Current driver/power amp for solenoid

L

Lyndon

Guest
Hi all,

I have a large solenoid that draws a maximum of 15A at 24V. I want to
be able to vary the current flowing into the solenoid so I can vary
the force it generates. I want this to be driven by DAC that has an
output voltage of 0-5V and minimal sourcing current ~100mA.

I've been thinking about power FET's or a BJT's but I haven't got much
experience in this sort of electronics so I really can't take it any
further. This system is all part of a feedback pedal design that will
provide more resitance the further you push in the pedal. We have a
potentiometer measuring pedal displacement and this goes into a
microcontroller, through a simple transfer function and produces the
output signal which will drive the solenoid. I'm stuck with the type
of current driver or amp I should use. Any advice, or links to
circuits etc., will be of great assistance.

Thanks,
Lyndon.
 
Lyndon wrote:
Hi all,

I have a large solenoid that draws a maximum of 15A at 24V. I want to
be able to vary the current flowing into the solenoid so I can vary
the force it generates. I want this to be driven by DAC that has an
output voltage of 0-5V and minimal sourcing current ~100mA.

I've been thinking about power FET's or a BJT's but I haven't got much
experience in this sort of electronics so I really can't take it any
further. This system is all part of a feedback pedal design that will
provide more resitance the further you push in the pedal. We have a
potentiometer measuring pedal displacement and this goes into a
microcontroller, through a simple transfer function and produces the
output signal which will drive the solenoid. I'm stuck with the type
of current driver or amp I should use. Any advice, or links to
circuits etc., will be of great assistance.

Thanks,
Lyndon.
Click to expand...
The load power is fairly large so the most compact implementation would
be a DAC-to-duty cycle modulation of the voltage across the solenoid.
The most linear and standard approach would use the DAC output as a
comparator threshold for a triangular waveform, comparator output drives
a switching power drive into the solenoid- like so:

Please view in a fixed-width font such as Courier.





10KHz
5- |\
/ \ /\ >-------|-\
/ \ / | >-----> to FET pwr switch
0- +---|+/
| |/
Vdac >---+
threshold
from DAC



5V --
/ \ / \ / \ / \
Vdac -----------------------------------------
threshold \ / \ / \ / \ /
from DAC \/ \ / \/ \/
0V --





comparator on---+ +------+ +-------+ +------+ +-------
output | | | | | | | |
| | | | | | | |
off +-+ +-+ +-+ +-+


Vdac
output duty cycle= ----
5V

SOLENOID
______
------
+----------+--UUUUUU-+-< 24V
| | |
comparator |\ |--+ | |
output >----| >---------|| PWR +--|>|----+
|/ |--+ MOSFET
| N-CH SCHOTTKY
MOSFET | DIODE
DRIVER ---



VDAC
SOLENOID VOLTAGE= DUTY X 24= ---- X 24VDC
5
 
"Lyndon" <webster@netlink.net.au> wrote in message
news:6864d8ba.0404270227.9c2fd1b@posting.google.com...
Hi all,

I have a large solenoid that draws a maximum of 15A at 24V. I want to
be able to vary the current flowing into the solenoid so I can vary
the force it generates. I want this to be driven by DAC that has an
output voltage of 0-5V and minimal sourcing current ~100mA.

I've been thinking about power FET's or a BJT's but I haven't got much
experience in this sort of electronics so I really can't take it any
further. This system is all part of a feedback pedal design that will
provide more resitance the further you push in the pedal. We have a
potentiometer measuring pedal displacement and this goes into a
microcontroller, through a simple transfer function and produces the
output signal which will drive the solenoid. I'm stuck with the type
of current driver or amp I should use. Any advice, or links to
circuits etc., will be of great assistance.

Thanks,
Lyndon.
Click to expand...
Lyndon - have you considered using a PWM motor controller? For a quick test
Dick Smith do a $20, 20A controller which I think is PWMable. Perhaps others
may be able to expand on this approach.

regards
rob
 
Fred Bloggs wrote:

Lyndon wrote:

Hi all,

I have a large solenoid that draws a maximum of 15A at 24V. I want to
be able to vary the current flowing into the solenoid so I can vary
the force it generates. I want this to be driven by DAC that has an
output voltage of 0-5V and minimal sourcing current ~100mA.

