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LED fade in/fade out

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ljcox

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@colin55
The circuit in post #15 will need adapting to get a 30 sec fade period. It currently gives a 3-4 sec period.
Re Ohm's law, take a look at the stated voltage at point X in the schematic and work things from there.
Thanks alec_t, that seems to be the point he is missing.
 

alec_t

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Mosaic

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If i were to try this I'd use an LM317 or 338 with a voltage divider and an RC component on the reference leg of the regulator. So basically you'd get a slow ramp up and down on the voltage which will translate into brightening and dimming of the LEDs via a dropping resistor. No other IC's or transistor drives needed. You will need a DC supply of about 1.5V over the target max voltage though.

I've used a PWM technique into an RC filter on such a regulator b4 to create control of a linear voltage for batt. charging.
 

1-3-2-4

Member
going to use the IRF510 for the mosfet but I was going over the design and with those bjt's it would lower the gate voltage on the mosfet too much so I was going to omit them in the circuit.
 

audioguru

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The transistors make a good gate driver because they supply enough current to quickly charge and discharge the high gate capacitance. Without the transistors the Mosfets will ramp instead of switch and will get very hot unless you reduce the switching frequency a lot.

Don't you have a 12V supply? Then the Mosfets will turn on fine with a gate voltage of +11.3V.
 
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alec_t

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The IRF510 has an Rdson of ~0.54Ω, so will run hot if the load current is significantly more than an amp, and may require a heatsink.
 

1-3-2-4

Member
I don't see how it's going to draw more then a amp since the lights right are are on a 12V 1A power supply.

Also the 510 was what I had on hand seems wasteful to buy another mosfet when I already have one (really two) that I'm not using at the moment.
 
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1-3-2-4

Member
I have a question about the switch in the post #11 is that needed because I had not planned to use a switch on the circuit since it's going to be on a walloutlet that the supply 12V is going to come from which is controlled by a switch.

Also my stuff arrived today but does anyone have a pinout for the CD40106BE

I can find one for the CD40106B but what changes does the (E) version have?
 

alec_t

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If you don't use a switch you won't get fade-out; only fade-in.
 

alec_t

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well this is being mounted behind a 40" tv so reaching behind would be a little odd.
If you mount the switch on a length of screened twisted-pair cable you can have it remote from the TV.
 
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