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Old 1st April 2005, 08:13 AM   #1
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Default VBIGC startup delay and softstart

Hello,

I have a question regarding a small circuit I would like to implement for the VBIGC amplifier.

My requirement is:
1. To switch on the mains supply for the LM3875 after about 1 minute.
2. To switch on the mains supply for the LM3875 using a softstart.

Unfortunately I am a software engineer and have no electronic experience

I attached a circuit which makes sense to me from a logical point but do you guys think this could work electronically?

The upper part is the relay switches and the bypassing resistors.
The middle part turns on after about 70 seconds.
The lower part of the circuit turns on the first relay and after the softstart delay (approx. 3 secs) the second relay.

Click the image to open in full size.

Excuse my newbish ignorance if the electronic part is nonsense. I'd appreciate any help.

Bye,
Sergiusz
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Old 1st April 2005, 08:40 AM   #2
digi01 is offline digi01  China
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Default Re: VBIGC startup delay and softstart

Quote:
Originally posted by sergiusz
2. To switch on the mains supply for the LM3875 using a softstart.
i think this step is unnecessary.
just drop a relay unit(1 minute delay) befor the second coils of tori


fyi,Projects for next hollidays (the world smallest VBITNGC??)

-Z
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Old 1st April 2005, 09:08 AM   #3
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Hello digi01,

Thank you very much for the reply. The background is that I built a VBIGC with two manual switches, one for the tube supply and the second for the LM3875s which I turned on manually after about a minute.

The problem is that due to the big inrush current (I use two 250VA xformers for the LM3875s) my household fuses blew regularly ... not always but sometimes.

That's the background ... I'd like to automate the process of switching on the amp and avoid blowing fuses

BTW, I found an error in the relay circuit which I corrected (I do not need a double switch relay on the second end):
Click the image to open in full size.

Anyway do you think this circuit would work?

Best regards,
Sergiusz
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Old 1st April 2005, 09:34 AM   #4
digi01 is offline digi01  China
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OK,then the K1 for startup delay and prime current limit thru series connections R4,R5,R6.
K2 for full action,the circuit should be ok

here is a simple design by P-A,it neglect startup delay function.(K1)the other is same.

LINK


good luck on your design,and enjoys...
Zang
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Old 1st April 2005, 06:44 PM   #5
Kermit is offline Kermit  Norway
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For inrush limiting I usually use a thermistor in series with the transformer primaries.
For turn on delay of the tube supply I'm using a 555 timer, like the one posted by Franz G:
'95 Ford Escort Speaker System Questions
Very simple and works like a charm.
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