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Power Supply

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mark_3094

New Member
Hi everyone,

Thanks to another thread posted recently, I've been looking into creating my own power supply for testing.

Up to now, I've been using a 9v battery for simple circuits (which covers all my circuits so far :D)

I want to have a power supply that will output 9v. It will have to step down from 240v 10A, which is the wall socket rating here in Australia (please correct me if I have this wrong - I don't want to electrocute myself or burn the house down).

I have attached a schematic that I think will do it. It's based on the one posted in the other thread, but I've done some research and put in values for most of the components.

I don't know how to get a part number for the Transformer though... Can anyone help with that?

Also, does this look like it will work? I don't want to have a meltdown! :)

Thanks!
 

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forumlicker007

New Member
Very simple little boy. Your regulator is 9V. You've to supply a voltage that can be varied between say 12V-25V(?) to get a constant output. dats all.got it. Measure the voltage at c1. A 18V X'former is convenient.ok. What's your application?
 

ericgibbs

Well-Known Member
Most Helpful Member
And also, should I have a fuse somewhere?
If so, where's the best place to put it?
hi Mark,
Look at this edited dwg.

A 12V 1A transformer will be OK, say 15VA rating
 

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mvs sarma

Well-Known Member
I propose to add 4 ( or 2 selective)capacitors of 0.01uF, across each diode or 2 selected diodes. this would help reduction of diode switching hum, if the O P wants to use for analog and audio purposes.
 

flat5

Member
I like the way you drew the diode bridge :)
ericgibbs circuit is traditional.
However, I would use a 200ma fuse on the AC side and a SPST switch.
I would use a 240v to 12v transformer rated at 12 watts or more. Any more voltage and you just heat the regulator for no good reason. Select a transformer that guarantees 1 amp output.
Construct in a metal case and mount the regulator IC to the case using a heat transfer-insulating washer set and silicon heat transfer paste. Maybe drill a few holes for air to circulate around the transformer and diodes.

Do include an LED-resistor at the output to verify output and bleed the supple when turned off and no load attached.
 

mark_3094

New Member
:) Couldn't figure how to draw the bridge rectifier traditionally in DipTrace

Wouldn't a 200mA fuse blow as soon as the current draw passes 200mA?
The rest of the circuit is rated at 1A, so shouldn't the fuse be so as well?

Does the switch have to be specially rated to be on the AC side? Does to be rated at 10A or something?
 

mark_3094

New Member
Would the voltage vary at all (outside of the Regulators specified variance) with a greater load?

That is, would the output voltage at 100mA be the same as the output voltage at 500mA? (Example values only)
 

ericgibbs

Well-Known Member
Most Helpful Member
Would the voltage vary at all (outside of the Regulators specified variance) with a greater load?

That is, would the output voltage at 100mA be the same as the output voltage at 500mA? (Example values only)
Mark,
Ref the regulation, the 7809 datasheet gives this information.

Look under 'load regulation' on the sheet.
 

mvs sarma

Well-Known Member
Would the voltage vary at all (outside of the Regulators specified variance) with a greater load?

That is, would the output voltage at 100mA be the same as the output voltage at 500mA? (Example values only)
For such small loads, there is no point in using a transformer too big. As suggested by Flat5, better use 12VA secondary, so that the idle power wastage could be reduced.

Now coming to fuse , like the voltage gets reduced, the wattage gets transformed. 12VA at 12V is 1 amp but at say 240V primary it is0.05 or 50mA excluding the iron loss, thus it is far less. So Flat3, has suggested a smaller fuse.
 

ericgibbs

Well-Known Member
Most Helpful Member
For such small loads, there is no point in using a transformer too big. As suggested by Flat5, better use 12VA secondary, so that the idle power wastage could be reduced.

Now coming to fuse , like the voltage gets reduced, the wattage gets transformed. 12VA at 12V is 1 amp but at say 240V primary it is0.05 or 50mA excluding the iron loss, thus it is far less. So Flat3, has suggested a smaller fuse.
The transformer on the dwg I posted is a 12V 1A 15VA transformer.???

I would still suggest a 1A fuse rating.

