Partial digital PI design

[simeon webber]

Re: Partial digital PI design




if you useing just 5v

hum less than a diode drop




perhaps using a nchannel is best at lower voltages and to use the clamp accross the coil this makes a nice spring shock absorber affair
you can rotary
pulse

also perhaps a transistor {scr } is a better choice of switch than a fet? ???? what do you think

i like the dinky pcb size 80mmm by 20 wow

nice

a nice scr is buz devices i think

these are fast at

[simeon webber]

Re: Partial digital PI design

here is a standard power scr
normaly fount in a good old washing machine tuble dryer etc

high voltage fast to220 but you can use a similar smd device also made by the same company smd version of this link


maybe a good solution offers fast trigger and reset from just one driver transistor

and is easy to reset fast...... offereing huge piv rating so the damper diode may be dispenced with

a nice idea to try and see what sort of pulse decay etc you get
in a sim first ....



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[simeon webber]

Re: Partial digital PI design

hum noise yes this could be a problem

the best way i think you have found is some sort of stop filter... perhaps a little smd choke {ferite block } on each pin

here is a good ferrite site

they will deal direct small orders also

ecorecorp i used them before
they are extreamly high quality and fast service
and will also provide a make to spec.... service for a little cost...

i think you need to separate the supply rails to the fet stage using a choke like a small ferrite beed and a decoupling cap 1nf -47nf at the non fet side of the choke
{for smd} a square sleave on the center pin of the fet aswell {if you still plan to use a fet}

place decopling for its power rail caps etc as close the the uc as possible

and use 220 R res in series with any data i/o a/d d/a drive pins to limit the current {this will reduce also the noise from any pins} noise in micros means they are working hard and not efficiently or as efficienty }
remembering to take into account this for any r/c calculation for pot's for any a/d or d/a used



and use copper foil over the cpu section just trailing i/o to the fet {or drive stages} with a ground plane under side {or above}


using groundplanes on these boards
at HF the rule are VCC VPP TOP coppers
with gnd plane and any drive pins then VSS fill then vss fill the underside also

so all the power runs on a gnd plane


appart from this noise may still be an issue so some sort of low pass of band stop filter {to take out the upper shelf about 15K could be cool also}
but a ferrite will get rid of most of it
it you choose a 1 mhz value then anything above will go....



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[SIMEON WEBBER]

Re: Update




hi robert and all

after some concideration i decided to modify the front end slightly of my own design

here is the modification i carried out on the multi fet tap coil drivers


i also decided auto blanking is better

incase you run over a mains supply and the switching goes funny and it missfires

so i used a low tension transistor {100 v or so is ok here} and a few load resistors and an oa 90 to recify of some bias that can then be tweaked for best blanking level using a meter or scope to set the pot

i also decided that differental ampilifcation can be switched with standard single end
on both taps {per coil} so both types of amps in the one just switched filter and feedback would be realy cool

i invite comments....

and points

dont worry about componet vaules too much just the layout that is of interest here