Author Topic: My first power supply  (Read 6951 times)

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Offline dom0

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Re: My first power supply
« Reply #25 on: September 21, 2019, 04:33:23 pm »
Powers on and functions great, still waiting on my fan to come in.

I would recommend a larger heatsink instead of a fan at these power levels, since the thermal resistance (K/W, kelvin per Watt, calculations just work like electrical resistance) of these tiny heatsinks is pretty bad and doesn't improve that much with a fan.
,
 
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Online MarkF

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Re: My first power supply
« Reply #26 on: September 21, 2019, 05:05:26 pm »
Powers on and functions great, still waiting on my fan to come in.

I would recommend a larger heatsink instead of a fan at these power levels, since the thermal resistance (K/W, kelvin per Watt, calculations just work like electrical resistance) of these tiny heatsinks is pretty bad and doesn't improve that much with a fan.

I agree with @dom0.  Your heatsinks are really small even with a fan.
The LM78xx's are going to get hot if you expect to pull their full power.
It looks like you are using a full wave bridge IC.  It could use a bigger heatsink too.

Here is a picture of a 51mm and two 38mm tall heatsinks on the triple supply circuit I showed earlier.
Even these get hot at or near full power.

840876-0
« Last Edit: September 21, 2019, 05:17:43 pm by MarkF »
 
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Offline queennikki1972Topic starter

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Re: My first power supply
« Reply #27 on: September 21, 2019, 10:17:39 pm »
Also I noticed there is a small spike from the fan noise? on the the 12v side, since thats where the fan is connected. I agree about larger heatsinks as well. Is there anything you can put inline with the fan to suppress the spikes? Maybe a larger output capacitor? It is minimal but just wondering. The 5v side is much smoother.
« Last Edit: September 21, 2019, 10:21:39 pm by queennikki1972 »
Siglent SDS 1202X-E - Heathkit IO-4105 - Dr. Meter 0-30v 5a power supply - 862d+ combo unit - Weller WLC100 - Kunkin KL283 DC load. Not much gear yet.
 

Offline xavier60

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Re: My first power supply
« Reply #28 on: September 21, 2019, 10:34:46 pm »
Also I noticed there is a small spike from the fan noise? on the the 12v side, since thats where the fan is connected. I agree about larger heatsinks as well. Is there anything you can put inline with the fan to suppress the spikes? Maybe a larger output capacitor? It is minimal but just wondering. The 5v side is much smoother.
It's difficult to completely remove the spikes by increasing the output capacitor. It could help.
A simple series resistor will also reduce the spikes. You could experiment with the value. Larger values will give better filtering but also drop more voltage.
A DC choke wold be more effective, but check for excessive spiking on the fan side, A capacitor might be needed directly across the fan also.

Extra: A good option is some series resistance plus a capacitor directly across the fan.
« Last Edit: September 21, 2019, 10:37:46 pm by xavier60 »
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 

Offline OM222O

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Re: My first power supply
« Reply #29 on: September 23, 2019, 01:53:23 am »
using a common mode choke followed with 4 capacitors and an inductor (2 large value electrolytics / tantalums and 2 small value ceramics) in a pi filter configuration should basically drop that switching noise to nothing  :-+ although I think the pi filter alone should be good enough in this case.
 

Online MarkF

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Re: My first power supply
« Reply #30 on: September 23, 2019, 02:00:03 am »
You could also add a series resistor with the fan from the unregulated side (before the LM78xx's).  You will have to experiment a little with the resistor value to get the fan voltage down to 12V (and maybe 10 or 11 volts).  If the fan still puts out enough air flow, it will be a little quieter with a slightly lower than rated voltage.

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.

Edit:  I just checked your first post.  The transformer output is only 12V CT @ 500mA. 
You are NOT going to get a lot of power from you supply. 
Watch that the combined output of both regulators is less than 500mA.

At 500mA and larger heatsinks, you probably do not even need a fan.
« Last Edit: September 23, 2019, 02:12:23 am by MarkF »
 
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Online MarkF

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Re: My first power supply
« Reply #31 on: September 23, 2019, 02:02:10 am »
using a common mode choke followed with 4 capacitors and an inductor (2 large value electrolytics / tantalums and 2 small value ceramics) in a pi filter configuration should basically drop that switching noise to nothing  :-+ although I think the pi filter alone should be good enough in this case.

