“How to test LED screen?”

[budm]

Re: “How to test LED screen?”

Of course, the LED is the current device and it should be driven by constant current source, you just found that out? I guess you did not read any of the PDF I provided, what a waste of time.
The problem is that your circuit is not working and not limiting the current to be at 100mA.
You should have put variable resistor load to simulate variable load which within the power supply output voltage capability to produce 100mA of constant current. If the circuit is working when you turn up the pot it should maintain 100mA, the voltage is the one that varies to maintain constant current.
That is why do not believe what you see on the web and on you tube until you look at the circuit and see if it is even possible for the circuit function as claimed.
I would have build low voltage first and see if it works then scale it up or down as need.
Like they said, it if is on the internet it must be true, NOT!
Why don' t you read up on what constant current power supply is and how it works?
BTW, if you read the guy notes, he put 100K in PARALLEL WITH THE 500k POT AND ALSO ADD ZENER IN PARALLEL WITH POT and as I explained already that you do not put ZENER in the output of the power supply without current limiter resistor.
You really think he puts the 47K or 100K like you have done, if he did and if you bother the do the calculation, then there is no way that he claimed the circuit can put out 100mA of constant current, that will be pure B.S.
How are you going to learn when you do not even want to do some basic calculation.

Clue, the MOSFET is the control element (just think of it as variable resistor which is connected in the series with the load and its resistance varies to maintain constant current through the load) in the circuit, once you understand what constant current circuit requires to operate then you will see what is going on, so for now, just keep blowing things and burning things up.

Here is something for you to think about, lets say you want to build 100mA constant current source, you have 10VDC power supply and you have a 50 Ohms load resistor that you want to have 100mA of current flows through it, what is the value of the resistor you need to put in series with that 50 Ohms load to give 100mA of current. What is the Voltage drops on the 50 Ohms load resistor?
Now the load is changed to 25 Ohms and you still want 100mA of current flowing through it, then what what is the value of the series resistor needs to be to still give 100mA? What is the Voltage drops on the 25 Ohms load resistor?

[budm]

Re: “How to test LED screen?”

Do you see what is wrong with this diagram made by the same person (momename: http://www.eleccircuit.com/the-varia...supply-0-300v/ )you build his circuit?
Notice the POWER P-CH MOSFET and the body Diode of the MOSFET?
It is on the web so it must be true, NOT!

From the website: http://www.eleccircuit.com/many-cons...urce-circuits/

Sometimes we need a constant supply to the load.To prevent damage to the load.For example, when we apply a voltage that ever-changing to LEDs. However,LED needs to have the constant current and voltage. As usual, we provide current limiting resistor to it. But this works we can not use because the input voltage changes all time. We must make a constant current through the LED.
If you do not understand. Try to preview the circuit below.

The Safe constant current source.

Figure 1 the below is a Safe constant-current source circuit, how it works?
A cmos op-amp (number ICL 7611) controls the input current through a P-channel Hexfet power transistor (No. IRF 9520), then to keep up a constant voltage across the R1.
As they are connected in a serial form, so use the together current by: I = VREF /R1 , while the Vref to be defined by the IC2 is 1.25V.

The advantage of this outline are:
1. The load current is limited by R1 when the load is too heavy.
2. The op-amp and Hexfet there are the overhead voltage very low.

[Peter Chiu]

Re: “How to test LED screen?”

[music] https://www.youtube.com/watch?v=_W1_shm7vdE

Will try this (pic)

The circuit work perfectly,(0V-350V), nothing wrong basically,it's very hard to handle 350v, so I will low down to 110 x 1.14=155.5v , and put first stage current limited resist array for prevention. Or use 1:1 smaller transformer, let it no power to burn anything.... 2.5V x 60= 150V still can test about 60 LEDs (not full brightness)..... See, what's will happen ....

[budm]

Re: “How to test LED screen?”

So which resistor in the circuit is going to be 16K to limit the current to 10mA? The current sensing resistor that is supposed to be used to regulate the current to 10mA so the if the UNKNOWN LOAD is CONNECTED (10 LEDS or 20 LEDS for example) it still maintain 10mA?
The whole purpose of the constant current source is to be able to connected any unknown LED string to it and it will maintain 10 mA.

[Peter Chiu]

Re: “How to test LED screen?”

