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redwire
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Posts posted by redwire
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Liquibyte, That is a beast!
Looks well organized with no expense spared. I have a couple of questions:
What size transformer is in the middle (to power the display I assume?)? Is the rectifier for that mounted on the bottom?
What is the VA of the large transformers?
It looks like you have 2 output transistors per half mounted to the rear. What kind of heat sink is on the back?
How many turns are your 4 Potentiometers and where did you get them.
You have 2 heat sinks near with transistors, attached near the bridge rectifiers are those the BD139's?
I see you have headers with the green and black wires so you will have no need to additional pinouts on the board for the microcontroller connections for R7. -
liquibyte, R7is the sense resistor, meaning if you measure the voltage drop across the resistor you can determine how much current is being drawn using I = V/R. If you use a microcontroller to drive your display you can utilize one of the ADC pins to measure the voltage drop in order to compute current. Likewise Pin 3 of U3 controls the current limit of the device. For example if you set Pin 3 to 1.0V (by adjusting P2) then there will be no current cutoff until I = 1.0/0.47ohms = 2.1amps. By also hooking up another ADC pin of you microcontroller to Pin 3 you can measure the voltage on Pin 3 and display what the current control is set to. Without a display you don't know the current limit setting.
By the way, R7 is typically a 5 to 10W resistor that takes up a large chuck of real estate. I didn't see anything like that on your board so I assumed you were mounting it to the frame. If not you may want to make adjustments. -
Liquibyte, I assume you are going to eventually have a some sort of display. You may want to determine if you need any connections from your board to the microcontroller for power. If you want to display the max setting of the current control, will you need to measure the voltage of Pin 3 on U3? Another decision, do you want to add "green power on" led for the board indicating both boards have powered up? On my board I had one onboard led for current control and a set of jumpers for the LED on the case. While testing I didn't have to bother with hooking up a led. Are your power paths wide enough (I did not examine ).
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Hi Zinci, Welcome to the forum. It's good to hear a new member's perspective of where we are. I think there is one basic design that that been fairly consistant. Audioguru reposts the sketch about every 2 pages because of the tremendous number of pages to weed through but that basic sketch is shown on the first post and the parts are listed on the 2nd post. Sure there are two trimmers without part numbers but the values are listed. If you look at the photo of my board (built off the sketch shown) you will see a date of 9/25/08. Note that that design is still current despite 5 years of discussion. Sure we might have tweaked one or two component values but it works fine. You are correct I didn't post the .sch file because it was my first Eagle attempt and it was/is a mess. I never bothered to clean it up so I never posted it, but the board file could be used to make pcb's. I built a 30V 3A version, a 50V 5Abut all have the same basic design layout. Just for the fun of it, I built a SMD version by taking my original Eagle .sch and changing compontents. Many individuals post sketches during the design and build phase but how do you know they work?
There might be minor component changes but many are preferences. For example, the heat sinks for the 3055's run 9 times the cost of the transistor. While the 3055's output transistors are readily available, economical and work fine, I prefer to use a beefier and more expensive MJ11016 given the cost of the transistor is incidential to keeping it cool, and I can delete the heat sink on the BD139. I prefer to use a .027 ohm sense resistor instead of the 0.47.
If you use the sketch on the the first post and parts on second you will have a proven design that has been built by many users. I will bet if you build the board a couple of times you will likey change a few parts to suit your preference. Good Luck. -
Liqidbyte
Trace back from the bridge rectifier to pin 7 with your voltmeter to find where your voltage is dropping off. You have a lot of solder on that board. Perhaps you have a short somewhere.
If you are getting 10 V output it seems U2 (on the original project) is functioning properly. With an output of 3.92V on Pin 6 of U1 feeding U2, that has a gain of approx 2.6 equals approximatly 10 volts. You problem may be minor. -
Liquidbyte,
On U1, Pin 7 is the supply voltage from the bridge rectifier, it should be around 41V. You state that the U1 Supply is around 38V on the right side and 37.5 on the left. I don't know how that is possible. You list the voltages for every pin but 1 and 8. Those pins are not utilized. Did you accidently connect pin 1 or 8 to the high side instead of pin 7. It appears you have a error on your schematic and both boards are incorrect. -
Liquidbyte, can you post the values of all of the pins for U1
They should be close to:
Pin 2 5.6v
pin 3 5.6v
pin4 0V
Pin 6 11.2V
Pin 7 41 V
Also check the resistance value of R5 and R6 to see if they are both 10K. -
liquidbyte, what is the voltage at pin 6 on U1 and what is the voltage of pin 3 and pin 6 on U2 when you are at max voltage?
