OPA2991: Transformer control

DRUILHE yvan

Part Number: OPA2991

Hello

Provide case details or comments:

Max. frequency of use sinus 10Khz 7.07Veff max. output current 30mA
This OP amp can drive a transformer type load?
What are the protections of uses ?

Case used OPA2991IDGKR in VSSOP
You can also propose me another reference but in the same type of case.
Thank you for your help
Best regards

over 3 years ago

0 Tim Claycomb over 3 years ago

TI__Genius 15410 points

Hi Druilhe,

The OPA2991 can swing to about 1V from the positive supply with 30mA output current. I recommend taking a look at Figure 6-14 and 6-15 in the OPA2991 datasheet to see the output voltage vs output current capabilities of the device.

The OPA2991 has a slew rate of 21V/us so I do not see any potential issues related to full power bandwidth limitations (Figure 6-39). For more information I recommend taking a look at our TI Precision Lab Videos on Bandwidth and Slew Rate.

Thank you,

Tim Claycomb

0 Michael Steffes over 3 years ago

Guru 47535 points

Transformer loads do appear as a DC short, be careful to include a blocking cap - a schematic would help,

0 DRUILHE yvan over 3 years ago in reply to Michael Steffes

Intellectual 460 points

A diagram is attached.

The impedance in Dc of the transformer input is 100R3175.Schéma.docx

0 Tim Claycomb over 3 years ago in reply to DRUILHE yvan

TI__Genius 15410 points

Hi Druilhe,

If you need to output 7.07V into a 109 ohm load the op amp will need to be able to output ~65mA. The OPA2991 can output 65mA and swing to within about 2V of the positive supply. On +/-15V supplies this means the output can swing up to 13V with 65mA output current at room temp. Please see Figure 6-14 in the datasheet.

Another thing to consider the maximum power dissipation of the device. Be sure to check the power dissipation of the device if multiple channels will output high amounts of current and/or if operating at higher temperatures to prevent the device from over heating and triggering the thermal protection. Please see Section 7.3.3 in the datasheet for more information.

Thank you,

Tim Claycomb

0 kai klaas69 over 3 years ago in reply to DRUILHE yvan

Guru 140200 points

Hi Yvan,

7H is a hugh inductance. Usually, such an inductance comes with a considerable stray capacitance (winding capacitance). This capacitance must be taken into consideration when doing the stability analysis. Can you give some numbers?

Kai

0 DRUILHE yvan over 3 years ago in reply to kai klaas69

Intellectual 460 points

HI Kai

You will find enclosed the dasheet of the tansformer

Have a nice dayZ1604 issue 14.pdfsheet du transformateur utilisé.

0 kai klaas69 over 3 years ago in reply to DRUILHE yvan

Guru 140200 points

Hi Yvan,

ah, we are talking about an audio transformer? Well, in this case the load current is determinated by the load you connect to the output side (secondary side) of transformer. Can you post a schematic which shows what you want to connect at the output side of transformer?

In any case you should provide AC coupling at the input side of transformer, as Michael already mentioned. A bipolar electrolytic cap of >10µF might be a good choice (depending on the load connected to the output side of transformer). Or two standard electrolytic caps mounted in series with reversed polarity ("back-to-back").

In addition a 50...220R "isolation" resistor should be mounted close to the output of OPA2991. See section 7.3.4 of datasheet :-)

Kai

Amplifiers

Amplifiers forum

OPA2991: Transformer control