Square Wave Based Inverter (Switch Mode) - Page 2 - Electronic Circuits Projects Diagrams Free

ericgibbs · 21st April 2008, 09:30 AM

[quote=C47]well for q3 i will use an opamp inverter, is that okay?
Thats OK, something better than a 741 if possible.

im sorry i didnt understand the linking resistor part?
No problem, its easier to draw a rectangular box than a zigzag resistor.

is the red 5V suuposed to be 12V
On your drawing you show a 555 with a 5V supply, I was just trying to keep the drive transistor the same.

or is it part of the BJT inverter that you meant to use?
It just powers the invertor.[/QUOTE]

Quote:

What college year is this project for.?

Hi,
If its easier the 555 can run at 12V, as can the BJT invertor, just calculate the appropiate resistor values.

C47 · 21st April 2008, 09:37 AM

im simulating it in pspice i will use vpulse instead of 555, so its faster and its 14V (sorry my mistake) so that the bjts can operate in switch mode

C47 · 21st April 2008, 10:22 AM

i just popped the 555 when i connected to output to base of the red transistor....are you sure of your circuit?

ericgibbs · 21st April 2008, 10:26 AM

Quote:

Originally Posted by C47

i just popped the 555 when i connected to output to base of the red transistor....are you sure of your circuit?

Yes Im sure.

What value of resistors do you have in the 555 output to the transistor and opa invertor.?

EDIT: post a drawing with the component values on.

ericgibbs · 21st April 2008, 10:38 AM

hi,
Double checked my circuit, OK

If you have popped the 555 you have connected something incorrectly.

Check the supply to the 555 timer make sure its not greater than 15V or so volts, also the connections to the 555, especially pin #3.

C47 · 21st April 2008, 11:18 AM

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 · 21st April 2008, 11:23 AM

Quote:

Originally Posted by 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.

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 · 21st April 2008, 11:35 AM

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 · 22nd April 2008, 08:39 PM

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 · 23rd April 2008, 06:51 AM

Quote:

Originally Posted by 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....

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 · 28th April 2008, 04:14 PM

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 · 28th April 2008, 04:33 PM

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 · 28th April 2008, 08:01 PM

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

ericgibbs · 29th April 2008, 06:37 AM

Quote:

Originally Posted by mneary

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 · 29th April 2008, 08:36 AM

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

21st April 2008, 10:38 AM	#20 (permalink)
ericgibbs Experienced Member Join Date: Jan 2007 Location: U.K. Posts: 3,783	hi, Double checked my circuit, OK If you have popped the 555 you have connected something incorrectly. Check the supply to the 555 timer make sure its not greater than 15V or so volts, also the connections to the 555, especially pin #3. __________________ Eric "Good enough is Perfect" PIC tutorials: Nigel's site: http://www.winpicprog.co.uk/ Gramo's site: http://www.digital-diy.net/

28th April 2008, 04:14 PM	#26 (permalink)
C47 New Member Join Date: Apr 2008 Posts: 18	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 Last edited by C47; 28th April 2008 at 04:28 PM.

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21st April 2008, 09:37 AM	#17 (permalink)
C47 New Member Join Date: Apr 2008 Posts: 18	im simulating it in pspice i will use vpulse instead of 555, so its faster and its 14V (sorry my mistake) so that the bjts can operate in switch mode

21st April 2008, 10:22 AM	#18 (permalink)
C47 New Member Join Date: Apr 2008 Posts: 18	i just popped the 555 when i connected to output to base of the red transistor....are you sure of your circuit?

21st April 2008, 11:18 AM	#21 (permalink)
C47 New Member Join Date: Apr 2008 Posts: 18	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.

21st April 2008, 11:35 AM	#23 (permalink)
C47 New Member Join Date: Apr 2008 Posts: 18	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

22nd April 2008, 08:39 PM	#24 (permalink)
C47 New Member Join Date: Apr 2008 Posts: 18	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....

28th April 2008, 08:01 PM	#28 (permalink)
mneary Experienced Member Join Date: Feb 2007 Location: California Posts: 1,261	Your PNPs are upside down. You should swap emitter and collector on both of them.