Square Wave Based Inverter (Switch Mode)

[C47]

well the 555 timer had 15VDC input....i just thought of checking the "BJT inverter" that you drew....i think all values were ~1.4kohm

i just made the 555 timer and then the BJT inverter, when the 555 popped.

 

[ericgibbs]

well the 555 timer had 15VDC input....i just thought of checking the "BJT inverter" that you drew....i think all values were ~1.4kohm

i just made the 555 timer and then the BJT inverter, when the 555 popped.

hi,
Are you saying that connecting as the attached circuit, popped an 555.?

If yes, you must be doing something wrong...Have you checked the 14V with a meter.?

 

[C47]

yup that was it....hold on plz i got a professor working now with us....if it gets fixed, I will then post it here

 

[C47]

sorry mate, must have made a mistake somewhere....i managed to invert the signal from the 555 using the inverting buffer (bjt)...also the two signals are 176 degrees out of phase instead of 180, which means that during the run (at a certain point and time) all four switches are open....

 

[ericgibbs]

sorry mate, must have made a mistake somewhere....i managed to invert the signal from the 555 using the inverting buffer (bjt)...also the two signals are 176 degrees out of phase instead of 180, which means that during the run (at a certain point and time) all four switches are open....

hi,
Pleased to hear you are making progress.
Its the transistor invertor thats causing that 176deg problem, a comparator, used an invertor could could be set to give a switch over near 0Volts, in order to give 180deg.

 

[C47]

ok we made this really big circuit....with three 555 timers - one of them providing the clock for the other two

with the other two we can vary the duty cycle and make it work.....this is still in progress as one timer give 70% (as we want) and the other is giving 1% (we want 20-25%) - i tried changing the values of the resistors and capacitors .... anyway this problem is being worked on....

your idea of having two pnps...i have tried it in pspice... i will post it soon

 

[C47]

here is the ckt

it works in pspice...had a bitof difficulty finding proper pairs.....then had to adjust the R values for the base for each transistor

thanks a lot ericgibbs

 

[mneary]

Your PNPs are upside down. You should swap emitter and collector on both of them.

 

[ericgibbs]

Your PNPs are upside down. You should swap emitter and collector on both of them.

hi,
I agree, I would have thought his simulation program would have burped and thrown up a warning... the 'base' voltages, wrt 0V, on the reversed transistors should have been an indication.

Check it out C47..

 

[C47]

it doesnt seem to make a difference...i am building the ckt now...will keep that in mind

 

[C47]

arrgghhh!!!

the legs work separately but when i put the whole thing it doesnt work....i think that the timer cannot drive all four...

 

[mvs sarma]

arrgghhh!!!

the legs work separately but when i put the whole thing it doesnt work....i think that the timer cannot drive all four...

legs drive 2 transistors only at any time
now worry. please take care of base current needs by managing the series base resistor.
555 has adequate capacity.

 

[ericgibbs]

arrgghhh!!!

the legs work separately but when i put the whole thing it doesnt work....i think that the timer cannot drive all four...

hi,
The circuit you have built, NOT simulated, does it have the 10K resistor as the load or the motor and is it the last circuit you posted.?

If its a motor, whats it voltage and current rating.? The 20K/10K base resistor look too higher a value.

The 555 should be able to drive that bridge with no problem.

 

[mneary]

At extremely low currents, emitter and collector of many BJTs are almost interchangeable. This is one of the traps of simulation.

Lesson: Simulate with your intended load!

 

[C47]

well its done....a 555 timer with an inverting buffer driving four NPN H-Bridge...it didnt work the first time coz of the base resistances...and also becoz the inverting buffer had popped (the second time)...so my 12VDC power supply showed a short circuit

it works.... finally

thankyou very much everybody

 

[shaifymehtadnn]

i want the analysis setting of this circuit or attach project files.....

 

[shaifymehtadnn]

plz attached the project files of the pspice....