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/diy/ - Do It Yourself

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626227 No.626227 [Reply] [Original]

I need to make flashing led circuts, but I have never made any actual circut. I think I could modify the circut from:

http://www.instructables.com/id/LED-flashing-circuit/

But I'm going to use different input voltage (5V and 12V) and the LEDs I'm going to use are super-brigth (3.3V and 30mA)

I have almost no knowlege about circuts, I need some kind of equations to calculate what resistors and capacitators shoud I use, can you help me, /dyi/?

>> No.626229

just look up oscillating circuit. most people use 555 timer chips for this for ease. there are also flashing leds with timer circuits built into the die.

>> No.626230

>>626229
I can't use the LEDs with timer built-in, they are not avalible in bright enough for my use. I'll try to google some oscillating circuts.

>> No.626254
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626254

What's there to modify?
>Output of the 555 can only source or sink a current of up to 200mA
It'll run on 5-12V

just add a series resistor to the LED

>> No.626257
File: 77 KB, 736x482, 555-v-slow.gif [View same] [iqdb] [saucenao] [google]
626257

>>626254
here's this if you're interested in how it works

>> No.626340
File: 2 KB, 197x213, esaki.gif [View same] [iqdb] [saucenao] [google]
626340

If it's only 12V you can use this one.
Won't work with 5v though.

>> No.626346

>>626340
How would that even work?
base NC
E & C backwards

>> No.626357

>>626346
That circuit originally discovered by Mr. Esaki who later create tunnel diode (aka Esaki diode).

The transistor on that circuit act like tunnel diode.

>> No.626498

>>626257

555 oscillator:
Charges capacitor through both resistors
Time_High = .693 * (R1 + R2) * C

Discharges capacitor through R2
Time_Low = .693 * (R2) * C

Frequency = 1 / (Time_High + Time_Low)
Frequency = 1.44 /((R1 + 2*R2) * C)

>> No.626505
File: 10 KB, 320x346, neon.gif [View same] [iqdb] [saucenao] [google]
626505

>>626357
The transistor in that circuit is very different from a tunnel diode, both in construction and in operation, even if there are similarities.

>>626346
When the capacitor's voltage is high enough, the transistor breaks down and the capacitor starts discharging through the LED. When the capacitor voltage drops enough, the transistor turns off and the capacitor starts charging again. You can make a similar circuit with a neon bulb, pic related.
Fun fact: you can actually reverse the transistor so that the collector is more positive. The required supply voltage will be much higher in that case, since the C-B diode has much higher breakdown voltage than the B-E diode.

>> No.626508

>>626505
Afaik, what you're describing is what happen to tunnel diode when reverse biased.

In forward biased tunnel diode, current flow linear with voltage until it reach certain values.
Once exceed this value, you'll get current dropping with increase in voltage.
This operating region are called negative resistance region.

Reverse the diode bias, and you'll get the effect what you just write.

>> No.626515

>>626508
Ok, after further reading i found out tunnel diode reverse breakdown are designed to be 0V.
So i guess the closer representation is Zener diode.
Once exceed reverse breakdown, it'll conduct.
Anyway, both diode works due to electron quantum tunnelling.

>> No.626520

>>626515
Yes, transistor B-E diodes are sometimes used as 6V zeners and low-voltage zener diodes use tunneling. They're still very different from tunnel diodes.
If you plot transistor's VI curve base open, you'll get a plot which resembles a shitty trigger diode.

>> No.626530

>>626520
I see. Thanks.
Now i know it's actually due to avalanche not tunneling.