UC3844 is popular current mode controller which is commonly found on DC-to-DC converter circuits and switch mode power supplies. This motor speed controller is also based on UC3844 and it is specifically design to drive 20V - 24V DC motors.

In this given configuration UC3844 produces (approx.) 50kHz to 240kHz PWM output and this range can be adjust by changing the value of C2 timing capacitor. As per the datasheet UC3844 is capable to produce PWM output frequency up to 1MHz.

UC3844_PWM_TRACE.jpg
UC3844 waveforms on RT/CT (Pin 4) and OUT (Pin 6).

This circuit is quiet sensitive to the noises, and to get the accurate output construct this circuit on PCB. As per our observations long wires on oscillator circuit may change the stability of the output signal.

According to the ON semiconductors, UC3844 is now discontinued product but it is still commonly available in the market for less than Rs. 40.00 (LKR). For this circuit either DIP (UC3844N) or SMD (UC3844D1) version of UC3844 can be used but the PCB design available with this article is based on DIP version of UC3844.

Project Related Downloads


PCB and schematic diagram of UC3844 base motor speed controller.

References


UC3844 - High Performance Current Mode PWM Controller
IRF510 - Power MOSFET