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HELP! project abt DC power supply.


infinity.o3

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helo, i new here. and oso new to electronic stuff.  ;) i would like to ask how to build a power supply? it is a triple output power supply (o/p= +15v, -15v and -5v) of not more than 15 components. where can i find more about this stuff? any link? i would also want to find a schematic diagram of power supply. 

thank..!!  :)

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Guest SM2GXN

Hi infinity.o3!

Going from left to right:

1. Marked 230 volts were the mains cable is to be connected, that side is called primary side.

2. F1 is a fuse 33mA/250 volts that one will blow if there is a short in the transformer windings or if there is to big load on the secondary side of the transformer which can be a faulty/shorted component. F1 is important!

3. Tr1 transformer with 230V primary and secondary 2X15volts/33mA center tapped meaning if you measure from centertap (line going in the middle marked GND=ground) to one of the outer taps you will get 15volts and if you measure across the outer taps 30 Volts AC.

3. D1-D4 As you correctly noted, diodes. These diodes will rectify the AC to DC, the two upper are for the positive/plus side and the lower diodes are negative/minus.

4. C1 & C2 are electrolytic capacitors these are filter capacitors, without them you will get an annoying hum. If you live in a country where the line frequency is 50Hz you'll get 100Hz hum and if 60Hz then 120Hz

5. IC1 & IC2 are voltage regulators they make sure that the voltage comming out from your power supply wont drop when you connect a load, they stabilize the voltage.
7815= 15 volts positive voltage regulator.
7915= 15 volts negative voltage regulator.

This power supply is for light loads meaning that you can't draw much current from it.

Bjorn

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Hi infinity,

Just adding some to Bjorns detailed answer:
To your first question; there are no resistors needed in this circuit!
You can learn more about the voltage regulators here: http://www.aleeanne.org.uk/datasheets/datasheet2/LM7815.PDF
You can use the same circuit for heavier load by using a higher rated transformer and maybe slightly bigger caps if you need more current.
I don’t know where you live but it’s possible that you don’t have 230VAC mains but 120 VAC or perhaps something else.

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In another post long ago, I had this idea. A voltage multiplier, which is typically low current, makes a good DC source from an AC or analogue signal. Of course in order to make them high current, you need high capacitance. High capacitance makes them low voltage capacitors. Therefore, it is only impractical to take a high voltage source, use some capacitors and diodes, and realize a DC source. A transformer with capacitors and diodes is used in it's place.

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Hi timothy,

You can do this one of two ways; either you connect the input of the 7905 to the input of the 7915 or to the output of the 7915. Then connect the ground pin of the 7905 to the 0v rail and last the output pin of the 7905 will be your -5V output. Add a capacitor on the input side as well as to the output side just like it has been done with the other regulators.

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