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.
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.
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
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
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.
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.
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.
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.
Attachments
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.
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.
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.
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.
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.
The auxilary transformer specs are as follows:
9-0-9 secondaries power rating of 6VA.
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