Hello everyone,

I am having a strange problem here,until now i have been using the PDIP package of CD4049 inverter IC.It works as it is supposed to.
But once i changed it to the SMD version, it heats up a lot.It does the inversion as it is supposed to ,but is so much heat a normal phenominon?

The exact mouser part number is : CD4049UBDR
At first i thought there was some problem with my circuit,but then i did a bread board test. on a bread board i soldered the IC and just gave VCC(15v) and VSS to it,it still heats up a lot.It consumes about 110 ma current.

Is that really supposed to happen?

 

Do you have all the gates connected? All unused inputs have to be connected either to gnd or vcc.

 

Do you have all the gates connected? All unused inputs have to be connected either to gnd or vcc.

No i have just connected 15v and ground.But still it is sinking 110 mA!!

 

Check, but do not mix (reverse polarity) whether you are the polarity of the supply source.

 

yes checked it,double checked it. As i said earlier the inverter is working ,but it is cunsuming over 110mA and heating a lot!!

 

No i have just connected 15v and ground.But still it is sinking 110 mA!!

That is exactly what you would expect. NEVER leave unused inputs unconnected, on ANY kind of CMOS part. The result is a phenomenon called "shoot-through current," wherein the floating input assumes a voltage that allows both the NMOS and PMOS transistors inside the gate to be ON simultaneously, allowing large currents to flow through them from VDD to VSS.

ALWAYS connect unused CMOS inputs to a valid logic level. NEVER leave them floating.

 

That is exactly what you would expect. NEVER leave unused inputs unconnected, on ANY kind of CMOS part. The result is a phenomenon called "shoot-through current," wherein the floating input assumes a voltage that allows both the NMOS and PMOS transistors inside the gate to be ON simultaneously, allowing large currents to flow through them from VDD to VSS.

ALWAYS connect unused CMOS inputs to a valid logic level. NEVER leave them floating.

yeaks!! i never though it would be such a problem.
I will ground the inputs and try...

 

Here is a good article on the subject of floating CMOS inputs.

 

i never though it would be such a problem.

I early-on learned to tie all unused inputs to ground after I burned up a CMOS gate on my breadboard.

 

After grounding all the inputs ,its drawing around 2 mA ,IC is not heating anymore.
Thanks OBW0549

 

After grounding all the inputs ,its drawing around 2 mA ,IC is not heating anymore.

That still seems quite high.
It should be microamps, not milliamps.

 

My power supply cannot measure micro amps,it constantly varries between 0.001 and 0.002 Amps.I think that just a measurement issue.
Just to be sure i left my bread board powered on for about an hour and there was no change.

 

My power supply cannot measure micro amps,it constantly varries between 0.001 and 0.002 Amps.I think that just a measurement issue.

I think it would be a worthwhile investment for you to get a DMM that can measure current down into the microamps. It need not be an expensive one; I have several very inexpensive meters on my workbench that go down to 2 mA full scale, with 1 μA resolution.

You might not need that capability very often, but it's handy when working on low-power stuff.

 

I think it would be a worthwhile investment for you to get a DMM that can measure current down into the microamps. It need not be an expensive one

Harbor Freight occasionally gives them away.

 

Do you have all the gates connected? All unused inputs have to be connected either to gnd or vcc.

The gates can oscillate at very high speed if inputs are not connected.