Over-Temp Disconnect

by VladM

11 parts

An NTC thermistor (10 kΩ at 25 °C, β 3435) under a 10 kΩ pull-up gives a voltage that falls as it warms. U1 disconnects the load through Q1, a high-side P-MOSFET, when that voltage falls below 0.762 V (59.75 °C), and reconnects only above 0.947 V (50.56 °C). Drag the NTC's temperature. Real packs: 60 °C is a common discharge cut-off for lithium cells, and the hysteresis keeps the pack from cycling on and off at the limit.

• V3V3 3.3V
• Rpu 10kΩ
• NTC 10kΩ@25°C
• U1
• Ra 100kΩ
• Rb 32.4kΩ
• R2 412kΩ
• Q1 Vt 2V
• Rload 33Ω