Thermistor comparator (30 °C alarm)

Open it in Benchspice to change it☆ BookmarkCopy it, change any value and run every analysis, free in your browser.

Over-temperature alarm: an NTC thermistor divider is compared with a fixed 2.23 V reference; above 30 °C the open-drain comparator output goes low and lights the red LED. Use the Tc slider to set the temperature.

Parts

Picture

Simulation

This circuit is set up for a operating point analysis: .op. Run it in your browser, change values and see the waveforms update.

SPICE netlist

* Thermistor comparator (30 °C alarm) - Main
.param Tc=30
R1 vcc vy 10k
R2 vy 0 8.06k
R3 vcc vx 10k
XR4 vx 0 NTC_10K R25=10k B=3900 T={Tc}
XU1 vx vy vcc 0 out LM393
D1 vcc n001 LED_RED
R5 n001 out 680
V1 vcc 0 5
.include MOTOR_DC.sub
.include NTC_10K.sub
.subckt LM393 inp inn vp vn out
* output transistor sinks current when IN- is above IN+
Bc c 0 V=0.5+0.5*tanh(2000*V(inn,inp))
Rc c c2 1k
Cc c2 0 0.3n
Bo out vn I=V(out,vn)*V(c2)/50
Rleak out vn 100meg
.ends LM393
.model LED_RED D(Is=1e-18 N=1.8 Rs=10 Cjo=10p)
.meas tran vx FIND V(vx) AT=0.5m
.meas tran vy FIND V(vy) AT=0.5m
.meas tran vout FIND V(out) AT=0.5m
.meas tran iled FIND I(R5) AT=0.5m
.op
.end