# Amplifying current in a sine wave

Discussion in 'General Electronics Discussion' started by macabnv, Sep 7, 2016.

1. ### macabnv

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0
Sep 2, 2016
Hi,

I am looking for a way to amplify the current in my sinusoidal wave of voltage range 0- 5V and a current range of 5mA to 15mA. I require a sine wave of 370mA to open a EVP proportional valve according to the sine wave. I have satisfied the voltage requirement, but the current is too low to open the valve. Is there any way to amplify the current?

2. ### AnalogKid

2,497
718
Jun 10, 2015
Can you post a datasheet for the valve, since your question is not clear? What frequency or frequency range? Is the AC waveform symmetrical about ground? What is EVP?

ak

3. ### macabnv

5
0
Sep 2, 2016
Hi

The data sheet can be accessed here: http://www.clippard.com/part/EV-P-05-25A0

The sine wave is being generated from labview and is output through a DAQ. Since the DAQ cannot output more than 15mA, I need to amplify the current. The sinewave have a frequency of 1 Hz. I also wanted to vary the frequency.

4. ### CDRIVEHauling 10' pipe on a Trek Shift3

4,960
651
May 8, 2012
You can use BJTs to do this but you'll need a Vcc > 5V.

Chris

5. ### AnalogKid

2,497
718
Jun 10, 2015
Since I already asked what the frequency range is, is there a reason you won't tell us?

So, you want a small amplifier circuit that can produce a peak current of 0.37 A at an output voltage of 5.0 V. The amplifier circuit has unity gain because the input signal varies between 0 V and +5 V. You have one power supply that can supply at least 400 mA at some voltage greater than +5.0 V. Correct?

ak

6. ### macabnv

5
0
Sep 2, 2016
@CDRIVE I have a DC output of 5V from one Analog out of DAQ to power the circuit and another sine wave,which id the input, out of another analog out of voltage 0 - 5V and current range of 5 mA to 15 mA. Using a BJT, I would have to supply more than 5V. So I was wondering if there would be other options.

@AnalogKid I apologize for missing out the question on frequency range. I would like to have a frequency range anywhere between 0.5 Hz to 2 Hz. I do not have an external power supply other than the DC output voltage of 5V supply from the analog pin 0 of the DAQ which also output the sinewave from the analog pin 1.

7. ### BobK

7,682
1,688
Jan 5, 2010
Something must be powering the DAC. They do not produce a voltage by themselves.

Bob

Arouse1973 likes this.
8. ### CDRIVEHauling 10' pipe on a Trek Shift3

4,960
651
May 8, 2012
I said that you'll need a Vcc >5V because even using an OpAmp with Rail To Rail capability it won't actually = 0 to +5V or (if a split supply is used) -5V to +5V . You need some overhead to do this and still maintain linearity.

Chris

9. ### BobK

7,682
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Jan 5, 2010
A class D amplifier can get pretty close to 5V peak with 5V power.

Bob

10. ### CDRIVEHauling 10' pipe on a Trek Shift3

4,960
651
May 8, 2012
Yes but his signal is sinusoidal.

Chris

5,165
1,087
Dec 18, 2013
Don't they use class D for audio?
Cheers

12. ### BobK

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Jan 5, 2010
Yes. A class D amplifier can handle sinusoidal signals. If the DAC output is 0-5V he most likely has a 2.5V peak signal with 2.5V DC offset, well within the range of a class D amp running off 5V, assuming you remove the DC offset. In fact, if I am right about that, a bridged class AB amp could do it.

Bob

5,165
1,087
Dec 18, 2013
Yes it could but I guess not as efficient

14. ### BobK

7,682
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Jan 5, 2010
Yes, now that class D amp modules are so cheap, they are the way to go.

Bob

Arouse1973 likes this.
15. ### CDRIVEHauling 10' pipe on a Trek Shift3

4,960
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May 8, 2012
Admittedly I've never worked with a class D amplifier but I thought they needed to be heavily filtered like this...
https://en.wikipedia.org/wiki/Class-D_amplifier

If this description is accurate filtering the ultra low frequencies the OP desires (.5Hz - 1Hz) won't be easy using LC filtering as described. That said I don't know squat about class D amps so I'll take your word for it.

Chris

16. ### BobK

7,682
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Jan 5, 2010
It is easy to filter to pass sub sonic frequencies. You are trying to filter out the switching frequency, typically 100KHz. Say the the upper end of the passband is 1Hz, this is far simpler than if you had to pass 20KHz.

For example, if the 3dB point is 2Hz, 100KHz will be down by 94dB using a 6dB / octave filter.

Bob

17. ### CDRIVEHauling 10' pipe on a Trek Shift3

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May 8, 2012
As I stated "I've never worked with them". Apparently I don't fully comprehend the PWM theory of operation involved with it. ... I'll read more!

Chris

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18. ### TedA

156
16
Sep 26, 2011
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.

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

CDRIVE likes this.
19. ### CDRIVEHauling 10' pipe on a Trek Shift3

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May 8, 2012
TedA made some very insightful observations. I'm surprised macabnv hasn't responded.

Chris