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Recitfier heat problem

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ravuz

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Hello,

situation
currently i'm doing an internship assignment. right now the company has a motor controller with a TRIAC (on/off and phase cutting to control) and a LED dimmer.
The problem of the TRIAC is that it gets very hot, so they need a cooling plate, which cost a lot money when the need to produce a controller.

Assignment
i need to design 1 circuit (universal) without cooling plate for:
1) control for a single phase motor with capacitor (6A/230Vac and 12A/230Vac)
2) LED dimmer (LEDs are also 230Vac)

Problem
This will be done with MOSFETs, so i gonna need a rectifier.

The problem is that when i want to attach that motor, i definitely know that there will be high current flowing through the rectifier which will result in heat. is there any option to either design a bridge with minimal heat dissipation where i dont need a cooling plate or design a circuit without a rectifier.

it needs to be a design where i dont need a cooling plate, because this is expensive for production.

information
supply voltage is from mains (230Vac 50/60Hz)

daniel
 

Hi,

the TRIAC has a voltage depending on load current. The values are given in the datasheet. --> read it to find out disspated power.

This will be done with MOSFETs, so i gonna need a rectifier.
The rectifier has a voltage drop, too. I assume this voltage drop is higher than the voltage drop of the TRIAC. Thus you don´t only shift the heating porpbelm to the rectifier but you increase overall heating. It seems you make things worse.

Maybe a two_anti_series_MOSFET circuit is the solution.

Klaus
 

Do you mean to rectify the mains voltage with a half MOSFET bridge? Doesn't this add a lot of complexity for control but also for EMC directive?
 

1) control for a single phase motor with capacitor (6A/230Vac and 12A/230Vac); 2) LED dimmer (LEDs are also 230Vac)

It is better to treat these two cases independently because the same trick will not work for in both cases. LEDs will have internal circuits that may not respond well to external controllers.

If you split this into two questions, then there will be less confusion.
 

Hi,

Do you mean to rectify the mains voltage with a half MOSFET bridge? Doesn't this add a lot of complexity for control but also for EMC directive?
No. Neither rectify nor half bridge.

Just two MOSFETS in series, but in opposite direction. Usually two N-Ch MOSFETs are used, both sources are connected.
--> https://lmgtfy.com/?q=mosfet+anti+series+schematic

Then you are able to switch AC. For sure the gate control is somehow difficult.

Klaus
 

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