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

[king.oslo]

That is a good suggestion! The guy who built the circuit that you kindly liked to, said he was using it for car amplifiers. If I have a bigger voltage-regulation-range, will this unit be suitable for small electronics as well, or will I need to make modifications?

Thanks.M

 

[Reloadron]

A power supply is a power supply. I am sure they were small car amps. My wife's sound system in her truck is fused with a 50 amp fuse.

The trick for higher current is more transistors. Like KISS mentioned. It is not unusual to see ten or more 2N3055 transistors in there. Just remember a big heat sink and a small fan. Also the importance of those emitter resistors. No two transistors of the same make and part number are absolutely identical. One will conduct a little harder and faster than another. Those resistors are there for balance.

Ron

 

[KeepItSimpleStupid]

You can put transfomers in series and in parallel. In series they will dd or subtract and thus, you can determine the phase.

In parallel, the voltage needs to be the same. They MUST be phased to be in phase, otherwise smoke.

battery chargers typically have high amperage secondaries and they are heavy too, I have a commercial battery tester/charger/booster that i got for peanuts (free). A couple of pressed in diodes was all it needed. Big and heavy.

Get the idea: https://www.govdeals.com/index.cfm?fa=Main.Item&itemID=926&acctID=176#.TofE2823Ogc

Yea, it's a Marquette charger.

 

[king.oslo]

Thats great.

Now I am a newbie, but this is what I was thinking. Please correct me where I am wrong. I thought: If I want ampere regulation, and I set the regulation to 8A and 12V. If I put a 1ohm resistor across the output, the only way I can regulate the amperage down to 8A is if the 12V is dropped to 8V. Is this correct?

In my opinion, it seems this current does exactly that:
**broken link removed**

Is that correct? Or does it completely shut down the power supply once it reaches more than 8A?

Thanks.M

 

[KeepItSimpleStupid]

That looks like it's basically a current limiter. It compares 2 or 3 base-emitter drops (3*~0.6) to the voltage across R1 and then starts removing current from essentially a darlington triple composed of Q3, Q4 and Q1.

It's not a constant current supply. Now the problem is, where is the regulation of the 12v. It would have to be after.

AN issue is that it's difficult to calibrate, because the be drop varies with temperature. about 3*26 mv/deg C. I think it's minus.

 

[4pyros]

Which appliances usually have easily retrievable transformers of the size I need circa 500VA -> 30V 16A?

UPS's Thay are made to charge 12 or 24 volt batterys. Oh wait thay are power supplys.

 

[king.oslo]

You know a lot, KeepItSimple. Why is there a temperature fluctuation issue?

Is there an easy way to make the current limiter without the issue?

Thanks!M

 

[Nigel Goodwin]

You know a lot, KeepItSimple. Why is there a temperature fluctuation issue?

Is there an easy way to make the current limiter without the issue?

No, ohms law applies - to limit the curent you have to reduce the voltage.

But the current limiting would be an integral part of the PSU, not separate as in your diagram.

 

[king.oslo]

Oh! Alright. Is the concern that the temperature changes the resistance of the resistors in the circuit, or the transistors? If so, I could isolate the resistors and keep them at room temperature. How will that work?M

 

[Nigel Goodwin]

Oh! Alright. Is the concern that the temperature changes the resistance of the resistors in the circuit, or the transistors? If so, I could isolate the resistors and keep them at room temperature. How will that work?M

The important thing is to keep the reference voltage correct (which shouldn't be temperature dependent), and the feedback in the rgulator will keep the voltage constant (until it reaches current limiting).

 

[KeepItSimpleStupid]

Here is a design using the 723. **broken link removed**

Which is ALMOST what you want. Note, multiple output transistors. You may have to double for 16 Amps and a FAN. Since the transistors are in parallel, it makes sense to match the beta's on them or at least make sure that none are more than 25% different.

Silicon has a temperature coefficient and diodes are actually used as a temperature sensor. There are actually transistors that contain an integral diode just for that purpose.

 

[Reloadron]

On another trivial note, something not always shown in schematics is the wire gauges used. For example in the case of 16 and 20 amp supplies you need to make sure the wire gauge used supports the current. Even the output terminals used need to support the current. That or smoke happens which is a bad thing.

Ron

 

[king.oslo]

Thanks! I am still concerned with what KeepItSimpleStupid said. He talked about the problems of calibration in regards to temperature. What exactly are the problems? It be difficult to calibrate what?

Thanks.M

 

[4pyros]

Thanks! I am still concerned with what KeepItSimpleStupid said. He talked about the problems of calibration in regards to temperature. What exactly are the problems? It be difficult to calibrate what?

Thanks.M

You just need to keep a constent temperature and calibate at that temperature.

 

[KeepItSimpleStupid]

Temperature messes things up in some applications like audio amps and the current limiter schematic you posted. Voltage references don't heat up, so they don't change. When the output transistors heat up in the 723 design, regulation changes the amount of drive current. When the temperature gets too hot, a fan turns on or a very good supply, it turns off when it gets too hot.

 

[king.oslo]

When the output transistors heat up in the 723 design, regulation changes the amount of drive current.

Are you saying that transistors conduct other quantities of voltage when heated up (

about 3*26 mv/deg C. I think it's minus.

), even when the reference voltage stays the same?Thanks.M

 

[ericgibbs]

Are you saying that transistors conduct other quantities of voltage when heated up (), even when the reference voltage stays the same?Thanks.M

hi K.O.
If the feedback circuit is correctly designed, it should not effect the regulation, IF the Vref was stable.

 

[king.oslo]

hi K.O.
If the feedback circuit is correctly designed, it should not effect the regulation, IF the Vref was stable.

How is a correct feedback circuit designed? I would very much like to build a circuit like this.

Thanks.M

 

[ericgibbs]

How is a correct feedback circuit designed? I would very much like to build a circuit like this.

Thanks.M

hi,
If you are into designing circuits of various types, I would suggest downloading the free LTspice simulator.

In that way you can try out different circuits under different conditions and temperatures.

There are number of LTS user on ETO who would be happy to help.

 

[Nigel Goodwin]

Since the transistors are in parallel, it makes sense to match the beta's on them or at least make sure that none are more than 25% different.

No such need, and it wouldn't make any difference - the design correctly uses emitter resistors to ensure equal current sharing, so the spread of the transistors is compensated for.