Carlos' snubberized Gainclone Power supply - Page 62

PauloPT · 15th March 2012, 08:05 PM

Hi,

I if want to use this design with a few LM338 in parallel, do the caps and resistors of the snubbers stay with same values or divide the values by the number of paralleled devices?

Thanks.

gootee · 17th March 2012, 11:37 PM

The snubber is the resistor. The cap is just there to determine which frequencies the snubber resistor gets to see, so it doesn't dissipate too much power. So I think that the cap value would stay the same, since the frequencies involved would be the same.

Not sure about the resistor but don't see any reason to change its value.

mikelm · 18th March 2012, 09:19 AM

You could say that you are snubberizing the power supply and the what you connect it to doesn't change the snubber circuit

or . . .

You could add a snubber for each chip

It will depend on your layout.

PauloPT · 04:52 PM

So if I parallel 3 LM338 I don't get 3 times less the output impedance and I don't have to take this in to account when calculating the resistor/cap value?

The values of the cap/resistor are different in the unregulated and regulated supplies. Shouldn't it be the same values?
~
The schematics I'm using is the one on the pic.

thanks.

Gopher · 18th March 2012, 07:35 PM

PauloPT

You can't just parallel 3 regs. You'd have to use ~0R1 balancing resistors on the output of each reg to prevent one reg hogging all the current.

PauloPT · 18th March 2012, 09:05 PM

Quote:

You can't just parallel 3 regs. You'd have to use ~0R1 balancing resistors on the output of each reg to prevent one reg hogging all the current.

Yes, I know that.

What I don't know is how to change the parts in the snnuber to acomodate the new impedance of the 3 paralleled circuits.

mikelm · 19th March 2012, 01:22 AM

just leave it the same - that's what I would do

mike

gootee · 19th March 2012, 04:57 AM

I don't know that it's acting as a typical snubber, anyway. It looks more like a way to guarantee at least 0.47 Ohms of ESR for the 47 uF output cap, maybe since the cap's own ESR would drop quickly as frequency increased.

You could either use one snubber per regulator, or one snubber after their parallel outputs have been merged together, or, one per regulator and also one after the outputs have been merged.

If you want to know how snubber component values are calculated, there are several good papers on the web. Just google "snubber design".

If you have a scope and can put some fast-rising square waves into the amp that's being driven by the PSU, you might be able to use the practical method, at:

paralleling film caps with electrolytic caps

15th March 2012, 08:05 PM	#611
PauloPT diyAudio Member Join Date: Jan 2010 Location: Lisboa, Portugal	Old thread, new question Hi, I if want to use this design with a few LM338 in parallel, do the caps and resistors of the snubbers stay with same values or divide the values by the number of paralleled devices? Thanks. __________________ Kind Regards, Paulo.

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17th March 2012, 11:37 PM	#612
gootee diyAudio Member Join Date: Nov 2006 Location: Indiana Blog Entries: 1	The snubber is the resistor. The cap is just there to determine which frequencies the snubber resistor gets to see, so it doesn't dissipate too much power. So I think that the cap value would stay the same, since the frequencies involved would be the same. Not sure about the resistor but don't see any reason to change its value.

18th March 2012, 09:19 AM	#613
mikelm diyAudio Member Join Date: May 2003 Location: England	You could say that you are snubberizing the power supply and the what you connect it to doesn't change the snubber circuit or . . . You could add a snubber for each chip It will depend on your layout.

18th March 2012, 07:35 PM	#615
Gopher diyAudio Member Join Date: Nov 2005 Location: UK	PauloPT You can't just parallel 3 regs. You'd have to use ~0R1 balancing resistors on the output of each reg to prevent one reg hogging all the current.

19th March 2012, 01:22 AM	#617
mikelm diyAudio Member Join Date: May 2003 Location: England	just leave it the same - that's what I would do mike

19th March 2012, 04:57 AM	#618
gootee diyAudio Member Join Date: Nov 2006 Location: Indiana Blog Entries: 1	I don't know that it's acting as a typical snubber, anyway. It looks more like a way to guarantee at least 0.47 Ohms of ESR for the 47 uF output cap, maybe since the cap's own ESR would drop quickly as frequency increased. You could either use one snubber per regulator, or one snubber after their parallel outputs have been merged together, or, one per regulator and also one after the outputs have been merged. If you want to know how snubber component values are calculated, there are several good papers on the web. Just google "snubber design". If you have a scope and can put some fast-rising square waves into the amp that's being driven by the PSU, you might be able to use the practical method, at: paralleling film caps with electrolytic caps