Noiseless power supply for SD2200V2?

[bklein]

Bill,
Take a look at the TI TPS54229E. It is a 2A switching regulator that runs at 650khz and can accept up to 18Vin. I just characterized one for our use at work. Man it has great transient response, efficiency, and low noise. Maybe 2A isn't enough - I don't know what these things draw as mine doesn't work! It has an enable pin you could use to shut it down whenever you want. A linear regulator is probably not appropriate due to the heat it generates and inefficiency. A lot of guys talk down switchers but they are referring back to their history with much lower frequency parts.

Barry

[Mechanic]

Hi Barry,

The problem with using the enable pin is it normally takes a long time to restart when it is re-enabled. In this datasheet, according to the graph on page 10, start up waveform, it is 150ms, but earlier on, there is an equation given to figure out the cap required for the desired start up time. For the graph I would assume this would be the minimum startup, adding extra C would make it take longer. Please check this for yourself though....

The other problem with this one is it has its own clock. The switchmode must be synchronized to a clock source inside the detector, so it does its switching at exactly the same times within the cycle.
The current one in the sd series is synct to a clock source, but it is on all of the time.

So the requirement is that the switchmode is synchronized to 2 sources, 1. the switching frequency from somewhere in the detector, and 2. the tx pulses so the power supply is on only during tx. With SM regs that are synchronizable, if you don't send a clock signal for a certain amount of time it goes into shutdown, then we have to wait for the restart time, which is often over a ms. The complete cycle time of the detector is around 1ms(depending on what timings are used).

I agree that the linear regulator will be an inefficient way to drop the voltage, and I do remember attaching a heatsink and fan to mine I thought I had just made a crappy cct, was one of my first drawn up with the good old cct marker pens! All I have to say is presensitised are the best! Love being able to make fine tracks with small spacings!

The other way to go about it is to put some 2 or 3A diodes in series with the battery's to drop the voltage down to 7.8 or so.

Cheers Mick

[mario]

What's the advantage of running at 8v as opposed to 7.4? Is it worth the risk frying your board? No public schemas exist for this model, so a repair may be tricky using the available schemas for the older models.

Also, to answer one of your original questions, some changes between the 2200v2 and 2200s include a partially reworked front end (the V2s have the AD797s). The V2s also have a fixed toroid coil, making them slightly quiter. Steve Herschback from akmining wrote a good comparisons overview of the different models here: http://www.akmining.com/forums/showt...-and-GP-models

Would you mind posting a photo of your model's circuit board? I would enjoy confirming some obvious changes from the 2100s.

Also, from my understanding, the SD series detectors consume slightly under an amp/hour.

[bklein]

I am not really in support of toggling the converter enable at TX for efficiency/noise reduction concept. Basically if you step back, this is what it does all the time at 640Khz! It is a very efficient converter - something like mid to upper 80% at high currents. As far as noise goes - I'm not kidding - this thing is quiet. Even if you were to toggle it off and on at TX rates, you have a high voltage toggle signal now - that you didn't have before - running around.
If you just want something to adapt higher voltage DC inputs to the detector, this should work well. Perhaps you'd like a longer soft start - I'm not sure if this is an option on this part. I don't see any overshoot of output voltage at turn on as I've been testing (with CC and CR electronic load as well as 600uS very fast edge pulse load).
After speaking with the Minelab tech about lipoly and turn-on issues I think a soft start circuit is needed. This could use this part or something else - like maybe one of the power switch IC's used for hot plug RAID systems. That and perhaps a large TVS across the input to kill transients and I'd say you're done. I wouldn't think that having a higher input voltage is magical and going to give the detector more depth. Naw, Minelab would have designed it that way in the first place.

Hi Barry,

The problem with using the enable pin is it normally takes a long time to restart when it is re-enabled. In this datasheet, according to the graph on page 10, start up waveform, it is 150ms, but earlier on, there is an equation given to figure out the cap required for the desired start up time. For the graph I would assume this would be the minimum startup, adding extra C would make it take longer. Please check this for yourself though....

The other problem with this one is it has its own clock. The switchmode must be synchronized to a clock source inside the detector, so it does its switching at exactly the same times within the cycle.
The current one in the sd series is synct to a clock source, but it is on all of the time.

So the requirement is that the switchmode is synchronized to 2 sources, 1. the switching frequency from somewhere in the detector, and 2. the tx pulses so the power supply is on only during tx. With SM regs that are synchronizable, if you don't send a clock signal for a certain amount of time it goes into shutdown, then we have to wait for the restart time, which is often over a ms. The complete cycle time of the detector is around 1ms(depending on what timings are used).

