Pulse Generator

Thread Starter

warp

Joined Jan 20, 2014
18
Hi,
I am trying to build a dc pulse generator with a 50% duty cycle but I would settle for a bit less.
It needs to be about 3MHz or more, but Im not too fussy about the wave form right now.
It doesn't have to be too square. I dont mind if it comes out triangular even.

I am looking at a LMC555CN which the data sheet says capable of three MHz astable, a TC4426A, fet driver, and an IRF540N fet.

The fet and its driver are little bit hard for me to get given my personal situation right now, so I would like to be pretty sure that Im ordering the right thing.

My question is, can these three components be used together to achieve my desired outcome.

Thanks
Regards
Wil.

.

I forgot to mention that I will be switching 12 volts.

Thanls
 
Last edited:

bertus

Joined Apr 5, 2008
20,230
Hello,

Why do you need such a high frequency for the pulse generator?
The gate capacitance of the fet might give you troubles at that speed.

Bertus
 

Thread Starter

warp

Joined Jan 20, 2014
18
Hi Bertus,

That was one of my concerns.
It is for an experiment. I want to pulse a transformer and induct a standing quarter or half wave into an open ended secondary without having to have too longer wire for the secondary.
 

Thread Starter

warp

Joined Jan 20, 2014
18
I often wind my own transformers but I am also going to try a 2 KV xennon trigger trans as well.

Hi
Assuming the above mentioned fet and driver work ok together what kind of frequency could I expect from that arrangement.

Thanks
Wil
 
Last edited by a moderator:

alfacliff

Joined Dec 13, 2013
2,458
whaty voltage are yo supplying to the fet? voltage and current specs are necessary. sounds like a solid state tesla coil. might google (or whatever) solid state tesla coil for ideas.
 

Thread Starter

warp

Joined Jan 20, 2014
18
whaty voltage are yo supplying to the fet? voltage and current specs are necessary. sounds like a solid state tesla coil. might google (or whatever) solid state tesla coil for ideas.
I was hoping to feed the gate with 12 volts also as well as switching 12 volts. I was hoping the gate driver would amplify the voltage to that, but this would be ny first using gate drivers so I will have to play with it. I have used NE555 before directly bias IRF540 from pin 3 with 3906 pnp to help switch off the fet. This worked ok to about 100 to 150K then things started to go pear shaped.
 

GopherT

Joined Nov 23, 2012
8,012
Pear shaped? Do you mean that your inductively loaded square-wave signal didn't look like a square beyond 150kHz? And more like a pear? Or does pear shaped mean something else?
 

Thread Starter

warp

Joined Jan 20, 2014
18
Thanks for your time posting the info Bertus. it does look like those nanoseconds are starting to add up when I look at all 3 rise and fall times and delay ect.

@alfacliff Yes something like a tiny little Tesla coil. At the moment Im driving it with a PN222A wirelessly with a clip lead clipped to the base. It is going at 270KHz.
Kind of wierd that frequency counter on my muktimeter went off before I plugged it into the circuit. Unfortunately I have no frequency control so I dont know whether
it is pulse transformer type resonance or seconday quater or half standing wave resonance.
 

Thread Starter

warp

Joined Jan 20, 2014
18
Pear shaped? Do you mean that your inductively loaded square-wave signal didn't look like a square beyond 150kHz? And more like a pear? Or does pear shaped mean something else?
Sorry about the slang. Ill stop that, it makes for to much confusion. I dont have a scope so I cant describe the wave form but according to my multimeter at 100K it has a duty cycle of 52% and at 240K it is up to 75% and thats just off pin3 of the NE555 I was too scared to see what was coming out of my fet. Im not too fussy about the wave form but even I couldnt have that. I would like to keep the duty cycle about 50 but much rather less than more. I would be happy enough just to make some kind of impression at small MHz frequencies.
 

alfacliff

Joined Dec 13, 2013
2,458
thnat would be the quarter wave resonance. the best frequency for your coil if it were used as a tesla coil. if you go higher, you will probably have an insulation breakthrough at the quarterwave point of the frequency you are trying to use.
 

Thread Starter

warp

Joined Jan 20, 2014
18
Hi
ScottWang Thanks How variable is this arrrangement for tuning purposes.

alfacliff Thats interesting. I thought the frequency might have needed to be higher. Using rough figures from memory I had a 1MHz wavelength at about 250 meters then divide by 4 then multiply by the velocity factor in wire of ???. I lost a bit of data when i reloaded windows. I havnt measured the secondary on my xennon trigger coil yet. Perhaps the electrical wave is compressed when coiled due to the magnetic flux in the coil.

The 270 K does seem a little fast for pulse transformer res. Thats shaping up to be good news for me electronically as the frequencies needed might be much lower than I anticipated. Any thoughts welcome.
Thanks
Wil
 
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