Re: LM3914 --help :/

On Fri, 02 Dec 2005 11:57:51 -0800, blender wrote:
>
> so all in all what does make all the leds blinking while the last one
> is ligthing ?

The output current for the LEDs is a 10x current mirror of the output
of the REF OUT pin. When the signal input goes above the reference
voltage of 1.25, The last LED turns on. Because of C1, this causes MORE
current to be output by the ref out pin, causing more current in the
output of all the LEDs, and making the voltage across C1 drop even more
due to the 100 ohm resistor. Over time, the voltage at the REF OUT pin
climbs back up to 1.25, and the current out of REF OUT diminishes. If you
recall, this current is amplified 10x by the mirror, so this decrease
causes the voltage at pin 10 to start to increase, because the voltage
across the 100 ohm resistor depends on the current. This voltage drop
decreases the current out of REF OUT even more; thus, this positive
feedback turns off the output at pin 10, causing the voltage to spike up
on the REF OUT pin. This turns off the output completely, because now the
ref high pin is > the signal input. While the voltage at the REF OUT node
is higher than the reference, the current out of the ref out pin is
basically 0. This is what shuts off all the LEDs.

The voltage decays for a while through the 1.2k resistor. When it gets
down to the signal level, the LED at pin 10 is turned on again, causing
the CAP to pull the voltage down, restarting the cycle...

The off time depends on the cap and the resistance to ground it drains
through when it spikes, I think. The on time depends on how quickly the
REF OUT pin can charge the 100uF cap.

---
Regards,
Bob Monsen

The question of the ultimate foundations and the ultimate meaning of
mathematics remains open; we do not know in what direction it will find its
final solution or even whether a final objective answer can be expected at
all. "Mathematizing" may well be a creative activity of man, like language
or music, of primary originality, whose historical decisions defy complete
objective rationalization.
- Hermann Weyl in 1944
.

Relevant Pages

  • Re: PMOS in parallel with NMOS
    ... Connect 5 volts directly to the emitter. ... The 0 volts on the base is provided by a microcontroller pin. ... happens to come from an LM7805 voltage regulator. ... I am not as worried about the LEDs as I am the MCU. ...
    (comp.arch.embedded)
  • Re: LEDs for dummies
    ... I have been given a bowling pin. ... I will be using 18-24 LEDs of various colors. ... My first problem is that I don't know for sure if those voltage specs ... Each string of LEDs has a nominal Vf of ~18.9 volts. ...
    (sci.electronics.basics)
  • Re: LEDs for dummies
    ... I have been given a bowling pin. ... I will drill holes or wiring and try to place the LEDs in little ... measurement of the voltage drop, or even if there is a difference ...
    (sci.electronics.basics)
  • Re: LEDs for dummies
    ... I have been given a bowling pin. ... I will be using 18-24 LEDs of various colors. ... My first problem is that I don't know for sure if those voltage specs ... 1/2 in series resistors. ...
    (sci.electronics.basics)
  • nighthawk 550 electrical problem
    ... > Maybe you're not clear on the concept of the rectifier regulator unit. ... The rectifier and the *voltage* regulator. ... > on the voltage regulator to the DC positive output pin. ... check with the black lead from the AC input pin to the DC ...
    (rec.motorcycles.tech)