AD811AN(PDIP Package) Getting Heated for +/-12V Power Supply

HI Jigar,

Below, please find the equation that will allow power dissipation total to be calculated.  This equation is used to compute the total average power being dissipated in the amplifier due to sine wave signal processing.  As you can see from the equation, there are a few things to consider.    So far, you've only accounted for the quiescent power (384mW) which is the small and simple equation above the red box.  Referring now to the equation in the red box, the middle piece is collector input power, and relates the supplies, signal amplitude, and the load resistance when a sine wave is being processed by a push pull output stage.  Included in that quantity is load power which is the third term and must be subtracted from the total because it's being dissipated in the load, not in the amplifier. This equation will help you determine the power that is being dissipated by amplifier.

To answer your questions:

1) Dissipating heat in a package (PDIP) that has no exposed thermal pad is not very easy nor very effective...This is due to the poor thermal conductivity of the plastic that encapsulates the amplifier.  You haven't told me anything about the Rload (RL) in the equation below so it's difficult to know exactly how much power you are talking about. But generally,  if power is a concern, select an amplifier with an exposed thermal pad so that the heat can be conveyed to the PCB thru highly conductive thermal vias and dissipated thru the PCB copper plane and into ambient air.

2) You'll have to give us more information on the load and signal content, frequency etc before we can recommend an amplifier for your needs.  And the only amplifier that dissipates no power are the ideal kind .

3) What are the frequencies of the receive signal in your ultrasound system?  <10MHz? What are the gain ranges in question?  What are your noise requirements?  Distortion requirements?  I don't know of a detailed document on ultrasound receivers but I'll look.

Regards,

Bob

HI Jigar,

Below, please find the equation that will allow power dissipation total to be calculated.  This equation is used to compute the total average power being dissipated in the amplifier due to sine wave signal processing.  As you can see from the equation, there are a few things to consider.    So far, you've only accounted for the quiescent power (384mW) which is the small and simple equation above the red box.  Referring now to the equation in the red box, the middle piece is collector input power, and relates the supplies, signal amplitude, and the load resistance when a sine wave is being processed by a push pull output stage.  Included in that quantity is load power which is the third term and must be subtracted from the total because it's being dissipated in the load, not in the amplifier. This equation will help you determine the power that is being dissipated by amplifier.

To answer your questions:

1) Dissipating heat in a package (PDIP) that has no exposed thermal pad is not very easy nor very effective...This is due to the poor thermal conductivity of the plastic that encapsulates the amplifier.  You haven't told me anything about the Rload (RL) in the equation below so it's difficult to know exactly how much power you are talking about. But generally,  if power is a concern, select an amplifier with an exposed thermal pad so that the heat can be conveyed to the PCB thru highly conductive thermal vias and dissipated thru the PCB copper plane and into ambient air.

2) You'll have to give us more information on the load and signal content, frequency etc before we can recommend an amplifier for your needs.  And the only amplifier that dissipates no power are the ideal kind .

3) What are the frequencies of the receive signal in your ultrasound system?  <10MHz? What are the gain ranges in question?  What are your noise requirements?  Distortion requirements?  I don't know of a detailed document on ultrasound receivers but I'll look.

Regards,

Bob