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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I don't know. The TL431 just conducts like a zener diode. For a charge and dump oscillator, you want something that fires and latches on like a SCR. (anyone remember unijunction transistors?)
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I just happen to have some here I ordered together with 2950 low drop regulators, wich I wanted to implement for voltage regulation on 4046 chip.
To make a relaxation oscillator you need a component with negative resistance region, like diac, UJT's, SCR (in self-triggering circuit), neon bulbs and spark gaps, etc. (I think there are some interesting oscillators based on neon bulbs on bjorn's site)
Zener diodes and 431 regulators (wich are actually just something lke adjustable zeners) pwn no negative resistance and they will just 'conduct' once enough voltage is applied, mantaining constant voltage drop on themselves.
Since 431 is adjustable, feedback pin could *maybe* be used to make some kind of negative feedback/relaxation oscillator of sorts, but I'm not quite sure how would it look in reality. I need to dig around a bit more..
Registered Member #312
Joined: Mon Mar 13 2006, 01:50AM
Location: Georgia, USA
Posts: 27
<i>Since 431 is adjustable, feedback pin could *maybe* be used to make some kind of negative feedback/relaxation oscillator of sorts, but I'm not quite sure how would it look in reality. I need to dig around a bit more..</i>
Like "name that tune" I can draw an LED flasher/oscillator circuit with a 431, three resistors and one capacitor (and of course the LED and a power source). With an r-c network in its feedback path, a 431 can't help but oscillate. Calculating frequency and adjusting on/off ratio will require a little more thought and calculation, but shouldn't be a big deal.
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TL431 IC for low voltage LED flasher
