Searching \ for 'PIC A/C switching' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/power/priswitch.htm?key=switching
Search entire site for: 'PIC A/C switching'.

Truncated match.
PICList Thread
'PIC A/C switching'
1994\12\07@141652 by crocontroller discussion list

flavicon
face
Martin Kirk writes:

          I am using a 16C57 in a project driving nitinol "muscle wires"
  which contract when heated.  I believe that I will use alternating
  current to heat the wires so that I don't have to regulate the all that
  power just for heating wires.

          1)  Would someone suggest an efficient way to switch A/C power using
  PIC outputs.

          2)  I have been looking into using a triac but I have little
  experience with them and I am not sure just how they work.  Does a triac
  switch on and off with it's control or does it stay triggered as long as
  the A/C power is applied?


A triac will switch on when a gate signal is applied and if there's enough
forward current through the device, it will continue to conduct until voltage
across the main terminals drops to zero (ie. there won't be enough holding
current to maintain the conduction state.)

Martin, I'll assume you need to have a continuously variable capability when
driving the wires, so this implies using AC phase control rather than the
zero-crossing circuits which have binary capability only, if you're not going
to get too complicated.

Motorola has a pair of devices, TDA 1085/1185 which provide all the functions
to drive triacs for phase control. The input is a continuously variable
voltage, so you'll have to generate that somehow by the PIC, which, if I'm
correct, doesn't have a DAC. Maybe you could get PIC to generate a PWM signal
which could be averaged with appropriate signal conditioning, shouldn't be
hard, and apply this to the triac controller. Any fuzzy stuff in my message
should be cleared up with a quick look at the data and application sheets.


Anthony Lithgow
Dept. of Electrical & Computer Engg.
Ryerson Polytechnic University
Toronto, Ontario, Canada
email: spam_OUTalithgowTakeThisOuTspameccles.ee.ryerson.ca

1994\12\08@011729 by crocontroller discussion list

flavicon
face
>
>Martin Kirk writes:
>
>           I am using a 16C57 in a project driving nitinol "muscle wires"
>   which contract when heated.  I believe that I will use alternating
>   current to heat the wires so that I don't have to regulate the all that
>   power just for heating wires.
>
>           1)  Would someone suggest an efficient way to switch A/C power using
>   PIC outputs.
>
>           2)  I have been looking into using a triac but I have little
>   experience with them and I am not sure just how they work.  Does a triac
>   switch on and off with it's control or does it stay triggered as long as
>   the A/C power is applied?
>
Using pulse width modulation at the pic output to trigger the triac may result
in beating or heterodyning of the pwm with the A/C. This could result in
unpredictable varying currents through the triac.

To fix this, The PIC's clock could be locked in phase with the A/C, with a
PLL. Or A/C zero crossings sensed with an input port, and a time delay,
based on the desired output current, choosen to trigger the triac (or SCR)
and vary its conduction period.

1994\12\08@011729 by crocontroller discussion list

flavicon
face
>
>Martin Kirk writes:
>
>           I am using a 16C57 in a project driving nitinol "muscle wires"
>   which contract when heated.  I believe that I will use alternating
>   current to heat the wires so that I don't have to regulate the all that
>   power just for heating wires.
>
>           1)  Would someone suggest an efficient way to switch A/C power using
>   PIC outputs.
>
>           2)  I have been looking into using a triac but I have little
>   experience with them and I am not sure just how they work.  Does a triac
>   switch on and off with it's control or does it stay triggered as long as
>   the A/C power is applied?
>
Using pulse width modulation at the pic output to trigger the triac may result
in beating or heterodyning of the pwm with the A/C. This could result in
unpredictable varying currents through the triac.

To fix this, The PIC's clock could be locked in phase with the A/C, with a
PLL. Or A/C zero crossings sensed with an input port, and a time delay,
based on the desired output current, choosen to trigger the triac (or SCR)
and vary its conduction period.

1994\12\08@035017 by crocontroller discussion list

flavicon
face
 >Martin Kirk writes:
 >
 >           I am using a 16C57 in a project driving nitinol "muscle wires"
 >   which contract when heated.  I believe that I will use alternating
 >   current to heat the wires so that I don't have to regulate the all that
 >   power just for heating wires.

Hmm.  Just because you are using DC doesn't mean you have to "regulate all
that power".  Just rectify and filter (perhaps only a little) your
transformer output (you probably need the transformer anyway!), and use
the unregulated DC as the "high side" of your nitinol driver supply.  You
standard high-current drivers, or even ordinary transistors to tie the
other end of the nitinol to "ground" - All the "driver" ICs can handle
voltages above the "supply voltage" on the output pins without problems.

All the messages about messing with AC makes me think this would be a
much easier way to go - once you have DC, you can easilly PWM the driver
pins to get variable amounts of heating...

BillW

1994\12\08@035017 by crocontroller discussion list

flavicon
face
 >Martin Kirk writes:
 >
 >           I am using a 16C57 in a project driving nitinol "muscle wires"
 >   which contract when heated.  I believe that I will use alternating
 >   current to heat the wires so that I don't have to regulate the all that
 >   power just for heating wires.

Hmm.  Just because you are using DC doesn't mean you have to "regulate all
that power".  Just rectify and filter (perhaps only a little) your
transformer output (you probably need the transformer anyway!), and use
the unregulated DC as the "high side" of your nitinol driver supply.  You
standard high-current drivers, or even ordinary transistors to tie the
other end of the nitinol to "ground" - All the "driver" ICs can handle
voltages above the "supply voltage" on the output pins without problems.

All the messages about messing with AC makes me think this would be a
much easier way to go - once you have DC, you can easilly PWM the driver
pins to get variable amounts of heating...

BillW

More... (looser matching)
- Last day of these posts
- In 1994 , 1995 only
- Today
- New search...