Re: LM3914 --help :/

On 02/12/2005 the venerable blender@xxxxxxxxx etched in runes:

>
> petrus bitbyter napisal(a):
> > <blender@xxxxxxxxx> schreef in bericht
> > news:1133522743.341705.29910@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> > > Hi all!
> > >
> > > Could someone explain me how does design from page 12 of
> > > http://boss.iele.polsl.gliwice.pl/pdf/National_Semiconductor/lm391
> > > 4.pdf works.
> > >
> > > Why all the LEDs are blinkink while the last one begins to lighth
> > > ??
> > >
> > > Best regards
> > >
> > > DM
> > >
> >
> > Most likely your circuit starts to oscillate when that last LED
> > comes on. Carefully decouple the power supply (pins 2 and 3.)
> > Let's say 10uF elco // 100nF ceramic. Make sure the power traces
> > are wide (thick) enough. Especially the GND trace should have a
> > very low resistance.
> >
> > petrus bitbyter
>
>
>
>
> You did not understand me. The circuit does oscilate as it should, but
> I do not understand the idea of oscilating, I know that whe the last
> LED begins to ligth then something is going on with capacitor and ...?
> why does it blink ?

First, you need to look at the block diagram of the chip on page 6 of
the data ***. You will see that the comparator chain comes out on the
'Rhi' pin. In the circuit on page 12 the 'Rhi' pin is connected to one
end of the capacitor via a 470 ohm resistor and the other end of the
capacitor to the last LED driver pin. The capacitor acts as feedback
and as LED 10 lights it discharges the capacitor and causes the
comparator chain input to be modulated thus turning all the LED's off
again. Then the cycle repeats.

--
John B
.

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