Linear lab power supply

[spec]

Looking good. Your case has a sort of military look to it.

Just one thing: I would suggest having the fans sucking or blowing out. You don't want to have the hot air from the heatsinks blowing into the case.

Apart from the power transistor/s, the components including transformers, rectifiers and reservoir capacitors will be OK with convection cooling and do not need fan cooling, providing you have sufficient vents on the case.  The bridge rectifier may need a heatsink, but the chassis will do for that.

PS: Don't let anything get in the way of your studies. Good exam results are essential- you can do PSUs anytime.

[JuanGg]

Looking good. Your case has a sort of military look to it.

Just one thing: I would suggest having the fans sucking or blowing out. You don't want to have the hot air from the heatsinks blowing into the case.

Apart from the power transistor/s, the components including transformers, rectifiers and reservoir capacitors will be OK with convection cooling and do not need fan cooling, providing you have sufficient vents on the case.  The bridge rectifier may need a heatsink, but the chassis will do for that.

It must be the green I guess. It just happens to be the only filament I have around.
Having the fans blow the hot air out is what I wanted on the first place. I will try to cut the fans out of their support and mount them reversed.
Can't the bridge rectifiers be mounted on the same heatsink as the power transistor? I won't have much metal chassis, but just a cover. (Not shown).

PS: Don't let anything get in the way of your studies. Good exam results are essential- you can do PSUs anytime.

No worries. I have my priorities right. I don't work on this on weekdays.

[spec]

Can't the bridge rectifiers be mounted on the same heatsink as the power transistor? I won't have much metal chassis, but just a cover. (Not shown).

Not advisable- look upon the power transistor heat sinks as heaters as far as other components are concerned.

Normally an aluminum bracket or sheet is sufficient. The bridge rectifiers will only be dissipating around 500mW each anyway. Rectifier cooling is not an issue.   

PS: Don't let anything get in the way of your studies. Good exam results are essential- you can do PSUs anytime.

No worries. I have my priorities right. I don't work on this on weekdays.

That's the way

[perieanuo]

The ventilation for even 1 amp is overkill,I did more with 1 40x40 quiet one.with those and 2-3 power transistors you can go to 10 amps.I end up putting an termistor on the heatsink with pwm control at 3 different temps(I have atmega328 board monitoring U-I with ina sensor showed on oled white,looks fine).And the atmega can easily monitor between U and I the temp and put some pwn on the ventilation, cost bucks and works fine, coding is simple.
Regards,pierre


Envoyé de mon iPad en utilisant Tapatalk

[fsr]

When i buit mine, i went fanless. It had 34W max dissipation. I put the transistor with mica and carefully applied thermal grease on the heatsink. The MJ15003 transistor did most of the magic. Rth J-C of 0.7 °C/W and 200 °C max junction temperature. I don't really know how much i used it at full load + low voltage, but the magic smoke remains contained up to this day
Look at the attached datasheet for details of how to calculate this stuff. Page 10, "Heatsink Requirements". Just substitute the PD and other characteristics with the ones for your transistor.
TO-3's are hard to mount, but with that thermal figures, it's worth the effort for me! Check other power packages, anyways, but it's probably hard to beat a metal can mounted with two screws.

Remember that CPUs sometimes reach power dissipations up to 135 watts (but obviously not all CPUs). So that's probably too much cooling in this case.

Also remember that hot air moves up, so you need to put ventilation holes or fans near the top of the case blowing air out. That's why good vertical computer cases have the PSU on the top, and input ventilation holes on front, near the bottom.

In my case, i just put the heatsinks on the outside, so i didn't have to deal with that. Just natural convection, and it goes up unimpeded.

[spec]

The ventilation for even 1 amp is overkill,I did more with 1 40x40 quiet one.with those and 2-3 power transistors you can go to 10 amps.I end up putting an termistor on the heatsink with pwm control at 3 different temps(I have atmega328 board monitoring U-I with ina sensor showed on oled white,looks fine).And the atmega can easily monitor between U and I the temp and put some pwn on the ventilation, cost bucks and works fine, coding is simple.
Regards,pierre


Envoyé de mon iPad en utilisant Tapatalk

I take it that by ventilation, you mean fan cooling. I don't like the term overkill- it is a sweeping statement that can be used to criticize pretty much anything. After all, your house, car, PC are all overkill.

