Ic 4017 with multiple leds on every output

Thread Starter

irishron40

Joined Feb 26, 2014
34
Hi. I am building a LED Chaser Circuit using IC 4017 and IC555
i would need each 4017 output to switch about 50 LEDs..

can a transistor on each of the 10 ic4017 outputs handle this?

all LEDs are parallel connected.

would really appreciate if someone has a diagram of such circuit

thank you all

ron
 

AnalogKid

Joined Aug 1, 2013
8,804
Yes, maybe ...

Current requirement for each individual LED?

Power supply voltage and available current?

LED colors?

LED part numbers?

Wiring diagram or schematic showing how the LEDs are connected - !!!

ak
 
Last edited:

Audioguru again

Joined Oct 21, 2019
2,358
LEDs with the same part number have a range of forward voltage. When in parallel then the one with the lowest forward voltage lights very brightly (then burns out) and the ones with higher forward voltages do not light or are very dim.
Did you measure then match the forward voltages for each group of 10 LEDs?

Use a 9V supply and connect in parallel 5 strings of 2 LEDs in series to the emitter of each transistor. Then each LED conducts with 20mA and each transistor conducts with 100mA. The resistor will be 10 ohms/one quarter Watt.
 

djsfantasi

Joined Apr 11, 2010
7,192
View attachment 224806

White LEDs

20mA
I could adapt to any voltage and current supply


Thank you.
Ron vos
You are using the transistors as a switch, but your schematic has them wired wrong for that application. The LEDs should be wired between the led power supply and the transistor collector. The emitter should connect directly to ground. A high on the 4017 output will then connect the LED cathode to ground.

Each LED (or LED series string) needs a current limiting resistor. They cannot be connected to the transistor without one.

Usually there is a base resistor connected to the 4017 output. However, the 4017 cannot source much current. Each output at 5V will source 3.2mA. With the transistor, you will be able to drive the LEDs at ~30mA.

The LED power supply can be different than the supply for the 4017. Thus, you can drive several LEDs in a series string. But the Vf of the LEDs add, so for 10 LEDs at 3V, you would need a 30V LED power supply. For 50 LEDs, you need a 150V supply!

Here is where is gets complicated. For 50 LEDs, a series-parallel circuit is likely the best approach. But the voltage adds in the series strings and the current requirement adds for each parallel string.

For example, with 5 parallel strings of 10 LEDs, you’d need about 100mA (driving an LED at 20mA) of current with a 10V supply... But the transistor can only supply ~30mA.... So you need something other than a simple BJT (transistor). Perhaps an N-channel logic level MOSFET (maybe a 2N7000? I didn’t check it’s datasheet, but I think it can switch 109mA).

You’ve got the right idea. But the devil is in the details.
 

djsfantasi

Joined Apr 11, 2010
7,192
LEDs with the same part number have a range of forward voltage. When in parallel then the one with the lowest forward voltage lights very brightly (then burns out) and the ones with higher forward voltages do not light or are very dim.
Did you measure then match the forward voltages for each group of 10 LEDs?

Use a 9V supply and connect in parallel 5 strings of 2 LEDs in series to the emitter of each transistor. Then each LED conducts with 20mA and each transistor conducts with 100mA. The resistor will be 10 ohms/one quarter Watt.
He isn’t driving 10 LEDs at once. He is using one LED per output of the 4017 for an example. Hence 10 LEDs.

The 50 LEDs come from his verbal description. He wants 50 LEDs to be driven by each output of the 4017.

However, you make several relevant observations. I tried in my post to organize all of his requirements.
 
Last edited:

eetech00

Joined Jun 8, 2013
2,167
If a 12v volt supply is used, then each output of the 4017 could drive 10 parallel strings of LEDs, with each string consisting of 5x(2v/20ma) LEDs with a 100 ohm resistor. The total load 200mA each output. A couple of 8 channel mosfet arrays ( or three 4-channel arrays) could be used to drive the LEDs. The CD4017B and 555 will operate fine with a 12v supply.
 

Thread Starter

irishron40

Joined Feb 26, 2014
34
Thank you all for your replies.
I am just a beginner in electronics ,but have a great interest.
Just confused about one thing.