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liquibyte are you going to surprise us with something like this http://www.4dsystems.com.au/downloads/microLCD/uLCD-43/Docs/uLCD-43-Product-Brief-REV1.2.pdf
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liquidbyte , I I personally think you are splitting hairs on getting to exactly 44V or less on U2, but if it helps you sleep better, you could put a 5.6V zener between the positive rail and pin 7 of U2. Since you need at least one 5.6V zener for the project, it is likely you have a spare. Hey, if thing don't work out just put a piece of wire across the Zener.
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Using a TLE2141 opamp for U2, a negative supply is not needed. The inputs will work slightly below ground but go down to only 0V and the output will go almost to ground but goes only as low as about +1.1V in this circuit.
You are correct. I must have been thinking of another circuit.
On another note, there is no reason for U1 to need a 41V input rail. It only needs about 13-14V in order to supply a constant 12.2 V. Why didn't we connect the positive rail of U1 to the 10V zener like U3 and drop 10V? -
liquidbyte I have the Triad Magnetics VPS28-6250 (175VA) transformer and I am getting approx 41VDC rectified. Add another 2V for the negative rail on U2 results in 43V across U2. The TLE2141's are rugged devices. In my first unit, I used a home built transformer that puts out nearly 60VDC rectified. I was concerned about the TLE2141's operating well outside of their specifications so I put them on sockets in case I smoked one. I did blow one when I had wires crossed during fabrication but once corrected I never had a problem. I don't use the high voltage unit much but its been working for several years. I am fairly confident that operating the TLE2141's at 44-45Volts will not be a problem.
I just built a smd version of this board using smd TLE2141's using the same 175va,28V transformer. I haven't had any issues or temperature problems. JUST BUILD IT! -
I finished with working on power supply and made a test yesterday but just one think is not working properly, i can adjust the current only up to 3A then current blocking turning on.
I use elements for 5A project (Redwire) as i mentoined couple of times above but i have not idea where is the problem, i hope that i didn't overlook some element value, i will make a review of all elements in circuit once again.
What is the value of R7? if it is 0.47 Ohms, you need to use 0.27 Ohms. Did you adjust the 100k pot to allow a higher current? -
Unfortunately, both the op-amps MC34071 and TLE2141 is not available in my country but there is MC34074 available.
Are you using the single op-amps or the duals ?
Is it possible to replace the three MC34071s with one MC34074 ? but the problem remains in U2 for the pins 1 & 5
Audioguru wrote: An MC34074 will probably get too hot.
U1 and U3 need to provide very little output current. U2 is the real driver in this circuit. If electroguy utilized a darlington power transistor instead of the 2N3055 then the BD 139, and subsequently the MC3074 would need very little current to drive the BD139. I think the quad opamp could handle this load. I would suggest the MJ11016. Yes, you don't have the input offset pins, so setting the voltage to exactly zero may be impossible but a few millivolts should be a problem? I think this would be more preferable than building the old circuit. -
In your diagram you assumed the current flowed clockwise and then showed + and - convention over the resistors indicating a voltage drop across them. Your equation becomes 5v -I*R1 - I*R2 =0; With R1=R2 ; I = 0.025A.
Going back to the original diagram working from the voltage source to point A you have 5V- I*R1 = 2.5V. Note that if you had incorrectly assumed the current flow and it was really counter clockwise then I would be negative meaning you assumed the wrong direction but the answer would work out. -
both look like they operate at 5V.
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Try increasing the current by applying more voltage.
