CD4050B: CD4050 Input & Output characteristics

Hey Varunesh,

First - thank you for separating this question from the other thread - this helps us significantly with issue tracking, it helps me to understand the issue, and it helps anyone who has a similar question regarding the CD4050 in the future.

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To directly answer your question, I would recommend keeping the diodes. You might also have some trouble with excessive current and oscillations from the slow inputs. More details follow.

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The circuit shown will typically work, but there are a couple of important issues:

(1) The input RC circuit (4.7k + 220pF) produces a very slow edge into the device. This will produce excessive current and could possibly start oscillations as explained in this FAQ:

Just removing the resistor won't solve the issue - it will just mess up the timing you have configured. The whole point of the circuit is to have a slow input to produce a delay.

The only fix I know of for this would be to switch the device for a Schmitt-trigger inverter that is designed to have slow inputs, for example, the hex schmitt-trigger inverter CD40106B. Two channels can be placed in series to produce a Schmitt-trigger buffer.  Unfortunately, we don't have a ST buffer that supports 3-18V operation.

(2) When the device switches, there will be a sudden jump of the input voltage -- which is why you have the suppression diodes and I assume the reason you are asking this question is to determine if the CD4050's internal clamp diodes are good enough to suppress this event on their own.

The internal diodes of the CD4050 won't react fast enough to prevent damage if the voltage spikes go as high as I would expect (up to ~1.5x Vcc or 22.5V, which is larger than the abs max voltage rating fo the device). For fast changing signals, we always recommend an external clamp diode, preferably at a lower voltage than the internal diodes to prevent them from turning on at all.

If this answers your question, please click the green "this resolved my issue" button; or if you need additional assistance, just respond to this thread.