If you have any relevant capacitance decoupling cap in the circuit you are supplying there will be a high in/out voltage difference.
Output voltage always starts at 0 V and only then rises. That could exceed the maximum allowed value.
Same with an eventual short (or current at regulator limit) after the regulator.
Good, can look at the spec sheet. That's a tick.
You are thinking about each voltage regulator in isolation. Now, think about where all the negatives will be tied to... the same common potential?
Using a zener to drop the input voltage to reduce the dissipation needed, and a zener across the input-output pins to protect it from over voltage at startup, would that not satisfy both issues?
True that. Startup, shutdown, and error conditions need to be considered.
One could turn it into a Maida Regulator, but that seems like a hassle when the HV devices are available.
One could also make a simple zener regulator:
You can make a similar circuit with a PNP for a negative voltage. Of course, now you introduce a slight temperature dependence, both from the zener and from the BJT, but that shouldn't wreck anything.
I highly doubt you need much precision on those voltages. In fact, the schematic shows series resistors that take the +28 and -19 V and turn them into +24 and -18 V in the preamp section, so the tolerance on the voltage in the preamp section is worse than ±5 % already.
I'm not seeing any issues in the schematic. Would you care to let us know your thoughts or would you rather be cryptic?
Tom
Until the input voltage glitches beyond the sum of the two zener voltages and fries the zeners and the regulator. 🙂
I personally find it much easier to dissipate the power in a TO-220 bolted to a heat sink than in a DO-41 or similar Zener diode.
Tom
The LM317HV is available, but unfortunately, the LM337HV does not seem to be available anymore.
The input voltage doesn't rise to 40 V instantaneously. As it rises, so will the output voltage of the regulator, which limits the voltage across the regulator. If you further protect the regulator with a 39 V zener there shouldn't be any issues unless someone short circuits the output of the regulator.
Tom
Tom
Right. So one could build a negative Maida. I did that at one point to make a -225 V supply and it worked rather well.
Tom