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I don't think we have connected on the issue of programming the chip. When you asked the question
It concerns me that you don't recognize that it takes a programming board to move the program from the computer to your board. The pins that you have identified in question 4 are used as a connector to "Flash" the PIC12F683. I use AVR chips so I don't know which programmers are the cheapest to complete the job. That's why I suggested an Arduino because it uses a simple cable to flash the program. No separate programming board is required.4) What circuit element is labeled in the photo as Vpp, NC, data, Ck, Vcc, Gnd,
your other questions are easy to answer
A 1/2 watt 1N4001 diode will easily do the job
A basic 5mm red led will work
Just about any off/on switch that fits a pcb board will work as the project consumes very little current
the rs-232 is a label for the right angle male headers that connect to the chip, but frankly without reviewing the data sheet for the PIC I don't know how you would know how to connect the wires from the header to the PIC because it is now shown on the site you referenced. -
How far do you need to transfer the signal? Have you looked into XBee modules? This guy has a 5 part series on features and setup. The video starts out kind of weird but the content is excellent.
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Have you thought about using something like this http://learn.adafruit.com/adafruit-data-logger-shield ?
You would need to get a Arduino to plug the shield into, but the Arduino could be used for numerous other projects. The listed project will require a programmer to flash the microchip whereas the Arduino can be done with a simple cable and there is plenty of available programs . There are battery power supply cords that plug right in to the Arduino when separated from the computer or the complete setup
http://www.adafruit.com/products/249 -
sonycman, Good luck. Did you check out http://www.electronics-lab.com/projects/test/007/index.html ? It will give you a starting point for a MCU output display. The hex file provided is for a Atmega8 chip so don't purchase a Atmega88 chip.
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sonycman, U3 requires a voltage between 0 and 1.5V (for 3A output) and U2 requires a voltage between 0 and 11.2V to adjust the output voltage. If you are using a microcontroller, couldn't you delete U1, and U3 and feed a DAC signal to U2 of 0-5 V to control voltage (Yes you will need to adjust the gain for U2 by changing R12 to about 70K and R1 to about 10K so you get a gain of about 6 so that the 0-4.5V signal will provide the same amplification as the original project). The microcontroller would also control the current by measuring the voltage drop across R7 and replace U3. If the voltage drop across R7 was greater than your set voltage, then the microcontroller could automatically drop the voltage to U2 until it matched or was lower than the set voltage. You could also incorporate a temperature sensor that could also reduce current if a certain value is achieved. Make sure you pick a processer that has enough pins to support these features and a LCD display. Not sure if a digital potentiometer is necessary.
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denci,
This is a picture of a MJ11016 (upper left hand corner of picture) I was using to test my new smd board
http://www.electronics-lab.com/forum/index.php?action=dlattach;topic=7317.0;attach=19559
At this time I was using a brake light bulb (about 2.5 A). The previous 5A test was done on a cold day in my garage and the heat sink was not in a project case. These are not the worst case conditions. When you package things up and contain the heat you are going to need at least 2-3 transistors. large heatsinks and a small fan if you want 5A and rock solid durability. Then your output will likely be determined by what size transformer you can afford. Digikey and Mouser have a nice 6.25 A, 28 V transformer by Triad for about $32.
Note that the worst conditions are at low voltage and high current (or a short). When the voltage was at 1 V using a 0.27 Ohm, 10W resistor just like the one on the board, you could feel the heat pouring off the MJ11016. The same happened when I set the current for 2.5A and shorted the output. I didn't hold the shorted conditions for an extended period because heatsink was getting quite. The bd139 without a heat sink was not hot. -
On my unit with an output of 30.0V, U2 pin 6 has an output of 30.07, pin 2 11.46V, Pin 3 = 11.44. No load
If U2, pin 6 has an output of 13.8V, pin 2 = 5.02, pin 3 =5.00V
R12 is 55.6K , R11 with pot = 34.5 KOhms; amplification = 1+ 55.6/34.5 = 2.61. This is very close to measured values.
Values measured with Radio Shack multimeter so digits shouldn't be taken too far.
0-30V Stabilized Power Supply
in Projects Q/A
Posted
Liquibyte , Do you have any pictures of the back side with the fans. I never thought about searching Ebay for heat sinks.
Did you ever resolve the issue with the low voltage output?