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PostPosted: 18.12.2007 19:13 
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Meter is connected correctly. Voltage rating of the transistor doesn't matter that much. Just get any with higher voltage rating that is affecting your circuit.

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PostPosted: 18.12.2007 19:49 
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Junior Modder
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okay ill take 30dc voltmeter , thank you Japala. :!:

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PostPosted: 20.12.2007 22:02 
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Junior Modder
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one last thing. im makeing my modlab out of old psu, i have both 12 and 5 volts. So if i put 7805 to 5 volt line and 7812 to 12 volt line the its ok? i think that, in this case i dont need cooling for 7805 because its not on 12 volt line, am i right?

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PostPosted: 20.12.2007 22:12 
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You don't need to regulate the 12 and 5 volt lines in this case. You can place the regulators there but they will not give out enough voltage as they need a certain amount of extra voltage to work properly.

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PostPosted: 21.12.2007 00:27 
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Junior Modder
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and how much is that extra juice? if i look at the scheme there is also 12v line with regulators. whats the diferens? you saing that regulators are built into psu?

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PostPosted: 21.12.2007 01:15 
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You have to check the regulator's datasheets for this information. I believe the 7812 needs around 15 volts or more to give out steady 12 volts and the 7805 needs around 7-8 volts to give 5 volts. Exact values are stated on the datasheets.

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PostPosted: 21.12.2007 11:22 
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Junior Modder
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okay but if i use ac adaptor
model no: AA-121ABN
INPUT:230v~50Hz140mA
Output:12~1A

will i'll be abel to use regulators? what did u use for electrical source?

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PostPosted: 21.12.2007 13:12 
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12 volts on the label doesn't state if it the transformer is regulated or not. Use a multimeter and see what is the actual voltage. Unregulated power supply, even when the label states 12 volts, the output can be 15-17 volts. This kind of PSU works well with for example 7812.

Edit: Oh, and if the transformer is indeed AC and not DC, you need to make a circuit to convert the AC to DC before offering it to the regulator.

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PostPosted: 21.12.2007 18:01 
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what happens in situation weher i have ac not dc?
and if my adaptors output is 500mA will it burn the fuse?

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PostPosted: 21.12.2007 18:13 
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AC = alternating current = voltage is on the plus side for a moment and then goes to negative. DC = Direct current = Voltage stays positive all the time. BIG difference. For the regulators to work, you need DC.

500mA is the current rating. It means how much current you can get from the transformer before it starts to lose its ability to source more power. This means that you can't take more than 500mA via your circuit.

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PostPosted: 23.12.2007 17:08 
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Junior Modder
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like i said i am newb in english, i dont understant that 500mA part :P so is 500mA adaptor to much? ill have to get under the 500mA ? fuse is 500

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PostPosted: 27.12.2007 17:57 
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what happens if i have no fuse and i connect +12 with ground? i accidentally connected power supply +12 with modlab ground and power supply ground with modlab +12.

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