audioguru2
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I understand that the mood lamp uses Pulse-Width-Modulation to dim the LEDs. The outputs of the microcontroller are pulsed. They don't need to have a current that exceeds the manufacurer's absolute maximum current rating. You don't understand??MP said:
Yeah, i do understand. I read the source code. That is where you see nase does not have a current problem with his setup. But it is not that big of an issue since you have misinformed him on the safe side. Hence, my comment, "never mind".
MP
MP
audioguru2
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The author's supply current graph indicates a max peak current of only 232mA that is far less than the max current ratings for the LEDs which is 350mA x 3= 1.05A.
My analog Mood Lamps use cheap ordinary LEDs but have a very bright max current peak of 300mA.
Therefore in the source code what is the max PWM duty-cycle that is used for each colour?
If the source code indicates that a high duty-cycle is used then the reduced max current is caused by the incorrect 10k base resistors for the transistors.
With a reduced value for the base resistors then is the max current rating for the LEDs exceeded?
The choice of 100 ohm base resistors for the transistors is also incorrect in the opposite direction since the max current rating of the outputs of the PIC is exceeded.
My analog Mood Lamps use cheap ordinary LEDs but have a very bright max current peak of 300mA.
Therefore in the source code what is the max PWM duty-cycle that is used for each colour?
If the source code indicates that a high duty-cycle is used then the reduced max current is caused by the incorrect 10k base resistors for the transistors.
With a reduced value for the base resistors then is the max current rating for the LEDs exceeded?
The choice of 100 ohm base resistors for the transistors is also incorrect in the opposite direction since the max current rating of the outputs of the PIC is exceeded.
In another topic you asked why a member would email me instead of you when they found a problem with a design you were involved in. Look at this thread. The reason should be perfectly clear. You have exhausted this subject.
Everything you use in normal everyday life uses this same principal. Pulse a cheaper motor with DC pulses so that you do not have to incorporate a more expensive higher voltage/current rating motor in the design. It does not hurt the motor. It does not hurt the micro.
I am finished with this. Do you actually have a degree in theory, or is this a self-proclaimed title?
MP
Everything you use in normal everyday life uses this same principal. Pulse a cheaper motor with DC pulses so that you do not have to incorporate a more expensive higher voltage/current rating motor in the design. It does not hurt the motor. It does not hurt the micro.
I am finished with this. Do you actually have a degree in theory, or is this a self-proclaimed title?
MP
audioguru2
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MP,
Why do you disagree with manufacturers and use excessive supply voltage for opamps and excessive output current on Cmos microcontrollers and on power transistors in inverters?
Why do you disagree with manufacturers and use excessive supply voltage for opamps and excessive output current on Cmos microcontrollers and on power transistors in inverters?
Well, that question doesn't make any sense. I guess it was an attempt at insult or avoidance?
I noticed you avoided my last question. The reason for this question was not insult. I was told that you do not have a degree. That you are a retired Stereo technician proclaiming to be a theory expert.
MP
I noticed you avoided my last question. The reason for this question was not insult. I was told that you do not have a degree. That you are a retired Stereo technician proclaiming to be a theory expert.
MP
audioguru's comments made plenty of sense to me, reading over the last few threads.
25mA is the absolute maximum current rating from a PIC, exceeding this will lead to putting the device under conditions that will deteriorate its life span.
Pulsed or constant, absolute is absolute
25mA is the absolute maximum current rating from a PIC, exceeding this will lead to putting the device under conditions that will deteriorate its life span.
Pulsed or constant, absolute is absolute
audioguru2
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MP:
What is a degree in theory? I have a Bachelor of Electronic Engineering degree from Ryerson University in Toronto, Canada. I never had a mentor so I did not become a P. Eng. I worked at designing communications and sound systems for my entire career. I am an old geezer and have been retired for 6 years.
I noticed that you proclaim yourself as an engineer but you don't do any engineering on this site. Are you a salesman?
I just read the datasheet for a device and avoid operation beyond the manufacturer's absolute maximum ratings. The manufacturer says that operation above the max rating may cause permanent damage and may affect reliability. I believe them, you don't.
Some heavy duty items like motors and rectifier diodes have a continuous rating and a higher rating for short pulses. Light duty items like ICs don't have a higher rating.
What is a degree in theory? I have a Bachelor of Electronic Engineering degree from Ryerson University in Toronto, Canada. I never had a mentor so I did not become a P. Eng. I worked at designing communications and sound systems for my entire career. I am an old geezer and have been retired for 6 years.
I noticed that you proclaim yourself as an engineer but you don't do any engineering on this site. Are you a salesman?
I just read the datasheet for a device and avoid operation beyond the manufacturer's absolute maximum ratings. The manufacturer says that operation above the max rating may cause permanent damage and may affect reliability. I believe them, you don't.
Some heavy duty items like motors and rectifier diodes have a continuous rating and a higher rating for short pulses. Light duty items like ICs don't have a higher rating.
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That's the course that allows you to be eligible for "Engineer in training" upon graduation, but does not recognize you as an Engineer, isn't it?
