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sg3524 final version-is it working

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SSShocked

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hi everybody
this is the last version of my 2.5-100v 0.1-25a laboratory smps
SG3524 SMPS.jpg
is it working
 

FvM

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Si8420 seems to be a digital isolator, it can't work for analog signals like voltage and current feedback.

I have general doubt about overvoltage of the push-pull output stage. Depending on the transformer leakage inductance, it might be difficult to absorb it with a simple rc snubber.
 

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ok
si8420's datasheet says that it can be used in smps feedback?
then it will be with optoisolator
or not isolated-will isolate it with gate drive transformer
i will absorb it somehow
any ideas
maybe active or lossles clamp
if i change these things, is it going to work
 

kabeer02

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yes si8420's should work because i have a smps that uses it but what i am thinking is the over voltage at the push pull output stage.
 

goldsmith

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Hi
I think you can prevent from complexity and do it more simpler . you are using push pull arrangement . so it won't need any auxiliary driver for your mosfets because both sources of your mosfets have been connected to the ground . hence you won't need any float driver . and your PWM driver is able to create enough surge current for your mosfets .
and for feedback from out put voltage , you can easily use an opto coupler and a resistive voltage divider and an op amp and a variable reference voltage . and a relaxed network to make your variations a bit relax to prevent some damages of your mosfets while you're going to change out put voltage very fast . and for current you can measure current of primary to prevent large value of dissipation in your current sensor resistor . or perhaps a CT in alternative section .

On the other hands you can do it more simpler than this and of course more better than this !

Best Wishes + Good Luck
Goldsmith
 

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ok, so current transformer, but this is a low noise, high accuracy lab. smps-the CT is a bit inaccurate as i heard
can you draw what you mean for the feedback and relax network
 

kabeer02

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what he simply means is the total control of your feed back circuit to prevent getting damage from surge,i don't have much time to stars designing a circuit but i believe you can see similar circuit in the forum when you search.
 

goldsmith

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ok, so current transformer, but this is a low noise, high accuracy lab. smps-the CT is a bit inaccurate as i heard
Hi again
Wait ! are you sure you need it for a your laboratory ? if so , why very high precision is required ?
Anywhere , i hope you know resistors are not very accurate ( i.e : zero percent resistors are a bit expensive hence my mean is not those resistors ) .
For my opinion it is a good idea to control current through the primary instead of taking feedback from secondary ! ( current feedback ) ( because of economical reasons ) .
can you draw what you mean for the feedback and relax network
A simple RC network can create enough delay for you ! guidance : you have a fed signal . try to give it to an RC network to relax it . but in fact it is not a good idea to create such a delay in feedback loop .
hence you'd better to add such a network in your reference voltage . it means when you're going to change reference voltage to change the out put voltage variations in reference voltage should be relaxed .
I hope you got the idea .
Good Luck
Goldsmith
 

SSShocked

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awww
nice idea for the primary sensing
it will be with CT-as you said the high quality resistors are expensive, and it will decrease the efficiency
i am going to produce custom power supplies,amplifiers,osciloscopes...*will use already tested schematics
this is why i want it to be low noise high accuracy


but i cant still get your idea about the RC in the ref. voltage
can you give me a schematic for an example
 

goldsmith

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but i cant still get your idea about the RC in the ref. voltage
can you give me a schematic for an example
Hi again
Just consider that you've a DC PSU ( vref ) then tie an RC network across it and then get your voltage from across the capacitor . i.e: capacitor has a common node with the ground .
By the way , pay attention to the time constant of this RC network . you shouldn't select it very high .
Good Luck
Goldsmith
 

FvM

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I don't exactly get the meaning of the "RC network" discussion. If I understand right, it's about adjusting the voltage control loop frequency characteristic.

Generally speaking, the control loop must be always compensated for stability and good load step transients. It's true, that e.g. the low-pass effect ("pole") of an optocoupler can and must be considered in the compensation. But slowing down the loop (decreasing the loop bandwidth) is most likely unwanted for a lab supply. It affects ripple attenuation and can possibly cause inacceptable load step response.

A special point with lab supplies is a smooth interaction of current limiting and voltage regulation. Bad designed instruments (there are some examples available from DIY shops) may show a voltage overshoot on a negative load step, at worst damaging the supplied electronics.

These considerations suggest to start the design of a lab supply with a good control concept rather than trying to trim an existing design.

Electrical safety is another essential point. You should know the basic regulations in this field and e.g. understand, which parts of the design require reinforced insulation.
 

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ok
igot it
if i do these tweaks
is it going to work-2.5-100v 0.1-25a low noise high eff.
 

goldsmith

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I don't exactly get the meaning of the "RC network" discussion. If I understand right, it's about adjusting the voltage control loop frequency characteristic.
Hi Dear FvM
my mean was in path of reference voltage . it means when he wants to change reference voltage , voltage across the capacitor will be changed but not very fast ! as a relaxed function ( however a bit )

Best regards
Goldsmith
 

SSShocked

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i got it about the rc
but as i said:
is it going to work-2.5-100v 0.1-25a low noise high eff.
 

goldsmith

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nothing
i am just asking
do you think it is going to work
What do you think ? it depends on your abilities ! if that is your first time to build an SMPS , i suggest you , to start with a simpler project . e.g : a simple 0-30 volts 0-6 amperes . what is the advantage of such a supply ? it requires lower price and of course lower time to consume . and you can obtain enough experience with lower price !
When you're asking will it work or not , it means your experience in this case is low . hence i think you'd better to go through my suggestion .
Best Wishes
Goldsmith
 

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well
any suggestions, schematics...
because it will be out of the thread-PM
 

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