LM4780 Question

hongrn · 14th October 2005, 05:35 AM

Hi Guys,

Just got my Avel Lindberg 330VA 25V+25V toroid in. Well, the secondaries are not exactly 25V, about 26 something. I hooked them up to the rectifier boards and got almost 38VDC. The LM4780 datasheet specifies 35VDC. Am I going to fry my chip with the extra 3 volts? Thanks.

Hong

Nordic · 14th October 2005, 05:55 AM

Lol if it was an old transformer, I would tell you to remove some windings till you got to a safer voltage....

motherone · 14th October 2005, 08:08 AM

The transformer is probably spec'd at 25VAC under load. Since you have no load on it right now, it's probably going a few volts over. Under load, you should have ~35VDC.

Tweeker · 14th October 2005, 07:08 PM

Absolute max supply voltage is listed at +/- 42 volts, with 10% overvoltage your still under it. Your rails are high due to the no load condition.

hongrn · 14th October 2005, 10:03 PM

Thanks everyone. I feel better now. Better ask a stupid question than be sorry.

Hong

14th October 2005, 05:35 AM	#1
hongrn diyAudio Member Join Date: Mar 2005 Location: Placentia, CA, USA	LM4780 Question Hi Guys, Just got my Avel Lindberg 330VA 25V+25V toroid in. Well, the secondaries are not exactly 25V, about 26 something. I hooked them up to the rectifier boards and got almost 38VDC. The LM4780 datasheet specifies 35VDC. Am I going to fry my chip with the extra 3 volts? Thanks. Hong

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14th October 2005, 05:55 AM	#2
Nordic diyAudio Member Join Date: Sep 2005	Lol if it was an old transformer, I would tell you to remove some windings till you got to a safer voltage....

14th October 2005, 08:08 AM	#3
motherone diyAudio Member Join Date: Apr 2003 Location: Seattle	The transformer is probably spec'd at 25VAC under load. Since you have no load on it right now, it's probably going a few volts over. Under load, you should have ~35VDC.

14th October 2005, 07:08 PM	#4
Tweeker diyAudio Member Join Date: Dec 2004 Location: Cincinnati, Ohio	Absolute max supply voltage is listed at +/- 42 volts, with 10% overvoltage your still under it. Your rails are high due to the no load condition.

14th October 2005, 10:03 PM	#5
hongrn diyAudio Member Join Date: Mar 2005 Location: Placentia, CA, USA	Thanks everyone. I feel better now. Better ask a stupid question than be sorry. Hong

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