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The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB

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#1,742
Can anyone have a look at what's wrong here?
Bildschirmfoto 2025-04-06 um 21.05.59.png
 

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#1,745
Try bypassing the LT4320 with conventional bridge to see if it works. I have never used the model for LT4320, just know that it works. The cap multiplier is a well designed and tested circuit. I think Jhofland did LTspice simulations on it even. The output should rise from zero to final value about 1.5 to 3v less than the DC rail at the input.
 
#1,746
Try bypassing the LT4320 with conventional bridge to see if it works. I have never used the model for LT4320, just know that it works. The cap multiplier is a well designed and tested circuit. I think Jhofland did LTspice simulations on it even. The output should rise from zero to final value about 1.5 to 3v less than the DC rail at the input.
Click to expand...
for one rail everything is ok, the problem arises when both rails are connected to GND. With a conventional bridge, the same thing happens
 
#1,749
Hi guys, need some help...
I have build my own 'SLB-PSU', it is a combination of Salas L-adapter, SLB and Rod Elliot.
It has a voltage ref with LED's and a JFET CCS in it so I can choose any fixed voltage. It 's intended use is for a +12V 850mA power supply for a DAC.
See PIC's and schematic.

20250516_170649.jpg


20250516_170710.jpg



20250516_170747.jpg


W2DAC-PSU-anaolg.jpg

The problem is that if I measure over R3, the ripple with my multimeter on AC voltage, it goes wildly up and down. Also on a scope this gives a very unstable image. See pic below.
I have build exactly the same PSU's but without the Ideal bridge, with a normal bridge with schottky diodes, and everything is stable and I can read off the ripple in milliVolts on both the multimeter and scope.

20250516_171603.jpg


Strange enough, DC wise everything is OK. The expected voltages are OK. All stable. And the cap multiplier filters all ripple off. but it seems to be a tiny bit higher then with the diode bridge.

Is this normal behaviour for a LT4320 Ideal bridge?
What do you guys measure over there? Should it be 'Smooth like butter' or is it very wild oscillating like mine?

(the datasheet says to put a 1uF ceramic capacitor over pin 5 and 6, so I did, there is also a 1uF MKP over it)

Grz, Walter
 
#1,750
The cap multiplier should not be combined with another circuit within its own feedback loop as you have done here. It would be fine to have the Rod Elliot LED based FET voltage regulator after the cap multiplier with its own power pass transistor. A two stage affair. I am afraid what you have made is an 16.7MHz oscillator. Since you say there is no oscillation when the active bridge is replaced with a passive bridge, I suspect that there is an interaction between the bridge MOSFETs and the cap multiplier. Too many actives. If you model this on LTspice, the oscillation will probably show up. Not sure if this will work but try putting a 10uH inductor in parallel with R2 and increase R2 to 10hms.
 
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