Although I tend to agree with you that fan cooling is probably is not necessary, you cannot say for sure without doing a thermal budget and to do that you would need to know the thermal resistance of the heatsink being used. Besides which, the OP already has the fans and heatsinks which were pulled from another unit.

The other point is that, not only will this PSU design and construction result in a usable PSU, but it will be a very good experience for the OP, who is just starting in his electronics career. It is probable that this PSU will be further developed, maybe to have more output voltage and current, at a later date, so a low thermal resistance heat sink would then be an advantage.

You mention about your own power supply- feel like posting a schematic? There is always great intrest in PSUs on EEV.  

[spec]

When i buit mine, i went fanless. It had 34W max dissipation. I put the transistor with mica and carefully applied thermal grease on the heatsink. The MJ15003 transistor did most of the magic. Rth J-C of 0.7 °C/W and 200 °C max junction temperature. I don't really know how much i used it at full load + low voltage, but the magic smoke remains contained up to this day

That is real class. The MJ15003 is a beauty. Unfortunately the more mundane, but cheaper, 2N3055 has a thermal resistance junction to case of 1.52 DegC/W, more than twice that of the MJ1503. But the 2N3055 safe operating area (SOA) is better.

https://www.onsemi.com/pub/Collateral/MJ15003-D.PDF
https://www.onsemi.com/pub/Collateral/2N3055-D.PDF

Would be great to see a schematic of your PSU.

Update: just checked prices from DigiKey UK, the MJ15003 costs £6.36 and the 2N3055 costs £4.60, so not a vast price difference.

[spec]

There has been quite a bit of discussion about heat sinking, both on this thread and elsewhere on EEV.

Just to give give an overview, here is a description of a thermal budget using an actual heatsink and power transistor.

Assume, due to space and cost considerations, that the following heatsink must be used in an equipment: https://www.apexanalog.com/resources/mechdrawings/hs14.pdf. This heatsink is quite expensive at £51.11UK and fairly large at 5 by 3 by 1.3 inches. Its thermal resistance in free air is 2 degC/W.

You have one 2N3055 transistor and you want to know how much power you can theoretically dissipate.

So the list of parameters is:

• 2N3055 maximum junction temperature (Tjmax): 200 degC
• 2N3055 thermal resistance junction to case (ThRjc): 1.52 degC/W
• Insulating washer between 2N3055 case and heat sink thermal resistance (ThRwasher): 1 degC/W
• Heat sink thermal resistance to air (ThRhs): 2 degC/W
• Air temperature in the vicinity of heatsink (Tamb): 70 degC

Armed with this information, a thermal budget can be calculated from the following formula:

Tjmax = P (ThRjc + ThRwasher + ThRhs) + Tamb

P is required, so transposing gives,  P = (Tjmax-Tamb) / (ThRjc + ThRwasher + ThRhs)

Inserting actual values gets, P = (200 - 70) / (1.52 + 1 + 2) = 28.76W

That is the maximum theoretical dissipation and does not include, a safety margin, SOA considerations, and temperature effects on SOA, for example.

At the end of day, you would probably end up with a practical maximum power dissipation of 20W to 25W.

[fsr]

Would be great to see a schematic of your PSU.

I have some screen captures back from the days i built it. It's just a circuit it used to be on the LM317 datasheet i attached before, with some modifications, and also a negative version. I didn't really ever tested it, but seems to do the job. I had to build it in 3 boards, because of limitations on Eagle PCB.

If someone is interested on the PCBs, i can open Eagle and PDF them, or upload the files.

I posted it on another forum back in tha day, but it didn't catch much attention, so i never released much about it.

Again, the power transistors are MJ15003 and MJ15004.

[JuanGg]

I have printed and glued the back panel together. I won't bore you with the details, but sufices to say that big abs pieces don't get 3d printed without putting up a fight. I just printed it in pieces and acetone welded it together. Attached are some photos.
I think I am keeping the fan and heatsinks as they are, just blocking the inner sides, so air enters the back, goes through the heatsink and exits through vent holes on the sides, without going into the case.

