LM3909 DATASHEET PDF
LM datasheet, LM circuit, LM data sheet: NSC – LM LED Flasher/Oscillator,alldatasheet, datasheet, Datasheet search site for Electronic. LM datasheet, LM pdf, LM data sheet, datasheet, data sheet, pdf, National Semiconductor, LED Flasher/Oscillator. LMN Datasheet, LMN National Semiconductor LED Flasher/Oscillator Datasheet. LMN – LM LED Flasher/Oscillator Datasheet.
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When our Keurig coffee maker quit, I wanted the bright blue LED that shines at the bottom of the water tank. There is something about blue LEDs that are just so bright and look so cool. So when the coffee maker quit, I quickly extracted the blue LED without much of a fight not much else comes out without a fight.
In this article, I’ll discuss a little circuit that I made for my granddaughter. For my granddaughter, the assembled unit needed to be small datashfet fairly indestructible she’s currently about 3. To keep it small and light weight, I wanted to use a little 3V lithium button battery. So even as datasheef button batter fades away, the unit should operate for a dayasheet time. Finally, it was important to me to make this toy last as long as I could. Kids quickly tire of things and why have the battery expend itself when it eventually finds its way to the bottom of the toy box?
There is always the grandson following, who may want to play with it when he gets of age. This gives the child some interaction with the flasher unit. The LED flasher circuit could be built with a timer, or some other circuit. But the Adtasheet has the advantage of being extremely dxtasheet and use the fewest number of components.
It also has the advantage of being able to pump current into the average LED, even with a batter voltage as low as 1.
The LM is still being sold on ebay, if you need to source them.
datasheett The flasher circuit itself, is taken straight from the LM datasheet, with the exception that I changed the uF capacitor to uF, to make it flash more frequently 3 year olds don’t have a lot of patience. Notice how few external components datashee involved:. To automatically turn the unit off, you know that either a capacitor charge or a digital circuit would be involved. A digital circuit would be overkill and require much expense and circuitry for this tiny project.
The 2N transistor is an enhancement mode FET, which requires a positive voltage to activate the transistor.
LM Datasheet pdf – LED Flasher/Oscillator – National Semiconductor
Capacitor C1 initially has no charge when the circuit is turned on, but is slowly charged up through R2, which completes the circuit to ground. When the capacitor has no charge, all of the battery voltage 3V appears across R2.
So initially the FET sees a very positive gate, which turns it on. Eventually, as C1 charges up fully, the voltage at the gate will drop below 1V and eventually drop as low as 0V.
To reactivate the flasher, we simply have a push button to temporarily short out C1. After C1 has been shorted out, it must recharge again after the button has been released, before the unit will turn off again.
LM3909N – LM3909 LED Flasher/Oscillator Datasheet
The values shown in the schematic, should give you an on time of about 50 to 60 seconds. When I bench tested this, I decided to change C1 and R2, since finding a 10 megohm resistor was impossible with my current stock. Another thing to watch is to choose a good component for C1, as leakage current might prevent it from working altogether.
This circuit however goes from on to off when M1’s gate voltage drops below. The 2N threshold voltage is somewhere between 1.
(PDF) LM3909 Datasheet download
If we assume a threshold voltage of 2V, then the time for the to go from 3V to 2V represents about one third of the entire charge cycle for C1. The time constant is computed from:. However, to have go from 3V down to 2V, is one third of this cycle. My stop watch trial yielded about 20 seconds.
dataeheet So this is well within the tolerance of the parts and sloppy stopwatch timing with an iPhone. To restate the formula completely, we could say the on time is determined by:. The above formula relies on the fact catasheet the FET’s threshold voltage is near 2V.
If you have a 2N with a higherit may stay on for a much shorter than calculated time, or even not come on at all if near 3V.
On the other hand, if your 2N part has a low threshold, it may stay on for longer than calculated time. When ordering this part, order several, so that you can choose the one that works best.
If you want a more generalized formula, where is known, you could use:. If your auto off circuit doesn’t work, there are three likely datadheet. I would check the following in order:. My Auto Off Doesn’t Work. So summarized, these were the design goals: Notice how few external components are involved: The values I settle on in the end were: To restate the formula completely, we could say the on time is determined lmm3909 If you want a more generalized formula, where is known, you could use: I would check the following in order: Wiring – this circuit is so simple, yet it is easy to make wiring mistakes.
Check that you have the pins on the 2N correct.
It is easy to get Source and Drain backwards. Capacitor C1 – make sure this part is a low datawheet capacitor. If it leaks badly, the circuit may never turn off. You may have one that needs a high gate voltage to conduct. Swap the part for another requiring a lowerideally around 2V.
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