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By using our site, you acknowledge that you have read and understand an884 Cookie PolicyPrivacy Policyand our Terms of Service. I am looking at the test circuits on the data sheet for the AN VU dwtasheet IC, and I cannot understand the connection to pin 8 in the following diagram: Pin 8 accepts a positive input voltage. The potentiometer is clear, but the 2. It appears to be reversed. If I “correct” the orientation, the circuit does not work at all.

That’s clear, because the input in my test circuit is DC. This circuit will light the LEDs as the input voltage on pin 8 increases relative to pin 7.

As displayed, the LEDs go from fully off to fully on over roughly the entire turn range of the potentiometer. If I remove the 2.

That is to say that the LEDs all come on at a much dataxheet turn of the potentiometer. Can someone explain what the reversed capacitor is doing here?

Your description doesn’t agree with that in the datasheet. Pin 7 is the output of the internal amplifier, and pin 8 is its input, designed to accept a low-level AC input 57 mV for a 0-dB indication.

It sounds like you’re trying to drive this circuit with a signal that includes a considerable DC bias, which explains why all of the LEDs light up right away when you remove short out the capacitor.


AN Datasheet(PDF) – Panasonic Semiconductor

However, if that’s the case, I can’t explain why reversing the capacitor doesn’t work, unless the actual polarity of the capacitor is backwards from what you think it is.

Have you tried a non-polarized capacitor e. Per AN’d datasheet. Pin 8 datzsheet the signal input pin, and it’s the internal Op amp’s positive input. That means there is a small current flow out from the pin.

So it determines the DC bias of the datashet capacitor’s polarity. By darasheet “Post Your Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies. Home Questions Tags Users Unanswered. Reverse biased capacitor on IC input pin Ask Question.

Fadecomic 2 6. Right, I get that pin 7 is the output of the amp, but it’s part of the negative feedback loop on the amp. Placing it at a higher voltage within the datasheet’s max ab6884 V will both lower the amplification and raise the lower rail of the comparators in the block diagram. To be clear, removing the capacitor doesn’t light up the LEDs all at once.

It just shortens the range of turn over which the potentiometer works. There’s still a much shorter range over which a varying number of LEDs come on. I’m not following you. How does doing anything to pin 7 or pin 8 affect that? I’m not reading it that way. Vref is the high side of the 5 LED comparators in the datasheet block diagram.

The LED pins connect to the negative side of the LEDs, and the pins go low when the output of the internal amp goes above Vref dropped by voltage dividing resistors at each comparator. Setting 7 higher than ground biases the low side of dahasheet comparators, allowing them to turn on with a lower output from the amp.

By “low side”, you’re referring to the datashheet inputs of the comparators. Very confusing terminology, since the inverting input can have a higher voltage than the noninverting input. Indeed, it must in order for any of the LEDs datasheet turn on! Most people use “low” to refer to either a lower voltage, or a lower position on the diagram.

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I know the correct names, but I conversely find “inverting” and “noninverting” confusing when dealing with comparators, since those terms make more sense when dealing with op-amps.

Datashet will be certain to use them here from now on. Per AN’d datasheetPin 8 is the signal input pin, and it’s the internal Op amp’s positive input. Ah6884 makes sense, but why not a diode? Passing Vin through a reverse capacitor seems to be potentially more prone to failure.

5+1 led vu-meter with AN6884

Capacitor with polarity can be used ac couple or blocking. It’s the DC bias determine the polarity. The diode will mess up the response of the chip due to its forward voltage drop. There is also no discharge path with your arrangement. You might want to edit to explain your answer a bit more. You should fix the capitalisation of sentences and electrical units ‘F’ for farad dstasheet improve legibility and credibility.

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(Datasheet) AN pdf – 5-Dot LED Driver Circuit (1-page)

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