Power Supply Project

Discussion in 'The Projects Forum' started by mbxs3, Feb 18, 2011.

  1. mbxs3

    Thread Starter Active Member

    Oct 14, 2009
    Hey guys... looking for a little input on a project I am doing...

    A little pre-question background...I built a regulated DC power supply IAW "Tab Electronics Guide to Understanding Electricity and Electronics" by G. Randy Slone a while back. The build went great and everything works as designed and I learned a little bit along the way. The one thing I want to change is the enclosure it is in and I also want to add a few things to the design such as a few LED's for visual indications like "power on" and "stand-by" as well as indicating whether the "positive" or "negative" circuit is energized. I also want to add a digital volt meter that indicates anywhere from -50 to +50 vdc. And lastly I want to put a fan in the enclosure linked up with a thermal switch to help keep everything cool incase it starts getting warm. I realize some of these features are overkill and the main reason I want to do them is for the learning experience.

    At the moment I am teaching myself about PIC microcontrollers so I want to utilize a PIC to control the LED's, fan, and a relay that will switch the power input to the voltmeter.

    So my question is basically, is a PIC the correct way to go about making this circuit? The inputs and outputs are going to be as follows:

    Power Switch "on" ------------------------> Green LED
    Power Switch "off" ------------------------> Orange LED
    Voltage Selector Switch "positive" -------> Red LED "1"
    Voltage Selector Switch " negative" -----> Red LED "2"
    Voltage Selector Switch "negative" ------> Control Relay Coil
    Thermal Switch ----------------------------> Fan

    Should the PIC I choose to control this circuit be picked based solely on inputs and outputs available or are there other factors I should consider? I have the following PIC's in my possession: PIC12F508, PIC12F675, and PIC16F54. Unless I think of anything else I want to incorporate, it looks like I am looking at 5 inputs and 6 outputs.

    Any input, positive or negative, will be greatly appreciated.
  2. SgtWookie


    Jul 17, 2007
    Adding a PIC to perform these functions will add unnecessary complexity, reducing the reliability of the supply.
    You have not posted a schematic of your supply, so it'll be rather difficult to give anything but general suggestions.

    Use a simple green LED and current limiting resistor to indicate when the unregulated portion of the supply is powered.

    Use a neon indicator across the fuse on the primary side of the transformer to indicate that the fuse is blown.

    Use two LEDs in parallel with a single current limiting resistor to indicate polarity.

    The fan control is kind of a separate issue. First of all, do you have 12v available to power a computer-type fan?
    Powering a fan from the secondary side will reduce the supply current available; you may want to simply use a 120v powered fan.
    PackratKing likes this.
  3. madman6233

    New Member

    Mar 4, 2011
    Yes please do post a schematic I have spent most of the night learning how to use the paint program so that I might be able to start a thread about all the problems I am having trying to construct my own power supply. although at this point I have parts gathered enough for several I think.
  4. Wendy


    Mar 24, 2008
  5. mbxs3

    Thread Starter Active Member

    Oct 14, 2009
    Sorry it took me a while to respond with any information. I went ahead and followed Sgt's advice on not using a PIC for this project. I am sure I will find a project that involves PIC's in the future to help me further my education. I ended up taking a regulated 5vdc wall wart apart and mounting it in my PSU to provide 5vdc for my LEDs and digital voltmeter so it is separated from my actual regulated dc power supply.

    Madman- I built my power supply unit IAW "Tab Electronics Guide to Understanding Electricity and Electronics" by G. Randy Slone. The PSU is capable of providing regulated positive and negative dc output, from approximately -35vdc to -4.5vdc and 4.5vdc to 35vdc. I definitely recommend this book for anyone new to electronics. Here is a scanned image from the book of the control circuit used for the positive and negative legs...note that the control circuit being fed by 2 transformers(24v @ 2 amp/ 120vac primary), 2 capacitors(4400uF, 50 WVDC) and 1 6-amp, 200 volt PIV bridge rectifier. The reason for 2 transformers and 2 caps is that one transformer/cap is for the positive side and one is for the negative side. If you only want a positive dc output you could leave out half of the components I am mentioning.

