Electronics > Projects, Designs, and Technical Stuff
My first power supply
mariush:
My recommendation would be to replace those green prototyping boards with stripboards like this: https://www.ebay.com/itm/1PCS-DIY-Prototype-PCB-Matrix-Circuit-Board-Stripboard-Universal-8-5-20cm/253234159272?
It does restrict you a bit because you'd have to place components like 3 pin regulators in such a way that each lead is on a separate 4 hole strip, but you have the added benefit of those continuous strips which can potentially carry more current that thin wires.
You can also tin those continuous traces and floodfill the holes with tin if you wish.
You can also place components closer to how they sit on a prototyping board and use short lengths of solid core wire to make connections between 4-hole segments.
For capacitance after the bridge rectifier you can sort of estimate how much would be needed based on your minimum desired voltage.
Capacitance = Maximum Current / [2 x Mains AC Frequency x (Vdc peak - Vdc minimum desired)]
So you're saying you have a 12v AC 1.8A transformer and ou're in US where mains frequency is 60Hz... that means your peak DC current will be approximately 0.62 x Iac = 1.16A but let's round it up to 1.2A
Let's say you want minimum 14v dc voltage, because the 7812 regulator will have approximately 2v drop at 1A of current.
When your bridge rectifier converts 12v AC to DC you get a peak voltage of sqrt(2) x Vac - 2 x voltage drop on rectifier diode so your Vdc peak is 1.414 x 12 - 2x 0.8v = ~15.37 v ... let's round it to 15.5v
So you can put the numbers in the formula and the minimum capacitance you need to have minimum 14v would be:
C = 1.2A / [ 2 x 60 Hz x (15.5v - 14v) ] = 1.2 / 180 = 0.0066666 Farads
... so you should have at least a 6800uF 25v rated capacitor there to get your minimum 14v.
MarkF:
Personally, I like the green protoboards. Stick with them.
--- Quote from: queennikki1972 on September 24, 2019, 11:23:53 am ---
--- Quote from: MarkF on September 23, 2019, 02:00:03 am ---
Also since you are driving both regulators, the current capabilities of both the transformer and the rectifier bridge must be large enough for both (i.e. greater than 2A). The capacitance of the filter cap must be large enough for both also. You might actually be better off with two before the regulators.
--- End quote ---
Bridge Rectifier is 6A and the one large cap is 6800uf . When I redo the new board Ill put 2x2200uf cap 35v per side.
--- End quote ---
I think that is a bad idea. Stay with the 6800uF 35V capacitor on the input and use 100uF caps on the output.
At full load, you may actually need something bigger than 6800uF depending on the transformer and rectifier bridge voltages.
If you already have 2200uF caps, leave room to add one later on if you find that the voltage is too low.
I see nothing wrong with your original design other than the transformer is under sized for what is possible.
A 3-5A CT transformer would maximize your output. But, what you have is fine.
With that, you probably should keep an eye on the 6A rectifier. It may or may not get hot without a heatsink also.
I show LEDs on the outputs which provide two functions. First, they indicate the power is ON.
Second and more important, they provide a minimum for each regulator to work properly.
YOU HAVE NO CURRENT LIMITING. Careful or you may have a BAD day. Not ideal, but okay as minimal supply.
Stay with:
Or with a CT transformer you could reduce the voltage drop (i.e. heating) of the 5V regulator:
MarkF:
F.Y.I.
Here are the heatsinks I've used:
https://www.digikey.com/products/en?keywords=EA-T220-38E - 1.5" height
https://www.digikey.com/products/en?keywords=EA-T220-51E - 2.0" height
OM222O:
--- Quote from: MarkF on September 23, 2019, 02:02:10 am ---It is not a switching power supply. A linear power supply with fan noise on the one output.
--- End quote ---
one shall ask about noise / EMI reduction and one shall receive answers for noise / EMI reduction :-DD
it doesn't matter what's switching, a PSU or a fan, that will significantly reduce the sharp edges and fast rise / fall times to basically nothing. Think of it as adding a lot of momentum to a heavy object. small bumps to it here and there won't change how steadily it moves (i.e: how stable the voltage is). the resistor method works fine too, but is less efficient and not as good when it comes to noise reduction
queennikki1972:
--- Quote from: MarkF on September 24, 2019, 05:17:40 pm ---Personally, I like the green protoboards. Stick with them.
--- Quote from: queennikki1972 on September 24, 2019, 11:23:53 am ---
--- Quote from: MarkF on September 23, 2019, 02:00:03 am ---
Also since you are driving both regulators, the current capabilities of both the transformer and the rectifier bridge must be large enough for both (i.e. greater than 2A). The capacitance of the filter cap must be large enough for both also. You might actually be better off with two before the regulators.
--- End quote ---
I've taken notes and saved the schematics MarkF. Thank you. I get it now, just a little slow learner at times.
Bridge Rectifier is 6A and the one large cap is 6800uf . When I redo the new board Ill put 2x2200uf cap 35v per side.
--- End quote ---
I think that is a bad idea. Stay with the 6800uF 35V capacitor on the input and use 100uF caps on the output.
At full load, you may actually need something bigger than 6800uF depending on the transformer and rectifier bridge voltages.
If you already have 2200uF caps, leave room to add one later on if you find that the voltage is too low.
I see nothing wrong with your original design other than the transformer is under sized for what is possible.
A 3-5A CT transformer would maximize your output. But, what you have is fine.
With that, you probably should keep an eye on the 6A rectifier. It may or may not get hot without a heatsink also.
I show LEDs on the outputs which provide two functions. First, they indicate the power is ON.
Second and more important, they provide a minimum for each regulator to work properly.
YOU HAVE NO CURRENT LIMITING. Careful or you may have a BAD day. Not ideal, but okay as minimal supply.
Stay with:
(Attachment Link)
Or with a CT transformer you could reduce the voltage drop (i.e. heating) of the 5V regulator:
(Attachment Link)
--- End quote ---
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