this should be easy

Hi,

You have not said what this whole thing is for. From the description you have given, it could be an electric cigar lighter. You get better directions if you let people know just where you are going.

sine

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resistors

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OK, sometimes I have trouble "reading between the lines", but how did we get from a 30khz amp at 120 deg C to RS-232 ??????????

mikey

RS-232 to TTL??? You have something against 1488 and 1489 ?:-)

...Jim Thompson

That's 330mA delivered from a 4.5V supply with a 3.5V rail-to-output drop allowed, right? What's wrong with unbiased NPN and PNP followers inside an opamp feedback loop? There won't be any thermal runaway, and < 1% distortion shouldn't be any problem with high opamp f_T.

You didn't check out Luhan Monat's website ?:-)

...Jim Thompson

This is probably not so easy because of the +125°C operation limit. If you want something stable and with adjustable current limit, I recommend the OPA547. With 1.5W dissipation and moderate heat sinking the die temperature will be still below 160°, where it shuts down. Not too cheap tho, but certfied up to 125° operation temp.

Yo,

Those are fine for putting in a design itself. This unit was for quick hookups to bench prototypes so each one does not need rs232 just to try out an idea. Also, it provides for 'network' type mixdown to a single ttl with 'echo suppression'.

All of this could be done with the chips you suggest, or, as most of my other later designs did, just a single pnp transistor for transmit, and a cmos inverter gate for receive.

Ambient temperature may go higher than 160C 125 is the minimun temrpature of oparation.

the thrustof my question is if anyone knows of an audio type IC tat doesn't have thermal shudoff or it can be disabled?

If a discrete design must be used, what would be the most stable biasing scheme for the most reliable operation overwide temperature swings? (hence my concern about thermal runaway)

In my business I know for a fact that garden variety transistors, opamps and other components will work for several hours at 200C if they are well selected. Thats all i need.

One thing. Consider this when using multi-layer boards:

I once encountered a similar problem, but with 180°C temp spec. Impossible to do reliably with silicon, I had to assemble these brittle GaAs chips on a hybrid. It was supposed to be for "Telecommunications". By chance I found out later that this circuit was mounted above the gates of those F16 bunkers and was used to arm the atomic weapons in the last possible moment. The afterburner was heating up that area, that is where that spec came from. Well telecommunication was not exactly wrong...

In article , Winfield Hill wrote: [...]

.... and highish frequency transistors. At these currents that should be no problem. This is one application where you don't want the TIP35/36 pair.

Maybe reduce the dissipation in the Tr's with a resistor in series with each collector. Up to 10 ohms looks possible.

This sounds reasonable to me. The class B operation will also cut down on dissipation. I would look for semiconductors intended for automobile operation. It gets pretty hot under the hood. There would also be some advantage to transformer coupling; that would let you match the 2V P-P to the +/- 4.5 V supply. Lastly, for a single frequency amplifier, why not tuned class C (or class B) ?

Tam