Thank you for your supporting...
will use 10 points rotary switch, add power resisters together ,so can choice from 1ma, 5ma, 10ma, 20ma, 50ma, 100ma......

If use (1...2....4...8.) In logically, we can get all the value we want ,like 1ma, 4ma, 8ma, 11ma 12ma 13ma....etc......up to 15ma.... use with 4p dip switchs

[Peter Chiu]

Re: “How to test LED screen?”

[music] https://www.youtube.com/watch?v=aH63RKQ7OEw

How to make triacs and LEDs get along

http://powerelectronics.com/lighting...leds-get-along

[Peter Chiu]

Re: “How to test LED screen?”

Simple LED Bulb Circuit
http://www.homemade-circuits.com/201...b-circuit.html

5630 SMD LED Driver/Tube light Circuit
http://www.homemade-circuits.com/201...t-circuit.html

1 Watt LED Emergency Lamp Circuit Using Li-Ion Battery
http://www.homemade-circuits.com/201...uit-using.html

Surge Protected Cheap Transformerless Hi-Watt LED Driver Circuit
http://www.homemade-circuits.com/201...merless-3.html

Mains Voltage Indicator with a LED
http://www.eleccircuit.com/mains-vol...or-with-a-led/

[budm]

Re: “How to test LED screen?”

You are still not telling me where 16k Ohms resistor is being used at.

[Peter Chiu]

Re: “How to test LED screen?”

if circuit pass 10ma @ DC155.6V current limited resistor will be 16k ohm (@ first Pic top-right resistors group #43), and I will use 10k 20k to limited the Total current not over too much...

[budm]

Re: “How to test LED screen?”

https://www.badcaps.net/forum/showth...934#post553934

You still do not get it do you?
https://www.badcaps.net/forum/attach...6&d=1429977976
or this one?
https://www.badcaps.net/forum/attach...8&d=1429977997

Also take the Voltage reading at the output with no load connected and try all the current setting and tell us what DCV you have.

[Peter Chiu]

Re: “How to test LED screen?”

Sorry, I thought you were ask everybody.....
Here is something for you to think about, lets say you want to build 100mA constant current source, you have 10VDC power supply and you have a 50 Ohms load resistor that you want to have 100mA of current flows through it, what is the value of the resistor you need to put in series with that 50 Ohms load to give 100mA of current. What is the Voltage drops on the 50 Ohms load resistor?

10v/50ohm=0.2A=200ma what is the value of the resistor you need to put in series with that 50 Ohms
A: 10v/100ma=100ohm, 100ohm-50ohm=50ohm What is the Voltage drops on the 50 Ohms load resistor?
A: 0.1a x 50 ohm=5v

Now the load is changed to 25 Ohms and you still want 100mA of current flowing through it, then what what is the value of the series resistor needs to be to still give 100mA? What is the Voltage drops on the 25 Ohms load resistor?
10v/25=0.4A=400ma value of the series resistor needs to be to still give 100mA
A:100-25=75ohm
What is the Voltage drops on the 25 Ohms load resistor?
IxR=V A: 0.300A x25ohm=7.5v
but realty is, If ohm too low current too high ,like a piece of metal can't measure any voltage( with my meter).

when I tested with 47k ohm resister won't burn anything ,so 10w LED limited to 7.5v P = V x I >>> 10w=7.5v xI >>>I=1.33A R=5.62ohm but it's not full brightness. so is not 10w maybe 1w I=0.13=130ma so they do limited to 100ma ((roughly) from R2=3.3).

when I by pass them burn like crazy.
The tester not working now, as soon as I change with IRF740 (IGBT most now is SMD ,hard to put a heat sink) will get back to you.

[budm]

Re: “How to test LED screen?”

Like I said, check the output Voltage with no load, BTW, if you bother to make the calculation you will see what happen with unknown load since the purpose is that you do want to open the panel to find out how many LEDs are in the circuit, your circuit will not handle unknown and maintain the set current.

[Peter Chiu]

Re: “How to test LED screen?”

