Using an LM317 as a galvo amplifer

[steve-o]

Yeah if I could just find a low voltage audio amp chip- they all seem to want +20-40V which is just overkill, especially since the galvos take such a low voltage..

[mixedgas]

Yeah if I could just find a low voltage audio amp chip- they all seem to want +20-40V which is just overkill, especially since the galvos take such a low voltage..

naw, run the galvo in constant current mode, ie use a current sense resistor or look up "howland current pump" see this appnote

http://apex.cirrus.com/en/pubs/appNote/Apex_AN13U_C.pdf

http://apex.cirrus.com/en/pubs/appNote/Apex_AN05U_D.pdf

I have a few the L149s, they work well !

if not a L149
LM10 or LM12 from national? 12 or less.

[mixedgas]

Steve-O

adding damping to the galvo circuit using a power op-amp is as simple as adding 2 resistors, 1 pot and 1 cap and improves settling time performance about 200% ie the galvo slams to a stop instead of ringing!

the 2 Rs derive the ideal AC non inductive feedback and mix it with the DC inductive feedback from the sense resistor, giving you adjustable damping, and its worth the time to do it.

how could you add the damping using a LM317?, you need it!

See attached bmp using ST l149 booster as I build it (missing some bypass caps)

rumors of my inability to draw without those green Beril schematics stencils are totally true!

it comes from here:

http://www.gs-scanners.com/pdfs/manuals/A102_AX200.pdf

Steve

[mixedgas]

Steve-O pm me with a shipping address, I'll send you a couple of L149s

Steve

[steve-o]

Thanx Steve!!
PM sent-- I'll give it a whirl

[steve-o]

"Generally Spinning". Catchy
What is the recommended Vcc/ Vss? Isnt Vcc usually + ?

[mixedgas]

"Generally Spinning". Catchy
What is the recommended Vcc/ Vss? Isnt Vcc usually + ?

Ah my dyslexia crept in. the opamp can probably go with +/- 5 , the ST L149 stage probably wants at least +5 to bias on, but I've never hooked one to a variable bench supply yet. data sheet doesnt spec a minimum voltage, but V sat is 3.5V, so I'm assuming it could go as low as v sat + two diode drops, so ~ +/- 5 to get going. best bandwidth is probably gonna be at somewhat higher voltage, but one never knows till one tries.

Steve

[steve-o]

Well i guess I'm gonna try- I did the layout today, and found the (2) L149V's you sent me a while back (from Mouser) --THANX!! The chip is obsolete tho, so I guess I'd better stock up in case of blow-outs .. I've been known to have a few .. hehe....
Gonna start breadboarding tomorrow.. or , actually proto-boarding ..
--unless I get caught-- I'm hoping management doesnt know the diff between eletronic repair and electronic experimentation and building.. I think it all looks like little "bugs" to them ...

[mixedgas]

There is a L262 or something higher power idnetical replacement.

Steve

[steve-o]

Well I decided to go with the LM1876TF isolated package dual amplifier with spike protection and temp shutoff just 'cause I like new stuff to xprment and play with plus the amp is real small, barely bigger than a G124 which saves a lot of space.
picys -