OPA549: single supply

Hello user6178255,

Yes, you are able to design the part with a single rail power source. 

If you can describe the design application in your 3A power amp, I can help you with the design or questions.  

I would like to know the following parameters.

1. What types of load are you driving? Resistive, inductive, capacitive load etc

2. What type of protective features do you want to implement? over voltage, over current, thermal protection  etc.?

3. What is operating bandwidth you'd like to have?

4. What is output voltage swing? Any S/N consideration? 

5. Are there any transient events during normal operation? Transient Response time, if any?

6. Any Harmonic Distortion, Noise or EMI consideration?

Regards,

Raymond

Hello user6178255,

I have several follow up questions about the design requirements. 

1.My load type is coil with resistance value of 18ohm, which is inductive load

What is the coil's inductance value? Based on the information you provide, the coil will dissiplate minimum 162W (I^2R). Is this a relay application?

2.The input is a waveform with a frequency of 15hz (5v).

What is the input waveform type? Square wave, sine wave or others?

3.The type of my protective feature is over current

Current limit protection can be configured by the OPA549. 

6.I need to use OPA549 to generate a stable 3A current

What is your +/- requirements for sourcing 3A current? 

If you can provide these design parameter, I will send you a TINA simulation or provide you with alternative solutions, and we can discuss further from there. 

Regards,

Raymond

Hi Raymond Zhang1,

1.My load type is coil with resistance value of 18ohm, which is inductive load

What is the coil's inductance value? Based on the information you provide, the coil will dissiplate minimum 162W (I^2R). Is this a relay application?

answer1:It is not a relay application.I plan to use the coil to generate a magnetic field 

2.The input is a waveform with a frequency of 15hz (5v).

What is the input waveform type? Square wave, sine wave or others?

answer2:square wave or sine wave can be ok

3.The type of my protective feature is over current

Current limit protection can be configured by the OPA549. 

answer3 : thank you ,I get it

6.I need to use OPA549 to generate a stable 3A current

What is your +/- requirements for sourcing 3A current? 

answer6:+3A,

if you have some questions about my answers,please tell me . Thank you for you reply!

Regards,

Harry

answer1: It is not a relay application.I plan to use the coil to generate a magnetic field 

I have to know the inductance value of coil before I can calculate the pole in the system, and perform op stability analysis.  What is coil inductance in uH?

What is your +/- requirements for sourcing 3A current? 

How accurate do you want your 3A? 3A +/- x, please specify x; x is 10% of 3A or 1% of 3A.

I am still not sure that the power Op Amp is suited for the application. This can be easily drive with a switching power supply with constant current as feedback. Since the AC signal is only 15 Hz frequency, it may be able to ride on the your DC input signal, and chopped by your PWM control signal.  And the injected frequency will not be attenuated by H(s) filter at output stage due to H(s) filter frequency response. 

With Op Amp, this may not be easily accomplished, if you want to sample current accurately. If the errors of the controlled current  can be large, then you may be  able to use voltage feedback loop to control the current, since the coil's current is unable to change instantaneously, because of inductor. 

regards,

Raymond

The coil inductance is 250uh

 3A +/- x,  X is 10% of 3A 

I just want to achieve the function I want, and I don't have to use opa549.

Maybe I can adopt your plan ,can you  send me a TINA simulation about your plan?

Hi Raymond,

I don't understand the meaning of "Use the same settings in the power amplifier in series with the DC source".Does this mean i have to get a power amplifier work at 60v and the output current is 3A

The DC power supply is setting up your DC operating point, in this case the DC power supply is a constant current source. The power amplifier is setting up the AC signal in which is riding on top of DC operating point or bias. The power amplifier is a low impedance device, therefore the voltage drop across will be very small (configured in series). You will need to use functional generator to simulation the AC modulation shown in the Tina Simulation. The voltage drop across the power amplifier will be small, 3A*Impedance of power amplifier, should be in sub Ohm figure. Only your constant current source will require higher voltage compliance. When the power supply is sourcing a constant current, the power supply's voltage rail will rise to whatever the figure that will satisfy the load impedance. Else, the required constant current sourcing conditions will not be met.  

If you are not sure, you can replace your load with a 18 ohm power resistor (the heat dissipation is approximately 165W) and measure the output amplitude and current across the resistor. It is fairly simple setup. 

Some fancier power amplifiers have a build-in functional generator as the feature, therefore, the setup will be very simple. 

Regards,

Raymond

 I didn't find some  power amplifiers which meet the requirements.

Can i use  the opa549 or the opa548?

Thank you !

my questions have been solved