Switchmode Constant Current Source


Posted on Feb 6, 2014

Operating a stepper motor using a fixed (constant) voltage supply results in poor torque at high speeds. In fact, stepper motors tend to stall at fairly low speeds under such conditions. Several approaches can be used to overcome this problem, one of which is to use a constant current supply in place of the more conventional constant voltage suppl


Switchmode Constant Current Source
Click here to download the full size of the above Circuit.

y. A disadvantage of many constant current supplies is that simple circuits are inefficient but that doesn`t apply to switchmode supplies such as the circuit shown here. Basically, this circuit is a conventional switchmode regulator adapted for constant current output and is specially designed for stepper motor drivers - although it could be used for other applications as well. The circuit works as follows: IC1 (LM2575T) and its associated components (D1, L1, C1, etc) operate as a switchmode power supply. Normally, for constant voltage operation, the output is connected - either directly or via a resistive divider - back to the feedback input (pin 4) of IC1. In this circuit, however, Q1 senses the current flowing through R1 and produces a corresponding voltage across R3. This voltage is then fed to pin 4 of IC1. As a result, the the circuit regulates the current into a load rather than the voltage across the load. Only one adjustment is needed: you have to adjust VR1 for optimum stepper motor performance over the desired speed range. The simplest way to do this is to measure the motor current at its rated voltage at zero stepping speed and then adjust VR1 for this current. The prototype worked well with a stepper motor rated at 80O per winding and a 12V nominal input voltage. Some components might have to be modified for motors having different characteristics.




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    Tracking System using GPS and GSM modem
    Beeper driver with 555
    Three phase square-wave output generator
    Inverting-sample-and-hold
    Acoustic Doppler Motion Detector
    Pulse Generator by IC LM350T and 555
    sine wave generator circuit
    building rf remote control
    Description of an active reversible in-phase/quadrature modulator carrying out frequency UDC
    UGN-3501T counter circuit diagram of a Hall sensor
    5W Valve RF Transmitter circuit



    Top