DESIGNING A VOLTAGE COMPARATOR WITH LM339 AND SPDT RELAY

Thread Starter

imani9009

Joined Nov 8, 2013
56
Hi, I am designing a circuit for operating spdt relay when my 24 battery volt system voltage decreases from 24 volt to activate a relay with LM339, I have tested LM339 with 9 volt battery power plus terminal to its 3 no vcc + and ground 12 no to negative terminal of battery. And applied different inputs +5 and +9 volt at 4 and 5 inputs. But no output at 2 no appears by checking through voltmeter. If I supply 4.5+ and 4.5- at 3 and 12 no through capacitor and resistor voltage divider then -4.7 stays at the 2 no output and all the outputs. What could be possible problem
 

MrChips

Joined Oct 2, 2009
27,113
A picture is worth a thousand words.
A circuit diagram is the language of electronics. We can communicate better with circuit diagrams. We would be able to see instantly what is wrong.

For example, do you have a load resistor from the +ve supply rail to the output pin?
1k - 10kΩ would do wonders to your circuit.

One of the biggest failing of beginners is failing to read the component data sheet.
 

Thread Starter

imani9009

Joined Nov 8, 2013
56
These are the combinations I have tried but no output in the first one and -4.7 output in other two cases whether i push button or not. The transistor used is 2222a
 

MrChips

Joined Oct 2, 2009
27,113
The 2nd and 3rd attempts are flawed because it shows two 9V batteries.
The two batteries are not connected because each is a floating power source.

Let us stick with the 1st circuit since it has a single power source.
Bias pin-4 to 4.5V using the two 1kΩ resistors as you have shown using the same battery.
 
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