Juan.

[spec]

so air enters the back, goes through the heatsink and exits through vent holes on the sides, without going into the case.

 

[JuanGg]

Thinking about the user interface, I saw the power supply attached, which is was very similar to what I had thought (withoght the middle chanel). I just think it is very simple and functional. The downside is that it would require isolated comunication between chanels (serial via optocouplers between arduinos?). Each chanel would have its display, and only one of them would read the encoder and buttons, sending information to the other via isolated serial. This way I could do tracking or whatever. Other way I thought of doing is using a central arduino that reads the encoder and keys, and sends the information to the other two, also providing an isolated USB, so the PSU can be interfaced with a computer. (See diagram attached). Is it feasible? Or maybe too much for a first power supply? I don't think it is very hard to acomplish, and given the arduinos are very cheap, I don't mind including three of them in the unit.

Juan

[wasyoungonce]

.............
If someone is interested on the PCBs, i can open Eagle and PDF them, or upload the files.I posted it on another forum back in tha day, but it didn't catch much attention, so i never released much about it...Again, the power transistors are MJ15003 and MJ15004.

Actually yes please...I need a basic fixed rail supply and some limited variable outputs.  I already have qty 2 PS-3005Ds 30V/5A but I really need something simple to drive small motors (want to monitor their start voltage currents) and logic ccts.  The others will do this but far easier to have a small supply with fixed and some variable outputs.  Eagle .sch .brd  etc would be great...also whats the I/P transformer ~ 15VAC?   In VA?  I do have some decent 30VAC ~@120VA but they are probably a little too high in output.

I'm supposed to be trying to use KICad but its so difficult to leave something you already know so well! 
Many thanks

edit.....Oh I love your PSU you have done.....:

https://easyeda.com/asokolsky/Analog-Lab-Power-Supply

I have to ask...why a 56V out as there is a 0-30V and other fixed O/P?.   Maybe a bit of self gratification and promotion is due your way.  I see you designed it in with your own Amp/Voltmeter and fan controller. 

https://easyeda.com/asokolsky/AmpVolt-Meter-with-Fan-Control

Well done.   Looking intently at them for an unashamed and undeserved diy for myself. 

[Mr. Scram]

Thinking about the user interface, I saw the power supply attached, which is was very similar to what I had thought (withoght the middle chanel). I just think it is very simple and functional. The downside is that it would require isolated comunication between chanels (serial via optocouplers between arduinos?). Each chanel would have its display, and only one of them would read the encoder and buttons, sending information to the other via isolated serial. This way I could do tracking or whatever. Other way I thought of doing is using a central arduino that reads the encoder and keys, and sends the information to the other two, also providing an isolated USB, so the PSU can be interfaced with a computer. (See diagram attached). Is it feasible? Or maybe too much for a first power supply? I don't think it is very hard to acomplish, and given the arduinos are very cheap, I don't mind including three of them in the unit.

Juan

Ask yourself whether you want to multiplex the controls.

[JuanGg]

Ask yourself whether you want to multiplex the controls.

I don't really know if it's worth it. I can try different ways and see how it works out. Anyway, the important thing is to get the analog PSU working. I just have a tendency to overcomplicate stuff. As I said, I'll leave the front panel to last.

[perieanuo]

The ventilation for even 1 amp is overkill,I did more with 1 40x40 quiet one.with those and 2-3 power transistors you can go to 10 amps.I end up putting an termistor on the heatsink with pwm control at 3 different temps(I have atmega328 board monitoring U-I with ina sensor showed on oled white,looks fine).And the atmega can easily monitor between U and I the temp and put some pwn on the ventilation, cost bucks and works fine, coding is simple.

I take it that by ventilation, you mean fan cooling. I don't like the term overkill- it is a sweeping statement that can be used to criticize pretty much anything. After all, your house, car, PC are all overkill.

Although I tend to agree with you that fan cooling is probably is not necessary, you cannot say for sure without doing a thermal budget and to do that you would need to know the thermal resistance of the heatsink being used. Besides which, the OP already has the fans and heatsinks which were pulled from another unit.

