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Old 26th February 2010, 09:36 PM   #1
john65b is offline john65b  United States
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Default Soft Start needed for SMPS?

Hey all,
Do I need a Soft start on a SMPS?

I have read a while back about never using a Variac to ramp up power on a SMPS (is this true?), so I though same thing would apply with a soft start on a SMPS...

Its a Icepower ASC1000 amp. Currently do NOT have a soft start.

Thanks all in advance.
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Old 27th February 2010, 03:44 PM   #2
dady is offline dady  Balearic Islands
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Is possible to modulate the pulse of the controller with a capacitor to ground, but i don't remember wich pin. Let me make a couple of calls in these days.
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Old 28th February 2010, 11:02 PM   #3
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Wink Soft start

If I understand what you want, I think you need a soft start circuit in SMPS, Specially to protect from the INRUSH currents at startup.

You can do that in SG3525, But dont know your circuit!


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Old 1st March 2010, 12:09 AM   #4
john65b is offline john65b  United States
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On Pass class A amps they use a CL-60 thermistor on the primary to tranny.

Can I use one on the Mains input to a ICEpower ASC1000 (has an internal SMPS)
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Old 1st March 2010, 01:41 AM   #5
john65b is offline john65b  United States
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Actually, after further reviewing the manual, it offers 450ms power supply start up delay, and another 1200ms on switch start up delay.

Never mind. Its good as is. This is the easiest amp I have ever built.
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Old 5th March 2010, 06:41 PM   #6
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On SMPSs, Soft-Start is most always done at the PWM Controller IC. For the SG1525, this is pin-8. Connect anything from 0.1uF to 10uF to ge the desired time-constant. For the MC33025, this is also pin-8. For the SG1846,. there is no dedicated SS pin, but you would connect the COMP pin to a buffered SS ckt. For the TL494, an RC combo with the Cap from V+ to the deadtime (pin4) and a resistor from pin 4 to ground will accompolish SoftStart.

Hope this helps,
Steve
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