please help me with my project, Anyone who's familiar with this circuit, can you help me to know what watts is this resistor? the circuit is in the link below..
And can u help me to have the PCB design, I little unfamiliar with the connection of 3 feet of the transistor. How many transistor in this circuit?
Thanks!



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hi,
There are 2 transistors in this Bistable circuit, all the same type, they are Darlington [ two transistors in one case.]

If you look at the inset diagram of the transistor you will see its marked C B E, these correspond to the circuit digarm C B E.

The wattage rating of the resistor, I would use either 0.125W or 0.25W whichever is handy.
OK.
EDIT: added d/s for the BD679

Attached Files

datasheet.pdf (115.5 KB, 7 views)

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Eric " Good enough is Perfect "
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thank you sir, can I have a PCB design layout?
Is that wattage is for 12-volts sir?

 

The resitors will be OK at 0.125W or 0.25W.

If you go online and search for expresspcb its a free schematic and pcb layout program.
Its very easy to use, do a layout and post it, we will guide you thru it.

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Eric " Good enough is Perfect "
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PIC tutorials: Nigel's www.winpicprog.co.uk/ Bill's: www.blueroomelectronics.com/

 

You should not use that simple circuit with a 12V supply. The max allowed reverse voltage for the emitter-base junction of the BD679 darlington transistors is 5V but with a 12V supply they will try to reach 11V and cause avalanche breakdown which is bad. The high avalanche breakdown current might cause the capacitors to blow up.

Use a 6V supply or add diodes to stop the avalanche breakdown.

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Uncle $crooge

 

sir, what if I use ceramic capacitor?

 

Ceramic capacitors probably will not blow up but their small value will result in a fairly high frequency. The emitter-base junctions of the transistors will still have avalanche breakdown which is bad for them.

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Uncle $crooge

 

That won't help. Head this warning:

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You don't need a quadraphonic Blaupunkt -- you need a curve
ball.

 

I wouldn't bother with a etched PCB for a simple project like this. Get a prototyping PCB with pre-etched tracks that you can cut with an exacto knife.
Also add the diodes as mentioned by AG:

Attached Thumbnails

 

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Inside every little problem, is a big problem trying to get out.

 

Diodes should be between transistor base and ground, reversed-biased.

__________________
You don't need a quadraphonic Blaupunkt -- you need a curve
ball.

 

No, you want the (-) side of the cap to go below ground when it's associated transistor turns on. Placing the diodes the way you suggested would result in high currents through the diodes and caps.

__________________
Inside every little problem, is a big problem trying to get out.

 

Sir, do I need to use 12 volt 100 microfarad for my capacitor? I used 16 volt 100microfarad capacitor and it blink a little and it stop.

0.125W or 0.25W can be used in 12 volts?

 

The capacitor charges to 10V or 11V so use 16V or 25V capacitors.

Calculate the power in the resistors. It is only 0.03W so any small resistors will be fine.

I don't know why your circuit stopped working. Maybe the polarity of the capacitors is backwards or maybe you connected the pins on the transistors backwards.

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Uncle $crooge

 

Good point about the high capacitance current with parallel diodes. The attached design uses resistors to limit the discharge current. The diodes clamp the reverse voltage across the BE junction of the transistor to less than 1V.

The problem I have with series diodes is that significant reverse voltage can still exist in the transistor's base, depending on relative reverse recovery times, leakage currents, etc. My design, although not commonly used, accurately controls the reverse voltage ( green trace in the waveform window ) The tradeoff is the limiting resistor must be carefully chosen to sustain oscillations. R7 would not be used in the acutal circuit. It's only included to get oscillations started in the simulation.

Attached Thumbnails

 

__________________
You don't need a quadraphonic Blaupunkt -- you need a curve
ball.

 

sir, I used ceramic 5 watts resistor, can this affect my circuit or is this a reason it doenst work properly?