I have question marks about my power supply circuit anyone can help?

Thread Starter

turgut

Joined Nov 4, 2022
28
Im designing a power supply but its my first design as high power. I have a device and its frequency is 22-25kHz. Im designing a filter and power supply for it. So device need 600mA 12V nearly.
Question-1: Is my filter okey for that?
Question-2: This circuit could get 600mA? (output regulator will LM317 or 7812)
Question-3: What kind resistor should i use for 50ohms. Im open for suggestions.

LTSpice results below the text.

Thank you all..

ltpsice frekans sonuçları 25 ohm snubber.png
 

panic mode

Joined Oct 10, 2011
2,872
i would say it is more than enough... what i do not see is smaller cap before and after regulator. they are meant to improve stability. large caps are not good at handling high frequencies. this is why for decoupling, several capacitors of different size are used ( for example 2200uF, 22uF, 0.1uF). what is the purpose of zener after voltage regulator? according to datasheet this is 250mW device. so 250mW/12V=20mA. your regulator is set to output 12.6V so diode would be conducting all the time... if you want clamping diode (because in front of it is a series regulator which cannot sink current), why not go for more powerful one and with slightly higher voltage?
 

Thread Starter

turgut

Joined Nov 4, 2022
28
i would say it is more than enough... what i do not see is smaller cap before and after regulator. they are meant to improve stability. large caps are not good at handling high frequencies. this is why for decoupling, several capacitors of different size are used ( for example 2200uF, 22uF, 0.1uF). what is the purpose of zener after voltage regulator? according to datasheet this is 250mW device. so 250mW/12V=20mA. your regulator is set to output 12.6V so diode would be conducting all the time... if you want clamping diode (because in front of it is a series regulator which cannot sink current), why not go for more powerful one and with slightly higher voltage?
okey i think i have to give more details.
im try to converting 250vac to 12vdc. my device's values which i will connect are 12vdc 600ma and it works near 22-25khz.

so im trying to do a filter which will cut higher than 35khz. and should give 12vdc and 600ma.
so what should i do in this circuit or what should change or delete?
its my first project about high power. so im confused.
from your answer, i understand that 12v zener diode is unnecessary and i deleted it. also i connected capacitors like that.


Adsız.png
 

panic mode

Joined Oct 10, 2011
2,872
why did you remove large value capacitors? they are used to filter most of the ripple out. without them output is going to be horrible. smaller caps are used in addition to them - not replace them. and why don't you put resistor to simulate load and check ripple?
12V/0.6A=20 Ohm
 

Thread Starter

turgut

Joined Nov 4, 2022
28
why did you remove large value capacitors? they are used to filter most of the ripple out. without them output is going to be horrible. smaller caps are used in addition to them - not replace them. and why don't you put resistor to simulate load and check ripple?
12V/0.6A=20 Ohm
First i added big capacitors again. and measures ripple voltage. You can see in the first image..


ripple voltage 2.png




im measuring that frequencies from red arrow. like image below this line is it true?


1.png


or am i should measure from there? i hope true measuring is like above image.

2.png
 

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panic mode

Joined Oct 10, 2011
2,872
you should be measuring ripple across DC output, before and after regulator, while PSU is under load.

if you are concerned with ripple, you can follow recommendations from the manufacturer on improved ripple rejection:

1685046283353.png
 

Thread Starter

turgut

Joined Nov 4, 2022
28
you should be measuring ripple across DC output, before and after regulator, while PSU is under load.

if you are concerned with ripple, you can follow recommendations from the manufacturer on improved ripple rejection:

View attachment 295023
No im not concerned about ripple its okey i think. im concerned about can this circuit work well with 12v-1a output values with defending itself above 35khz?
 

panic mode

Joined Oct 10, 2011
2,872
where is the 35kHz interference coming from? mains is 50Hz. then this is rectified and filtered so you get 0Hz.
the only possibility is if the load itself is the actual source but you said nothing about that. many circuits produce signals in various frequency ranges but that is what they are supposed to do. this is why sensitive logic is shielded, isolated, fed from different source. if derived from same source, it would need to be filtered to avoid harmful influence. what are you actually trying to accomplish?
 

Thread Starter

turgut

Joined Nov 4, 2022
28
where is the 35kHz interference coming from? mains is 50Hz. then this is rectified and filtered so you get 0Hz.
the only possibility is if the load itself is the actual source but you said nothing about that. many circuits produce signals in various frequency ranges but that is what they are supposed to do. this is why sensitive logic is shielded, isolated, fed from different source. if derived from same source, it would need to be filtered to avoid harmful influence. what are you actually trying to accomplish?
actually, i dont know where is the 35kHz interference coming from. but my manager wanted it from me. so im thinking circuit should work well right?
 

panic mode

Joined Oct 10, 2011
2,872
primary function of PSU is to deliver power to some load. PSU designs depend heavily on type of load. if you do not know what the load is, you cannot be sure that you have proper or optimal solution.
 
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