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Topic: Benchtop Power supply unit with LCD display (Read 6914 times) previous topic - next topic

Benchtop Power supply unit with LCD display

+5V supply 1Amp max,
-5V supply 1Amp max,
+3.3V supply 0.8Amp max,
+9V supply 1Amp max,
+12V supply 1Amp max,
-12V supply 1Amp max,
-1.25 to -12V Adjustable at 1.5Amp max,
+1.25 to +12V Adjustable at 1.5Amp max,
Uncontrolled +17 and -17V at 3Amp Max. Useful for charging battery.(-17 and +17 will make +34V also)
Total power load with all port will be max 72Watts.
Simultaneous real time analyzing and display of all(1-8) output's voltages and temperature in LCD with WARNING function in case of irregularity beyond +/- 10%.
All these will be monitored by an Atmega32 IC 16Mhz crystal and JTAG disabled for additional IO pins.
Highly noise free filtered pure D.C output at regulated terminals.
Current limiting circuitry not required as all carefully chosen regulator ICs(78xx, 79xx) will have thermal shutdown and overload protection.
The LCD is a 128x64 GLCD which is of enough size for proper reading of information. I'll not use the cheap nokia LCDs this time as I want a larger display.
Supply transformer is 12-0-12 3Amps transformer.
Wiring to GLCD will be done as the TUT by extremeelectronics, and the most chance is of using ProGFX.
http://extremeelectronics.co.in/avrtuto ... mega32.gif

The positive rails supplies will be fed to the ADC inputs through resistor divider. Negative voltages will be inverted and scaled to fit within 5V range by an op-amp as inverting amplifier.



Schematics for the same in Eagle [attachment=0]

The schematics is bit incomplete. I have to connect the GLCD and add the LM324N Op-amp and resistors for the voltage conversion for ADC.

This month's last week will be designing (virtual) stage, and when in  1st december I'll get December's budget, I'll buy the parts(Now I lack the GLCD, blank CCB, good multilayer decoupling capacitors, and some small things). Total BOM maybe near 50$.

Another concern is routing in single layer within the 100x80 limits in Eagle. Without the resistors and opamp, now the board looks to be much congested. And everybody knows, PSU unit will need 100mils~150mils track for power lines.
Still learning
-Arup

Re: Benchtop Power supply unit with LCD display

Reply #1 –
Have you considered using an old computerpowersupply? except for the variable voltage (easy to do with a LM317 and it's negative equivalent) and 17 V ( or -5V and +12V)  everyhting is present, beefy, nicely stabilezed and well tuned. Get one second handed for 10-20$ some nice bananajacks et presto!

overhere a picture of mine: viewtopic.php?f=19&t=3006

I basicly connected a 10watt 10ohm resistor in the 5v line (switching powersupplies need a load) and connected the poweron to gnd. There are lots of tutorials on the internet.

I believe arhi showed off his with variable voltage output based on lm317 somewhere in this forum

Re: Benchtop Power supply unit with LCD display

Reply #2 –
Yeah Sjaak, there's lots of instructables of creating bench top supply by ATX PSU, but I don't like the risky stuff. I'll never need the 34Amps at 5V. 1amps is enough for any of my hack/project, etc.
Here in India local brands' ATX PSU costs ~8$ only with 2 years warranty(which I love voiding).
As you can see my unit has both LM317 and LM337 for negative and positive supply.
The 3Amps 12-0-12 transformer is the best riskless thing IMO. ATX SMPS work in HV DC and lots of amps. Anything can happen.

EDIT: Thanks Sjaak, tomorrow's thanksgiving day. I give thanks to you in advance.
Still learning
-Arup

Re: Benchtop Power supply unit with LCD display

Reply #3 –
Overhere they come fully enclosed in metal (grounded) together with some fuses (I'm planning to use those resettable ones for this, currently the low voltage is unfused) I believe they are as safe as a lineair voltregulator with transformer (assuming you shield the mains part for prying fingers and use fuses)

But it is your project and love to see how it ends up.

happy thanksgiving!

Re: Benchtop Power supply unit with LCD display

Reply #4 –
Fruit machine PSU might also be a contender - wider choice of voltages available, individually fused outputs.  For example that from a JPM Impact based machine: http://www.ebay.co.uk/itm/JPM-POWER-SUP ... 0896975567

The 5/12/24V side should be well regulated as it's used to run the electronics in those machines, which is a custom MC68000 based design.

Re: Benchtop Power supply unit with LCD display

Reply #5 –
I noticed that I have eight led's. Looking at the schematic I believe I am supposed to solder 4 of them on the backside, is that correct Nice posts guyes i really like ......... thanks
"Chand"

Re: Benchtop Power supply unit with LCD display

Reply #6 –
[quote author="Sjaak"]Overhere they come fully enclosed in metal (grounded) together with some fuses (I'm planning to use those resettable ones for this, currently the low voltage is unfused) I believe they are as safe as a lineair voltregulator with transformer (assuming you shield the mains part for prying fingers and use fuses)

But it is your project and love to see how it ends up.

happy thanksgiving![/quote]
Hehe, this is an old post :) I'd just like to point out that the metal case of a ATX power supply is both connected to Earth mains wire, and to the black Ground wire....This in my opinion is a real problem, cause I can easily imagine myself leaving an exposed probe on top of it and causing a short.... Fix: The Ground wire is connected to the case through the PCB mounts, instead of screws yous a layer of hot glue to gold the pcb in place on the mounts...any other screw type insulation system, like the to220 heat-sink connections, etc
best regards FIlip.

Re: Benchtop Power supply unit with LCD display

Reply #7 –
I realize this ia an old thread, but as others may read this the info will beuseful.

1.  Your want 72W max power from all ports, however the stated port limits add up to 183W:
2.  Your chosed transformer is 72VA, which is not  enough to supply 72W let alone 183W.  Upgrade to a 250VA transformer
3.  You are relying on the thermal shutdown of the 78xx and 79xx ICs to provide current limiting.  Thermal cutoff does not current limit it prevent s the IC from overheating.  Using the themal cutoff as current limit will kill the ICs over time.  Every datasheep i've read doesn not recommend using the internal thermal protection as the primary protection.

Take alook at the OPA549 or whatever is current now for a robust power supply source.  Better yet, is to roll your own regulator circuit to learn how a PSU really works.  Linear regulators are simple to build -- minimum two transistors, one zener diode, three resistors.

Re: Benchtop Power supply unit with LCD display

Reply #8 –
[quote author="bahremu"]Take alook at the OPA549 or whatever is current now for a robust power supply source.  [/quote]

Some years back I bought a couple of the beefier OPA5** planning to build a uc-controlled PSU.  I never got around actually building it - I even never did a quick prototype. 

But I remember that they are not capable of reel-to-reel on the output and I wanted to be able to go down to true zero volts so I needed to to a dual supply to the OPA. I've got a nice ~500 VA toroid transformer that I can put some taps on to let the input voltage track the desired output voltage to reduce the loss in the OPA. 

But I'm not too sure if the negative supply rail to the OPA needs to be of the same power as the positive?  Like if I pull 10 amps at 0.5 volts from the output I'll definitely need 10 amps at the positive rail, but what about the negative rail - is only a few mA for some internal biasing necessary or is there some internal current mirror in the OPA so II'll also need 10 amps there?  (Probably not since it sounds just silly, but I'm not too knowledgeable about the actual internal magics of a power op-amp...)

Re: Benchtop Power supply unit with LCD display

Reply #9 –
LOL!  I did the same and ran into the same questions.