Question for advanced guys !

Then as load it can almost be disregarded, but at least we know =) You need a 555 timer circuit that can supply variable duty cycle and frequency in your range (should be easy) you'll want variable duty cycle and frequency simply because the variable part is not that hard to implement and gives you more control, to feed two power transistors in an npn/pnp totem pole configuration from the 300V supply. As far as putting that together goes it shouldn't be too hard, but unfortunately I have big problem with 'vested interest' in projects, as it's not something I want to do it's pretty much impossible for me to actually apply the effort to write the circuit schematic for it. I have a hard enough time trying to motivate myself to get my own projects done => Hopefully other users here will be able to provide more direction now that your actual specifications are known.

Okay. Thanks for your help Sceadwian. But it would be nice if somebody can help me a little with the totem pole configuration as I don't know anything about that.

No matter what thanks for you time Sceadwian. Helped me a lot.

I looked at a few pages on the totem pole and I don't understand why I would need this in my project....In my view, just one transistor that collector-emitter is connected to a 300 V source and it's base-emitter connected to the 555 timer would be good enough....tell me if I'm wrong

You could use a single transistor, but you'd have to use a pulldown resistor to allow the device to discharge when the transistor was turned off. That plate is going to have some degree of capactiance so it will still carry a voltage even after the power is disconnected unless it's allowed to bleed off to ground somewhere. A totempole driver would eliminate this and give you closer to a true square wave as when the lower portion of the totem pole is activated it will have a very low impedance path to ground.

when you say totem pole, do u mean the right part of this circuit, or the whole circuit ?

Digital Logic Gates Part-V

look at the before last topic below "totem pole output"

File:7400 Circuit.svg - Wikipedia, the free encyclopedia

Everything from V2 to the right.
I'll hazard a guess that a single transistor could do it with a pull down resistor, it depends mostly on the actual capacitance of your load, which should be pretty low, the totem pole drive is more flexible if the load is unknown though as it will be able to both source and sink current not just source it. With a single transistor the pull down resistor is relied upon to discharge the capacitance to ground when the transistor is turned off, this makes the R and C values into a little timer so there will be a curve rather than a straight cliff for the discharge.

I have some 2N3055 power transistor. Do you think these could work within the circuit ?

And for the resistors, should I use the values that are provided by the scheme u gave me ? Which means R2 = 1 Megohms, R3 = 130 ohms, R4 = 1 kilo ohms

Again I'm confused, I never posted any schematics.

lol u just posted a link to a circuit to tell me what is a totem pole.....

It's not my schematic, it's just a generic one from Wikipedia. What confused me was your notation. R2 isn't 1meg, it's 1.6k. The k in a resistor value is always the decimal place. Not sure if it will work for you I didn't analyze the circuit, I'm guessing a few component values are going to change. You should work this out in a simulator or on paper.

I know it comes from wikipedia....it is written everywhere on the page. But I tought maybe the resistors there are calculated in a certain proportion that is not dependent on the voltage load. If you can suggest me a page or something where they explain what is the role of the resistors there, I could study what calculations I have to do to make it work.

Thank you
khelz

Here's the circuit that I'm thinking :

That's not gonna work for several reasons, I'm playing around in my simulator now, I'll respond shortly. Sorry for the broken/distracted posts I make, I'm not used to headlining a thread, other users usually chime in at some point and by now someone has generally taken over helping with the schematic so I'm not used to it =)

One big thing is can you describe in much more detail what this is actually going to be hooked up to? For testing using a scope is fine, but figuring out the actual load itself specifically it's resistance and capacitance to ground is getting pretty important as it will effect the performance of the circuit not to mention weather or not it's actually physically possible.

This is a rough schematic I worked out simulating and playing with values, nothing blows up, it's pretty safe, resistors are 1/2 watt. But the load itself determines the rest. The components are really just 'stand ins' for what you intend to actually use as far as the transistors and diode goes.

It is gonna be hook up to an electrode of 25 mm by 2 mm of gold. Thickness is about 1 mm.

Sceadwian said:

That's not gonna work for several reasons, I'm playing around in my simulator now, I'll respond shortly. Sorry for the broken/distracted posts I make, I'm not used to headlining a thread, other users usually chime in at some point and by now someone has generally taken over helping with the schematic so I'm not used to it =)

One big thing is can you describe in much more detail what this is actually going to be hooked up to? For testing using a scope is fine, but figuring out the actual load itself specifically it's resistance and capacitance to ground is getting pretty important as it will effect the performance of the circuit not to mention weather or not it's actually physically possible.

Click to expand...

That doesn't describe the environment it's actually in though, what's near it, is it metallic, liquid, otherwise conductive etc.. You'll have two main power draws, conduction to ground, and capacitance to ground. You have to name every other electrically interactive substances within at least a few inches of it which is pretty much EVERYTHING. Is the electrode submerged in a liquid, etc.. etc.. There is nearly an infinite number of permutations you could put that electrode size through and come up with a vast different number of situations, and the component values you chose for that particular type of circuit will require you to know the ACTUALLY load you're applying it to if you want the full 300 volts.

I simply have no idea what to even guess randomly at as I'm not a biological engineer with an EE degree => I'm guessing very low resistance, maybe 1meg and moderate capacitance, perhaps 1000p but I'm only guessing. If that's the case connected to 300V the circuit I listed will provide approximatly 270 volts to the load. If the capacitance is lower it'll be higher, if the capacitance is higher it'll be lower. If the resistance is higher the applied voltage will be higher and lower if lower.

Okay I get it. It's as complicated as I thought. But it gives me the idea. Do the circuit is well connected though ?

The above circuit should work fine, remember the two points. One, you will not get the voltage you want at the load if it has a higher resistance to ground than about 100k, capacitance isn't going to be too much of an issue because the strip isn't large enough to make it one. Two, the input from the 555 is inverted, whenever the output of the 555 is low the circuit will output the high voltage and vice versa. This just requires you to change your values for your 555 circuit, you should find plenty of calculators out there on the net to help you with that.

ALLRIGHT ! thanks for all sceadwian !

Peace and joy !