That wasn’t aguru, that was me.

Oops... my post has been edited. I saw his post #11 and misattributed the concept.

 

Still don't know what a "star" is, or how the 50 LEDs are connected. If they are in parallel, then he needs 50 current limiting resistors. It would help if he addressed this. A complete schematic of one 4017 output section would be nice.

ak

 

Hello,

Or use two times a TBD6200X, the mosfet version of the ULN200X:

Features:
7 circuits built-in
High voltage : VOUT = 50 V (MAX)
High current : IOUT = 500 mA/ch (MAX)
Input voltage(output on) :
TBD62003A series 2.5 V (MIN)
TBD62004A series 7.0 V (MIN)
Input voltage(output off) :
TBD62003A series 0.6 V (MAX)
TBD62004A series 1.0 V (MAX)

Bertus

The only issue with the ULN2003 or TBD6200x series, is that while one channel can sink/output 500mA max (recommended 400mA), that is if only one channel is active at a time at 100% duty cycle. If all 7 channels are on, you are limited by total power dissipation, and at 100% duty cycle, you are limited to either 2 or 3 channels at 400mA, or all 7 channels at much lower currents, something like 100mA to 150mA. Even that datasheet shows at 50% duty cycle, some of those chips have limits of about 120-170mA/channel when all 7 channels are used. One cannot drive all channels to steady state ON at the same time at full load
That all said, one can parallel up the channels (both input and outputs) to provide more output current.

 

I welded 10 stars together and was hoping to secure a string of the purchased 40 Led,s to each star
so that when connected to ic4017. Each star lights up in sequence.

Now you talk about 'Stars" but we do not know what they are. Do they also have LEDs in parallel?
Then each parallel group of 40 LEDs and each Star needs its own current-limiting resistor.

Is a bd139 suitable with the ic4017. I know it can handle higher voltages and current. Just winder can the 4017 switch the base on the bd139.

I mentioned using Mosfets because the base current of a high current switching transistor is much too high for a CD4017. Read the datasheets!
1) How voltage does a Star use and much current? If it has 40 paralleled white LEDs at 3V like the 40 other white LEDs then 80 x 20mA= 1.6A.
2) The datasheet for a BD139 power transistor shows that its maximum allowed collector current is inly 1.5A so it cannot drive the 1.6A LEDs. a more powerful power transistor like a TIP31 has a maximum allowed collector current of 3A so it can be used but its datasheet shows that for a collector current of 1.6A then its base current must be 0.16A.
3) The datasheet of a CD4017 shows that with a power supply voltage of 5V then its typical output current is only 4mA. 40 times too low! But a Mosfet gate current is zero so a logic level Mosfet will work fine.
4) The current-limiting resistor for each group of 40 LEDs is calculated from the supply voltage minus the forward voltage of the group minus the saturation voltage loss of the Mosfet, divided by the group's current you want.

 

The only issue with the ULN2003 or TBD6200x series, is that while one channel can sink/output 500mA max (recommended 400mA), that is if only one channel is active at a time at 100% duty cycle. If all 7 channels are on, you are limited by total power dissipation.

The CD4017 has only one channel on at a time. It sequences its outputs.

 

The CD4017 has only one channel on at a time. It sequences its outputs.

Besides the 4017 only having one output at a time on, there is also the fact the TS stated that it was to be a chaser, And most illumination type white LEDs run a good bit more than 20 mA.

 

Maybe the LEDs with no part number are the ones that use 700mA each and are mounted on a star heatsink??

 

Maybe the LEDs with no part number are the ones that use 700mA each and are mounted on a star heatsink??

There is a large variety of LED sizes and shapes and power ratings. I have some strings that run on 35 volts at 200mA.

 

Those "star" boards are actually only breakout boards that also serve as heat spreaders, and those type of LEDs still must be attached to an actual heatsink.

 

. First of all thank you all for the patience you have shown me. I am a beginner .

Can you please tell me if these are the right ones to order?

Stp55nf06l Mosfet Logic N 60v 55a

When I mentioned the stars I mend this

I welded 10 metal frames in shape of a Xmas star
I have 40 LEDs in each star. As all stars are welded together I want them to light one at the time with the ic4017.

Hope I explaned it correctly this time.

