Regarding Audio amplifiers

Hi, Suneetha,

Welcome to e2e, and thanks for your interest in our products.

Unfortunately, we do not have a lot of information available for this application.

As long as the load seen by the amplifier on the primary side is within specification, you should be okay.

Class-D amplifiers are used in applications where high-efficiency is required.

-d2

Hi Sir,

Thanks for giving reply.Can we use the application circuit of Bridged Amplifier for our design.Can we drive the Output from this Application to 100V Step-up transformer?If So can we give the supply of ±35V DC to Supply Pins?

Suneetha.V

ARECA Embedded Systems

Hello Suneetha,

The LM4780 is capable of delivering 60Wrms into 8E SE load when it is powered by a split DC supply of +/-35V (Vcc & Vee of the IC).

A 100V transformer is normally used to carry the amplifier output over large distances or for power distribution.

Here is how I would calculate the transformer requirements:

1. 60Wrms into 8E load means 22Vrms at the amplifier output. (22*22/8 = 60.5Wrms)

2. 60Wrms into 8E means Irms = 2.74A flows through the 8E speaker.

3. Since the output transformer connects directly to the amplifier output, its primary rating will be 22vrms/ 2.74A.

4. The secondary rating of the transformer should be 100Vrms/ 0.6A. (V*I = 60W)

Remember:

a. The transformer needs to have CRGO core for good HF response.

b. The transformer will only be 85% efficient. So expect only 51Wrms at the transformer output.

c. At the 100V end of the transformer you will need another step down transformer to match the loudspeaker impedance.

d. If you want to use LM4780 in bridge mode, then the recommended supply is only +/-25V NOT +/-35V. The output power delivered into an 8E load in bridge mode will be 110Wrms. Calculate the transformer ratings using steps 1-4 above.

I hope that this helps.

Regards,

Ravindra.

Hello Ravindra,

Thanks for giving suggestions.I am new to Audio Analog Designs.

We want to be our design like this for the application of Audio Announcement in AC/Non-ACTrains using 100V Constant voltage system.

Audio CODEC or Microphone Audio --->Preamplifier---->Audio Power Amplifier --->Step up transformer-->Distribution network-->Step Down Transformer(which is at loudspeakers) --->Loud Speakers (Each- 6W RMS,8Ω)

Maximum No of speakers : 6 Nos.

Impedance of spekers:8Ω

Maximum Wattage of each Speaker: 6W,RMS.

We are in the stage of selection of Power amplifier with Volume Control.According to my knowledge our calculations are like this

Power Amplifier wattage - 6W,RMS x 6 -->36W RMS.We have to take double the Wattage rating of the Power amplifier for safe operation as 72W nearly 80W at 8Ω.

We searched in Class D Amplifiers with temperature range of -40 to 85*C but that much wattage Power amplifier is not available.There is a problem of EMI Interference.Any suggestable Part from Class-D with volume control whose Output is driving to 100V Output Transformer?

We searched in Class-AB Power amplifiers,We think LM4780 is sufficient (120W in BTL mode) but there is no volume control in this amplifier.Can you suggest any other amplifier with volume control?

Proper Heat Sinks should also be there for power dissipation for this IC.Can you provide any Evaluation Board Design of LM4780 in BTL mode.

Regards,

Suneetha.V

Hello Suneetha,

Here is just what you need:

1. Amplifier: http://www.ahujaradios.co.in/ProductSpecification.asp?prd_id=260&id=2&sc_id=60

2. Speaker: http://www.ahujaradios.co.in/Productdetail.asp?prd_id=160&id=7&sc_id=43

Regards,

Ravindra.

Hello Ravindra,

The power in trains is 110V DC.As you suggested Ahuja Products,they are not custom based as it is operated on 230V,AC. So we can't use the Ahuja Amplifiers.That's why we want to have our own design with Power supply operating with 110V DC.We are already using Speakers of Ahuja Make.

As a part of it we started searching the Audio Power amplifiers in TI website.

One more doubt in LM4780 is there,we have to add any snubber circuit before connecting the output of BTLto Primary of transformer or no need as it has SPIKE Protection.

Regards,

Suneetha.

Hello again,

Thanks for the additional information. If you see carefully, Ahuja amplifiers also work on 12Vdc.

If I were you, I would rather design a DC-DC (110V to 12V) converter. Something that you need to do anyway for some other voltage level. TI can easily help you there.

Also on a side note: if 60Wrms/8E is your target, then take a look at LM3886 also.

Regards,

Ravindra.

Hello Ravindra

We don't want to use Ahuja Power Amplifiers.If we use LM4780 with SE load configuration,with Output connected to Transformer,and I need to control the volume. Is it possible to put a Potientometer at the input like as shown in Fig 5 of the LM4780 datasheet?

For every power amplifier we must have a volume Control na Sir.Any protection ckt is required to the amplifier at the Output before connecting to Step-up transformer Sir?

Regards,

Suneetha.V

Hello,

Are you going to use single supply as given in fig. 5 of LM4780 datasheet?

It is ok to use a potentiometer at the input. However a better way would be to have a buffer in-between.

You had mentioned CODEC before. You can implement a volume control in there too.

You had mentioned mic input, remember you will need a mic pre-amp.

Regards,

Ravindra. 

Hello Ravindra,

No I am not using Fig.5 but Fig 39 of LM4780 datasheet.We want to bring up a board of 60W,RMS for our application..In that ckt I will add Potentiometer at the input side before input capacitors for volume control.And also there is Evaluation board is there for that design.

Will that ckt (Fig.39) provide 60W,RMS Output power of each channel?What is the supply voltage we have to give to VCC and VEE Pins inorder to get 60W RMS?Please suggest me how to select the supply voltage rails if wide range of supply voltage is given?Is the supply voltage selection depends on the Output Power Wattage?

Regards,

Suneetha.

It is getting quite long here.

We can discuss this out in 10mins over phone.

Regards,

Ravindra.

Hello Ravindra

I have doubt regarding Key specifications of LM4780 and Heat Sink Selection.Can I you call you once regarding these issues?

Regards,

Suneetha.V