OPA547: OPA547 Bidirectional Constant Current Source

Hi Krishna, 

krishna prasad said:

To get a negative current what modifications should i do to the Circuit to get -200ma which is PWM Controlled??

There are a couple power amplifier ICs that may work for the application, OPA547 and OPA593, but I need more information about the application. 

What types of load are the current source going to drive? What is output voltage swing? Is the output going to be square wave or other analog signals? 

If the PWM output signal is large amplitude signal, please specify the rising and falling edge timing requirements. 

krishna prasad said:

To get a negative current what modifications should i do to the Circuit to get -200ma which is PWM Controlled??

Assumed that the PWM control signal is above ground, you may use capacitor to couple the output to generate PWM signal below ground as shown in the example below. 

krishna prasad said:

What would be resolution of output Current for this range??

The current resolution should be excellent, if the circuit has a negative feedback. For instance, the application may implement the Howland Current Pump to drive +/-200mA, see the attached application note. 

https://www.ti.com/lit/an/sboa441/sboa441.pdf?ts=1668445650080&ref_url=https%253A%252F%252Fwww.google.com%252F

If you have additional question, please let us know. 

Best,

Raymond

. 

Hello Raymond Zhang

The Amplitude of the +/-  Pulsed Current Source should be +/-5V with 0.1ma Accuracy and Frequency 0-10Khz with Duty Cycle varying 0 to 95%.

Load Current +/-200ma. We can even increase to +/-2A

We already have developed a Programmable Unidirectional Constant Current Source and i have gone through both OP547 and OP593 Data sheets 

OP593 Seems to be very high Current output ~8A.

Generating the PWM Pulse to control the DAC is the trickiest part.

Let me know your inputs whether to go for MOSFET Based drivers or Power Opamp (Howland circuit).

Thanks n regards

Krishna.P.N.

Hi Krishna, 

krishna prasad said:

The Amplitude of the +/-  Pulsed Current Source should be +/-5V with 0.1ma Accuracy and Frequency 0-10Khz with Duty Cycle varying 0 to 95%.

10kHz will have a pulse period 100usec. OPA547 has a slew rate of 6V/usec and OPA593 has a slew rate of 40V/use. To have PWM's delta voltage in 10V, the rising and falling edge for OPA547 will be approx. 10V/6V/use = 1.67usec. Is this going to meet PWM pulse edge requirements?

Let us try OPA593 in Howland current pump for now. The MOSFET based low side bidirectional current source should work as well. 

Note: I used OPA192 as feedback buffer op amp. you may consider to use OPA189, OPA182 or other lower cost zero drift op amps for the application. If the rising and falling edge has tight specification, you may consider faster slew rate, zero drift buffer as op amp for the application. 

OPA593 Howland PWM 200mA Ipump 11152022.TSC

krishna prasad said:

Generating the PWM Pulse to control the DAC is the trickiest part.

Below is an example to generate 10kHz PWM signal. DAC will be your sinewave generator and you need to generate 10kHz sawtooth waveform from a current source (driving a capacitor) or MCU.  TLV3501 is a comparator, which we have many of them to choose from. 

https://www.ti.com/amplifier-circuit/comparators/overview.html?keyMatch=COMPARATOR

10kHz PWM Generator 11152022.TSC

If you have additional questions, please let me know.

Best,

Raymond 

Raymond 

Thanks for your inputs and generating Ramp as well as Sine wave can be done using DAC or Microcontroller. I will explore the same as both frequency and Duty cycle of PWM has to be varied as per requirement by the user

Thanks n regards

Krishna.P.N.