Looking forward to confirmation about this MOSFET.

Ron

 

The Mosfet will be fine and will stay cool.

Will you connect 40 LEDs in each group in parallel?
Will you use 20mA for each LED for a total of 0.8A?
Will you use a 5V 1A power supply?
I hope all your LEDs in each group of 40 have the same forward voltage, did you measure them all? What is the forward voltage?
Then use the 5V power supply voltage minus the LED forward voltage minus the turn on voltage drop of the Mosfet divided by the 0.8A per group to calculate the series current-limiting resistor.

 

Hi

Here is an alternate circuit.
It will save wiring up all those discrete mosfets. The timer runs at about 1hz. If you need 50% duty cycle, you could use a CD4093B oscillator instead of a 555.

 

Still don't know what a "star" is, or how the 50 LEDs are connected. If they are in parallel, then he needs 50 current limiting resistors. It would help if he addressed this. A complete schematic of one 4017 output section would be nice.

if you read his posts, he is buying pre-made strings of 40-50 LEDs. It would be really nice if he posted a link to what he is buying.

All the comments about dropping resistors likely do not apply to his project, as they are likely included in the commercial string. All the comments on various voltages may be irrelevant. He needs to switch the voltage required by the string and may not have the luxury of selecting a voltage.

If he provides the link, hopefully it will document operating voltage and current requirement. It is those parameters we need to address.

In this case, it really is a much simpler problem than the ones we are addressing. Typically, the issue is less an electronics one and more getting the right information from the TS.

@irishron40 Are you buying pre-made strings and can you provide a link to them?

 

He said he has 40 white LEDs all in parallel and they work fine.
I have a cheap Chinese flashlight that has 24 white LEDs in parallel and they are all with the same brightness.
I made many LED projects with parallel LEDs harvested from disposed Xmas lights and when I measure the forward voltages, most are the same except for a few.

 

It takes a higher resolution meter to see the difference in forward voltage, But certainly there are a lot of products that have strings in parallel with no resistor. That includes a number of different tube-lights that Ihave evaluated. So parallel can work, especially for those not quite so picky. And in the decorative stars, which btypically are 5 or 6 pointed geometric figures, a small variation will not matter because it will not be noticable.

 

The Mosfet will be fine and will stay cool.

Will you connect 40 LEDs in each group in parallel?
Will you use 20mA for each LED for a total of 0.8A?
Will you use a 5V 1A power supply?
I hope all your LEDs in each group of 40 have the same forward voltage, did you measure them all? What is the forward voltage?
Then use the 5V power supply voltage minus the LED forward voltage minus the turn on voltage drop of the Mosfet divided by the 0.8A per group to calculate the series current-limiting resistor.

Hi. Yes these are in parallel and were bought like that. They operate normally on 2 AA batteries. With NO resistor in the circuit.
I think these LEDs forward voltages is 3.2 volt. So no resistor needed on just 3 volt supply

I think a 5 volt ,1A would be the more likely power source I will use.

Ron

 

 

Hi. Yes these are in parallel and were bought like that. They operate normally on 2 AA batteries. With NO resistor in the circuit.
I think these LEDs forward voltages is 3.2 volt. So no resistor needed on just 3 volt supply

I think a 5 volt ,1A would be the more likely power source I will use.

Running them with batteries is very different than running on a power source. With batteries, you DO have a resistance in series with the LEDs. The battery’s internal resistance acts as a current limiting resistor. A power source doesn’t have this resistance.

Using 5V on LEDs that have a forward voltage of 3.2V will burn the LEDs out without a current limiting resistor.

How much current do the string of LEDs draw? You’ll need to know this to calculate the current limiting resistor for a power source. For parallel LEDs, the calculation is

Resistor = (Vsupply - Vled) / total current​

 

Which will burn out first, the LEDs that have no current limiting or the 5V/100mA overloaded power supply?
I think the overloaded power supply will be a fire hazard.

 

Have chased unit working the way I wanted. Ft
Just having a prob with mosfets.

I have the outputs from ic4017 connected to the gate of the stp55nf06l

The drain is connected to the power supply. ( 9 ) volts

The source of connected by to the strings of leds.

Nothing happening. Any suggestions as to why please