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What is wrong with this!!!!

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Sarac

New Member
Hi, All

i'm trying to buid a flip flop which supposed to flash 12 volt Lamp one and another.

Managed to hook up IC 555 as an astable multivibrator, it works fine with leds. the leds ( D1 and D2 ) are flashing as planned. But when i connect two power transistor to increase the current which the lamps will consume, lamp1 lits continuosly ( not flashing ) and lamp2 is not light up at all.

I have tried to light up leds instead of lamps by using small ( NPN, and PNP ) BC type transistor, the result was the same.

Can anybody tell me what is wrong with these transistors that not obeying my orders
 

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Sebi

Active Member
Via the PNP transistor E-B diode,always open the NPN. Apply two NPN, and drive the second NPN base from first NPN collector via resistor.
 

herbymcduff

New Member
Why would you put the lamp 2 on the emitter of the 2nd transistor. If the collector of the 1st transistor is connected to the base of the 2nd, well the emitter is in phase with the base. So assuming the lights will light, they will light at the same time. You need to rearrange your lights.

What I mean is that the way you have them now, as long as Q1 is conducting, Lamp 1 will stay on. What you need to do is place the lamp on the output of Q1 (right before the resistor to Q2) and tie to ground. Then you need to place Lamp 2 on the output of Q2 to ground. That may work.

Also something to consider. Your using resistor coupling between the two transistors. What a better way of doing it would be place a cap(10microf) on the output of Q1(right before your lamp you modified earlier) and kept that resistor there. Then do the same for the output of Q2. Then you block DC going to your lamps. As long as your output voltage doesn't go over 12v pulsating, it should work.

I hope I didn't confuse you. Let alone myself.
 

Sebi

Active Member
Just put the lamp2 to collector2.Same as lamp1.
When the 555 out is low, T1 closed, current flow via lamp1-R4 to T2 base and open it,the lamp2 in collector light.
When the 555 out is high, T1 open, collector go to GND(about +0.3V C-E sat), no enough voltage for T2 opening,(about 0.7V)

I wish You good work!
 

Phasor

Member
I suspect that your original design may work, if you use MOSFETs or IGBTs instead of bipolar transistors. An N-channel in place of the NPN, and a P-Channel in place of the PNP.
 

herbymcduff

New Member
Sebi said:
Just put the lamp2 to collector2.Same as lamp1.
If my mind serves me right, even if you do not put a signal into the base of Q1, you light will light. Both of them (if you haven't modifed your circuit) at the same time. If you do what Sebi said, they will still light at the same time. Your not getting it, sticking the lamp there is just like placing a resistor there. The lamp will drop voltage, and it won't turn off. The light would be dim, but it would light. As I said before, you need to put the lights on the output of the collector, just like you had it tied to the base of Q2. Read my post before this and tell me how it turned out. :)
 

pebe

Member
Sarac said:
Hi, All

i'm trying to buid a flip flop which supposed to flash 12 volt Lamp one and another.

Managed to hook up IC 555 as an astable multivibrator, it works fine with leds. the leds ( D1 and D2 ) are flashing as planned. But when i connect two power transistor to increase the current which the lamps will consume, lamp1 lits continuosly ( not flashing ) and lamp2 is not light up at all.

I have tried to light up leds instead of lamps by using small ( NPN, and PNP ) BC type transistor, the result was the same.

Can anybody tell me what is wrong with these transistors that not obeying my orders
Hi Sarac. Your problem is that with T1 and T2 bases connected together, their BE junctions are across 12v. Each will drop 0.7v and both will switch hard on and lower the 12v supply rail to about 1.5v. There will be a large current from your 12v source!

To correct it, disconnect T2 base from the circuit leaving R3 connecting only the T1 to junction R1/D2.

