Triggering CD4053 with Arduino

Thread Starter

ShopRat59

Joined Nov 27, 2013
56
I need to trigger a CD4053 with an Arduino. The CD4053 (16 DIP) requires a minimum of 2/3's Vdd (2/3 of 12Vdc or 8 Vdc in my case) to trigger. This is obviously a transistor solution but i am unclear how to route it. I am relatively new, but in my past use of transistors the load is always between the + and collector for a NPN and the collector and - for PNP. I don't see how to put an IC between the two? I don't think it will work with a NPN so I have attached a simplified spice diagram with a PNP connected in the manner i think required - does this look right?

Thanks in advance,

Tom
 

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crutschow

Joined Mar 14, 2008
34,285
........... I don't think it will work with a NPN so I have attached a simplified spice diagram with a PNP connected in the manner i think required - does this look right?
No.
The PNP won't work since it needs +12V on it's base to turn it off and you only have 5V.
Also you have the collector shorted to ground. :eek:

Here's the circuit with an NPN:
Note that the signal is inverted in phase from the Arduino.

upload_2017-5-31_13-56-16.png
 

Thread Starter

ShopRat59

Joined Nov 27, 2013
56
Wow, that is what i originally had drawn up, but i thought pin 9 would receive current whether or not the transistor was conducting.

Would you mind explaining the need for R2 and the value of R1 - most Arduino diagrams I see show a 1K at the transistor base?

Thanks for the quick response.

Tom
 

crutschow

Joined Mar 14, 2008
34,285
............Would you mind explaining the need for R2 and the value of R1 - most Arduino diagrams I see show a 1K at the transistor base?
If you don't have R2 then there is no voltage signal at the transistor collector, it would always be 12V (unless the transistor draws enough current that the power supply current limit is exceeded ;)).

So R2 is selected to be able to charge the stray capacitance, including that from the CMOS input, at the desired operating frequency.
If the operating frequency is low, then you could go up to 100kΩ as Dd suggested.
I used 3k, which should take you up to the maximum operating frequency of the CD4053.

The rule-of-thumb is that you select R1 to give a base current of about 1/10th of the collector current to fully saturate the transistor when on (forced Beta of 10).
The R2 current is 12V / 3k = 4mA.
The value of R1 is then (5V-0.7V) / 0.4ma = 10.75k.
I rounded that to 10kΩ.
 
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