Stuck with MOSFET circuit design to control a motor (230V and 12A)

Thread Starter

Daniel Schreven

Joined Sep 7, 2018
5
hello,

i'm doing an assignment where i need to replace a circuit with a TRIAC to a circuit with a MOSFET, because the MOSFET is easyer to cool than a TRIAC. The circuit is driving a motor.

But i have no idea how to start. I know a bit of MOSFETS. And i want as less heat as possible in the circuit because of the high currents. So an H-bridge is something i try to avoid.

Are there any tips for this assignment?
 

Dodgydave

Joined Jun 22, 2012
10,038
Is the Voltage is AC? What circuit are you using at the moment, ?

If you want to go with mosfets, your specs need to look at the lowest Rds on resistance and highest current.
 

AnalogKid

Joined Aug 1, 2013
9,291
Peak voltage could be over 350 V, so I'd recommend a 600 v, 20 A device. Those aren't cheap, and they do not have the super-low on-resistance of the much more common, lower voltage parts. Because it has an intrinsic zener diode in parallel with the drain-source, you need two of them back-to-back. This increases the circuit complexity, but decreases the operating temperature of the power components.

Given the increase in cost and complexity, why is the circuit being converted from a TRIAC? Those parts were invented specifically for this application.

ak
 

Thread Starter

Daniel Schreven

Joined Sep 7, 2018
5
Thanks for the advise AnalogKid.

They want to convert it, because the TRIAC gets very hot. Because of the heat they have installed huge coolerfans. To make production easier and make it cheaper in total, they want to look for an alternative, like MOSFET.
 

AnalogKid

Joined Aug 1, 2013
9,291
You can calculate the TRIAC heat from the on-condition values in the datasheet, and the MOSFET heat from its values, and compare. I recommend doing this first to see if there is any real advantage to making the change. The ultra-low power dissipation of *low voltage* power MOSFETs often is assumed to apply to all devices, and it does not.

ak
 

Thread Starter

Daniel Schreven

Joined Sep 7, 2018
5
allright, the above is a mess haha. i know how to go on but i have another problem now:

i need to design 1 circuit (universal) for:
1) control for a single phase motor with capacitor (6A 230Vac and 12A/230Vac)
2) LED dimmer (LEDs are also 230Vac)

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 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.

daniel

EDIT: my supply is from mains (230Vac 50/60Hz, 3 phase)
 
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