increasing transistor on time

Thread Starter

denison

Joined Oct 13, 2018
328
I am trying to make a sawtooth wave. The problem I am having is the npn transistor I am using does not stay on long enough to discharge the 1uf capacitor. The zero crossing pulse I am using to discharge the capacitor is too short.
Can anybody suggest a way to make the transistor stay on longer? What about a capacitor at the base? Would this do it?
 

Thread Starter

denison

Joined Oct 13, 2018
328
Please post a schematic of your circuit. This will save a lot of questions.
Please post a schematic of your circuit. This will save a lot of questions.
It would only encourage further questions as the circuit is complicated Dick.
Really just need suggestions as to how I can increase the transistor on time.
Have fixed it one way but requiring more real estate for the electronics.
I have used a 555 in monostable mode. This receives a positive zero crossing pulse and puts out a pulse of .76ms to the base of the transistor. This is then long enough to discharge the capacitor.
You can see how this raises more questions as the 555 normally needs a negative going pulse. I have been able to use a positive going pulse.
I would like to be able to do this without the 555 thus making the circuit simpler.
 

k1ng 1337

Joined Sep 11, 2020
911
It would only encourage further questions as the circuit is complicated Dick.
Really just need suggestions as to how I can increase the transistor on time.
Have fixed it one way but requiring more real estate for the electronics.
I have used a 555 in monostable mode. This receives a positive zero crossing pulse and puts out a pulse of .76ms to the base of the transistor. This is then long enough to discharge the capacitor.
You can see how this raises more questions as the 555 normally needs a negative going pulse. I have been able to use a positive going pulse.
I would like to be able to do this without the 555 thus making the circuit simpler.
I tried to imagine your circuit without a schematic based your description and my head started to hurt.
 

Papabravo

Joined Feb 24, 2006
21,008
It would only encourage further questions as the circuit is complicated Dick.
...
Are you kidding me?! If you want help you should seriously consider compliance with a reasonable request. Most of us have vast experience with circuits that are far more complicated.
 

crutschow

Joined Mar 14, 2008
34,048
Since you refuse to post a schematic, my WAG is that a diode and capacitor at the transistor base will lengthen the turn-on time.
I can't provide a schematic of that, since it would only encourage further questions. :rolleyes:
 

dl324

Joined Mar 30, 2015
16,691
It would only encourage further questions as the circuit is complicated Dick.
Really just need suggestions as to how I can increase the transistor on time.
You could, at the very least, show us the relevant circuitry around the transistor.
Have fixed it one way but requiring more real estate for the electronics.
I have used a 555 in monostable mode.
Does this mean that the fix needs to take less area than a 555 timer, and associated components?
 

MrChips

Joined Oct 2, 2009
30,494
Folks don't usually ask to increase transistor on time. They usually want shorter switching times.
Do you want longer signal ramp time instead? Then you need to show your circuit diagram.
 

MisterBill2

Joined Jan 23, 2018
17,827
If the TS believes that some circuit is "too complicated" for us then why ask us?
Really, telling us that it is too complicated for us is rather a nasty insult, and not any way to present a request for help, especially with a rather nebulous description of some circuit.
Examine the discharge portion of the circuit yourself and then determine what needs to be altered to produce the result you need..
 

ScottWang

Joined Aug 23, 2012
7,397
If your circuit is too complicated then you just post the part that you asked for help.

If you don't want to post the circuit then you only waste the time of our members, so this thread will be locked.

Warning--
Waiting for the circuit...
 
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