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question about LF347 op-amp with heat.

Do the LF347 op-amps have issues with ambient heat getting a little on the high side?

The PDF specifies 70c from what I can see.

For those of you that don't know what this is off the top of your head, this is a 4 package op-amp with JFET inputs with up to +/- 18 Volts at the Vcc,Vee.

I was wondering if this chip has a known problem of shorting or random behavior in high temperature environments?

It seems there has been a series of failures in a device that is being used. These devices are being used in a lot of different applications but this one application happens to have a lot of heat building up around it and after much work of reducing other factors that could be in the mix this is the last one.

We put the device in the cabinet, powered it and just let it live there for about 2 weeks, because the need for it wasn't in demand at the time and it failed with a shorted chip which took out the supply etc. we did notice when opening the cabinet after said machine was operating for sometime, it was like a heat wave hitting you in the face. We have since put some cooling in the area but have not done a long term operation test to see if it has corrected the issue.

Any experience with this?

Thanks Jamie

Reply to
M Philbrook
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What package? What's your supply voltage? Is there much load?

347's do run warm.
Reply to
John Larkin

back in the 70's I used many LF356 fet opamps in audio preamps. Just single amp in a a TO5 case. They did run a bit warm but not what I'd call excessive. No forced air but the chassis did have ventilation. Never had a failure. I have a couple of units here

Reply to
gray_wolf

Maybe the power supply went over-voltage, cooked the op-amp, then cooked itself.

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Reply to
Kevin McMurtrie

No, haven't used one in decades. But there is noticeable self-heating. Datasheet max current consumption 11mA which at 36V supply is 396mW which will raise junction temp 30degC above ambient and that is without any output current. If each amplifier is sourcing/sinking 4-5mA then die temp hits 150degC at 70degC ambient.

Are yours seeing that kind of load current?

piglet

Reply to
piglet

The circuit it's in has the Vcc and Vee at 18 +/-, which is at the top for that chip. This is the PDIP quad package.

In this last case, the op-amp that is shorted has package #3 output shorted to the Vcc with an internal R of ~103 ohms. Output of this op-amp leads to a series 1/8 watt 100R to an input of a LH0002 Buffer chip. The R and buffer chip are fine and so isn't all surrounding components that are related to the LF347N.

The 100 R is fine being that its such a small watt R it shows no sign of torture. So this leaves out the idea of the buffer chip failing and shorting the output. It appears the upper NPN transistor has become shorted. This test are cold test via a DMM.

The regulators in use are 7818 and 7918, both outputs are supplying the components through a SI diode, which drops the outputs down to ~17.4 +/-, which they do comfirm in the circuit.

WHen this control unit died, it was only powered, it wasn't even being used. The output of the LH0002 buffer was attached to a device that had it's fused yanked for other reasons, for which that divice has an isolated input. In otherwords, there was no chance of some unknown back tracking through the buffer chip. We have had other controllers in that same cabinet have its LF347 short but a different op-amp section.

Heat is the only factor I can put my finger on at the time and I do believe it is the only Fet chip on that board.

Jamie

Reply to
M Philbrook

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