ericgibbs

[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]

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

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Eric
"Good enough is Perfect"

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C47

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

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

ericgibbs

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.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
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ericgibbs

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:
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Bill's: www.blueroomelectronics.com/

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

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.?

Attached Images

HB1a.png (11.5 KB, 19 views)

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

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

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.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

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

Attached Images

	CKT.GIF (12.6 KB, 14 views)
	OUTPUT-1.GIF (27.8 KB, 5 views)

mneary

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

ericgibbs

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..

__________________
Eric
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PIC tutorials:
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C47

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

Attached Images

	pnp-inv.gif (16.6 KB, 12 views)
	output.gif (23.9 KB, 1 views)