Timer dimmer

[hanss]

Hello everybody

I used to work with electronics 20 years ago but I'm not good in developing and never was
This is a led fader
I've found this circuit and what i want to do is to get this work both ways
and replace the leds for a second power supply so that I can let the voltage come on in time period from 0 to 45 minutes and come of in time period I know that i have to put a separate power supply instead of s2 is this possible

 

[Mike odom]

you need a transistor switch instead of a power supply to replace S2, so that it turns back on after your off time is reached.
The LEDs will come on and stay 100% until the first stage (+) voltage goes below the adjustable (-) voltage. Then the LEDs will dim until the second stage (+) voltage goes below the LED voltage. Since the opamp can only deliver a limited mA into the load, this is probably ok. The only thing I see is that the first stage capacitor needs like 100 ohm resistor in series. You don't want to drive the full supply directly into the capacitor. The second capacitor charge current is limited by the first stage opamp output.

 

[hanss]

Thanks so far

I think I need to give you more info I need this for my bird breeding cages
every cage has his own led strip
I want to let the light go on slowly in the morning and dim it slowly in the evening like sunrise & sunset
so I think I need a second power supply for the transistor transitor switch
this circuit only fade the leds it has to work in reverse as wel

 

[Mike odom]

 

[hanss]

Thanks Mike I'm going to try this I'll get back on this

 

[Mike odom]

just adding a second power supply won't make it come on slowly. When the (+) voltage of the first stage goes above the adjustable (-), no matter how little above, the LEDs will come on hard.

The only way to start them out dim is to make the voltage going through the diode adjustable, to come up slowly.

Try this:



the one problem I see here is that the first timing stage has 1/3 the time constant of the fader circuit. You may have to go below 3.3M on the fader part, or increase the 1M (time constant now is 36 minutes).

 

[Mike odom]

or even: (duh)

 

[hanss]

happy new year to everybody!!!

Mike thanks so far I'm testing this circuit the leds com on slowly but I can't fade them they go of very quick.
If I hook the 2.2k from the base off the NPN to the +12v or ground or leave it loos nothing will change
The led voltage goes up if I shut down the power they go off quick
where am I'm going wrong on this one

 

[Mike odom]

the problem may be in the charge/discharge cycle. A capacitor's voltage changes 68% of the step voltage in the first tc (time constant, r * c = tc), so the voltage will go up very quickly and then will keep going up a lot slower, and when the opamp output goes low, it will go down very quickly so it is probably going below the threshold quickly.

try the circuit in post #6, but instead of putting a 1-10k to ground, use another 3.3M. This will give the discharge twice the tc as the charge cycle.

 

[Mike odom]

and what about your 5k pot, is it turned down?

 

[hanss]

I replaced the 5k pot for a 4.7k resistor because I hadn't one

 

[hanss]

do I have to place the diode back as in post 6

 

[alec_t]

You'll be lucky to get many minutes of fade, because capacitor leakage current will discharge the cap quicker than you'd like .

 

[Mike odom]

yes, the diode is necessary

 

[hanss]

Can't get it to work !
I will try to rebuild it maybe that will help

 

[Mike odom]

The leakage in the capacitor will be about equal to the charge/discharge current, so maybe you need to replace the high side resistor with 1M, although, you did see it charge up, so the leakage must be less. Looking about about 3uA.

what is the type/part number of the capacitor you are using?

 

[hanss]

I'm using capacitors from KSC 2200uF 25 v
There is no part number on it
Its a radial electrolytic

 

[Mike odom]

is there a two or three letter code on in, like NK, FC or FK?

 

[hanss]

No nothing else is on them

 

[hanss]

Got it going as in post 6 but I left the transistors out they where causing the problem it mow work both ways
But if c2 comes ad 5.6 volt it starts to charge very slowly witch also increases the discharge time I think I'm on the wrong path with
this one

I only need an automatic voltage regulator where the slow on and slow of is the same time and adjustable between 10 sec and 45 min
And the start voltage is also adjustable