I've been thinking about power FET's or a BJT's but I haven't got much
experience in this sort of electronics so I really can't take it any
further. This system is all part of a feedback pedal design that will
provide more resitance the further you push in the pedal. We have a
potentiometer measuring pedal displacement and this goes into a
microcontroller, through a simple transfer function and produces the
output signal which will drive the solenoid. I'm stuck with the type
of current driver or amp I should use. Any advice, or links to
circuits etc., will be of great assistance.

Thanks,
Lyndon.


The load power is fairly large so the most compact implementation would
be a DAC-to-duty cycle modulation of the voltage across the solenoid.
The most linear and standard approach would use the DAC output as a
comparator threshold for a triangular waveform, comparator output drives
a switching power drive into the solenoid- like so:

-- snip --
Click to expand...
Or use a microcontroller with PWM output and chuck the DAC and PWM
generator. You'll still need to drive the gate adequately, but if you
use slow enough PWM that won't be too much of a problem.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
 
Rob wrote...
Lyndon wrote ...

This system is all part of a feedback pedal design that will
provide more resitance the further you push in the pedal. We have
a potentiometer measuring pedal displacement and this goes into a
microcontroller, through a simple transfer function and produces
the output signal which will drive the solenoid. ...

Lyndon - have you considered using a PWM motor controller? For a
quick test Dick Smith do a $20, 20A controller which I think is
PWMable. Perhaps others may be able to expand on this approach.
Click to expand...
I wonder if Lyndon wouldn't be better off with a geared-down motor
i torque mode rather than a solenoid. They have rather poor force
vs. displacement characteristics, whereas motors are excellent.

Thanks,
- Win

whill_at_picovolt-dot-com (use hill_at_rowland-dot-org for now)
 
Winfield Hill wrote:
Rob wrote...

Lyndon wrote ...


This system is all part of a feedback pedal design that will
provide more resitance the further you push in the pedal. We have
a potentiometer measuring pedal displacement and this goes into a
microcontroller, through a simple transfer function and produces
the output signal which will drive the solenoid. ...


Lyndon - have you considered using a PWM motor controller? For a
quick test Dick Smith do a $20, 20A controller which I think is
PWMable. Perhaps others may be able to expand on this approach.


I wonder if Lyndon wouldn't be better off with a geared-down motor
i torque mode rather than a solenoid. They have rather poor force
vs. displacement characteristics, whereas motors are excellent.
Click to expand...
Lyndon, do you really only need pedal resistance to increase linearly
between 15% and 85% of displacement? A compression spring on your pedal
would automatically do the math and provide the proper resistance.

http://www.asraymond.com/spec/faq.asp


--Winston
 
"Winston" <Winston@BigBrother.net> wrote in message
news:-JGdnbKqaJ6NKRPd3czS-w@speakeasy.net...
Winfield Hill wrote:
Rob wrote...

Lyndon wrote ...


This system is all part of a feedback pedal design that will
provide more resitance the further you push in the pedal. We have
a potentiometer measuring pedal displacement and this goes into a
microcontroller, through a simple transfer function and produces
the output signal which will drive the solenoid. ...


Lyndon - have you considered using a PWM motor controller? For a
quick test Dick Smith do a $20, 20A controller which I think is
PWMable. Perhaps others may be able to expand on this approach.


I wonder if Lyndon wouldn't be better off with a geared-down motor
i torque mode rather than a solenoid. They have rather poor force
vs. displacement characteristics, whereas motors are excellent.


Lyndon, do you really only need pedal resistance to increase linearly
between 15% and 85% of displacement? A compression spring on your pedal
would automatically do the math and provide the proper resistance.
Click to expand...
Why do a simple solution when a much more complex one is (not) available ?
 
Lyndon, do you really only need pedal resistance to increase linearly
between 15% and 85% of displacement? A compression spring on your pedal
would automatically do the math and provide the proper resistance.

http://www.asraymond.com/spec/faq.asp


--Winston
Click to expand...
Good point - a company here that makes training simulators uses this method
sometimes in combination with rubber "bumpers".

For accellerators/throttles springs of various compression rates are stacked
on on top of the other to enhance the progressive feel. For brake pedals
rubber bumbers of different diameters / lengths are stacked up to give a
realistic feeling pedal.

This is of course irrelevant if you do need the electronic solution for
other reasons.

rob
 
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