Emiliano,
BTW, two questions: What kind of transformer do you use? How close to the maximum voltage of the op-amp are you right now? What I am thinking of is if there are some volts left to the max for the opamp and you have a transformer that can be applied with some turns of wire
BTW, two questions: What kind of transformer do you use? How close to the maximum voltage of the op-amp are you right now? What I am thinking of is if there are some volts left to the max for the opamp and you have a transformer that can be applied with some turns of wire
audioguru2
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Hi Ante,
His 75VA transformer is already overloaded since its peak voltage of about 34V must supply the project's rated DC output current of 3A, which is 102VA. At the transformer's limit, this project can supply a DC output current of only 2.2A.
I figure that with a very light load or none, the transformer's voltage will be 26VAC, 36.8V peak. The rectifiers will drop it to 35.4V. Therefore adding the 5.6V negative supply, the 36V rated U2 and U3 will be operating with a total of 41V!
Over here, if I use a 24VAC transformer that has a 115V primary on my 121V (very common) mains, the ICs will get 43V!
audioguru2
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Hi Ante,
A transformer doesn't dissipate much because it isn't the load, unlike a linear power transistor that is in series with the load. A transformer passes VA to a load, therefore shouldn't be rated in Watts. Its rating in Watts is how hot it gets (power input minus power output).
Since Emiliano's transformer is rated to pass a current of 3A at 24VAC, its VA rating is 3 X 24 = 72VA. It is expected to give 24VDC at 3A to a load (72W), plus maybe about 18W to heat the transistors and circuit, plus maybe about 12W to heat the rectifier bridge. So the total load on the 72VA-rated transformer is 102W and it is expected to pass 102VA. It is seriously overloaded.
A transformer doesn't dissipate much because it isn't the load, unlike a linear power transistor that is in series with the load. A transformer passes VA to a load, therefore shouldn't be rated in Watts. Its rating in Watts is how hot it gets (power input minus power output).
Since Emiliano's transformer is rated to pass a current of 3A at 24VAC, its VA rating is 3 X 24 = 72VA. It is expected to give 24VDC at 3A to a load (72W), plus maybe about 18W to heat the transistors and circuit, plus maybe about 12W to heat the rectifier bridge. So the total load on the 72VA-rated transformer is 102W and it is expected to pass 102VA. It is seriously overloaded.
audioguru2
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Hi Ante,
Thanks for the power factor article.
I don't think that a reactive load that is supplied by our Lab Power Supply will feed back into it. Even the huge filter cap isn't reactive because all of its charged energy ( ;D) flows as current in the load, or if the load is very light then the filter cap does almost nothing. If the transformer has reactance to the mains, it will have no effect on the output of our rectifiers.
Thanks for the power factor article.
I don't think that a reactive load that is supplied by our Lab Power Supply will feed back into it. Even the huge filter cap isn't reactive because all of its charged energy ( ;D) flows as current in the load, or if the load is very light then the filter cap does almost nothing. If the transformer has reactance to the mains, it will have no effect on the output of our rectifiers.
Hi, i'm thinking of using this cap as C1 but I'm not sure if its a good one for this project.
Some pictures:
There are four pins at the bottom, 1,2,3 and 5. The arrows for indicating the negative side are pointed towards pin 5.
My question: can this cap be used as C1, and how do i connect it (what pins do i use)?
thanks.
Some pictures:
There are four pins at the bottom, 1,2,3 and 5. The arrows for indicating the negative side are pointed towards pin 5.
My question: can this cap be used as C1, and how do i connect it (what pins do i use)?
thanks.
audioguru2
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Hi Zwieke,
That is an excellent cap that is perfect as C1 in this project. Google quickly found "BC Components" and their datasheet shows that pin 1 is positive and pin 5 is negative. The bottom view is here:
View attachment 35939
That is an excellent cap that is perfect as C1 in this project. Google quickly found "BC Components" and their datasheet shows that pin 1 is positive and pin 5 is negative. The bottom view is here:
View attachment 35939
Hi, does anybody know how to realize this circuit?
I had similar problem, but mine was with fluctuation of the panel all over. My solution was to power up the pannel on bipolar, i.e. +-5V with midpoint. I suppose your panels allow you to connect them this way, or hopefully they do. The good thing is that you only need few miliampers to power up the thingy. What I did is I used two zeners at 5.1V with resistors, and built basically the analogue scheme of voltage devider, but instead of 4 resistors, I used 2 resistors and 2 zeners. Zeners are connected together in series the resistors are connected again in series - one attached to each zenner. The midpoint between the zenners you can take as zero - it will be relative zero, so between the midpoint and the other pin of the zeners you will have relatively +5.1 and -5.1. The good thing is that you can take the power to power up the zener stabilizators from the rectifier bridge of the PSU, meaning no more transformers in the case. Resistor values will depend on the potential input - use ohm's law. This worked for me and hopefully it will work for you
Hi Everybody,
i'm a french fan of thie famous forum and i'm newbie...
