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rathmk

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Dear Sir, I have designed a astable multivibrator for flip-flop circuit with 22 LEDs(11 in each series), Transistors Q1 and Q2 are BC548, Rc1=Rc4=100 Ohm, Rb2=Rb3=150k-Ohm. C1=C2= 10mfd/50V,. circit is running with 220V AC. LEDs are glowing constantly without any blink. Please help.
 

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Presumably AG's forthcoming point is that the transistors will instantly blow, not because of Vce breakdown, but reverse Vbe breakdown, you need protection diodes to prevent this. Anything as high as 9V or so and above requires these diodes.
 
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With 22 LEDs in series then the reverse Vbe voltage will be fairly small. If the 22 LEDs are red and have a forward voltage of 2V then the LEDs will have 44V across them and the transistors will have a reverse Vbe of 5.3V.
 
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Thanks all for your quick response, I am attaching the circuit details. Pl. suggest any modification required for proper functioning of circuit.
 
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rjenkinsgb said:
That's rated at 45V.. Look at the collector-emitter voltage rating and pick a part rated well above 50V.

A BC546 is rated 65V, but there are many other types you could use.
Click to expand...
I have attached the circuit, kind request to suggest any modification for proper function of flip-flop circuit operation. any similar transistor circuit running with AC may be suggested.
 
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Your circuit has a deadly power supply. Its very high voltages probably killed its transistors and you are next.
Use a transformer and tell us the forward voltage and recommended current of your LEDs.
I see that you have "only" 11 LEDs in series then with 2V red LEDs the supply voltage can be only 24V.
 
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10uF 50V cap in a 230VAC feed? With no load, it is likely to blow up. Or is it a 500V cap?
100k resistor feeding the whole circuit likely means not enough current or too high a voltage to the rest of the circuit.
As AudioGuru says, this is a dangerous design, don't use it. Get a proper transformer with a voltage rating good enough to drive the LEDs that are in series (cumulative voltage drop across all LEDs)
 
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rathmk said:
I have attached the circuit, kind request to suggest any modification for proper function of flip-flop circuit operation. any similar transistor circuit running with AC may be suggested.
Click to expand...

Sorry, but I'm not suggesting anything in connection with a non-isolated circuit!
 
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