Author Topic: Help Me Design my SMPS  (Read 11772 times)

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Offline VEGETA

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Re: Help Me Design my SMPS
« Reply #25 on: May 31, 2017, 10:45:01 am »
I think a simple solution is to have a buck pre-regulator followed by a linear post regulator. Something like LT3081 which offers 1.5A or LT3083 for 3A. Switching pre-regulator should be relatively easy as there are many designs in the forum which has one, including my own which has SEPIC pre-regulator with a N-channel MOSFET post regulator.

Offline debininja

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Re: Help Me Design my SMPS
« Reply #26 on: May 31, 2017, 07:14:41 pm »

http://schmidt-walter-schaltnetzteile.de/smps_e/smps_e.html

I can't recommend this site highly enough for the beginning (or even an old pro) switcher designer. It's very handy and fairly accurate.

HINT - You always design the buck inductor for the maximum input - output differential at maximum load current.

PERFECT. That will help me out nicely since I'm in the works of making my first SMPS. A little 5V 1A flyback. It's just about done. I need to redo the transformer windings.
 

Offline John_HofmeyrTopic starter

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Re: Help Me Design my SMPS
« Reply #27 on: May 31, 2017, 10:07:08 pm »
Ok, so I took a look at this website (http://www.smps.us/topologies.html) to see what different topologies there are and I'm thinking of either a half bridge isolated buck converter or just a plain old buck converter. I'm leaning towards the isolated half bridge because according to the graph at the bottom of the website a half bridge converter will be able to handle the 90-120W of power that I want this supply to be rated at. Which one would you guys recomend.
 

Offline Zero999

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Re: Help Me Design my SMPS
« Reply #28 on: May 31, 2017, 10:27:58 pm »
So you're intending to use a buck converter? That will work fine for the higher any of the voltage range but will become challenging at low voltages. Why not shoot for a voltage half way between the two, about 12V to 15V, then use buck-boost? Despite the extra complexity it'll make achieving the large range of voltages easier.

The buck-boost (aka non-isolated flyback) also subjects the semiconductors, input and output capacitors to high stresses, and also suffers from the right half plane zero if the inductor current goes continuous. Without a transformer the output polarity is inverted as well.
I was referring to the type of buck-boost converter made with four switches, two transistors and two diodes. The output voltage is the same polarity as the input and it's no more stressful to the semiconductors than the standard boost and buck configurations. For a 0 to 30V output design, an input voltage of just under half the maximum would work nicely. The main disadvantages are increased complexity and switching losses.

https://en.wikipedia.org/wiki/Buck%E2%80%93boost_converter#Principles_of_operation_of_the_4-switch_topology_by_vannak_pov
 
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Offline John_HofmeyrTopic starter

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Re: Help Me Design my SMPS
« Reply #29 on: June 05, 2017, 01:17:36 am »
Ok so I have been doing some reaserch and this is the B.O.M I have come up with. If I'm missing anything (mostlikely) please let me know.

Topology: Buck/Boost converter
 
BOM:
 
Switch controller - SG3525A
 
MOSFETS - IRFZ48N
 
Shotky Diode - FFSP10120A
 
100uH Inductor rated at 15A
 
Some random huge full bridge rectifier from a pc power supply
 
120vAC to 20VAC transformer
 
ATtiny85 for temp regulation
 
10K thermistor for temperature
 
Voltage and current readout
 
LT1084 for final regulation
 
50k Potentiometers for adjustment
 
2X 5600uF 56V capacitor for filtering
 
Huge-ass heatsink
 
LM7805 for ATtiny
« Last Edit: June 05, 2017, 01:21:29 am by John_Hofmeyr »
 


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