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ScoreBoard problems cmos 14553B

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fastmx6

New Member
Hello all! i'm new to this community.

I'm and trying to recreate the diagram that is in the mc14553 chip with 3 7 segs model# lts 30801 and using a 7447 for the drivers and 4906 transistors.

So my problem I want to power it with a cpu power supply. I've only tested with a power supply and all i see is lots of flickering and it looks like it is counting but not working as it should. am i not giving it enough current or anyone tried this driving big led 7 segments displays?

Thanks sam
 

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  • datasheet[1].pdf
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  • mc14553bcp.pdf
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Last edited:

k7elp60

Active Member
It would sure be helpful if you could post a schematic of your circuit. I assume that you are using 2N4906 transistors as your digit drive, and you are using about 16 volts for the display voltage. What value of resistors are you using to limit the current to the segments of the displays?
 

mneary

New Member
Why 2N4906?

It's obsolete and super expensive. It's slow and you don't need the 5A capability. The gain is dismal and the TO-3 package is bulky. Maybe your display is flakey because of poor connections to the TO-3 case.

Consider a TIP part, maybe TIP32.
 

mneary

New Member
Since you are using a 7447 I am assuming your Vdd is 5V except for the LEDs. If your LED supply is greater than the supply to the 14553, then the PNP transistors will always be on as the output of the 14553 cannot go above its Vdd. The brightness may vary as the 14553 tries to go high and low but not much.

You can put some 7407 non inverting open collector buffers between the 14553 and the PNP bases (with base resistors of course).

If your drive is much more than 15mA per segment (105mA total per digit) the 2N3906 might not be strong enough. 2N3906 gain begins to suffer badly above 100mA. A higher current substitute could be the PN2907 (MMBT2907 etc.)
 

Blueteeth

Well-Known Member
Please post your schematic, or at least a 'rough connection' of what you're doing. Sounds to me like power supply filtering, or noise falsely triggering your counter. CMOS IC's have a very high input impedence, so even touching an unconnected pin can make it go 'gaga'.
 

fastmx6

New Member
ok on page 7 of the 14553 data i have attached i'm only using the first half with 3 digits.

so instead of the 7407 i can use a 7404 with the inverting in series?
Right now it should all just be straight forward but i dunno whats going on here.
I appreciate u guys helping me.
 

mneary

New Member
and i'm using a function generator with 100 hz just to test
100 Hz is too fast. All you will see is lots of flickering and it looks like it is counting but not working as it should., Slow it down to 2 Hz and maybe you will see it count.
 
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