2. The op-amp and Hexfet there are the overhead voltage very low.
The problem is ICL7611 can't stand DC 340v, I search a lot ICs for this kind of HV appication.
Supply Voltage V+ to V- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18V
Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . V- -0.3 to V+ +0.3V
Differential Input Voltage (Note 1) . . . . . . . . [(V+ +0.3) - (V- -0.3)]V
Duration of Output Short Circuit (Note 2). . . . . . . . . . . . . . Unlimited

I think #47 PIC 1 and 2 will be good to make LEDs tester will do the lab quick.

Sorry , Health is important , need to GYM. see U.

[kaboom]

Re: “How to test LED screen?”

Sorry, I thought you were ask everybody.....
Here is something for you to think about, lets say you want to build 100mA constant current source,

Go for it, at full line voltage the IRF740's gonna get rather hot. I guess you like blowing parts up.

you have 10VDC power supply and you have a 50 Ohms load resistor that you want to have 100mA of current flows through it, what is the value of the resistor you need to put in series with that 50 Ohms load to give 100mA of current. What is the Voltage drops on the 50 Ohms load resistor?

Another No-Code, err, No-Ohms-Law tech.

10v/50ohm=0.2A=200ma what is the value of the resistor you need to put in series with that 50 Ohms
A: 10v/100ma=100ohm, 100ohm-50ohm=50ohm What is the Voltage drops on the 50 Ohms load resistor?
A: 0.1a x 50 ohm=5v

Now the load is changed to 25 Ohms and you still want 100mA of current flowing through it, then what what is the value of the series resistor needs to be to still give 100mA? What is the Voltage drops on the 25 Ohms load resistor?
10v/25=0.4A=400ma value of the series resistor needs to be to still give 100mA
A:100-25=75ohm
What is the Voltage drops on the 25 Ohms load resistor?
IxR=V A: 0.300A x25ohm=7.5v
but realty is, If ohm too low current too high ,like a piece of metal can't measure any voltage( with my meter).

My car won't start- what could the matter be? You're shooting from the hip here, is it that hard to stay on the "straight path" with electronics nowadays, what with all the "makers?"

I long for the days of TAB Books and those "Mini-Notebooks" from Radio Shack...

when I tested with 47k ohm resister won't burn anything ,so 10w LED limited to 7.5v P = V x I >>> 10w=7.5v xI >>>I=1.33A R=5.62ohm but it's not full brightness. so is not 10w maybe 1w I=0.13=130ma so they do limited to 100ma ((roughly) from R2=3.3).

when I by pass them burn like crazy.
The tester not working now, as soon as I change with IRF740 (IGBT most now is SMD ,hard to put a heat sink) will get back to you.

Ya think??? And you want to change the pass transistor to an SMT part?!

So which resistor in the circuit is going to be 16K to limit the current to 10mA? The current sensing resistor that is supposed to be used to regulate the current to 10mA so the if the UNKNOWN LOAD is CONNECTED (10 LEDS or 20 LEDS for example) it still maintain 10mA?
The whole purpose of the constant current source is to be able to connected any unknown LED string to it and it will maintain 10 mA.

Does it really matter? The pass device will overheat, more so with SMT device, and short, wiping the load out.

[kaboom]

Re: “How to test LED screen?”

http://powerelectronics.com/lighting-systems/how-make-triacs-and-leds-get-along

Misleading title. The input to that will still draw large peak currents on the rapidly rising edge, as provided by phase control dimmers.

And the power factor increases with the number of LEDs, otherwise known as load. It is not a fixed value.

CFL lamps also must be driven by a magnetic or electronic ballast, and as such are not normally dimmable from the standard wall dimmers already installed in many millions of homes. In fact the usual result of putting a CFL on a conventional dimmer is severe flickering and in some cases damage to the CFL or dimmer electronics. The flickering arises from the phase cut method of operation employed by dimmers based on triacs when connected to capacitive loads typical of the electronic converters in CFL ballasts.

What isn't wrong here? "CFL lamps?" Excuse me, any discharge lamp fall under this category; CFLs, despite what certain interests would have us believe, are nothing special among discharge lamps. The CFL didn't come along and "redefine" fluorescent lamps, other than by physical size.

And for the record, the ballst is not a "capacitive load." Yes! There's a capacitor present, but it's after a rectifier. It's a non-linear load.

A true capacitive load simply draws its current before the voltage peak; however, the current is still sinusoidal.

