Transformer rating

xplod1236 · 5th July 2004, 06:38 PM

I'm planning to build a high-power amp using LM3886s in a bridged/paralleled configuration. What voltage secondaries should I use to get +/- 40v rails? Is 28v ac enough or do I have to go higher to compensate for diode voltage drop?

Let's say that I have a 1000 VA transformer. Is that good for a 1000 w rms amp or a 1000w peak amp?

xplod1236 · 6th July 2004, 07:32 PM

anyone?

ble0t · 6th July 2004, 09:39 PM

Well, the rectified output is approx 1.4 times the input of the secondaries. The diode losses shouldn't be too large a factor...

As for having +/- 40V per rail...that is probably too high. The maximum voltage input of the LM3886 is 84V. Allowing for voltage swing within your mains (conservatively +/- 5%) if you are not using a regulated supply, you could easily exceed that. Typically, for the LM3875 and LM3886, from what I have seen, 25V secondaries is the maximum you really want to use.

As for the power of the trans, to get continuous 1000W, you'd need to run quite a few of these suckers in a P/B config, so I guess you would need quite a bit of power...I'd refer to the datasheet for more info.

Hope that helps

xplod1236 · 7th July 2004, 12:58 AM

Quote:

Originally posted by xplod1236

Let's say that I have a 1000 VA transformer. Is that good for a 1000 w rms amp or a 1000w peak amp?

That was a separate question (just an example). I know that I will need to run them in P/B, and I know how to figure out how many I need.

The quesion was if a transformer is rated at 1000 VA is that continuous or peak?

5th July 2004, 06:38 PM	#1
xplod1236 diyAudio Member Join Date: Dec 2003 Location: On the couch	Transformer rating I'm planning to build a high-power amp using LM3886s in a bridged/paralleled configuration. What voltage secondaries should I use to get +/- 40v rails? Is 28v ac enough or do I have to go higher to compensate for diode voltage drop? Let's say that I have a 1000 VA transformer. Is that good for a 1000 w rms amp or a 1000w peak amp?

6th July 2004, 09:39 PM	#3
ble0t diyAudio Member Join Date: May 2004 Location: Milwaukee, WI	Well, the rectified output is approx 1.4 times the input of the secondaries. The diode losses shouldn't be too large a factor... As for having +/- 40V per rail...that is probably too high. The maximum voltage input of the LM3886 is 84V. Allowing for voltage swing within your mains (conservatively +/- 5%) if you are not using a regulated supply, you could easily exceed that. Typically, for the LM3875 and LM3886, from what I have seen, 25V secondaries is the maximum you really want to use. As for the power of the trans, to get continuous 1000W, you'd need to run quite a few of these suckers in a P/B config, so I guess you would need quite a bit of power...I'd refer to the datasheet for more info. Hope that helps __________________ gravity always wins

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6th July 2004, 07:32 PM	#2
xplod1236 diyAudio Member Join Date: Dec 2003 Location: On the couch	anyone?

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