Now connect the base of T2 via another resistor (same as R3) to junction R2/D1. Only one transistor can now be on at any time.
 

bogdanfirst

New Member
exactly, the problem is that you connected the 2 bases together. so connect them to the output of the 555 via 2 resistors, one for each transistor, it should work
 

pebe

Member
bogdanfirst said:
exactly, the problem is that you connected the 2 bases together. so connect them to the output of the 555 via 2 resistors, one for each transistor, it should work
The 555 o/p when high does not go up to full rail voltage because its o/p is formed by two emitter followers in series. It only goes to about V+ minus about 2v, so the PNP transistor will not turn off. By leaving D1 in series with the base as I suggested, will ensure that the base volts wil not be enough to turn on the transistor.
 

bogdanfirst

New Member
well ya, on output high you have about 2/3 of vcc, and low os 1/3 of vcc, so you could use 2 zenner diodes in series with the resistors too
 

Sarac

New Member
Hi All,
i realy thank you for helping me...

i have made necessarry modification. the circuit is now working perfectly,
the attached diagram shows how i did the modification

thank you alll.
 

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Sarac

New Member
bogdanfirst said:
does it woark. hope it does. good luck.
Yes, it works now. I have tested it with none stop 24 hours use. No mulfunction observed.

I am now planning to adjust the frequency at 50 HZ and feed 2 Mos-Fet Transistor by connecting them in place of the lamps and further feeding step up transformer then i wish to get 220 volts 50 Hz.

Charger, Voltage Monitor, Short Circuit Protection, Low Voltage Cut Off,
are my further project. ( i dont know how long it will take to complete. Condering only the Oscillator part took one week it may take ages to complete a total Ups :))

I may need your help again.

Thank You Again
 

bogdanfirst

New Member
:D be more OPTIMISTIC. the more things you built the faster you will learn to do them. i remember doing a simple oscilator, wich i used to blink 2 leds and it took me 2 days, but now i can do it in 20-30 minutes. :D
 

john1

Active Member
Hi Sarac,

That sounds like a substantial project.
I wish you the best of luck.
Have you considered 24 volts for the battery.
Two 12 volt batteries could make the circuit
design easier, and the output transistors
would not have to handle such high currents.

regards, John
 

Sarac

New Member
Hi John,

Initialy, i was planning to build up 1 KVA Ups/Inventer by using 2x12 Volts
high current batteries. But i was not sure how to charge 2 batteries in
serries then i have decided to reduce output power 500 watt then i think i can get enough supply current from a 60 Ah Battery since i will need 40-45 A to get 500 watt at the output.

i am going to use power Mos-Fet Transistor ( IRFZ 44 ) as it's catalog value it can handle 50A. just in case i will use 3 of them in parallel at each loop, then i think there will no problem. ( what you think?? )

Anyway, this is my experimental project and thus it is not necessary to be too big. 500 watts and 1 hour lasting time is enough for the beginning.

But if you have a good charging circuits that can supply 6A under 24 volts
i may reconsider building 1 KVA

can you help John,

regards,
 

john1

Active Member
Hi Sarac,

Charging two 12 volt batteries in series would be done
in the same way as a single battery.
The cells in a 12 volt battery are charged in series
anyway. (two 12v batteries in series is a 24v battery)
Below about 10.5 volts would be considered flat,
although barely usable if the battery is otherwise in
good order. (21v for a 24v battery),
full charge would be about 14 to 14.5 volts while on
charge at a low rate. (28 to 29 for a 24v battery)
During heavy discharge usage the terminal voltage can
drop to ten or eleven volts (20 to 22 on a 24v unit)

I would not think that the relatively minor problems
of making a battery charger to suit your needs should
have made you change your designs on the inverter you
intend to build.

Your original intention to use two batteries has much
to recommend it.
500 watts will be quite a draw from a 60 A/h battery.

The choice of transformer is another headache.

With clever circuitry a simple two winding transformer
(primary and secondary) can be used, these are usually
the easiest type of transformer to get hold of.

If a transformer with a halfway split primary can be
found, or if one is winding ones own transformer then
other, easier circuits can be made.

I have made small power supplies myself, but mine have
been oscillators rather than inverters, and only small
scale low power units. I find that the inverters are
ok for electrical items that do not contain any
electronics, but i find that they do have a very
spiky output and put electronic items at risk, unless
they are carefully damped.

In the drawings attached some of the more common
arrangements are shown. The transistors can be 'doubled
up' as you know. Ive never seen capacitor fed output
on inverters or oscillator power supplies, although
it is quite common on medium power audio outputs.

Best of luck with your project,
are you funding it yourself or is this done through a
company or some scheme ?

Regards, John
 

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