Need help with this circuit

Thread Starter

barrage

Joined Nov 7, 2009
3
Hi, need help with this thermostat circuit. I'm using a lm311n to try to activate the relay, but seem to have an output voltage reguardless of the voltage diff at the inputs. The circuit is below, except inputs at pin 2&3 are swapped, 500k hysteresis still at pin 2. Any ideas what might be going on? Thanks


 

SgtWookie

Joined Jul 17, 2007
22,230
Are you certain that the 1N4148 is installed with the cathode towards +V?
What is your +V?
What is the voltage rating of the relay coil, and what is it's resistance?
 

Thread Starter

barrage

Joined Nov 7, 2009
3
Supply voltage is ~12V. The output at pin 7 ranges from ~9.5-12V. I might have the cathode backwards - I had trouble deciphering which end was which on these diodes... And here's the info on the relay.10 AMP PC RELAYContact Res.: 50mΩ max.
Operate Time: 10ms max.
Release Time: 4ms max.
Insulation Res.: 100MΩ min.
Mechanical Life: 100M cycles
Electrical Life: 100K cycles
Resistive Load: 10A@28VDC or 10A@125VAC
Inductive Load: 3A@28VDC or 3A@125VAC[/B][IMG]http://www.mode-elec.com/main/getpicture.php?id=536&type=img_med2[/IMG]Circuitry SPDTOper. Voltage 12VDCCoil Resistance 400Ω
 

SgtWookie

Joined Jul 17, 2007
22,230
OK, 12v/400 Ohms = 30mA. That's well within the sink current limit of an LM311.
However, if you're using an LM339 comparator instead, you'll have problems - an LM339 can only sink up to about 6-8mA current.
 
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