The capacitive input rectifier, as used in electronic ballasts, power supplies, and more, draws current in brief, large peaks; the caps begin to charge back up (draw current) just before the AC peaks. Since this occurs in such a short time, the current peak, therefore, is rather high- several times its RMS value.

This is why it's such a problem for European countries, with their several-block-wide secondary distribution system and sparse HV:416Y/240V transformers.

Those current spikes, from the cap-input filters, occuring on each phase, symmetrically add, or "sequence" together, on the neutral.

If loads on each of the phases are dumping 1A each, of this non-linear current into the neutral, the neutral current is 3A! Aka , "triplens."

The neutral current does not cancel, even though the phases are supposedly balanced! The neutral has to be three times the size of the phase conductors.

With resistive loads of equal current, there would be no neutral current; even with leading or lagging loads, the neutral isn't overloaded to this degree.

In the US, it's not as much of a problem, suburban houses typically are fed from center-tapped single phase transformers. Only with 208Y/120V and/or "network" service do triplens become a problem. The big one here is office buildings, where the three-phase sub-distribution is subject to triplens the same way as the foreign 416Y/240.

[budm]

Re: “How to test LED screen?”

His thinking is like this: He has 160V (rounded out number) power supply, and he want to limit the current to 10mA, so his calculation is to put 16K resistor in series circuit.
So let see that he puts the load (5 LEDs, 10 LEDs, or what ever) to the circuit, do you think he will still get 10mA flowing through the circuit? That is what I am trying to understand his logic of what he is doing and show him that is not going to work.

"Does it really matter? The pass device will overheat, more so with SMT device, and short, wiping the load out. "
At 160VDC and 16K in series with the power MOSFET, so for sake of simplification, the output is connected to 0 OHm load to get 10mA flowing through 16K per his design if the MOSFET is fully on, the there will hard be any Vsd (the S-D resistance will be very low compare to the 16K series resistor) at all so the only thing will get hot will be the resistor, about 1.6W.
BTW, did you see Peter's circuit?

[kaboom]

Re: “How to test LED screen?”

His thinking is like this: He has 160V (rounded out number) power supply, and he want to limit the current to 10mA, so his calculation is to put 16K resistor in series circuit.
So let see that he puts the load (5 LEDs, 10 LEDs, or what ever) to the circuit, do you think he will still get 10mA flowing through the circuit? That is what I am trying to understand his logic of what he is doing and show him that is not going to work.

"Does it really matter? The pass device will overheat, more so with SMT device, and short, wiping the load out. "
At 160VDC and 16K in series with the power MOSFET, so for sake of simplification, the output is connected to 0 OHm load to get 10mA flowing through 16K per his design if the MOSFET is fully on, the there will hard be any Vsd (the S-D resistance will be very low compare to the 16K series resistor) at all so the only thing will get hot will be the resistor, about 1.6W.
BTW, did you see Peter's circuit?

Which one?


Hehe. We're not dealing with a true constant current circuit here, are we?

I can't understand all his effort, if, ultimately, a resistor will be doing all the work... All the "work" to arrive at the resistor value, oh but wait! Isn't this supposed to be a CCS?

Why bother? Once the load, or line voltages, changes, so will his "constant" current.

He could try for a switchmode CCS, but I ain't going there!

[newtothis]

Re: “How to test LED screen?”

OK I am no good whatsoever at being able to create circuits.. AT ALL... But even me reading this I see one big fat obvious flaw (I think). Stated was he would use a rotary switch to choose the mA ... But would you not need to know how many LED's there are in the first place to even set that correctly?.. Defying the point of the device?

[budm]

Re: “How to test LED screen?”

OK I am no good whatsoever at being able to create circuits.. AT ALL... But even me reading this I see one big fat obvious flaw (I think). Stated was he would use a rotary switch to choose the mA ... But would you not need to know how many LED's there are in the first place to even set that correctly?.. Defying the point of the device?

That is what I am trying to explain, if you have constant current source, then no matter what you connect to it it will maintain 10mA or what ever you set the regulated current to, you can only use the UN-KNOWN load up to the maximum power supply can put out since the output Voltage will VARY with the load for it to maintain CONSTANT CURRENT.
His latest great circuit design is here:
https://www.badcaps.net/forum/showpo...9&postcount=43

[newtothis]

Re: “How to test LED screen?”



Well it keeps making me chuckle anyway

Have Fun