CD4026 IC become very hot

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target1plus

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I am relatively new to electronics having just started 2 months ago. On the other hand, I tried dozens of circuits as well as assemblies with an Arduino and this without problem and everything always worked.

However, I received a small batch of CD4026 IC from Aliexpress this week so I wanted to test the product. I have tried more than 5 different circuits all unsuccessfully turning on the 7-segment display partially or not at all without ever incrementing either with an circuit including an NE555 or a pushbutton. I even burned one of my CD4026 IC while smoke was rising from it and two others got extremely hot. My NE555 or my 7-segment displays work perfectly in other assemblies. So my problem comes from the CD4026 IC. Do you have a foolproof circuit that I can try? I could have believed it once I misread 1 circuit, but not 5 differents.

Is it possible that the entire batch is defective?
 
What drivers are you using between the 4026 and the LED's? - as an absolute minimum you would need current limiting resistors, and only low power without a driver.
 
target1plus said:
I received a small batch of CD4026 IC from Aliexpress
.........
Is it possible that the entire batch is defective?
Click to expand...
Yes, there are lots of fake products on Aliexpress.

When you said that you tried them in 5 different circuits, were they different designs, or was it 5 examples of the same design. If it is one design, there could be the same mistake in all of them, such as the one that Nigel suggested.

Why go to Aliexpress? CD4026s are cheap and readily available from reputable sources:- https://www.mouser.ca/Search/Refine?Keyword=cd4026
 
i guess free shiping rules
 
I would reccomend to connect push button to clock, and check output pins with multimeter if it counts...
 
Nigel Goodwin said:
What drivers are you using between the 4026 and the LED's? - as an absolute minimum you would need current limiting resistors, and only low power without a driver.
Click to expand...
What do you mean by drivers?

I have jumper wires between the 7 exits of the CD4026 and the 7-Segment Display. I've put a 330 ohm resistor on the common cathode. I've also tried one resistor on each segment input but no difference.

One of the circuit I tried is this one:



Another one:



Another one:

 
MacIntoshCZ said:
i guess free shiping rules
Click to expand...

Effectively, it's for the free shipping (or almost free).

I am just a hobbyist who started with an Arduino kit in the beginning of December and I decided to purchase over a hundred components from Aliexpress to increase my knowledge range.

If I had a real product to make, I would go with more reputable sources.
 
i understand, when cost of electronics is 1/3 of cost of delivery it and its just for prototyping its ok. Unless you designing precision circuitry or high power power supply =).
btw irf 460 from aliexpress seems to work. In most of videos here 460s are used:
 
target1plus said:
What do you mean by drivers?

I have jumper wires between the 7 exits of the CD4026 and the 7-Segment Display. I've put a 330 ohm resistor on the common cathode. I've also tried one resistor on each segment input but no difference.
Click to expand...

That's why you're killing the chips - it's not designed to feed high current outputs - the datasheet specifies transistor drivers to feed LED's.

Maximum dissipation for the entire chip is only 500mW, and only 100mW per individual output.
 
Nigel Goodwin said:
That's why you're killing the chips - it's not designed to feed high current outputs - the datasheet specifies transistor drivers to feed LED's.

Maximum dissipation for the entire chip is only 500mW, and only 100mW per individual output.
Click to expand...
Do you have a circuit diagram showing how to? Everyone I found was similar to the three I posted previously.

If I have a 330 ohm resistor on each segment, I should have 15 mA on 5 V or 27 mA on 9V? So less than 200 mW for the entire 7 segments?
 
If you have a look at the voltage/current curve for the output (fig 8 of this datasheet https://www.ti.com/lit/ds/symlink/cd4026b.pdf) you will see that the outputs won't give more than about 20 mA with a 10 V supply and the outputs shorted.

You won't get 27 mA with the 9 V supply. There is the voltage drop across the LED and the voltage drop across the IC to consider. I don't know where you get the figure of 200 mW from.

With a 2 V LED and a 330 Ohm resistor you will get about 12 mA. There will be about 2 V drop across the LED, about 4 V drop across the resistor and about 3 V drop across the IC. That will give around 36 mW of heat in the IC. There are 7 segments, with between 2 and 6 segments lit at any one time. That is 72 mW to 216 mW depending on the digit shown.

That should be OK but the IC will be getting hot. The IC is rated to 500 mW, but that is with a junction temperature of around 150 deg C so I will be really hot to the touch.

As Nigel says, all the application circuits show a transistor between each output and the display.

The CD4026 dates back to the 1970s. The data sheet shows filament, Nixie tube and vacuum fluorescent 7 segment displays, all of which are long gone.
 

So if I try again one of the three circuits I've shown adding transistors between the CD4026 and the 7-segment so the 7 segment will take the power directly from the battery instead of passing into the CD4026 it should be ok?

Why no circuit diagram is showing that on the web?
 
target1plus said:
Thanks, I will try this tonight!
Click to expand...
I still have no success even with transistors... I try only the "A" segment unplugging the other six and passing the current by a transistor instead of the CD4026.

The CD4026 is becoming so hot in less than 5 seconds I can't even touch. And the "A" segment is never on even if it should be on 0,2,3,5,6,7,8 and 9

If I plug the "A" Segment directly on 5v rail it's lighting up as expected...

As a last try, which circuit should I try before give up and saying that the whole batch is defective?
 
With a 9V supply, A CD4xxx IC output high directly into a 2V red LED to ground produces a current of about 15mA as shown on Texas Instruments datasheets. Then the heating in the IC is (9V - 2V) x 15mA= 105mW but higher on some ICs. The maximum allowed heating of one output is 100mW. Use a series current-limiting resistor or transistors.

With a 5V supply the output current from a CD4xxx into a 2V red LED is very low at about 3mA.

Buy genuine CD4026 ICs locally not fakes from "over there".
 
Last edited:
I've done a last attemp with this circuit and four new CD4026 IC in the batch and no luck, the 7 segment is not lighting up and the 4026 become very hot really fast. I've disconnected output 6,7,9,10,11,12,13 and I've tried to connect directly a red led to ground one output at the time and on three of the four IC, only output #12 (segment B) was lighting up the red led. On the fourth IC no output was working.

I think the whole batch is defective or mislabeled (maybe it's something else then a CD4026BE? They all look the same so if they didn't printed the good thing on it...

Even if the clock was not working, any number would be lighting up a minimum of 2 segments (Number 1).

Or, I'm really bad and I don't understand something important.

 

Well despite the fact you've been told repeatedly that you can't feed LED's directly from the chip, you still keep showing circuits doing just that?. Also, as others have said, buy some reputable chips, those from China are quite possibly fakes anyway.
 

I ve also tried one segment at a time via a transistor but it's doing the same thing. So I guess that I will blame the fake chips.

I ve not seen a circuit with the transistor to show so I ve modified this one.
 
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