The other point is that, not only will this PSU design and construction result in a usable PSU, but it will be a very good experience for the OP, who is just starting in his electronics career. It is probable that this PSU will be further developed, maybe to have more output voltage and current, at a later date, so a low thermal resistance heat sink would then be an advantage.

You mention about your own power supply- feel like posting a schematic? There is always great intrest in PSUs on EEV.

hi,
for me overkill means too much.
I attached my schematic, it's not the final version, I upgraded current sense.But the idea is, I put also temperature measurement and tested the thing at 3.000 Amps with variable load.
The temp stabilised to 44-48 deg C if I remember right.I sense with 10K NTC thermister and I was calibrated with Volcraft PL-125-T2USB.
I pwm to fan starting at 30 deg C (33%, then 66% at 40deg then 100% at 50degC).
If my 40*40 fan succeed to cool the 2xTIPL790A transistors delivering 3amps at 5V from 24 Vac transformer that means those 2x80*80 fans will be toooo much for what OP wants( he has 2 amps rated transformers).
Imho, he can think of more current with those fan/cooler combination and he MUST reduce fans speed, a variable lab supply MUST be quiet, it's not just fancy stuff, when you're focused doing electronics and coding some dsp last thing you need is a stupid vent crying.
Same cooling technique I did for other people in scopes for example (one of my bosses had enough of his oscillo and power supply doing noise when he was working on research stuff).
I take seriously the cooling, I'm not perfect at this but even implement a fan cooling controled by a thermistor and a fet who starts at a defined temperature for me is a must.
Attached I'll put schematics of one of my bench ps with power stage.just for example.I had a case and stuffed inside toroidal, power stage, simple opamp regulation (V/I control) and measurement with custom atmega 328 board, current module down to 0.1mA resolution is not in schematics, but it's in the picture ).
regards,Pierre

[perieanuo]

Thinking about the user interface, I saw the power supply attached, which is was very similar to what I had thought (withoght the middle chanel). I just think it is very simple and functional. The downside is that it would require isolated comunication between chanels (serial via optocouplers between arduinos?). Each chanel would have its display, and only one of them would read the encoder and buttons, sending information to the other via isolated serial. This way I could do tracking or whatever. Other way I thought of doing is using a central arduino that reads the encoder and keys, and sends the information to the other two, also providing an isolated USB, so the PSU can be interfaced with a computer. (See diagram attached). Is it feasible? Or maybe too much for a first power supply? I don't think it is very hard to acomplish, and given the arduinos are very cheap, I don't mind including three of them in the unit.

Juan

yes it's feasible, but you can do it with only 2 arduinos not 3, or better even 1 if you put galvanic separations, but costs a little more, you can calculate.what you economise on arduino you put in isolation, but switch to clean and pro solution.I did arduino-like board and ina219 voltage/current sense (mA resolution) but only 1 channel, I had only a small box for the PS (see my earlier post).
When I'll find a bigger one, I'll do like you said, central supervision and screen on 2 oleds or a big LCD.take a look on my pdf's if you want, posted earlier.control as I sugested the vents speed, most of the time you'll need zero active cooling so zero noise...you can do it with microcontroller/dsp or a simple FET transistor+thermister, costs nothing...
regards,pierre

[JuanGg]

I pwm to fan starting at 30 deg C (33%, then 66% at 40deg then 100% at 50degC).
If my 40*40 fan succeed to cool the 2xTIPL790A transistors delivering 3amps at 5V from 24 Vac transformer that means those 2x80*80 fans will be toooo much for what OP wants( he has 2 amps rated transformers).
Imho, he can think of more current with those fan/cooler combination and he MUST reduce fans speed, a variable lab supply MUST be quiet, it's not just fancy stuff, when you're focused doing electronics and coding some dsp last thing you need is a stupid vent crying. ...

