ESP sound soft start

[Buzzy]

Anyone here built the project 39 of esp sound ? Does the schematic on the website work ?

[artquake]

I ordered a pair of pcb's of project 39 from esp about one year ago.
It works very well ! It's small, compact and therefore very recommendable. I'm using on each a 500VA toroid without any probs.

best regards
artQuake

[Buzzy]

The pcb version uses an IC. I was asking whether the circuit with the mosfet works.

[MJL21193]

Hi,
I used it (made my own layout and board). It works very well.
My transformer is 850VA.

[AndrewT]

Hi,
do you want soft start? to reduce the current surge that a toroid or large EI requires to start up
or
a slow start? to reduce the current through the rectifier trying to charge up discharged smoothing caps.

ESP does not clearly differentiate between these two options.
The solution to each is different, but both involve a bypass across a resistance (thermistor and/or resistor).

Soft start lasting 100mS to 500mS, is in the primary feed to the transformer.

Slow start lasting 1000mS to 5000mS, is in the secondary before the smoothing caps.

[MJL21193]

The ESP P39 limits current surge to the toroid.

There are easier ways of doing the same thing though. The P39 is fairly complex for what it does. A recent post in the chipamp forum by jackinnj shows a power supply with a simpler soft start.

Link:http://www.national.com/an/AN/AN-1849.pdf

[Buzzy]

Thankz for all the replies.

I am looking for a soft start circuit because the 500VA transformer draws so much current on startup blowing my 8 amp slow blow fuse.

MJL21193 may i know what kind of relay i should be using with the esp sound circuit ? Should it be 12 V SPDT Normally open type relay ?

And may i have a look at ur board layout for it ?

Thankz.

[AndrewT]

Hi,
relay can be single pole, single throw (SPST) normally open is OK.
Coil voltage depends on the transformer voltage you choose.

Relay contacts voltage must be rated for your mains supply voltage and load type/size.

[MJL21193]

Sorry, I don't like to show a board layout from ESP schematics as Rod sells these boards and was gracious enough to post the designs for us to use. Besides, my soft start was built specific to the project I was doing at the time, so it would need changes to adapt for other use.

The one from National is really a lot more simple and if I had my time back, I would have used it for my project. It has only a few parts and runs off the power supply transformer.
Very nicely designed really.

[Buzzy]

Yes the national soft start circuit is much simpler but i don't know how to modify it so that it can used. My supply voltages are +60 and -60 but the one in the national one is around +33 V.