It is not a switching power supply.  A linear power supply with fan noise on the one output.
 
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Offline queennikki1972Topic starter

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Re: My first power supply
« Reply #32 on: September 24, 2019, 11:08:31 am »


Edit:  I just checked your first post.  The transformer output is only 12V CT @ 500mA. 
You are NOT going to get a lot of power from you supply. 
Watch that the combined output of both regulators is less than 500mA.

At 500mA and larger heatsinks, you probably do not even need a fan.

I upgraded the transformer to one I had lying around that is 1.8 amps, not 500mA since this is just an experiment for learning..

I learned from this project that I needed not only separate smoothing caps, but also at least 2 per side for redundancy. I will probably redo the entire main board to have separate caps and larger surface area for heatsinks.
Siglent SDS 1202X-E - Heathkit IO-4105 - Dr. Meter 0-30v 5a power supply - 862d+ combo unit - Weller WLC100 - Kunkin KL283 DC load. Not much gear yet.
 

Offline queennikki1972Topic starter

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Re: My first power supply
« Reply #33 on: September 24, 2019, 11:11:05 am »
You could also add a series resistor with the fan from the unregulated side (before the LM78xx's).  You will have to experiment a little with the resistor value to get the fan voltage down to 12V (and maybe 10 or 11 volts).  If the fan still puts out enough air flow, it will be a little quieter with a slightly lower than rated voltage.

I don't know why I didn't think of that!!!
Siglent SDS 1202X-E - Heathkit IO-4105 - Dr. Meter 0-30v 5a power supply - 862d+ combo unit - Weller WLC100 - Kunkin KL283 DC load. Not much gear yet.
 

Offline queennikki1972Topic starter

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Re: My first power supply
« Reply #34 on: September 24, 2019, 11:23:53 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.

Bridge Rectifier is 6A and the one large cap is 6800uf . When I redo the new board Ill put 2x2200uf cap 35v per side.
Siglent SDS 1202X-E - Heathkit IO-4105 - Dr. Meter 0-30v 5a power supply - 862d+ combo unit - Weller WLC100 - Kunkin KL283 DC load. Not much gear yet.
 

Offline mariush

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Re: My first power supply
« Reply #35 on: September 24, 2019, 11:49:56 am »
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.

 
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Online MarkF

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Re: My first power supply
« Reply #36 on: September 24, 2019, 05:17:40 pm »
Personally, I like the green protoboards.  Stick with them.


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.

Bridge Rectifier is 6A and the one large cap is 6800uf . When I redo the new board Ill put 2x2200uf cap 35v per side.

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:
842310-0

Or with a CT transformer you could reduce the voltage drop (i.e. heating) of the 5V regulator:
842314-1
« Last Edit: September 24, 2019, 06:36:20 pm by MarkF »
 
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Online MarkF

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Re: My first power supply
« Reply #37 on: September 24, 2019, 06:43:05 pm »
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
 
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Offline OM222O

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Re: My first power supply
« Reply #38 on: September 24, 2019, 10:36:12 pm »
It is not a switching power supply.  A linear power supply with fan noise on the one output.

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
 

Offline queennikki1972Topic starter

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Re: My first power supply
« Reply #39 on: September 25, 2019, 12:01:55 pm »
Personally, I like the green protoboards.  Stick with them.


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.


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.

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)
Siglent SDS 1202X-E - Heathkit IO-4105 - Dr. Meter 0-30v 5a power supply - 862d+ combo unit - Weller WLC100 - Kunkin KL283 DC load. Not much gear yet.
 

Offline queennikki1972Topic starter

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Re: My first power supply
« Reply #40 on: September 25, 2019, 02:08:09 pm »
The Capacitor across the fan stopped the fan noise almost completely.
Siglent SDS 1202X-E - Heathkit IO-4105 - Dr. Meter 0-30v 5a power supply - 862d+ combo unit - Weller WLC100 - Kunkin KL283 DC load. Not much gear yet.
 