I'm just wondering about what kind of change i have to operate on the propsed schematic in order to be able to use a transformer which could deliver 6 A ? I would like to build a power supply with a max intensity of 6 A instead of 3 (that's because i have only one transformer).
I hope you will understand my request ...
Good Luck in all your project
SKAPPY
i'm a french fan of thie famous forum and i'm newbie...
I'm just wondering about what kind of change i have to operate on the propsed schematic in order to be able to use a transformer which could deliver 6 A ? I would like to build a power supply with a max intensity of 6 A instead of 3 (that's because i have only one transformer).
I hope you will understand my request ...
Good Luck in all your project
SKAPPY
audioguru2
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Hi Skappy,
Welcome to our forum and greetings to France.
If you want this power supply to produce 0 to 30VDC at up to 6A, then it will need modifications similar to those we dicussed in the other forum about converting it for 5A. Near the end of the other forum is a good schematic with parts' values shown. The other forum is here:
http://www.electronics-lab.com/forum/index.php?board=13;action=display;threadid=196
The modifications that you need are:
1) A 30VAC/8.5A (255VA) transformer.
2) A larger heatsink since with a 6A low voltage load, or with the output shorted when the supply is set for 6A, the 3 output transistors must dissipate a total of 230W!
3) R7 will need to be changed to 0.22 ohms/15W
However, if your transformer is rated at only 30VAC/6A (180VA), then this power supply will produce only about 4.2ADC at the transformer's limit. The remainder of the parts for the 5A modification will be fine.
Welcome to our forum and greetings to France.
If you want this power supply to produce 0 to 30VDC at up to 6A, then it will need modifications similar to those we dicussed in the other forum about converting it for 5A. Near the end of the other forum is a good schematic with parts' values shown. The other forum is here:
http://www.electronics-lab.com/forum/index.php?board=13;action=display;threadid=196
The modifications that you need are:
1) A 30VAC/8.5A (255VA) transformer.
2) A larger heatsink since with a 6A low voltage load, or with the output shorted when the supply is set for 6A, the 3 output transistors must dissipate a total of 230W!
3) R7 will need to be changed to 0.22 ohms/15W
However, if your transformer is rated at only 30VAC/6A (180VA), then this power supply will produce only about 4.2ADC at the transformer's limit. The remainder of the parts for the 5A modification will be fine.
audioguru2
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Hi Skappy,
Since your transformer doesn't have a 30VAC output, your project that uses it won't be able to have a well-regulated output up to 30VDC, as I explain half-way down page 18 in the other post.
The rating of your 300VA transformer is probably for the total of its 3 outputs, so maybe each output is rated at only 100VA. Its voltage and current aren't enough.
Since your transformer doesn't have a 30VAC output, your project that uses it won't be able to have a well-regulated output up to 30VDC, as I explain half-way down page 18 in the other post.
The rating of your 300VA transformer is probably for the total of its 3 outputs, so maybe each output is rated at only 100VA. Its voltage and current aren't enough.
audioguru2
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Hi Guys,
I just made another discovery to improve the 5A soup-up of this project on the other thread, and it also applies here.
The zener diode D8 is this project's voltage reference and must perform well. With R4 being 4.7K, D6 is operating at a current of only 1.2mA. Our project doesn't specify a part number for D8 and some guys have been using a 1W zener diode.
A 1W zener diode such as the 5.6V 1N4734A is rated and measured at a current of 45mA. At 1.2mA it just barely conducts and is about only 4.2V (the normally vertical voltage line has curved to be nearly diagonal, like an ordinary resistor).
A 500mW zener diode such as the 5.6V BZY79C5V6 (available worldwide) is rated and measured at a current of 5mA, where it performs very well. It also performs poorly at 1.2mA (5.3V) but is much better than a 1W zener diode.
Therefore we should change R4 to 1K (for a zener current of 5.6mA), and specify using BZY79C5V6 zener diodes for D7 and D8.
Edited Nov.6/04: in bold.
I just made another discovery to improve the 5A soup-up of this project on the other thread, and it also applies here.
The zener diode D8 is this project's voltage reference and must perform well. With R4 being 4.7K, D6 is operating at a current of only 1.2mA. Our project doesn't specify a part number for D8 and some guys have been using a 1W zener diode.
A 1W zener diode such as the 5.6V 1N4734A is rated and measured at a current of 45mA. At 1.2mA it just barely conducts and is about only 4.2V (the normally vertical voltage line has curved to be nearly diagonal, like an ordinary resistor).
A 500mW zener diode such as the 5.6V BZY79C5V6 (available worldwide) is rated and measured at a current of 5mA, where it performs very well. It also performs poorly at 1.2mA (5.3V) but is much better than a 1W zener diode.
Therefore we should change R4 to 1K (for a zener current of 5.6mA), and specify using BZY79C5V6 zener diodes for D7 and D8.
Edited Nov.6/04: in bold.
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