G05D23/1909
• WIPO field: Control
• WIPO sector: Instruments

Abstract

A thermostat circuit (FIG. 4) is provided which (i) works properly with very low supply voltages, (ii) does not need a separate constant value as a reference, and (iii) has improved temperature sensitivity over prior art thermostat circuits. The thermostat circuit compares two reference currents—IPTAT and IVBE. When IVBE>IPTAT, the output of the thermostat circuit is one logic state (either high or low). When IPTAT>IVBE, the output of the thermostat circuit is a different logic state (either low or high). Current IPTAT comes from a PTAT current generator (FIGS. 5-7), and current IVBE comes from a VBE current generator (FIGS. 8-10). The PTAT current generator and the VBE current generator may be implemented with cascode amplifiers. In an embodiment, the currents IPTAT and IVBE can be compared at a current comparator circuit (FIG. 11) with a summing node and an output node. The total current at the current comparator's output node is independent of temperature, and the output node exhibits a hysteresis behavior. The thermostat circuit can include a testing/tuning circuit (FIG. 12) which is capable of injecting a test current into or subtracting a test current out of the summing…