Better safe than sorry  . I will do temperature-controlled fans anyway. I did implement a pwm temperature controlled fan on my electronic load and it worked quite well. Plus, this fans are quiet enough (compared to the rigol 1054z's anyway...). In fact, one of the transformers I plan to use is 1A rated.

yes it's feasible, but you can do it with only 2 arduinos not 3, or better even 1 if you put galvanic separations, but costs a little more, you can calculate.what you economise on arduino you put in isolation, but switch to clean and pro solution.I did arduino-like board and ina219 voltage/current sense (mA resolution) but only 1 channel, I had only a small box for the PS (see my earlier post).
When I'll find a bigger one, I'll do like you said, central supervision and screen on 2 oleds or a big LCD.take a look on my pdf's if you want, posted earlier.control as I sugested the vents speed, most of the time you'll need zero active cooling so zero noise...you can do it with microcontroller/dsp or a simple FET transistor+thermister, costs nothing...
regards,pierre

I just thought it would be easier to have isolated digital comunications, so I don't have to deal with nonlinearities on analog optocouplers and such (any other way of getting galvanic isolation?). Plus, I would have to control two four-digit sevent segment displays for each chanel. Anyway, I will deal with that later.

I am waiting for the AC mains conector (it's taking ages to arrive!) so I can wire the raw psu and test it. Regarding that, do I go with tap-switching?

Juan

[fsr]

.............
If someone is interested on the PCBs, i can open Eagle and PDF them, or upload the files.I posted it on another forum back in tha day, but it didn't catch much attention, so i never released much about it...Again, the power transistors are MJ15003 and MJ15004.

Actually yes please...I need a basic fixed rail supply and some limited variable outputs.

I found the files, and posted them here: https://www.eevblog.com/forum/oshw/basic-lm317-based-cvcc-15v15v-1-5a-split-lab-psu/msg2003093/#msg2003093

[wasyoungonce]

.............
If someone is interested on the PCBs, i can open Eagle and PDF them, or upload the files.I posted it on another forum back in tha day, but it didn't catch much attention, so i never released much about it...Again, the power transistors are MJ15003 and MJ15004.

Actually yes please...I need a basic fixed rail supply and some limited variable outputs.

I found the files, and posted them here: https://www.eevblog.com/forum/oshw/basic-lm317-based-cvcc-15v15v-1-5a-split-lab-psu/msg2003093/#msg2003093

Many thanks watching that thread now

[coppercone2]

Exams more important then anything in engineering?? Set sail for the sales department!

Whats important is doing the job right at any cost.

[JuanGg]

Exams more important then anything in engineering?? Set sail for the sales department!

Whats important is doing the job right at any cost.

I try to do both things right. 

Here is some progress with the case. I have attached the transformers, changed locations a little bit. My idea is to have the raw PSU section between transformers and the rest on the sides. I'll try to wire the bridge rectifier and filter cap for one side this weekend. It will temporarily take the full 25 Vac, I'll eventually add a relay and make a PCB.

[fsr]

.............
If someone is interested on the PCBs, i can open Eagle and PDF them, or upload the files.I posted it on another forum back in tha day, but it didn't catch much attention, so i never released much about it...Again, the power transistors are MJ15003 and MJ15004.

Actually yes please...I need a basic fixed rail supply and some limited variable outputs.

I found the files, and posted them here: https://www.eevblog.com/forum/oshw/basic-lm317-based-cvcc-15v15v-1-5a-split-lab-psu/msg2003093/#msg2003093

Many thanks watching that thread now

[JuanGg]

Here are some photos of the wiring I have done so far. I just took the ac mains conector from my other power supply as it's running off a wall wart, I'll replace it when the new one arrives. I also changed the 10 A fuse that came with it with a 1 A one, which is the smallest I have around. I'll put a smaller one later.
I have wired all the transformers to the mains input, all conections heatshrunk and all exposed areas covered in electrical tape. (I know it's not the best, but it lessens the chance of me getting shocked). Transformer cores are grounded and I used reasonably thick wire. Wires coming out of the transformers are color-coded so I know hot to connect them so that the phases are in sync (I checked that with the scope). I will continue next weekend.

Juan

[JuanGg]

I have "bodged" the bridge rectifier and the filter cap just to try it out. Attached is a picture and some scope screenshots. Last one is the capacitor being charged and discharged by the 500 bleeder resistor after turn off. My electronic load can't handle more than 30 V, so I was unable to test it with it. I also don't have power resistors around, so I paralleled a dozen 1/4 W ones, but drawing 250 mA they still got too hot. Voltage dropped from 38 V to 36 V. I'll look for means of testing it properly.

Juan