Constant Current Source of about 300mA with variable frequency ranging from 1kHz to 100kHz

Muhammad Mansoor Malik

Other Parts Discussed in Thread: OPA547, OPA561, OPA564, OPA172

I want to make a constant current source for my project of "Designing of Eddy Current Testing Probe" at my research lab. This constant current source will excite the the coil of Eddy Current Probe and through the excitation of this current source eddy currents will be induced in a material when the probe is placed on that material. For that I need help.
The Constant Current Source should be having following specifications:

1) Output Constant Current = 300 mA

2)Constant Current Source Frequency Range= 1kHz-100kHz

If there anyone to help me?

over 12 years ago

0 Thomas Kuehl over 12 years ago

TI__Guru* 93105 points

Hello Muhammad,

Please see my previous OPA547 post showing how to apply an Improved Howland Current Pump in an ac current source application. Detailed information on the pump is included in that E2E forum exchange.

http://e2e.ti.com/support/amplifiers/etc_amplifiers__other_linear/f/18/p/53816/192847.aspx#192847

I expect your application will require a wider bandwidth power op-amp than the OPA547. Take a look at the OPA561 and OPA564 power op-amps. They will easily provide the required current and have wide bandwidth and high slew rate.

http://www.ti.com/product/opa561

http://www.ti.com/product/opa564

Regards, Thomas

PA - Linear Applications Engineering

0 Muhammad Mansoor Malik over 12 years ago in reply to Thomas Kuehl

Prodigy 30 points

Hello Thomas,

Can I only replace the OPA547 with one of the OPA561 or OPA564 in the circuit of "Improved Howland Current Pump"?
What rating of Current it will give me by replacing OPA547 with one of these Op-Amps?

Please reply.

0 Bruce Trump over 12 years ago in reply to Muhammad Mansoor Malik

Guru 21975 points

Muhammad,

All of these amplifiers are capable of your output current. Thomas is suggesting that the higher speed of the OPA561 or OPA564 may be required. Some of this depends on the nature of your load. What is the impedance of your load? What voltage swing is required on the load to produce the required output current?

Regards, Bruce.

0 Muhammad Mansoor Malik over 12 years ago in reply to Bruce Trump

Prodigy 30 points

Hello Bruce,

As the coil of the Eddy Current Probe is small so its calculated impedance is about 1ohm-2ohm. Will the design suggested by Thomas will give me 311mA current on this load?

Please reply.

Regards,
Muhammad Mansoor

0 Bruce Trump over 12 years ago in reply to Muhammad Mansoor Malik

Guru 21975 points

Muhammad,

I recommend the OPA564 operating on +/-5V power supplies. The improved Howland circuit that Thomas recommended can be implemented with this op amp.

Regards, Bruce.

0 Wayne Xu over 11 years ago in reply to Bruce Trump

TI__Prodigy 450 points

Dear Bruce, Thomas

My customer need a bipolar current source reference design (+/- 50mA output). Below is the requirement in detail. Could you help to promote a opamp and reference circuit for this requirement.

Thank you very much.

0 John Caldwell over 11 years ago in reply to Wayne Xu

TI__Genius 12325 points

Wayne,

Without knowing the load impedance and the available power supplies its difficult to recommend a solution for your customer. We also need to know what the required V/I transfer ratio is (output current per input voltage). Without knowing more about your application I would recommend implementing the Howland Current Pump mentioned above using an integrated difference amplifier to achieve high output impedance and linearity. One example of this type of circuit is shown in the applications section of the OPA172 datasheet.

0 Wayne Xu over 11 years ago in reply to John Caldwell

TI__Prodigy 450 points

Hi John

thank you very much for your reply.

the power supply of this circuit is +/-15V. the load is 50ohm resistor. V/I transfer ratio is 141.42V / A. customer want to transfer a +/-7.071V (50Hz) AC voltage signal to a +/-50mA (50Hz) AC current signal. could you help to design this circuit?

0 John Caldwell over 11 years ago in reply to Wayne Xu

TI__Genius 12325 points

Wayne,

Please see the attached simulation file. It should meet your customer's needs.

AC current source.TSC

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Constant Current Source of about 300mA with variable frequency ranging from 1kHz to 100kHz