PWM control through USB 6008/09

[nikhilvastarey]

Hi Lynn

Ok. If I have understood this right, is this what you are talkin about?

I have attached a file. please check it. 

Regards

Nikhil

Many more Kudos to give 🙂 

[nikhilvastarey]

t06afre

I actually will need an amplification of 2.4.

will tat circuit give me such an amplification?

and a current varying from 140mA to 300mA or so.

Regards

Nikhil

Many more Kudos to give 🙂 

[nikhilvastarey]

somebody reply please

[nikhilvastarey]

t06afre

Let me give more info.

As you all know, the USB 6008 has an output analog pin of 0-5V. The pump runs @12VDC and current varies the pressure.

The current specs (according to the data sheet ) varies from 320mA to 350mA.

Practical connections across the Variable voltage source indicates current varying from 140mA to 300mA.

Please refer the data sheet for more info.

http://www.hargravesfluidics.com/pdf/BTC-IIS/ST_D771-11_C.1F28G1.1F28N1.B12VDC_Rev_A.pdf

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[Coq_Rouge]

Hi my timezone is GMT+1 so I has been in dreamland for some time now

Well some quick answers

>C7 and C3 are variable capacitance

Nope they are standard polarized capasitors. The best thing to use is tantalum capacitors. They should be rated to 25V

> And also, what must be the gain of Q1?

A opamp may deliver max 20mA . Let us say we want to draw max 10 mA, so the Q1 need to have a b or Hfe equal to (max motor currunt/10mA) at least. Q1 boost only current the OPamp is the voltage booster.

Here is some stuff on wiki about OPamps

http://en.wikipedia.org/wiki/Operational_amplifier_applications

http://en.wikipedia.org/wiki/Operational_amplifier

Well back to work, the rest must wait

[nikhilvastarey]

Hey, thanks for your reply.

I need 350mA and maintain 12VDC. which means the resistance needs to be very low. can that happen with the darlington emitter?

PS: haha, m sorry about that mate.

Regards

Nikhil

Many more Kudos to give 🙂 

[Coq_Rouge]

> need 350mA and maintain 12VDC. which means the resistance needs to be very low. can that happen with the darlington emitter

Yes I will say so. Your darlington transistor should be rated for 1 Ampere. I am sure your school has something like it on the lab

[johnsold]

Nikhil,

The circuit you posted is the typical arrangement of an LM317 as a voltage regulator.  However, at least 5 mA needs to flow through the resistors at the point you marked as the LM317 connection point.  That is the maximum a the 6008 can produce.  The voltage at that point will be 1.25 volts less than the output voltage.  Since the 6008 can produce a maximum of 5 volts this would not drive the pump to full speed.

The attached circuit uses an op amp to amplify the USB6008 output to 10 V making the motor voltage about 11 volts.  By changing R2 to 120 kΩ or 150 kΩ you would get more gain and higher voltages.  R5 assures that the LM317 output goes to a low value if the USB6008 is not connected.  R3 provides a minimum load to keep the LM317 happy if the motor is not connected.  The diode protects the electronics from energy stored in the inductance of the motor.

Lynn 

[nikhilvastarey]

hey...thanks a lot. lets hope it drives my circuit. shall set it up as soon as I get my "ordered" USB 6008. am still skeptical of the ckt regarding the amount of current supply. none the less, thank you for the interface ckt...cheers mate

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[sufre]

Hi, committee.

Its is interesting topic that you have discussed, and seems to me there is relevant to my task. I am going to drive a fan motor which is varies with temperature output. The fan motor is rated as 12 volt, 0.32A = 3.84w.  I have checked the output voltage from the software (USB 6008 is very low). Can I use the posted circuit? I believe it is more than enough. Will it not damage the fan motor.

Kind regards

Sufre