Power losses in a switch (MOSFET, Relay, Thyristor)
Power losses in a switch (MOSFET, Relay, Thyristor)
(OP)
Hi, I'm in the process of designing a control unit that will be on the secondary of a 12V AC transformer. The control unit will control around 100W.
I am wondering what type of design should be used:
- Mosfet switch
- Thyristor switch
- Relay switch
What would be the average losts in % of each. Which one is the more economical to produce?
Thanks
Best regards
BeerBaron
I am wondering what type of design should be used:
- Mosfet switch
- Thyristor switch
- Relay switch
What would be the average losts in % of each. Which one is the more economical to produce?
Thanks
Best regards
BeerBaron





RE: Power losses in a switch (MOSFET, Relay, Thyristor)
- MOSFET's are generally used in DC applications
- Thyristors are usually confined to AC applications and are often used in antiparallel pairs.
- Relays are great for plain on-off control provided you don't want very high cycle rates or the ability to control the output between some minimum and maximum values.
The relay will have the lowest losses. The choice of the others depends on the load - one is basically an AC device and the other basically a DC device. There are other options - BJT, IGBT, triac.
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Sometimes I only open my mouth to swap feet...
RE: Power losses in a switch (MOSFET, Relay, Thyristor)
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Power losses in a switch (MOSFET, Relay, Thyristor)
Thanks
Beerbaron
RE: Power losses in a switch (MOSFET, Relay, Thyristor)
So, if you have your triac conducting 100 % (no dimming), you will have around 10 watts at 8 amperes. You can reduce losses very little by selecting a triac with higher current rating. The fwd drop seldom gets below 1.0 volts.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Power losses in a switch (MOSFET, Relay, Thyristor)
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Power losses in a switch (MOSFET, Relay, Thyristor)
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Power losses in a switch (MOSFET, Relay, Thyristor)
Thanks guys
RE: Power losses in a switch (MOSFET, Relay, Thyristor)
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Power losses in a switch (MOSFET, Relay, Thyristor)
Why not just switch the transformer primary. If you need more than on-off control - a lighting dimmer for example - then some thyristor / triac controller designs can deal with inductive loading. Otherwise use a relay. If the transformer is a toroid then be generous on the relay current rating.
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Sometimes I only open my mouth to swap feet...
RE: Power losses in a switch (MOSFET, Relay, Thyristor)
I believe it's going to be Triac in the end, 30W of losses is bad tough.
BeerBaron
RE: Power losses in a switch (MOSFET, Relay, Thyristor)
What we are building is a device that will be on the secondary of a 12V transformer. This device will make an On/Off switch with features like a timer or else. Ideally, this product would be all plastic molded because it is intended for outdoor operations. But my concern here is the heat losses, you could imagine that 30W of losses in a closed plastic box could raise the heat by a lot, making it very hard for UL approval (95°C max usually).
I'm not going to design the circuit myself but I do have to evaluate the costs of the whole thing. So knowing the heat losses will give me the chance to evaluate the plastic dimensions and the construction.
BeerBaron
RE: Power losses in a switch (MOSFET, Relay, Thyristor)
I think that Scotty's idea is the best. Switch transformer primary. Such a switch will be very low cost and very low loss.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Power losses in a switch (MOSFET, Relay, Thyristor)
I guess I'll have to think of a case with a metal face to dissipate heat.
Thanks for your inputs
BeerBaron
RE: Power losses in a switch (MOSFET, Relay, Thyristor)
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Power losses in a switch (MOSFET, Relay, Thyristor)
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Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com