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I'm not sure I entirely understand... The output of the LED Driver IC we are looking at is controlled internally by a comparator that will essentially connect the 'LED output' pin to 'ground' (or negative) when active.OK, so what determines the output from the LED output pins?
I'm not sure I entirely understand... The output of the LED Driver IC we are looking at is controlled internally by a comparator that will essentially connect the 'LED output' pin to 'ground' (or negative) when active.
Because the pin goes 'low' when it's active we are connecting it to a PNP transistor that works by taking current 'from' the base to turn it on.
Our PNP transistor will then take care of providing 24V to one of the input wires for the LED Tower.
Use Adam's circuit for each stage on the LED Tower and you should be complete.
(If the LED Driver IC output 5V on it's 'LED Output' pin, we would slightly adjust the circuit and use an NPN transistor instead... It may seem odd that 'On' is connecting something to ground but you'll get used to it. It's called an 'Active Low' output and is quite common from simple ICs to automotive electrical.)
Yes. Here's a zip of the latest versions of my 3914 and 3915 models, together with some test jigs.Alec did you get your LM3914 spice model working? Might be good to upload it if you can..
Hi Alec,Yes. Here's a zip of the latest versions of my 3914 and 3915 models, together with some test jigs.
I'm not sure I entirely understand... The output of the LED Driver IC we are looking at is controlled internally by a comparator that will essentially connect the 'LED output' pin to 'ground' (or negative) when active.
Because the pin goes 'low' when it's active we are connecting it to a PNP transistor that works by taking current 'from' the base to turn it on.
Our PNP transistor will then take care of providing 24V to one of the input wires for the LED Tower.
Use Adam's circuit for each stage on the LED Tower and you should be complete.
(If the LED Driver IC output 5V on it's 'LED Output' pin, we would slightly adjust the circuit and use an NPN transistor instead... It may seem odd that 'On' is connecting something to ground but you'll get used to it. It's called an 'Active Low' output and is quite common from simple ICs to automotive electrical.)
You will also need a resistor or two for the 'brightness' setting on the chip, this controls the current output of the LED pins, and was recommended that you pre-set it to a high value, then you can adjust afterwards.Ok I think I finally understand, so if I just copy that last section two more times over (for 3 total outputs) and use the resistors you recommended earlier (22k and 220K) i should be good to go? (adding in the stuff on the inputs such as the voltage reg, the 1volt IC chip and the two capacitors)
For the 24V supply I could use 2 12 volt batteries but as they are big and bulky could I use 3 9 volt batteries and then attached a 24V voltage regulator?
Finally because Im using the IC chip to limit the Voltage to 1V for the reference voltage do I need any resistors on the input side of the LM3914? And how do I calculate the size of capacitor I need for the voltage regulator?
You will also need a resistor or two for the 'brightness' setting on the chip, this controls the current output of the LED pins, and was recommended that you pre-set it to a high value, then you can adjust afterwards.
For the 24V supply, you will be drawing 50mA per tier it looks like, so the peak draw will be 150mA.
The 9V batteries you plan to use range from a 400mAh to 1200mAh capacity, which means you can light the entire tower anywhere from 2.5 hours to maybe 7 hours if you buy the expensive Lithium based batteries.
The 12V Lead Acid batteries are bulky, but for good reason; they have a LOT more capacity. You could also look into purchasing the 12V version of the tower instead of the 24V version. This would give you more freedom when selecting a battery or battery pack. (8 AA batteries for example)
As far as the input side of the LM3914, there are 'two' inputs you need to worry about.
The signal input does have a maximum current input limit... how are you making your signal, we 'may' need a resistor on the input.
The Voltage reference input. This one does not need a resistor unless you want to adjust the input voltage... The reference voltage IN pin is quite literally just connected to resistors internally. Totalling 10kΩ . This is why you could use a little math and make a voltage divider to provide 1V instead of a dedicated chip. Of course, this is your call based on the accuracy you require.
Amy, the files look like they are for LT Spice. This is the simulator a lot of us use on here and we have a few experts that know it very well. You can download a copy from Linear Technology for free. You can then copy the files into the relevant folder and away you go...
Adam
Yeah i realised thatTo start with your PNP transistors look like they are connected differently to my drawing
Adam