TP600 - TPU PULSER

[BEP]

Just a suggestion:

Instead of using the freewheel diode to direct the BEMF past the MOSFET to ground or negative or whatever - connect it so it redirects the BEMF to a counter-wound coil so the energy - as little as there may be - is used to promote the process.

You protect your MOSFET, create a faster fall-time for the coil generating the BEMF and make use of the energy.

Am I on the wrong track ZPE?

[MarkSnoswell]

Hi ZPE

Here are the features I would like in a generic lab pulse controller:

Controller
AD9959 Quad DDS
PIC (or ARM) controller - programm in place capability.
USB control option would be great for people wanting to drive it from their computers.
Stand alone unit like -- http://www.minikits.com.au/sweep.htm
Pulse width control down to 10ns  (the DDS's only output square and sine)

Output board
Opto isolated
Selectable Monostable mode for fastest pulse width for any given mosfet -- perhaps a triggered blocking oscillator design.

There are great benifits in keeping the controller and output stages separate...
I expect that the mosfet and diode selections will vary quite a bit depending on the project -- and will get blown up on occasion! I would be looking at a range of output stages including valve output stage.


The AD9959 is able to potput dar faster and more precisely timed signal then we require. But here are the specs I would anticipate using in the first instance:

30Khz - 1Mhz range
0.1Hz control
Slow sweep capability.
Fast frequency modulation on any output. - for sread band rather then off peak tuning.
Pulse width -- fastest possible by output device.


A note on mosfet rise times -- we arent driving current, we just want voltage spikes. At low current the rise time for the mosfet will be much higher than the full load figure -- so a 4V/ns device may in fact deliver 100+v/ns in the mode we are using it. This is why a triggered monostable output mode would be good -- to get the fastast pulse possible given output device and load.

cheers

mark.

[z_p_e]

Just a suggestion:

Instead of using the freewheel diode to direct the BEMF past the MOSFET to ground or negative or whatever - connect it so it redirects the BEMF to a counter-wound coil so the energy - as little as there may be - is used to promote the process.

You protect your MOSFET, create a faster fall-time for the coil generating the BEMF and make use of the energy.

Am I on the wrong track ZPE?

BEP,

This is an excellent idea and certainly an option for anyone to try.

It's just a question whether it will promote the process or detract from it. Also, shunting the bemf through the original coil (as shown) may be promoting or detracting from the process as well. So one should perhaps try both ways.

At any rate, SOMETHING has to be done with the bemf. It could even be used to charge a capacitor (eventually...these spikes are likely VERY short indeed).

Regards,
Darren

[z_p_e]

Hi Mark.

Thank you for the AD DDS chip info. I'm certainly interested in these, and have been since first seeing them a few months ago.

I would definately like to develop a generator based on one of these chips, but for now, the TP600/900 will do well for many folks, and for many applications.

Perhaps I will work with Peterae in developing one of these DDS generators soon.

Cheers,
Darren

[z_p_e]

in my opinion, the bemf is working against us, meaning it's a pulsed flow in the other direction as the one we want our magnetic field to go.
therefore we need to elimminate it resulting in a magnetic field which goes one way only so we can speed it up fast.

Darren, is there a way to add crystals to the circuit?

Marco.

Marco,

A crystal could be used, but not sure why?

Using a crystal eliminates, or at least severely limits frequency adjustment unless dividers are use. With dividers comes resolution limits too.

Crystals provide stability, but are inherently difficult to "adjust". One solution could be to use a PLL with a crystal reference osc., but again the frequency range and adjustment is limited. Also, this is becoming quite a different animal than the original intent of the circuit. I would sooner go the DDS route than use crystals and PLL's.

So, in the end a DDS unit might be the best. However, don't give up hope for the TP900. It will have a good frequency range and PW adjustment.

Regards,
Darren

PS. I hope to post the TP900 circuit very soon.