I agree that the linear regulator will be an inefficient way to drop the voltage, and I do remember attaching a heatsink and fan to mine I thought I had just made a crappy cct, was one of my first drawn up with the good old cct marker pens! All I have to say is presensitised are the best! Love being able to make fine tracks with small spacings!

The other way to go about it is to put some 2 or 3A diodes in series with the battery's to drop the voltage down to 7.8 or so.

Cheers Mick

[bklein]

The TI converter has a 1.5ms soft-start time.

[BillNEWAST]

mario,
I have little interest in the GP Extreme, Most of the people who do the Mods on these detectors say that the GP series is vastly different than the SD series. So if the two are kept on the Same thread then people who come here will not know which machine is being discussed and become confused, espesialy those who are new.

I thought that your thread on making an automatic ground balance(AGB) mod for the 2000 and 2100 would be a natural for this one on the SD2200D/V2, then a comparison could be made to the two machines. I personally don't think that the AGB on a series before the 2200 can be done without having a new pcb made that will be esentionally a 2200 board either a D or V2. I think that the PCB's for the D n V2 are vastly different.

BUT without having a schema for the two to compare there isn't much hope.

bklien,
the difference in the IR numbers is the first Character is a 1 not an I, it took me a couple of hours seaching and chopping the search words in google back to Just the Numbers and I finally found the correct Part and realized what the problem was. I apologize for not giving you a heads up on that eailer.


mario, MY SD2200V2 is in perfect working order and I hesitate to pull it apart, mainly because I have two other projects on the bench now and can only get to them intermittently. One is a 1940's A-10A AirCraft Bubble Sextant and the other is a milligram gold balance scale i'm building to measure down to 0.006gr/0.4mm and I just started a Microgram electronic scale.

BUT, I will pull it apart on the Kitchen Table early next week(see how dedicated I am) and probably have to clean up after supper and do the dishes, yada, yada, take Pic's with the 14meg pixel nikon and with the USB Microscope. This may help folks have a reference to start with. I am not going to Take the Paint off except to replace the input power Fet. as they came in yesterday. btw I have 20 and only need 2 so have 18 for sale for $5 for 2 including priorty postage to lower 48 USA. or you can buy them here;
http://us.element14.com/international-rectifier/irlml0060trpbf/n-channel-mosfet-60v-2-7a-sot-23/dp/60R6446?Ntt=60r6446

I'm not sure how Carl will feel about Posting the Actual Pics here so may have to post a link to the offsite source.

CARL???

Have to run now guys I have to get ready for the movie production meeting/rehursal on sunday I'm helping on.

More later
Sincerly
Bill Adams

[bklein]

Bill,
You have my permission to edit out my participation in this thread to whatever degree you prefer. Just tell Carl what to do and do it. I knew the risk of slight deviation from the topic but usually we learn something from ongoing discussions that sometimes is not directly related to the first post. I have my goals and you have yours and you posted first so do whatever you want with the thread history.

Barry

[BillNEWAST]

Barry,
I agree with you and mechanic and mario that the speed of the switching devices aren't fast enough to NOT enter new Noise to the CCT. I just heard about that and wanted to see what others thought of it.

I don't want to delete your posts, or anyothers for that matter. All I was suggesting was to try to Stay on Topic. I and I am sure everyone has read threads that got hijacked by off topic posters and then others who had something to say just didn't because they had to jump from page to page to refer and remember what was said. I know I have problems just trying to keep the last few posts in my little PEA Brain long enough to respond some what intellegently. That doesn't include the posts I make and then for some reason I lose the post and just skip posting or give a short stupid post because I'm discourged. When I have more time I'll do some searchs on the forum and archives to try to get the questions I asked originally answered. But it'll take me a long time to finish. I just bought some German CCT software that was supposed to let me take a picture/bitmap and bring it in and then trace the CCT to a different layer and do the same with the parts layout mask side.
OH Well, it didn't work and I don't have time to figure it out, so just Blew another $60 for NADA.

Tired so signing off for now.
Sincerly
Bill Adams

[mario]

Well Bill, I hate to disappoint you but your detector has some vital functions more in common with the GP Extreme than the older SD models. Like the GP Extreme, the SD2200D handles timing functions (for ground balancing) through a microprocessor. The addition of the processor simplifies the circuit, but makes it much more tricky to modify, just like the GP Extreme.

