Thanks for posting the link to a data sheet for your valve. That helps us understand much better what you need.
I hope you have already solved your problem, but here are some thoughts that might still be of use.
As the original post suggested, there is no need for a complex drive circuit. Just something to boost the current of the 0 to +5V DAC output. Some sort of "audio" power amplifier, class D or otherwise, might work, but is not necessary.
This valve has a coil that accepts up to 5VDC. The current through the coil controls the size of an orifice for gas flow through the valve.
There is no flow at zero current and the maximum flow is reached somewhere short of 5V. The flow varies continuously between zero and maximum as the current is increased.
The drive for the coil can be unipolar. Reversing the direction of the current through the coil will not change the results. So it might be useful to think of the required drive to the coil being a varying DC voltage, rather than an AC waveform.
As already mentioned, some source of DC power will be required to provide the actual current for the coil. An independent DC power supply may be the easiest. A "wall wart" type supply could be used. If a PC type of computer is being used to run the DAQ system, it may be possible to tap power from it. A disc drive power connector is often an easy place to find 5 and 12 volts. A USB jack might possibly supply suitable power, particularly if slightly less that 5.0V can open your valve far enough.
I believe that the 5V rated Clippard valve can be driven satisfactorily from a 5V rail using a power FET, or even a bipolar transistor. A low voltage op-amp with rail to rail inputs can be used with the power transistor to make a voltage follower that will follow essentially all the way to the supply rail.
A transistor such as this one
http://www.digikey.com/product-deta...80P03P4L04AKSA1/IPP80P03P4L04AKSA1-ND/2338161 is complete overkill, but why not, at $1.63 each? The data sheet shows 5V gate drive typically producing 0.003 ohm RDS.
It would not be too difficult to devise a transconductance coil driver circuit that would control the coil current rather than the voltage.
If a PWM output is available from the DAQ system, that could be used instead of a linear DAC output. A 5V logic output can easily drive a power transistor directly.
Making one of these valves do what you want in a system can be a challenge, beyond just driving the coil.
There appear to be no actual specifications for flow versus electrical input, beyond the endpoints falling somewhere between 0 and 370mA. The system design may need to take this into account!
Clippard provide a "typical performance" graph for some other valve in this series that may provide some insight into the valve's behavior.
Scroll down for the graph on this page:
http://www.clippard.com/cms/wiki/evp-selection-tips
This graph shows fair linearity between a moderate flow and near maximum flow. The graph shows that the flow does not exceed zero until the current is about 25% of the maximum. The graph shows significant hysteresis.
Clippard may be able to provide some help, beyond what is seen in their catalog. A nice application note could be very useful reading.
Ted