    The components used in the control circuit are as follows:

    D1-D6= 1N4001 (NTE 116) General Purpose Silicon Diode
    R1 and R2= 1000 ohm, 2 watt resistors
    R3 and R4= 2.2k ohm, 2 watt resistors
    R7 and R8= 470 ohm, .5 watt resistors
    R5 and R6= .4 ohm, 5 watt resistors
    P1 and P2= 1000 ohm, linear taper, 2 watt potentiometers
    C3 and C4= .1 uF, ceramic disk cap
    Q3 and Q5= TIP 31C (NTE 291) transistor
    Q4 and Q6= TIP 32C (NTE 292) transistor
    Q1= 2SC3281 (NTE 2328) transistor
    Q2= 2SA1302 (NTE 2329) transistor

    I used PCB's, banana jacks, fuses, fuse holders, and switches that I had acquired from other tasks. Later today or tomorrow I will get a picture up of the PSU if anyone wants to see it.
  6. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    No comments on your new design, but from a human standpoint, I would suggest that LED1 and LED2 be different colors, perhaps green and red, respectively.

  7. mbxs3

    Thread Starter Active Member

    Oct 14, 2009
    When I get the pic up of the PSU it will probably make more sense but the way I have it hooked up, only 1 output can be on at a time, positive or negative. The output selector switch determines this and the associated LED lights up when the output banana jack is live. I have the positive side controls and jacks on the left side of the enclosure and the negative controls/jacks on the right side. So having 2 red LEDs for indicating which output is on isn't an issue.
  8. mbxs3

    Thread Starter Active Member

    Oct 14, 2009
    Here are some pics...please excuse the ugliness of the enclosure. My next task is to get it painted.

    In picture 1, the PSU is not plugged up to a live outlet so there is no LED indication.

    In picture 2, the PSU is plugged into a live outlet, but is not turned on so the red power LED is illuminated. (Power is coming from 5vdc regulator that is connected to 120vac through a fuse)

    In picture 3, the supply is turned on and the positive output is selected(the selector switch is the lowest switch in the center). The green LED is illuminated because the power switch is on( power switch is above green LED). Although the positive output is selected and indicated on the voltmeter, no power is on the positive output jack(leftmost red banana jack).

    Picture 4 shows the red positive LED illuminated because the positive control switch is on(switch above the jacks on the left). This allows me to secure power to the output jacks if I need to make a change, without cycling the unit on and off. The magnitude of the positive voltage output is controlled by the silver knob on the top left of the unit.

    Picture 5 is the same as picture 3 but for the negative side.(I apologize for the picture being upside down.)

    Picture 6 is the same as picture 4 but for the negative side.

    Picture 7 shows the left side of the enclosure where the power cord plugs, a switch to turn a 120vac fan on or off, and 3 fuse holders. One fuse is for the 120vac input. One fuse is for the positive output, and one is for the negative output. There are 2 other fuses that are inside the enclosure. One is for the fan, and the other I mentioned is for the 5vdc circuit that powers the voltmeter and LEDs.(Picture 7 will be attached to next post due to 6 attachment limit)

    Like I said, one of these days I will take the face plate off and paint it up so it looks nicer. Another thing I would like to do is get some decent placards for the switches and what not, something nicer then a label maker sticker if you know what I mean. If anyone has some advice on what to use for that, please throw it my way. Any other comments, positive or negative, are also welcome.
  9. mbxs3

    Thread Starter Active Member

    Oct 14, 2009
    Here is picture 7...
  10. SgtWookie


    Jul 17, 2007
    Gee, having to select which output is active and not being able to have both on at the same time completely defeats the idea of having a dual-rail power supply.

    Rather than switching which output is on, why don't you switch which output is being measured by the meter?
  11. mbxs3

    Thread Starter Active Member

    Oct 14, 2009
    Funny you say that Sgt because I actually just discovered that, due to the way I wired it, both outputs are available at the same time while only one output will be displayed on the meter. I'll have to do some rewiring though because the LED of the output that is not selected does not light up even though voltage is present if the corresponding switch is turned on.

    I am at a very low level of knowledge when it comes to all of this so I do not realize the benefit of having a dual rail power supply. Oh well, this is how I learn so I am sure that one day I will have some clue of what I am doing and it will be useful to me.