newbie question!!!

electro samurai · 21st March 2004, 06:56 PM

ok.
this might come to some of u as a shock.
when a ic needs a Vcc (+) voltage of 20, and a Vee (-) voltage of -20, does this mean a 20v ac-dc adapter? a 40 v ac-dc adapter?

oh, and another thing, ive downloaded this Power Supply Unit Designer, and simulated it, and when using a 20v transformer, the design gave away 26v.
when i plugged my 9v adapter, and found out its gives a steady 14 volts!
how come?

is this a problem?

electro samurai · 21st March 2004, 06:57 PM

oh, almost forgot, the supply is 4 a lm1876, an audio chip about 15 to 20 w.

ir · 21st March 2004, 08:41 PM

it's becuase there's no load. if you plug your 9v adapter in to something, then measure it, you'll see it gives out almost exactly 9V

if an IC needs +/-20 then 20V is not enough. a 40V adapter puts out 40V and 0V, you need +20, 0, -20. you can make a voltage divider but it won't work very well with a chip amp as it will needs to draw a lot of current

what i use for testing my amps is a power adapter from an old Hewlett Packard Deskjet 500. the adapter is nothing but an external transformer giving out 10-0-10V which after rectifying is +14, 0, -14. it does pretty well. worth noting tho, the transformer is only 40VA so if you run the amp at high volumes it wil lget VERY hot so it's only good for testing.

you really need a dedicated trasnformer anywhere between 15-0-15 and 25-0-25 volts

21st March 2004, 06:56 PM	#1
electro samurai diyAudio Member Join Date: Feb 2004 Location: haifa, israel	newbie question!!! ok. this might come to some of u as a shock. when a ic needs a Vcc (+) voltage of 20, and a Vee (-) voltage of -20, does this mean a 20v ac-dc adapter? a 40 v ac-dc adapter? oh, and another thing, ive downloaded this Power Supply Unit Designer, and simulated it, and when using a 20v transformer, the design gave away 26v. when i plugged my 9v adapter, and found out its gives a steady 14 volts! how come? is this a problem?

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21st March 2004, 06:57 PM	#2
electro samurai diyAudio Member Join Date: Feb 2004 Location: haifa, israel	oh, almost forgot, the supply is 4 a lm1876, an audio chip about 15 to 20 w.

21st March 2004, 08:41 PM	#3
ir diyAudio Member Join Date: Aug 2003 Location: WGTN, NZ	it's becuase there's no load. if you plug your 9v adapter in to something, then measure it, you'll see it gives out almost exactly 9V if an IC needs +/-20 then 20V is not enough. a 40V adapter puts out 40V and 0V, you need +20, 0, -20. you can make a voltage divider but it won't work very well with a chip amp as it will needs to draw a lot of current what i use for testing my amps is a power adapter from an old Hewlett Packard Deskjet 500. the adapter is nothing but an external transformer giving out 10-0-10V which after rectifying is +14, 0, -14. it does pretty well. worth noting tho, the transformer is only 40VA so if you run the amp at high volumes it wil lget VERY hot so it's only good for testing. you really need a dedicated trasnformer anywhere between 15-0-15 and 25-0-25 volts

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