Soft/Slow start - high current - low voltage class A PS for a Pass F5 amp

[sekess]

Originally Posted by Zen Mod

PSUD have "soft start" function under "options"

Actually,
Just to see what it looked like, I made the first section after the rectifier an RC instead of a C. This way, the first thing after the rectifier was a resistor. So, I placed a so called soft start resistor right on the rail. Then when you cange the resistor value, you can see how long it takes for the caps to reach steady state voltage for various resistances.

It would be nice to do this with a resistor on the transformer primary and also on the secondary (before the rectifier) -- And even better with various thermistors.

Thanks,
Steve

[sekess]

Another interesting thing that I saw on Duncan's program is:

As I stated in my first post, I'll be using a CLC supply (with a 2.5mH choke). With no soft-start, there is approximately a 54 amp surge of current through the choke on start-up. That is huge. Of course, I have a 7.5 ohm resistor as the load for this power supply. The atual amp will provide a more complex load. So obviously this 54 amps is not accurate. But, I don't know how off it is.

However, by placing a 5 ohm resistor on the rail after the rectifier you drop the surge current from 54 amps to 3 amps. Of course when you bypass the resistor, you will incurr another surge. But, I assume it will be less violent.

Anyway -- just an interesting observation.

Thanks,
Steve

[Zen Mod]

use CCS as load

[Magura]

Originally Posted by Zen Mod

that way - you'll kill them fast

new circ - instead soft start you'll have hard stop

Not really. the CL-60 can carry 5A, so two in parallel is good for 10A, which is plenty enough for use in the secondaries for a F5.


Magura

[Zen Mod]

think inrush

[AndrewT]

Originally Posted by Magura

the CL-60 can carry 5A, so two in parallel is good for 10A,

don't put Power Thermistors in parallel. The one that heats up quicker, then tries to pass most of the current, leaving the other one cool and high resistance.

Select a higher current capacity Thermistor and use them in series.

[Magura]

Originally Posted by Zen Mod

think inrush

I have measured the AVX version of CL-60, it is capable of short term overload of 4 times the rated current.


Magura

[Magura]

Originally Posted by AndrewT

don't put Power Thermistors in parallel. The one that heats up quicker, then tries to pass most of the current, leaving the other one cool and high resistance.

Select a higher current capacity Thermistor and use them in series.

They just need to be thermally coupled, not really rocket science.

If you take a closer look at the datasheets of thermistors, you will find that if you need 10R at 25C, they don't come much bigger than 5A, unless you are willing to pay through your nose.

Magura

[jacco vermeulen]

Epcos/Siemens B57464-S0100M
10R, 8A, 6.7W (25C)

[giulia67]

For a man with a pair of 3.6KV toroidal transformers that put 80 volts across caps what do you (anyone) suggets?