i ran an LTspice simulation on my DiY TL072 model (which !! i guess !! draws up to some 2x of the current the actual thing uses)
and it used quite steady (near-below the) 140mA per channel 560mW per package ← i guess its your exaggerated upper limit
( half a Watt is actually quite a lot for a small package to loose off )

 

i ran an LTspice simulation on my DiY TL072 model (which !! i guess !! draws up to some 2x of the current the actual thing uses)
and it used quite steady (near-below the) 140mA per channel 560mW per package ← i guess its your exaggerated upper limit
( half a Watt is actually quite a lot for a small package to loose off )

The quiescent current of a TL072 is 1.4mA per amp. He claims that it gets hot with no load, so that is only 30x 0.0028 = 0.084 mW.

An opamp with no load should not be noticeably warm.

 

An examination of the actual data sheet will reveal the average idling current of the IC, and that number can be compared with the device that you have and reveal any large difference that may exist. But that scheme will require measuring the current with reasonable resolution.

 

Wait...how hot is it?

Often people panic when they feel a semiconductor get warm but often without a feel for what 100 feels like (boiling water). How hot does the chip get? Which package are you using?

From back in my teen-years before I had a any kind of thermometer to measure temperature, my friends and I decided that if a transistor (there were few IC's back then) got hot enough to "fry spit" it needed a heatsink. that worked pretty well back in those days.

He stated that it is 155°F with no load and 160°F with a 10 kΩ load.

 

I have two TL072 chips, that seem to run warmer than I thought they would. I'm trying to figure out if my results are typical.

What package are your TL072 op-amps in?

 

An examination of the actual data sheet will reveal the average idling current of the IC

That is where I got the 1.4mA from.

 

That is where I got the 1.4mA from.

Actually, that is the typical value for each amplifier in the package. You can check the datasheet for the single TL071 and see it is the same value.

For a safe design, you should use the maximum value of 2.5 mA per amplifier, or 5 mA total for the dual amplifier package. With +/-15 V supplies, that's 5 mA x 30 V or 150 mW of power with no load. The SO8 package has a thermal resistance to ambient of 125 C/W, so the maximum expected temperature rise should be about 19 C (or 34 F). With an ambient room temperature of 75 F the junction temperature could be 109 F. The resistance junction to case is 40 C/W, so the temperature delta to the case would be 6 C (or 11 F), so the case temperature should be no more than 98 F, or very close to body temperature. Typical amplifiers should be less than this maximum value.

 

I used the typical value x 2. Sure, max value be better. So I agree. Not going to get to 55C (131F) even worst case with no load.

 

I used the typical value x 2. Sure, max value be better. So I agree. Not going to get to 55C even worst case with no load.

 

All that remains is to actually measue the current. If you put a 1000 ohm resistor in series with each supply line then measure the voltage across the resistor with a sensitive accurate meter. The scale factor will be one millivolt per milliamp

 

All that remains is to actually measue the current. If you put a 1000 ohm resistor in series with each supply line then measure the voltage across the resistor with a sensitive accurate meter. The scale factor will be one millivolt per milliamp

1 Volt per milliamp?
If the op-amp is getting that hot, probably 10Ω might be better, because there is a lot of current going somwhere!

 

If the current is correct then one MILLIVOLT per MILLIAMP will work.

 

If the current is correct then one MILLIVOLT per MILLIAMP will work.

1mV/1mA=1Ω

 

1K would likely perturb the current too much. I expect it is drawing over 10mA, which would mean a least a 10V loss.

But why not just use the current range on the multimeter anyway?

 

He stated that it is 155°F with no load and 160°F with a 10 kΩ load.

In that case, it is too hot. I would remove the chip from the socket and check again. If made according to the schematic the problem is with the chip.

 

My guess is that it is actually a device designed for a lower voltage.
A real TL072 (correct me if I'm wrong) has no protection diodes to the positive supply, so you can soon check with a multimeter.

 

"Whatever" My suggestion about using a series resistor was to avoid the chance of damaging the meter from excessive current. The low current ranges on many multimeters are not adequately protected from over-current burn out. THAT is the reason for my suggestion to use a resister and measuring the voltage drop. No other reason.

 

I rarely use the internal shunt resistors on my DVM for current measurement. If a resistor in the meter is subject to overload (or just plain burnt) that's a problem.

Usually I will use an ordinary 5% or 2% resistor externally. Haven't had to repair a meter since I started doing this about 20 years ago.

 

With that same digital meter it is simple to actually measure the value of the external resistor and thus KNOW the value of the "R" used to calculate the current.

 

Seems like the op amps are either connected incorrectly or they are faulty.