EDIT:
the 50mA is the primary current when both the electrolytic caps are charged,, at switch ON, for a few cycles the primary current will be much higher while the caps are charging. A 200ma could blow sometimes at switch ON.
 
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ericgibbs

Well-Known Member
Most Helpful Member
Yes Ericgibbs , You took care of the Inductive surge surrent art the time of switch on/off time.
hi Sarma,
You saw my EDIT.:)
A 1A fuse will give adequate protection in the event of a txr/cap short

EDIT:
test for EM
 
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Willbe

New Member
1A current from a capacitor with, let's say, (20-11)v ripple, would need
C = I dT/dV = 1 x .005/9 = .00055 = 550 uF.
You need to make sure that the I squared T rating of the 1N4001 can stand these pulses of charging current.
OH Shade did work on this in 1943, but it doesn't seem to be online. His paper had several pages of graphs to solve for the currents and voltages, percent ripple, the whole bit.
 
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flat5

Member
I'm sorry, ericgibbs.
I saw the 15VA and thought you were saying 12 to 15 volt transformer. I should look more than twice before I question you engineers. I still think a 200ma slow blow fuse is correct but if a 1 amp fast will protect the components in the supply then that's the right fuse.
 

ericgibbs

Well-Known Member
Most Helpful Member
I'm sorry, ericgibbs.
I saw the 15VA and thought you were saying 12 to 15 volt transformer. I should look more than twice before I question you engineers. I still think a 200ma slow blow fuse is correct but if a 1 amp fast will protect the components in the supply then that's the right fuse.
hi flat,
Its not a problem.:)

I prefer a standard 1A fuse, its so irritating when sometimes the lower rated fuse pops off when you switch ON.

I suppose a 200mA, as you suggested, in a A/S or slow blow version would work OK.
 

mark_3094

New Member
Ok, today I went out and got some stuff, and I'm trying to figure out how to wire it without anything going wrong.

I got a 1A Multitap transformer (MM-2002), which can step 240v down to 12.5v (among other values). I also got an IEC male plug with switch and fuse built in. I went with the 1A fuse.

This is the type of plug I mean:
IEC Fuse Chassis Male Power Plug with Switch - Jaycar Electronics
Fused Snap-In IEC Chassis Plug with Switch > Maplin

On the back of it, there are connectors for 'L', 'E' and 'N'.
There are only the blue and brown wires coming out of the transformers primary coil, so I guess I don't connect anything to 'E'. Is that right?

'L' also connects to one side of the fuse, and has it's own terminal. There is another terminal for the other side of the fuse.
I think I have to connect the blue wire to 'N', and the brown wire to the terminal connected to the fuse. This means that I leave the terminal that is directly connected to 'L' alone. Am I right so far?

Lastly, the switch is DPST. Do I run both Active and neutral through the switch?

Thanks everyone. Sorry for asking such obvious questions, but I feel it's better to be safe than sorry when dealing with mains power for the first time.
 

ericgibbs

Well-Known Member
Most Helpful Member
On the back of it, there are connectors for 'L', 'E' and 'N'.
There are only the blue and brown wires coming out of the transformers primary coil, so I guess I don't connect anything to 'E'. Is that right?

'L' also connects to one side of the fuse, and has it's own terminal. There is another terminal for the other side of the fuse.
I think I have to connect the blue wire to 'N', and the brown wire to the terminal connected to the fuse. This means that I leave the terminal that is directly connected to 'L' alone. Am I right so far?

Lastly, the switch is DPST. Do I run both Active and neutral through the switch?

Thanks everyone. Sorry for asking such obvious questions, but I feel it's better to be safe than sorry when dealing with mains power for the first time.
On the dwg I posted you will see the EARTH is used, connect the E wire to the bolt/screw which fixes the transformer to the psu chassis.

Have you got the mating IEC wired cable socket to suit the chassis mount connector you have bought.?

On the back of the chassis connector 'N' goes to one of the wires on the transformer primary, the 'L' on the connector goes to the other transformer primary winding.

As its a double pole switch I would have thought the 'N' would be internally switched on the connector.
 
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