Also, to clear up some confusion regarding my auto ground balancing work, no hard core modification work will be required to the circuit board for auto ground balancing.

To get an idea of how I will get ground balancing accomplished, you can view the video here (http://www.youtube.com/watch?v=16t7p6tNEuE). Last minute programming difficulties have set me back, which is why I have decided to devote more time to the project. Here's a photo of my working prototype connected to the board(https://lh6.googleusercontent.com/-1...ft_avr_dss.JPG) . No, it's not pretty, and it's getting more messy as I make revisions to the hardware. I'm now considering designing a second board to accommodate the entire circuit. However, if I go this route, I would like to use a different micro because I have already maxed out the resources of the my current micro (I have used up all 28 pins, 80% of memory, 90% of the eeprom, and all timers). Unfortunately, if I do this, it will set the entire project back by several months because the micro I intend to use (an ARM Cortex) has very little in common with my atmega...decisions...decisions...

[Mechanic]

Hi Guys,

As far as posting pictures, check this thread,
http://www.geotech1.com/forums/showthread.php?t=17106 page 3 in particular.

Anyway, as for this topic, I keep getting confused!
Basically Bill wants a way to step down a higher voltage source to 7.6 or so volts from a higher voltage.
Woody talked about replacing a fet so the detector would work at 8v input, and also mentioned about replacing the internal power supply(-5 5+) with a module power supply and synchronizing it to only turn on during tx, to reduce rx noise. Now this is all good and well, but as I said earlier, the supply needs to sync to 2 sources, an internal clock source for the switching frequency, and be set to turn off during rx and turn back on during tx. The problem with the commercially available chips is if they are synchronizable to an external clock source, their turn on time is far too slow to also sync to the tx. As far as I can tell, the only way to achieve this is with a discreet switchmode controller. A few years ago I made a small mod that did turn off the power supply during rx but it did not work properly as there were other things that needed to be done as well to make the voltage stable. Anyway, I don't think this is the direction Bill wants to go. All he really wants is to utilize a higher voltage source and step it down before entering the detector?? Am I correct?!

Cheers Mick

[IBGold]

Bill, if all you are wanting to do is use a higher voltage battery do as I do I run a variety of batteries 12V gel cells and Li-Po's and use a simple Voltage regulator whose output is variable between 6.8 volts to 8.4 volts and run both my SD2000M and my GP3500M I run the 2000 at 8,4V max and run the 3500 on 7.2v but in your case you could fix the out put at 7.2 volts the circuit is available as a **** Smith kit but I upgrade the regulator to a LM350K and have had no problems at all over many years of use I have even done a condensed circuit board layout if you are up to making your own board.

Regards, Ian.

[IBGold]

The **** in above post are part of a company name here in Australia not a rude word!!

Regards, Ian.

[BillNEWAST]

I only asked about the pic's because some in the posts on the thread you refered to Mechanic were unreadable (had + -) instead of pics.

mario, you aren't disapointing me by sharing the Similarites of the 22 and Extrem. That is the kind of info that is needed on this thread, I haven't read anywhere of this similarity, and now its good to know.

mechanic, having a higher source is what would be nice, But it seems that the only way to get from a higher source to a lower input voltage is to use some type of Switching CCT. And it seems to be the general consencious that will Enter some Switch Noise into the RX CCT however slight, but noise none the less. Am I correct in thinking along these lines. now the only way I know of droping Vdc from higher to lower is to use diodes that drop 1.7vdc accross their junctions, thus eliminating the noise, BUT having to Dissapate the Power somehow. so thats the trade off for the No Noise, BUT you have defeted your purpose by loosing AmpHours on your Battery. So back to adding another one in Parralel to get the Detecting Time extended. Right????

IBGold, maybe you could PM me the particulars on the regulator. I promise NOT to be offended by the Name. I'm 61 and heard most all that could be heard like that.

As promised here are the pic's of the SD2200V2. They are in the next posts, because I don't know how long it will take to UPLoad each one as they are from my 14Mg pixel camera. So will try one and see what happens!

[BillNEWAST]

SD2200V2 CCT
Power Supply is comming in from Upper Right Side.
TX and RX are on the Upper Left Side.

Well guys I looked at the upload window and will have to either upload to my Photo Bucket acct. or I'll have to seriously down grade the resolution to post them.
Heres what I got, If anybody could explain or tell me where to go to learn to post larger better resolution pic's PLEASE Shout Out!!!

[Mechanic]

Hi Bill,

Check your pm's...

Cheers Mick