Will LM308 work with single polarity supply?

[oladiladio]

Re: LM308 Question

what on earth are you guys doing out there?
The answer is very simple: even when the output of LM308 is low (approx. 1V) there is still to much base current going into T1 (switching transistor).
All you have to do is change the value of R7 into 50k. This value can be different depending on the load and the transistor.

 

[CMOS]

Re: LM308 Question

what on earth are you guys doing out there?
The answer is very simple: even when the output of LM308 is low (approx. 1V) there is still to much base current going into T1 (switching transistor).
All you have to do is change the value of R7 into 50k. This value can be different depending on the load and the transistor.

Already tried that but in vein. The relay then chatters when output just switches to high state. when input is just near threshold current is too less to drive transistor. I need atleast 14V at input to turn on the transitor completely which is not possible or not feasible to do because it wii damage the battery over long run.

So to solve this I used LM311. Read the above posts for modifications that I've done. The chatter problem is still there but for shorter voltage range only of 20-30mV. Thus in my circuit it chatters for around 15-20 minutes before voltage reaches exactly 6.9V or above.

Thanks.

 

[Rope]

Re: LM308 Question

To avoid chatter you must ensure so called HYSTERESYS for the OP AMP used as comparator .The simpliest way to do this is by adding a high impedance resistor between the OP AMP output and the positive input there will be a positive feedback but small enough to ensure once triggered the comparator not to trigger back again!! One more thing the output of 311 is a OC tranzistor did you pulled it high or for that reason you are using PNP transistor to drive the relay??

P.S. I saw your circuit and i have to tell that you must use two resistors : 1 of say 1K between the so called reference voltage and the noninverting input and the other say 330K between the output of the OP AMP and the non inverting input. This shematics is very simple why dont you use a CA3140 or LM358 which can deliver almost 0V on the output- i think every OP AMP with higher current in a low state (0V) will do!!