Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

can triacs rapidly switch AC into a transformer

Status
Not open for further replies.

Zak28

Advanced Member level 2
Joined
Aug 19, 2016
Messages
579
Helped
6
Reputation
12
Reaction score
6
Trophy points
18
Activity points
4,681
Can a triac thyristor chop standard AC mains into 1-20Khz to transformer step up voltage as higher frequency than standard mains frequency?

There might already be applications for this but Im not sure whether it can be used to step up voltage into higher frequency using transformer. This would suit a tesla coil much more efficiently than low voltage step up methods.
 

KlausST

Super Moderator
Staff member
Joined
Apr 17, 2014
Messages
17,757
Helped
3,999
Reputation
7,996
Reaction score
3,890
Trophy points
113
Activity points
117,469
Hi,

The biggest problem is that triacs, thyristors, SCRs can't be switched OFF like transistors.

Once they are triggered they stay ON until current goes to zero.

Klaus
 
  • Like
Reactions: Zak28

    Zak28

    points: 2
    Helpful Answer Positive Rating

Zak28

Advanced Member level 2
Joined
Aug 19, 2016
Messages
579
Helped
6
Reputation
12
Reaction score
6
Trophy points
18
Activity points
4,681
I thought light dimmers switched the current quicker than mains frequency.

Would there be a workable solution implace of thyristors to have the high frequency?
 

Easy peasy

Advanced Member level 5
Joined
Aug 15, 2015
Messages
2,542
Helped
922
Reputation
1,844
Reaction score
920
Trophy points
113
Location
Melbourne
Activity points
14,344
forced commutation was used to turn off SCR's ( mainly ) and triacs - however a lot of extra circuitry is required - then along came mosfets & IGBT's so much easier to chop the mains or whatever, given that you can now easily buy 1200V SiC mosfets at > 50A SCR's & Triacs are seldom if ever used in modern times.
 
  • Like
Reactions: Zak28

    Zak28

    points: 2
    Helpful Answer Positive Rating

Zak28

Advanced Member level 2
Joined
Aug 19, 2016
Messages
579
Helped
6
Reputation
12
Reaction score
6
Trophy points
18
Activity points
4,681
forced commutation was used to turn off SCR's ( mainly ) and triacs - however a lot of extra circuitry is required - then along came mosfets & IGBT's so much easier to chop the mains or whatever, given that you can now easily buy 1200V SiC mosfets at > 50A SCR's & Triacs are seldom if ever used in modern times.
If this is the suggested MOSFET switch, what is gate driver lowside common to? Or there is a better MOSFET topology.

mosfet-switch.png
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
47,211
Helped
13,984
Reputation
28,217
Reaction score
12,626
Trophy points
1,393
Location
Bochum, Germany
Activity points
274,949
Gate driver should be of course referenced to common source node.

There are several reasons why the "chopper" circuit can't be used in the shown basic configuration:

- Mains input filter required to comply with EMC rules
- Switching inductive loads creates large overvoltage that kills the MOSFETs if not clamped approriately
 

Easy peasy

Advanced Member level 5
Joined
Aug 15, 2015
Messages
2,542
Helped
922
Reputation
1,844
Reaction score
920
Trophy points
113
Location
Melbourne
Activity points
14,344
your approach is a little bit simplistic - you will need snubbers across the mosfet switch, and source referenced gate drive, you will get maximum power near the mains peaks ( 325Vpk for 230Vac )

Per your question about SCR's closing faster - inverter grade SCR's - hard to find now, could switch up to 20kHz if force commutated or in a resonant ckt - typically 0.3uS turn on time - a good idea to have a close read of a data sheet for a good SCR ... to see its limitations, hold current, latching current etc, turn on time ...

mosfets or IGBT's far easier to use.
 
Last edited:
  • Like
Reactions: Zak28

    Zak28

    points: 2
    Helpful Answer Positive Rating

Zak28

Advanced Member level 2
Joined
Aug 19, 2016
Messages
579
Helped
6
Reputation
12
Reaction score
6
Trophy points
18
Activity points
4,681
This seems far more simple and practical. It would need a ballast or other current limiting element. Do SMC rectifiers typically fail short or open?

img.png

There are tesla coil diagrams depicting several series 1kv slow rectifiers to prevent short circuit issues if diode is damaged. But fusing the circuit at power entry side should prevent any short circuit issue.

At mains voltage a snubber diode is fine over resistor capacitor. The only issue is neutral can be within several volts or less to gate turn on voltage. Is there a remedy for this?
 
Last edited:

Status
Not open for further replies.
Toggle Sidebar

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top