How come I have 40 white LEDs light up without any resistors on 2 AA batteries.these I bought like this for Xmas decorations.
All of these are connected parralel

ron vos
 

Thread Starter

irishron40

Joined Feb 26, 2014
34
He isn’t driving 10 LEDs at once. He is using one LED per output of the 4017 for an example. Hence 19 LEDs.

The 50 LEDs come from his verbal description. He wants 50 LEDs to be driven by each output of the 4017.

This is what I meant. You are 100% right djsfantasi
 

Audioguru again

Joined Oct 21, 2019
2,358
White LEDs need a voltage from 2.8V to 3.6V. Maybe you found some 3V ones.
Two series AA cells are 3V. So the series batteries lighted 40 of the LEDs in parallel. You are lucky that the LED voltages and the battery voltages matched.

I see that you asked about 50 LEDs on each transistor. Then 50 paralleled and matched LEDs use 1A, 25 parallel strings of 2 series LEDs use 500mA and 16 parallel strings of 3 LEDs use 320mA, for each output of the CD4017.

You can use a 5V supply for the 50 LEDs per output but the CD4017 output currents are too low to drive power transistors so logic level Mosfets will be needed.
25 strings of 2 series LEDs need a 10V to 12V power supply and ordinary Mosfets.
16 strings of 3 series LEDs need a 15V power supply and Mosfets or suitable transistors.
 

Thread Starter

irishron40

Joined Feb 26, 2014
34
White LEDs need a voltage from 2.8V to 3.6V. Maybe you found some 3V ones.
Two series AA cells are 3V. So the series batteries lighted 40 of the LEDs in parallel. You are lucky that the LED voltages and the battery voltages matched.

I see that you asked about 50 LEDs on each transistor. Then 50 paralleled and matched LEDs use 1A, 25 parallel strings of 2 series LEDs use 500mA and 16 parallel strings of 3 LEDs use 320mA, for each output of the CD4017.

You can use a 5V supply for the 50 LEDs per output but the CD4017 output currents are too low to drive power transistors so logic level Mosfets will be needed.
25 strings of 2 series LEDs need a 10V to 12V power supply and ordinary Mosfets.
16 strings of 3 series LEDs need a 15V power supply and Mosfets or suitable transistors.
Thank yyou

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.
ron.
 

MisterBill2

Joined Jan 23, 2018
7,689
Thank you all for your replies.
I am just a beginner in electronics ,but have a great interest.
Just confused about one thing.

How come I have 40 white LEDs light up without any resistors on 2 AA batteries.these I bought like this for Xmas decorations.
All of these are connected parralel

ron vos
Lighting the LEDs in parallel off of two AA cells you certainly DO have a current limiter which is the internal resistance of those batteries.
 

Thread Starter

irishron40

Joined Feb 26, 2014
34
Ok. 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
 

bertus

Joined Apr 5, 2008
21,025
Hello,
Use two ULN2003 Darlington chip, they have 7 buffers per chip.
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
 

Attachments

djsfantasi

Joined Apr 11, 2010
7,192
Ok. 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
The problem isn’t the BJT transistor you select. The problem is at 5V, the 4017 can only source 3.2mA of current. When used as a switch, the typical gain is 10, hence any transistor connected to a 4017 running on 5V can only switch 32mA.

So you’ll need another device. Not a BJT. Darlington transistors or logic level MOSFETs are necessary. If you were to switch the LED’s anode, you could use an N channel logic level MOSFET to drive a P channel power MOSFET, and have more current for your LEDs.

As [USER=208630]@eetech00 stated you can run everything at a higher voltage. 12V. But the 4017 can only switch 68mA at 12V and you’d still need a different device to switch the LEDs.
 
Last edited:

MisterBill2

Joined Jan 23, 2018
7,689
If the TS really needs to drive all of those LEDs in parallel then the project gets rather complicated, and certainly the LEDs need to be as the collector load of some bigger transistor. If that power device is an NPN, or mosfet equivalent, an gain stage will also be needed to switch on the transistor when the 4017 output goes high. So the whole thing will not be super-simple.
 
Top