Online MarkF

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Re: My first power supply
« Reply #41 on: September 25, 2019, 07:29:56 pm »
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.

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.

You don't have sides unless you are going to use a CT transformer as in my second circuit.
In your original circuit, all I was trying to say is you might want to add a 2200uF to the 6800uF since you are at the minimum as shown in @mariush's calculation.  I don't think it is necessary for you to disassemble what you have.  If you don't expect to pull maximum current, you could stay with just the 6800uF with larger heatsinks.

If you want four 2200uF capacitors in parallel, that's okay too.

Oh, you don't need LEDs either since your meters will provide the minimum load.

You might want to review the calculation for the ripple capacitor value.

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 you'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.
"The LM7812 dropout voltage is 2V."

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.

With some visual aids.  See also:  https://www.electronics-tutorials.ws/diode/diode_6.html

The minimum capacitor is
   C = ILOAD / (2 * fLINE * VMAX_RIPPLE)




« Last Edit: September 25, 2019, 08:18:13 pm by MarkF »
 

Online MarkF

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Re: My first power supply
« Reply #42 on: September 27, 2019, 02:24:56 am »
So, I did go back and add the protection diodes, green banana jacks tied to PE, larger heat-sinks and a larger transformer of 12v 1.8 amps. I did not use the adjustable pots as the LM7812 and LM7805 are not variable. I measured the ripple and it looks good. I am purchasing a electronic dc load after December so Ill be able to test the load. I've tested about .25 amp load and seems to run nice and cool.

I've since built a variable supply with LM317T and working on a dual adjustable supply of 1.5-60vdc. With each type I learn more. After I fully understand the linear supplies Ill try some switch-mode supplies or some built using IC's and Transistors.

BTW
If you would like to build a DC Load, here is a link to the one I built:
   https://www.eevblog.com/forum/beginners/struggling-with-dc-load/msg2698044/#msg2698044
 
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Offline queennikki1972Topic starter

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Re: My first power supply
« Reply #43 on: September 28, 2019, 03:49:51 pm »
I did build a different power supply using a positive +12 and Negative -12 with a common in the middle and a center tap transformer.  I used the protection diodes, the led indicators and larger heat sinks. Yes I am very interested in building the load. I was actually going to buy one but this sounds fun.
« Last Edit: September 28, 2019, 04:10:40 pm by queennikki1972 »
Siglent SDS 1202X-E - Heathkit IO-4105 - Dr. Meter 0-30v 5a power supply - 862d+ combo unit - Weller WLC100 - Kunkin KL283 DC load. Not much gear yet.
 

Online MarkF

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Re: My first power supply
« Reply #44 on: September 28, 2019, 07:13:02 pm »
I did build a different power supply using a positive +12 and Negative -12 with a common in the middle and a center tap transformer.  I used the protection diodes, the led indicators and larger heat sinks. Yes I am very interested in building the load. I was actually going to buy one but this sounds fun.

You will want a large heatsink for the MOSFET.  I used:
   https://www.digikey.com/products/en?keywords=RA-T2X-64E
It will definitely will need a fan also.

The MOSFET I used was an IRFP064.  I reworked the PCB and going to use an IRFP250 that's cheaper.
I suggest something in a TO-247 package.  Twice the size of a TO-220 for better heat dissipation.


Design guidelines:
 - The (+) op-amp input (and hence the sense resistor) voltage range is 0V to 0.5V. 
You set the maximum current capability by selecting a sense resistor knowing its max voltage will be 0.5V. 
In the circuit the sense resistor is 0.200 Ω which results in a 2.5A maximum load current setting. 
I recommend you select a sense resistor in the range of 0.100 to 0.500 Ω  (i.e. 5A to 1A respectively).
« Last Edit: September 28, 2019, 08:08:43 pm by MarkF »
 
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Online MarkF

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Re: My first power supply
« Reply #45 on: October 01, 2019, 10:18:51 pm »
While building your Electronic Load, this schematic of the HP-6060 may be a helpful reference
(It was posted somewhere here but I can't find the reference):

846488-0
 


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