Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

help: 3A transformerless power supply 0-30V, No IC

Status
Not open for further replies.

tibzero

New Member
hi to all. im new here. my project is a 3A transformerless power supply Adjustable 0-30V with auto shut off. using IC is prohibited. can anyone help me?
I already search in google and yahoo for several weeks but i only found 300mA or less. i also try it to make the current higher but the required wattage for the resistor will be higher too and it has a large heat sink also.

tnx for helping me...
 
When you say no IC, does a comparator count as an IC? Because you definately need at least that unless you want to build your own comparator out of several dozen transistors.
 
yes, comparator is counted as an IC. do you know how to build a comparator using transistors or do you have a link for tutorial? tnx.
 
Maybe a little more information:
Is it powered from the mains?
If so do you actually build it or just do proof of concept.
You can use all parts except IC's and transformers?
What do you mean by auto shut off?
Any other specs. like ripple voltage?
 
Its possible but it wont have true isolation from the main power source. Its just a standard capacitive coupled current limiter circuit with a large transistor using a zener diode for a voltage reference. The rest is just a basic variable voltage divider using a potentiometer to vary the transistor bias from zero up to the zener diode reference voltage.

Its sloppy will have poor voltage and current regulation in most cases but does the job any way.
 
yes. it is powered by the mains. 220-250V AC.
Autoshut off- the circuit will shut down when there will be a short circuit. like the standard power supply. the green light will become red when it will have a short circuit.
we are not allowed to use IC because thats the project given to us by our professor.
we must build a transformerless power supply with 3A maximum current.
adjustable regulator 0-24V. auto shutdown or shutoff. and IC is not allowed.
last year we also build a 3A power supply adjustable 0-24V. but IC and transformer is allowed.
 
yes. it is powered by the mains. 220-250V AC.
Autoshut off- the circuit will shut down when there will be a short circuit. like the standard power supply. the green light will become red when it will have a short circuit.
we are not allowed to use IC because thats the project given to us by our professor.
we must build a transformerless power supply with 3A maximum current.
adjustable regulator 0-24V. auto shutdown or shutoff. and IC is not allowed.
last year we also build a 3A power supply adjustable 0-24V. but IC and transformer is allowed.

that is the stupidest project i have ever heard of! the right inductor and a handfull of transistors would do it
 
Its possible but it wont have true isolation from the main power source. Its just a standard capacitive coupled current limiter circuit with a large transistor using a zener diode for a voltage reference. The rest is just a basic variable voltage divider using a potentiometer to vary the transistor bias from zero up to the zener diode reference voltage.

Its sloppy will have poor voltage and current regulation in most cases but does the job any way.

not at 3A...
 
Why not at 3 amps? Care to elaborate?
 
3 Amps /( 60 Hz x 220V x 1.414 ) = 161,000uF @ 400V, now with a 20uF HV cap costing $10, I seriously doubt anyone will be making it that way!

Huh? What formula is that? The capacitive reactance formula is 1/(2 pi(frequency * capacitance in farads))

On a 120 VAC 60 Hz line the power supply producing a 30 volt 3 amp output would need a roughly 88 UF capacitor and at 240 VAC that would need roughly a 44 uf capacitor.

For line voltage and frequency rated capacitors all you need to look for is a common power factor correction capacitor. A 44 uf one is about $6 new and 88 uf is around $9. Both are common items that can be found for even less too if you know where to look. ;)
 
Huh? What formula is that? The capacitive reactance formula is 1/(2 pi(frequency * capacitance in farads))

On a 120 VAC 60 Hz line the power supply producing a 30 volt 3 amp output would need a roughly 88 UF capacitor and at 240 VAC that would need roughly a 44 uf capacitor.

For line voltage and frequency rated capacitors all you need to look for is a common power factor correction capacitor. A 44 uf one is about $6 new and 88 uf is around $9. Both are common items that can be found for even less too if you know where to look. ;)

that is not what he said... 220VAC NO TRANSFORMER AND NO ICs

a strict capacitor limited linear would require 160KuF .. the formula is charge transfer to create 3 A by charging the capacitor from the AC line in the manner that you suggested, though it is actually worse since he is likely looking at 50Hz instead of 60.

Charge (Q) = Capacitance (C) times Voltage (V)
Charge (Q) = Current (I) times Time (t, 1 second)
and the more descriptive if archaic: Frequency (f) = Cycles (c) divided by Second (t)

f=c/t, Q=CV, Q=It

it has nothing to do with reactance in that sense since you are talking about infinite harmonics harmonics. i also screwed up a factor of 2 since the capacitor charges from -300 to +300 every cycle.

lol formula was right but i slipped the DP.

3A/50Hz/220V/2/1.414=96uF
 
I just used the standard equation I have been using for most of my life for converting capacitance in an AC circuit into a resistance equivalent at a fixed frequency.

I have built many power supplies that way. Here is a site I use for doing the calculations fast and easy. Free Online Calculators for Engineers - Electrical, Mechanical, Electronics, Chemical,Construction, Optical, Medical, Physics, etc... I just used the resistance-frequency-capacitance calculator to get my estimated values.

I reasoned it out like this, given a line voltage of 220 volts and 60 Hz and a peak output of 30 volts I would need a resistance equal to 63.33 ohms at 60 Hz. From the calculator I get 42 uf as a value. If it is a 50 Hz system then I get a value closer to 50.3 uf.

I added 5% more capacitance to my earlier recommendations for overhead purposes on the 3 amps part to help with peak power capacity and to compensate for forward drops and the misc power losses associated with these type of circuits when used in real world working conditions.

As far as harmonics go the OP never said anything about them anyway he just wanted down and dirty basic design with no IC's.
 
Last edited:
I just used the standard equation I have been using for most of my life for converting capacitance in an AC circuit into a resistance equivalent at a fixed frequency.

I have built many power supplies that way. Here is a site I use for doing the calculations fast and easy. Free Online Calculators for Engineers - Electrical, Mechanical, Electronics, Chemical,Construction, Optical, Medical, Physics, etc... I just used the resistance-frequency-capacitance calculator to get my estimated values.

I reasoned it out like this, given a line voltage of 220 volts and 60 Hz and a peak output of 30 volts I would need a resistance equal to 63.33 ohms at 60 Hz. From the calculator I get 42 uf as a value. If it is a 50 Hz system then I get a value closer to 50.3 uf.

I added 5% more capacitance to my earlier recommendations for overhead purposes on the 3 amps part to help with peak power capacity and to compensate for forward drops and the misc power losses associated with these type of circuits when used in real world working conditions.

As far as harmonics go the OP never said anything about them anyway he just wanted down and dirty basic design with no IC's.

harmonics have to do with how the power is drawn in the circuit, not what is supplied.

I have actually designed power supplies this way. While strict impeadance is a common approximation, the accurate way to do it is charge transfer. You can not get more current though the capacitor than charging it to peak in one direction and then to peak in the other direction and that is 2*Vpk*F*C
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top