Circuit setups for pulse motors

[hoptoad]

... and I don't quite get the joke.... but I'm willing to laugh at my own expense   
The knowlege I have gained here has been invaluable in pursing my goal - thanks!
CH

I assure you capthook, the joke was not meant to be at your expense.....Just musing on my own behalf, from my own experience.....   
Cheers

[capthook]

oh - I get it now! 

Funny the myriad ways the written word can be interpreted vs. the spoken...

Thanks again gyulasun for the excellent links.

The LT1933 - 600mA, 500kHz Step-Down Switching Regulator in SOT-23 appears to be exactly what I need ( http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1042,C1032,C1064,P7531#descriptionSection )

And Linear Technology has a cool/free Spice program for download - a first for me!

Anyhoo - the circuit below is the additional components required to implement the LT1933.  Nothings easy!  Guess it's not too bad - but this:

http://www.dimensionengineering.com/DE-SWADJ.htm

seems to offer almost the same thing - all in one package.  I need easy for now.....

Recommendations wanted:

LT1933 - cheap - exactly what I need? (but I have to get/assemble/spec the other parts)
DE-SWADJ:  expensive, maybe not exactly what I need - but EASY?
Option 3:  use another method than a DC/DC switched converter

(I guess if I don't want to be a wuss - and if it IS exactly what I need - option 1: unless option 3 applies)

And if you don't have a SPICE program get the LTSPICE free @:

http://www.linear.com/designtools/software/switchercad.jsp

TIA

CH

[gyulasun]

Hi CH,

Your radio shack LT317 adjustable voltage regulator is an excellent regulator but not for you present application IMHO, for it is a linear regulator.

The LT 1933 is a good choice but it needs a minimum input voltage of 4.5V and you set the lower limit to 2V for your 4700uF cap, hence I suggested LT3502 that needs 3V minimum as the best trade off. It is up to you to decide.

Re: on http://www.dimensionengineering.com/DE-SWADJ.htm  This seems also good (maybe its 1A output current capability is a bit overkill for your needs)  but nevertheless it is ready made and no need any tinkering from you to build it,  for 15 bucks of course     The only info I did not find in its datasheet is its quiescent current which is about 1.5mA for both LT type circuits. (quiescent current gives info how much current is needed to by the inside  circuits of the regulator when there is no load at its output)

Both LT1933 and 3502 circuits are adjustable and a formula is included in their data sheet for calculating the value of R1 for your desired output voltage when the recommanded R2=10kOhm. A 22kOhm trimmer or normal potmeter connected as a two pole variable resistor is good for you in both cases to adjust the 1.5V output voltage in advance you need. Of course a calculated fix value resistor is just as good if you need no variable output voltage.

There is this sentence you wrote today I do not understand, would you clarify?
And I guess then a small resistor of (x? ohms) to drop output from 1.65 watts to .5 watts?  Or one that will output .5 watts?    Where and why you would use any resistor for dissipating power? This is why switchmode supplies are used, aren't they?

So all in all: I recommend your option 1 with either one of the LT chips (additional component cost will be under $10 I guess. Have a look round for component costs first, probably out of them the dearest will be the coil for the LT circuits.

rgds,  Gyula

[capthook]

The LT 1933 is a good choice but it needs a minimum input voltage of 4.5V and you set the lower limit to 2V for your 4700uF cap, hence I suggested LT3502 that needs 3V minimum as the best trade off. It is up to you to decide.

Both LT1933 and 3502 circuits are adjustable and a formula is included in their data sheet for calculating the value of R1 for your desired output voltage when the recommended R2=10kOhm. A 22kOhm trimmer or normal potmeter connected as a two pole variable resistor is good for you in both cases to adjust the 1.5V output voltage in advance you need. Of course a calculated fix value resistor is just as good if you need no variable output voltage.

There is this sentence you wrote today I do not understand, would you clarify?
And I guess then a small resistor of (x? ohms) to drop output from 1.65 watts to .5 watts?  Or one that will output .5 watts?    Where and why you would use any resistor for dissipating power? This is why switchmode supplies are used, aren't they?

So all in all: I recommend your option 1 with either one of the LT chips (additional component cost will be under $10 I guess. Have a look round for component costs first, probably out of them the dearest will be the coil for the LT circuits.

rgds,  Gyula

Many, many thanks for your detailed, informative posts!!  A few days ago - I was completely lost as how to accomplish this need.  Thanks to you - I have a decent grasp of it now!

Minimum voltage on the cap can be raised by upsizing my capacitor giving me greater chip options - as well as giving me more storage. (Probably going with 1000,000 uF vs. 4700 uF)

The LT chips will offer ~10% more efficiency over the DE-SWADJ, so I'm going with the LT (haven't picked the exact model yet)

Thanks for the R1 resistor info - that was another aspect I was concerned with figuring.

The clarification of the additional power dissipating resistor component was that I wasn't sure I could fine tune any of the chips enough to get the exact power wanted.  Now that I know a little more - the task can be accomplished without this additional wasteful component.

Once again - many, many thanks!!!  I slept well last night - having spent a few previous night tossing and turning lost in thoughts of how to approach this task!   

CH

[capthook]

I have decided on this step-down switch mode buck converter from LT.
(last week I didn't even know what that last sentence meant!    Hey hoptoad - THAT is satisfaction earned by overcoming a frustrating obstacle   )

It's an IC so saves the trouble of assembling the other components.  And it is EXACTLY what I need - for $7.

SCORE!!  Thanks Gyula!

LTM8020 - 200mA, 36V DC/DC ?Module

http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1424,P39256