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.

 

[MJL21193]

No, the one from National is +/-72VDC. It will work unchanged for a +/-60VDC supply.

In any case, Rod explains how to adapt a different supply voltage for use in his P39. It's fairly simple math. The affected parts in the National soft start would be Rz1 and Rz2.

 

[AndrewT]

but remember what ESP said about a slow build up of voltage on the secondary side of the transformer.

That's where it becomes confusing since he is using the soft start as a dual purpose slow start.

And ESP warns against this by suggesting the overload % passing the soft start to allow the slow start part to be implemented.

The circuit works MUCH BETTER when supplied from a separate low VA dedicated transformer. ESP repeats this advice throughout his paper.

 

[Buzzy]

I am almost abt to complete building the circuit. But i have a little confusion.

Must the relay be wired as initially closed to the 3 ceramic resistors ?

 

[AndrewT]

Hi Buzzy,
no, the relay is open when there is no mains supply.
At start up the mains feeds through the Power Resistors.
After a short delay the relay closes, effectively taking the resistors out of circuit.
The relay stays closed when mains stays live.
The relay drops out (contacts open) when mains fails or is switched off.

 

[Buzzy]

I tested the circuit without connecting the ceramic resistors. But the relay won't close. The voltage across the relay coil is 2.5V. I have checked that i have wired correctly but can't seem to find the error. Any idea on what i should check ?

Thankz

 

[AndrewT]

where does the relay get it's 2.5V from?

 

[Buzzy]

I have built the rod elliot soft start circuit with auxilary transformer. However the auxilary transformer gets very hot. I can't keep my finger on it for more than 4 secs. Is this suppose to happen ?

The auxilary transformer specs are as follows:

9-0-9 secondaries power rating of 6VA.

 

[Buzzy]

Should I use a higher VA rated transformer ?

 

[Buzzy]

BTW is it correct to wire the relay as normally open to soft active. So that upon switching on the switch, the relay connects to soft active ?

 

[richie00boy]

6VA is plenty. What relay coil are you using? My guess is that it's too low voltage and is overloading your power supply which makes the transformer hot and the circuit fail.