High power Amp with OPA445

Dj BASS AMP · 2nd August 2004, 11:07 PM

what the parts i need to put in the pic......that it will realy work.

and how mach power is with 35V + -...

thanks....

tamir

Dj BASS AMP · 3rd August 2004, 10:57 PM

what worng?!

cunningham · 4th August 2004, 11:26 PM

Looking at the picture, I guess that the op-amp has a VAS stage as the output from it, and then drives a 'similar to' darlington output EF stage. The drivers appear to be biased by a current source, I think this could work.

Dj BASS AMP · 5th August 2004, 07:52 PM

it is need to work !! it is have to be...!! it is from the compeny of the opaamp.

but my Q is.... what kinds of transistors i need to connect to get him work....

and how much power that is?

thanks
tamir

cunningham · 5th August 2004, 10:09 PM

Q3 & Q4 could be darlington drivers, Q2 is bias servo, and should be comparable in beta (Hfe) to be mounted with outputs for thermal stability. Make sure that the transistors you select have a breakdown Vce of at least 100V. I would say you may realistically get 90-100W RMS!

Q1 is an emitter follower, and has no voltage gain...but has a current gain. Rb should be a potentiometer(maybe 47K), and Rt (4.7K) might work, if servo is a darlington type device. As Q2 saturates it turns off the output bias. Turning Q2 off some will allow the outputs to bias class AB and also be linear as far as temp. coefficient.

I would use a current source\current mirror circuit for Ibias as it is more accurate.

Include negative feedback just like any other op-amp circuit, and referenced to ground(0V).

Get a cross reference book to determain the type of devices you may want to use for drivers and outputs. This dosen't look to complex, Good Luck!

Dj BASS AMP · 6th August 2004, 02:41 AM

thanks u !

buy how kind i need to use for the darlingtons.......

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3rd August 2004, 10:57 PM	#2
Dj BASS AMP Account Disabled Join Date: Jul 2002	what worng?!

4th August 2004, 11:26 PM	#3
cunningham diyAudio Member Join Date: Jun 2004 Location: Knoxville	Looking at the picture, I guess that the op-amp has a VAS stage as the output from it, and then drives a 'similar to' darlington output EF stage. The drivers appear to be biased by a current source, I think this could work.

5th August 2004, 07:52 PM	#4
Dj BASS AMP Account Disabled Join Date: Jul 2002	it is need to work !! it is have to be...!! it is from the compeny of the opaamp. but my Q is.... what kinds of transistors i need to connect to get him work.... and how much power that is? thanks tamir

5th August 2004, 10:09 PM	#5
cunningham diyAudio Member Join Date: Jun 2004 Location: Knoxville	Q3 & Q4 could be darlington drivers, Q2 is bias servo, and should be comparable in beta (Hfe) to be mounted with outputs for thermal stability. Make sure that the transistors you select have a breakdown Vce of at least 100V. I would say you may realistically get 90-100W RMS! Q1 is an emitter follower, and has no voltage gain...but has a current gain. Rb should be a potentiometer(maybe 47K), and Rt (4.7K) might work, if servo is a darlington type device. As Q2 saturates it turns off the output bias. Turning Q2 off some will allow the outputs to bias class AB and also be linear as far as temp. coefficient. I would use a current source\current mirror circuit for Ibias as it is more accurate. Include negative feedback just like any other op-amp circuit, and referenced to ground(0V). Get a cross reference book to determain the type of devices you may want to use for drivers and outputs. This dosen't look to complex, Good Luck!

6th August 2004, 02:41 AM	#6
Dj BASS AMP Account Disabled Join Date: Jul 2002	thanks u ! buy how kind i need to use for the darlingtons.......

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