Can the 338 regulator handle 4 Ohms?

[moamps]

Originally posted by johnnyx
Does the soft start slow it down all the time, or just at start up?

Just at start up.

[d3imlay]

I think it might be a good idea to review the requirements of a voltage regualtor. Most of the regulators I've seen by diy's look only at the output voltage with normal input voltage. However, it's important to consider the worst case current, and input voltage.

A standard practice for worst case input voltage is +/_ 10 percent of nominal. Assuming nominal to be 120 volts then the power supply must regulate the output voltage between 108 and 132 VAC. Rarely is the low end taken into consideration. It appears that the LM338 input voltage needs to be 5 volts greater than the output voltage. Consequently the the raw DC voltage at Low Line (108) has to be 5 volts above the output. At the high end the Vin-Vout will be much higher and the regualtor must have enough heatsinking ability to keep the regulator from failing or shuting down. This is the biggest disadvantge of linear regulators. You end up with a lot heat to get rid of.

The regulator should be monitored with an oscilloscope while the input voltage is changed with a variac while providing full load current. I have seen many regulators become unstable and break into oscillations at low input voltages.

[erictoucan]

I think because the capacitor at the output discharge to the input through the regulator and damage the regulator. So just connect a diode across output and input can serve the task without worrying about blow up the regulator.

I think it is hard to say what value of capacitor at the 3875 is safe. Using a diode is the way. You may refer to the application notes of national pdf file for details.