Hi All,
This is my first post so a quick Hello to you all and a big thanks for taking the time to read this..
Quick Summary of my question
I wish to modify the attached circuit so the relay activates and deactivates at two different voltages. Ideally using just a few extra passive components. I am sure it is possible but need some help finding a solution...Ive thought about this for a while and been unable to find a good solution. (I know there are many ways of achieving the desired end but I have to use a transistor and handful of components - nothing fancier, I could buy an IC to do the job but that is not an option)
The pdf shows the basic idea and I believe this circuit will energise the relay coil when the power supply is at approx the same voltage as the zener diode breakdown voltage.
But how can I make the voltage at which the coil de-energises a few volts lower? Could I use the second set of relay contacts to switch in a lower voltage zener diode? There must be another way.
OriginallyI tested a circuit without the transistor. Just a zener diode in series with a relay. This did achieves the desired effect. But power dissapation in the zener will be very large if the relay current is high. And I am concerned that if it were manufactured in quantity the on/off voltages may change from one unit to the next due to fluctuations caused by component tolerances and environmental heating/cooling effects.
Please if you have any ideas/comments I am very keen to hear them? Any advice is very welcome.
Regards
PhilVr
This is my first post so a quick Hello to you all and a big thanks for taking the time to read this..
Quick Summary of my question
I wish to modify the attached circuit so the relay activates and deactivates at two different voltages. Ideally using just a few extra passive components. I am sure it is possible but need some help finding a solution...Ive thought about this for a while and been unable to find a good solution. (I know there are many ways of achieving the desired end but I have to use a transistor and handful of components - nothing fancier, I could buy an IC to do the job but that is not an option)
The pdf shows the basic idea and I believe this circuit will energise the relay coil when the power supply is at approx the same voltage as the zener diode breakdown voltage.
But how can I make the voltage at which the coil de-energises a few volts lower? Could I use the second set of relay contacts to switch in a lower voltage zener diode? There must be another way.
OriginallyI tested a circuit without the transistor. Just a zener diode in series with a relay. This did achieves the desired effect. But power dissapation in the zener will be very large if the relay current is high. And I am concerned that if it were manufactured in quantity the on/off voltages may change from one unit to the next due to fluctuations caused by component tolerances and environmental heating/cooling effects.
Please if you have any ideas/comments I am very keen to hear them? Any advice is very welcome.
Regards
PhilVr
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