power supply using silicon controlled rectfier (SCR)

1. power supply using silicon controlled rectfier (SCR)

hi!
i am trying to make a 48V 600W power supply using SCR
here's the block diagram for the project

my problem is there is a very large current between the mains and the SCR bridge. it is more or less 100 amperes. any comments and suggestions would be very much appreciated
the scr that i am using is 2N6404
and the optocoupler is 4N25

2. Re: power supply using silicon controlled rectfier (SCR)

Hi,

48V, 600W means 12.5A average.

Now the SCR is ON for maybe 10..12 degree (every 180 degrees), so it is ON for about 7% of the time.
During this 7% of time you need to achieve 12A average. So it is no wonder that the peak current is at 200 A or more.

What did you expect?

You may relax this a bit by connecting a series inductance (and maybe a diode, Anode to GND) between SCR and LOAD capacitor.
With the inductance the ON time increases and thus the peak current decreases.

Klaus

1 members found this post helpful.

3. Re: power supply using silicon controlled rectfier (SCR)

What kind of load it is and what is included in "Filter"?

•

4. Re: power supply using silicon controlled rectfier (SCR)

ok i'll try this in my simulation.
thanks!

•

5. Re: power supply using silicon controlled rectfier (SCR)

my filter is only a 10000uF 100V capacitor

6. Re: power supply using silicon controlled rectfier (SCR)

Step down transformer....? between the mains and the SCR's doing the rectification? output choke to reduce the peak current in the SCR's?

•

7. Re: power supply using silicon controlled rectfier (SCR)

Is there a particular reason it has to be a SCR based power supply?

As others have mentioned, regulation via SCR phase control will introduce an excessive amount of harmonics back to the mains line.

8. Re: power supply using silicon controlled rectfier (SCR)

I agree with schmitt trigger, you better use step-down switching regulators. SCR are from the dark ages before we had power mosfets. You can also use HF inverter like the PSU in your computer.

9. Re: power supply using silicon controlled rectfier (SCR)

Add an inductor in Filter (between SCR bridge and capacitor). About 100mH to limit current at 20A.

1 members found this post helpful.

10. Re: power supply using silicon controlled rectfier (SCR)

@Vbase "scr's are from the dark ages..." yes they may be, but the most reliable and long lived power supplies that money can buy are SCR based...

11. Re: power supply using silicon controlled rectfier (SCR)

this is our final project for our industrial electronics subject.
i dont know why our professor let us use SCR, maybe to make things more complicated. he likes it that way

12. Re: power supply using silicon controlled rectfier (SCR)

Hi,

"scr's are from the dark ages..."
Thatīs a too general statement.

We work with industrial current controllers, SCR controlled up to 2500V AC and up to 6000A AC.
Is there an alternative to SCRs?

Klaus

•

13. Re: power supply using silicon controlled rectfier (SCR)

One could mention that the SCR design is obsolete according to newer power quality regulations which restrict the usage of phase angle control considerably. If you don't care about this point, the design can well work with an appropriate inductor. But no chance to implement the project without it.

14. Re: power supply using silicon controlled rectfier (SCR)

Hi,

why our professor let us use SCR
It seems to be a school project.
Itīs for learning purpose.
Maybe they donīt worry about power quality.

***
In my industrial application (above) they have a special 10kV / several Megawatts supply network. Itīs not operated on public mains.
So they donīt care about power quality.

Klaus

15. Re: power supply using silicon controlled rectfier (SCR)

As "KlausST" and "Easy Peasy" indicated, this design needs an inductor before your 10000 uF capacitor. Since you want 12 A, this inductor likely will not be small, or lightweight. So at some point you are no better off (wrt size and weight) than if you simply stepped down the voltage using a transformer. And then an SCR if you are intent on that approach.

Related to this, a hazard of running off the mains is how to ground your system. You will need to be careful that the "0V" in your output waveform diagram is not referenced to a high side of the 220V line.

A transformer also solves this.

--[[ ]]--