Need advice for 74VDC power supply

[mister_e]

usually 10uF tantalum + 0.1uF ceramic at the input and at the output cover almost everything.

[Christopher4187]

For my information, what does the 10uF tant do? What does the .1uF ceramic do? I am assuming the material has a lot to do with the type of operation it is used for.

[mister_e]

to make a short story.. both do the almost the same job (filtering, noise supression, ... ,.. ) but on different frequency range. Of course the 10uF react slower.

that was the short story. Now for a better explanation you could Google for decoupling Capacitor.
http://en.wikipedia.org/wiki/Decoupling_capacitor
http://hsi.web.cern.ch/hsi/s-link/de...c/decouple.pdf

http://www.satcure-focus.com/tutor/page6.htm

[Pic_User]

Hi Chris,

The capacitors Mister E mentioned are important for input filtering and noise suppression.

These active voltage regulators look simple, like a power transistor. But if you look at the schematic, of the IC, inside the package, they are complicated. There are about 20 transistors inside. The circuit is a high speed error amplifier, that responds quickly to anything that throws it off equilibrium. When the load changes, the error amplifier corrects to balance the output back to normal. Any noise or variations are also reacted to.

Because of the high gain of the regulator, sometimes the correction overshoots.
If the AC filter capacitor is far enough (few inches) from the regulation device, the circuit has enough inductance in the leads to cause a small time delay. The inductive delay and the high gain of the regulator amplifier, create oscillations.

I have seen regulators rated at 1 ampere output get smoking hot and shut down with a minimum load. Checking with a fast oscilloscope, shows a strong AC waveform at 20 MHz. Adding a 10 microfarad Tantalum capacitor near the input pin cured the problem. That’s how I learned input caps are needed on these guys.

Also, do the math on the Watts, you will need a huge heat sink as Mister E said. Depends on your final circuit but looks like 40 Watts or so!

-Adam-