230VAC to 1.5V-24V adjustable 0-16A current. Which chips do I need?

[king.oslo]

Hello,

I am a newbie, and I want to make a power supply that can convert 230VAC to 1.5V-24V ourput with adjustable current of 0-16A.

Which are the major ICs and components I should lookup to get the job done?

- Is it better to use a transformer or resistor to reduce the voltage from 230V to, say 30V?
- I thought I could use a rectifier to convert 30VAC to DC
- But still I need some kind of circuit to convert 30VAC to adjustable current 0-16A 1.5-24V. This I have no idea how to do. The largest adjustable voltage regulators I found could not do this (as far as I can tell). I thought maybe I can use a transistor with a PWM signal and a capacitator to adjust from 1.5-30V? Will this work?
- But how to I get the adjustable current?

Thank you for your time.M

 

[ronsimpson]

1) transformer! not a resistor.
2) Rectifier to convert AC to DC at 30 volts.
3) "PWM and Cap to adjust voltage" ????
4) Adjustable current? Lets assume you are making a bench power supply. Adjustable current....there often is a current knob. It does not adjust the current but is a current limit. Lets say you are powering a radio with your power supply and then you drop a screw driver into the radio. The current limit will cause the power supply to 'shutdown' until the short is removed.

This is a big project. (16A) I think you should start with a 1 or 2A supply. Later when you understand power supplies move up to 16A.

 

[king.oslo]

Thank you for your reply.

3. Perhaps a square wave signal output by a transistor can be converted to a constant voltage by using an capacitator? If it can, then I can control the transistor with an IC to get a variable output voltage of 1.5VDC - 30VDC. Is this correct? Is there a better way to make a high current power supply?
4. Yes, you are correct. I want to make a bench power supply. How can I best make a current-limiter like this?

I want to ask why you think it is best to start with a 1A supply? What problems will arrise from building one which is 16A?

Thank you for your time.

Kind regards,
Marius

 

[Ziddik]

hi king oslo," Try LM317 adjustable voltage regulator IC" and circuit schematic of it is available from google, but it can provide only 1500mA(1.5A) Current u can also try LM338 - 5 Amp Adjustable positive Regulator,

 

[Nigel Goodwin]

I want to ask why you think it is best to start with a 1A supply? What problems will arrise from building one which is 16A?

A 16A variable power supply is a VERY substantial project, and would be VERY expensive to build - it's not really a beginners project.

Why do you think you need 16A?.

 

[king.oslo]

I want 16A because I don't need that much. I don't want to build a 5A supply, only to find I need a bigger one for a particular project.

I imagine it would cost a few hundred dollars to build, but why is it so substantial? Apart from the cost, what makes it so big?

 

[Nigel Goodwin]

I want 16A because I don't need that much. I don't want to build a 5A supply, only to find I need a bigger one for a particular project.

I imagine it would cost a few hundred dollars to build, but why is it so substantial? Apart from the cost, what makes it so big?

Massive mains transformer, massive heatsinks and multiple regulators, probably fan-cooled as well - it could probably double as a toaster as well.

 

[ronsimpson]

For those looking to make a bench supply; The LM317 is a good old part. I now use a LT3080. Its voltage and current are about the same. The LM317 can not output less than 1.25 volts, while the LT3080 goes down to 0 volts. The LT3080 also parallels very nicely. You can run 2,3,4,5 or more in parallel and they load share. I only takes one resistor to set the voltage. It is not in the application note but the LT3080 can be set to current limit at low levels while the LM317 can not--easily.

For a first bench supply, I would use a 24V wall wort or brick power supply to get off the power line and down to something safe. I have in my hand a 24V 4A supply I wish I could reach through the internet and hand to you. Then with some LT3080s and a pot you could have 0 to 23 volts out.

 

[Ziddik]

he might also needed a 16A expensive Transformer as well as other equipments like regulators,fan etc as nigel stated, i have got five 12v 5 amp transformers in my junk bag.. Btw What are you gonna do with a 16A transformer?

 

[ronsimpson]

And you can't really get 16A from a 16A transformer.
The 16A is into a resistive load, not through a bridge and to a cap. (see data sheet)

40Vdc (with current limit set to 16A) into a short = 640W. The box will have to have fans much like a space heater.

 

[alec_t]

The box will have to have fans much like a space heater.

It will be a space heater !

 

[KeepItSimpleStupid]

I have a 0-32 V 10 A foldback current limited supply that I purchased for $15 back in the 80's.

A short drops the voltage to nearly zero with the current going to 10 A.

It's big and heavy. It has a 17" x 4 x 4 heatsink populated with 10 2N3055 transistors and a fan.

The uA723 regulator is common for this type of supply.

I purchased about 14, 40V 35 A supplies for work and they are a piece of work.

 

[king.oslo]

Thank you. That was very helpful!M

 

[4pyros]

The LM317 is a good old part. I now use a LT3080.

Wish thay made the pinout the same as the 3 pin regulaters.

 

[king.oslo]

If I don't want to use a voltage regulator, how efficient will a npn transistor be?

Say I have a 350W npn transistor, on the collector is 30V, ideally I want to put 1.65V on the base and get 1V on the emitter. When looking in the data-sheet, I want to find what the minimum voltage that can be delivered to the emitter. What should I look at in the datasheet. Is this the "Base-emitter saturation voltage"? This npn-transistor has a typical value of 1.1V: https://www.electro-tech-online.com/custompdfs/2011/10/hrBUX22_e.pdf Perhaps it is suitable. What do you think?

Thanks!

 

[KeepItSimpleStupid]

Transistors don;t work that way. They are current devices. Ie = Ib + Ic and Ib*beta = Ic. The problem is beta which is the current gain is varies wildly. 20-100. Some transistors have grades depending on the value of beta. Darlington transistors can have really high vales of beta.

MOSFETS (N channel) on the other hand are a voltage controlled device. Once you get above Vgs the device starts to conduct. Again, the parameter transconductance varies

Most power transistors have a SOA or Safe Operating Area defined. That's where you need to be when using such a device.

 

[king.oslo]

Thanks for that!

I am struggling to find transformers that are low enough (physical dimensions). Is it possible to parallel the inputs and output of several smaller transformers, or is this bad practice? Thanks!M

 

[Reloadron]

Transformers with a low voltage secondary like 12 volts and high currents do get large and heavy. To answer your question yes, they can be paralleled but you end up with a larger mass that if you use a single transformer. Also note what KISS mentions:

It's big and heavy. It has a 17" x 4 x 4 heatsink populated with 10 2N3055 transistors and a fan.

This is how high power regulators work. They use a regulator like the LM723 to drive several power transistors like the old 2N3055. Their bases are tied together and their emitters have resistors of about 0.3 Ohms to ground. Power resistors!

**broken link removed** and you will see a 10 amp supply driven by a LM7812. Note how the 2N3055s are used.

Ron

 

[king.oslo]

Reloadron, your link was excellent. I am looking at it now.

By the way, I thought maybe I could find a big transformer in a junk yard or elsewhere. Which appliances usually have easily retrievable transformers of the size I need circa 500VA -> 30V 16A? Thanks!M

 

[Reloadron]

A junk yard would be a good bet. I think up in the attic I have an old 12.6 volt 20 amp transformer. That thing weighs a ton. I must have put it up there when I was young.

I also have a few old and large linear supplies down at my mother's house I need to get moved out of there. My dad used them before he passed away years ago. Big and heavy. Makes us appreciate SMPS units. But they are brute force supplies. That link should help and more transistors could be added.

Not sure which appliance would use something like that. Sometimes old welding machines maybe?

Ron