[sdiy] Overdriving 4069UB

[Scott Gravenhorst]

Harry Bissell Jr <harrybissell at prodigy.net> wrote:
>
>Content-transfer-encoding: 8BIT
>
>One other problem might be that you are using two stages
>  in linear mode. These will get hotter than normal. Make sure it
>  does not run TOO hot. Its probably Ok.
>  
>  The resistors do not limit this power... it flows from N to P channel device
>  which are both 'half on'. It will be worst with no signal input
>  
>  H^) harry

I'm thinking of trying a +/-5Volt supply version where I can then run the 4069UB (or 4007) and  the
opamp from the same supplies.  Lowering the voltage from 15 to 10 will produce less heat.  I've
made several circuits using 4069UB inverters in linear mode and with only mild heat.  However,
those were devices that did not have a chance for outputs to sit halfway between the supply rails.  

Just letting it sit powered up with no input is the worst case test for heat production.

>
>Seb Francis <seb at burnit.co.uk> wrote:  René Schmitz wrote:
>
>> Hi Harry, Seb and all,
>>
>> Harry Bissell Jr wrote:
>>
>>> with a 10K resistor in the inout you might be over the edge. I'd be
>>>   concerned. You might want to use shottky clamp diodes instead
>>>   of allowinng the CMOS input diodes to clip.
>>
>>
>> A few mA into the diodes won't hurt. There is a parasitic thyristor 
>> which might fire when a certain current is exceeded. No need for extra 
>> shottkys IMO, I'd rather make that resistor a little larger.
>> Ok, this is stretching the ratings in the datasheet a little, but does 
>> work.
>>
>> Btw, this sort of overdrive is explicitly allowed for the 4049 and 
>> 4050, to be able to do a 15V to 5V crossvolt conversion. Check the 
>> datasheet on these.
>>
> From what I can tell from the datasheet the 4049 doesn't have the 
>protection diode from input to VDD.   Instead it has a 30V zener from 
>VSS to input.  So there's still no clue as to the max current that can 
>flow through the protection diode(s) without damage.
>
>But you have encouraged me just to try a larger input resistor (e.g. 
>100K).  Perhaps I should leave it running for some time with a 
>full-scale-input and see if any damage occurs (i.e. if it stops clipping 
>at the input I'll know I've burnt out the diode)
>
>Seb
>
>
>
>
>

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