Soft On/Off circuit help

[Ziddik]

hello ppl

i want to build the circuit posted below which is a soft On/Off circuit and i need some advise. I want the circuit to work from a 4V battery by replacing relay with a bunch of white LEDs so what modifications I need in this circuit to make it work from a 4V battery? Also is there any fault in the circuit? The IC is flip flop CD4027. All kind of infos will be greatly appreciated

 

[ericgibbs]

hi,
There are some errors on your circuit.

You should not leave pin #4, floating, also assuming a current gain of 10 in the transistor, the 8k2 is far to high a value, you only have 1mA Base current.

There should also be a back EMF clamp diode across the relay coil.

Check the CD4027 Source current drive specification ref image

 

[jpanhalt]

It appears that you just want to latch on an string of LED's with a momentary push button switch. Your circuit uses a second switch to reset.

Would you prefer to use a single switch to latch on and then latch off the LED's? That is, one push is "on" the next push is "off," and so forth.

John

 

[Ziddik]

Hi Thanks for pointing out the errors eric so assuming i should connect the pin #4 to ground?

 

[Ziddik]

Yes Jp...just a push and the circuit should turn ON and turn off by next push..i'm not talking about the mechanical switch because mechanical switch makes the LEDs flick as the current drops in the battery..so i want use an electronic switch..any simple circuits that you could recommend? Thanks jp

 

[jpanhalt]

Here's a link to a Dave Johnson circuit (Discover Circuits): http://www.discovercircuits.com/DJ-Circuits/latch-cir6.htm

It is a little clearer here (without the water mark):



John

 

[ericgibbs]

Hi Thanks for pointing out the errors eric so assuming i should connect the pin #4 to ground?

hi,
The CD4027 SET and CLEAR pins are active High, look at this image showing all the states.

Remember the CD is a CMOS device so all inputs must be held High or Low, never left Open [floating]

E.

 

[Ziddik]

Here's a link to a Dave Johnson circuit (Discover Circuits): http://www.discovercircuits.com/DJ-Circuits/latch-cir6.htm

It is a little clearer here (without the water mark):

View attachment 71312

John

Thanks for the circuit jp..but i'm not sure whether those ICs will available here or not i will try anyway.thanks again jp

 

[jpanhalt]

Any Schmitt inverter will work. You could even wire up a pair of NE555's as Schmitt inverters.

John

 

[Ziddik]

hi,
The CD4027 SET and CLEAR pins are active High, look at this image showing all the states.

Remember the CD is a CMOS device so all inputs must be held High or Low, never left Open [floating]

E.

Thanks eric so i should set the pin high or low and change the resistance to low and put a diode to prevent back emf but i don't use relay in this circuit actually its to turn On/Off some white LEDs..maybe 5 of them. Is there anything else i should aware regarding this circuit? I'm gonna build that soon if everything else is ok..don't wanna waste time by making mistake and burn them that's why i need your help thanks jp and eric

 

[audioguru]

Here's a link to a Dave Johnson circuit (Discover Circuits): http://www.discovercircuits.com/DJ-Circuits/latch-cir6.htm

The unusal IC is not needed and the circuit does not need Schmitt-trigger inverters. An ordinary CD4069 has six Cmos inverters and it works with a supply down to 3V:

 

[Ziddik]

Does the cd4027 false trigger the output if i connect the battery to a charger while the circuit working?