Gramo: There is most certainly a difference in voltage and current output between pulsed and constant. The output voltage is not the same on a switched circuit as a constant one. Especially with varying on and off times. This is the whole purpose of PWM. Absolute ratings given in a data sheet are performed with a constant source.
MP
Gramo: There is most certainly a difference in voltage and current output between pulsed and constant. The output voltage is not the same on a switched circuit as a constant one. Especially with varying on and off times. This is the whole purpose of PWM. Absolute ratings given in a data sheet are performed with a constant source.
MP
audioguru2
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Hi Gramo,
You have read the datasheet for the PIC. You saw that it does not have a higher pulsed max current rating like a motor and a power rectifier do. Absolute maximum means absolute maximum, not "sometimes".
Read the forum of the author of our Mood Lamp project. He forgot to use base resistors and some people did fry their PIC. Then the author used 10k resistors with a value much too high for our project. Kade used 100 ohms which is too low.
MP:
You didn't answer my question about what is the max PWM duty-cycle in the PIC's code. The author's max peak current measurement is far from the max current rating of the expensive LEDs.
You have read the datasheet for the PIC. You saw that it does not have a higher pulsed max current rating like a motor and a power rectifier do. Absolute maximum means absolute maximum, not "sometimes".
Read the forum of the author of our Mood Lamp project. He forgot to use base resistors and some people did fry their PIC. Then the author used 10k resistors with a value much too high for our project. Kade used 100 ohms which is too low.
MP:
You didn't answer my question about what is the max PWM duty-cycle in the PIC's code. The author's max peak current measurement is far from the max current rating of the expensive LEDs.
You are right. I did not answer that question. You are telling me how it works, but at the same time, asking me how it works.
At this point I see that I have allowed this thread to get away from being useful to members of the community. Thus, I will withdraw from the debate. I encourage you both to continue your education and to take a few chances on parameters that are not listed on the data sheet.
When a spec is not listed on a datasheet, this does not mean it is not allowed. A datasheet is only a guide or starting point. It would be a fairly large book if the manufacturer listed all possible test parameters. It only gives you the basics. From there, you must use your own knowledge and experience, or perform your own testing.
MP
At this point I see that I have allowed this thread to get away from being useful to members of the community. Thus, I will withdraw from the debate. I encourage you both to continue your education and to take a few chances on parameters that are not listed on the data sheet.
When a spec is not listed on a datasheet, this does not mean it is not allowed. A datasheet is only a guide or starting point. It would be a fairly large book if the manufacturer listed all possible test parameters. It only gives you the basics. From there, you must use your own knowledge and experience, or perform your own testing.
MP
audioguru2
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That is gambling.MP said:
The datasheet for the PIC is very clear: Do not use an output current of 25mA or more.
audioguru2
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Why was Gramo's reply deleted?
It was important.
It was important.
audioguru2
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Hi Gramo,
I started this thread because the value of the base resistors is too high to allow the transistors to conduct the high currents needed for the expensive tri-colour LED.
I also noticed that the value of the current-limiting resistor for the red LED was too low and would cause the current to be too high and the value for the blue LED was too high.
The author made his first Mood Lamp using the transistors as emitter-followers that did not need base resistors.
Then he made this one with the transistors as common-emitter type but did not include base resistors. People on his forum complained that their PICs were frying. I have attached his schematic here.
He added 10k base resistors to our project without calculating their value properly.
Kade in his forum also mis-calculated and used 100 ohm base resistors.
I don't know if it is the switching speed of the transistors or the program PWM that limits the currents in the LED too much. Maybe the author burned a few LEDs because his heatsink is too small. Then maybe he reduced the PWM max duty-cycle to reduce the average current for less heating.
View attachment 40412
I started this thread because the value of the base resistors is too high to allow the transistors to conduct the high currents needed for the expensive tri-colour LED.
I also noticed that the value of the current-limiting resistor for the red LED was too low and would cause the current to be too high and the value for the blue LED was too high.
The author made his first Mood Lamp using the transistors as emitter-followers that did not need base resistors.
Then he made this one with the transistors as common-emitter type but did not include base resistors. People on his forum complained that their PICs were frying. I have attached his schematic here.
He added 10k base resistors to our project without calculating their value properly.
Kade in his forum also mis-calculated and used 100 ohm base resistors.
I don't know if it is the switching speed of the transistors or the program PWM that limits the currents in the LED too much. Maybe the author burned a few LEDs because his heatsink is too small. Then maybe he reduced the PWM max duty-cycle to reduce the average current for less heating.
View attachment 40412
audioguru2
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Hi ante,
The BC517 darlington transistor has a typical base-emitter voltage of 1.4V at the current used by the LED. When a PIC output goes high then a base resistor is needed to limit the current to less than 25mA.
The max current in this project is much lower than the 350mA rated current of each of the 3 colours at max brightness simultaneously. I don't know why the current is so low.
The BC517 darlington transistor has a typical base-emitter voltage of 1.4V at the current used by the LED. When a PIC output goes high then a base resistor is needed to limit the current to less than 25mA.
The max current in this project is much lower than the 350mA rated current of each of the 3 colours at max brightness simultaneously. I don't know why the current is so low.
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