Soft Start needed for SMPS?

john65b · 26th February 2010, 08:36 PM

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.

dady · 27th February 2010, 02:44 PM

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.

microsim444 · 28th February 2010, 10:02 PM

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!

Fox

john65b · 28th February 2010, 11:09 PM

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)

john65b · 1st March 2010, 12:41 AM

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.

N-Channel · 5th March 2010, 05:41 PM

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

26th February 2010, 08:36 PM	#1
john65b diyAudio Member Join Date: Jan 2005 Location: Chicago	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. __________________ All right, but apart from the sanitation, medicine, education, wine, public order, irrigation, roads, the fresh water system and public health, what have the Romans ever done for us? Life of Brian

27th February 2010, 02:44 PM	#2
dady diyAudio Member Join Date: Oct 2002 Location: Punta Prima, Menorca, Spain	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. __________________ Esteban Bikic

28th February 2010, 10:02 PM	#3
microsim444 Account Disabled Join Date: Oct 2008	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! Fox

28th February 2010, 11:09 PM	#4
john65b diyAudio Member Join Date: Jan 2005 Location: Chicago	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) __________________ All right, but apart from the sanitation, medicine, education, wine, public order, irrigation, roads, the fresh water system and public health, what have the Romans ever done for us? Life of Brian

1st March 2010, 12:41 AM	#5
john65b diyAudio Member Join Date: Jan 2005 Location: Chicago	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. __________________ All right, but apart from the sanitation, medicine, education, wine, public order, irrigation, roads, the fresh water system and public health, what have the Romans ever done for us? Life of Brian


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5th March 2010, 05:41 PM	#6
N-Channel diyAudio Member Join Date: Mar 2003 Location: Sol System	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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