I don't own one of the Carsteen controllers, but have always respected that he has the right design for linear MOSFETs. Other than the necessity for active cooling to prevent thermal runaway, I'm still convinced that there could be some real advantages to a linear MOSFET design. I've been doing quite a bit of research on MOSFET amplifiers and MOSFETs used in voltage follower applications. Jeff does know his transistors but I don't think his MOSFET knowledge is AS strong. This is a high-side configuration so that's why a high-side driver is used to raise the gate voltage approx 10V above the track voltage. The power supply's positive terminal (white) is connected to the MOSFET's Drain and the motor lead (black) is connected to the source. There's a control circuit that generates the pulses based on trigger position and a driver that raises the gate voltage approx 10 volts above track voltage to turn the MOSFET on. In a MOSFET based controller, the trigger doesn't drive the MOSFET gate directly. That's why the wipers on electronic controllers don't wear out as fast as they do on resistor controllers.įor example, the current flowing into the transistor's base terminal in my controller is on the order of microamps.thousands of times less than the current flowing through the motor. Since a transistor is essentially a current amplifier, a low current flowing through the board is used to control the large current flowing through the motor. This current flows through the wiper and resistors on the PC board. In a transistor based controller the trigger is controlling the voltage and/or current supplied to the base terminal. That's why you see Difalco controllers with 50% more bands than before and my own controller, the Linear 100 with 24 bands. The more steps you have.the better control you have over motor speed. Either can use a potentiometer (for a continuously variable MOSFET pulse width or transistor base voltage) or a series of resistors to provide a number of steps. How you determine the trigger position is independent of whether you use MOSFETs or transistors.

I wrote an article for Slot Car Bulletin that explains the two approaches to controller design. When turned on and off very rapidly, the average DC voltage the motor sees is proportional to the time it's on vs the time it's off. It's either completely on, delivering full power to the motor.or completely shut off. In linear mode the transistor supplies a voltage or current that is proportional to the voltage or current applied to its base terminal.Ī MOSFET on the other hand is used like an on-off switch or relay. Most of the controllers available today use a transistor operating in linear mode.

Transistor keyboard or controller