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rathmk

New Member
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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atferrari

Well-Known Member
Most Helpful Member
Nothing like showing the actual schematic instead a lot of words.
 

audioguru

Well-Known Member
Most Helpful Member
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.
 

rathmk

New Member
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.
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.
 

audioguru

Well-Known Member
Most Helpful Member
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.
 

sagor1

Active Member
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)
 

rjenkinsgb

Well-Known Member
Most Helpful Member
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.

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

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