12 V Bidirectional Motor Control Circuit

This simple circuit drives DC motors with a maximum current of 1 A and can be built with readily available components.The output voltage is adjustable between 0 and 14 V and the polarity can be changed so that not only motor speed but also rotation direction can be adjusted by turning a knob.

The circuit is also ideal as a controller for a DC model railway or small low voltage hobby tool. Power for the circuit is supplied by a 18 V mains transformer rated at 1.5 A. Diodes D1to D4 rectify the supply and capacitor C1 provides smoothing to give a DC output voltage of around 24 V. A classic ‘H’ bridge configuration is made up with transistors T1/T3 and T2/T4. Transistors T5 and T6 together with resistors R7 and R8 provide the current sense and limiting mechanism. The maximum output current limit can be changed from 1 A by using different value resistors for R7 and R8: IOUT = 0.6 V / R where R gives the value for R7 and R8. For increased current limit the mains transformer and diodes will need to be changed to cope with the extra current as well as the four transistors used in the bridge configuration.

Circuit diagram:

  12 V Bidirectional Motor Control Circuit Diagram

Motor speed control and direction is controlled by a twin-ganged linear pot (P1). The two tracks of P1 together with R1/R2 and R3/R4 form two adjustable potential divider networks. Wiring to the track ends are reversed so that as the pot is turned the output voltage of one potential divider increases while the other decreases and vice versa.

In the midway position both dividers are at the same voltage so there is no potential difference and the motor is stationary. As the pot is rotated the potential difference across the motor increases and it runs faster. The voltage drop across D5 and D6 is equal to the forward voltage drop VBE of the bridge transistors and ensures that the motor does not oscillate in the off position with the pot at its mid point.

Author :Christian Tavernier

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LV8741V PWM Stepping Motor

Using the LV8741V PWM stepping motor driver IC can be designed a very simple and efficiency DC motor driver electronic project . As you can see in the circuit diagram , this electronic project require few external electronic parts . The maximum output current that can be provided by this PWM current-control stepping motor driver IC is up to 1.5 ampere . The reference voltage is set by the voltage applied to the VREF pin and the two inputs ATT1 and ATT2.

LV8741V PWM Stepping Motor Circuit Diagram

When the output current is below the output short-circuit protection current, the output is controlled by the input signal. The setting conditions for the above PWM current-control DC motor driver circuit diagram are as follows : Auto recovery-type output short-circuit protection function (EMM = Low), Output enable function fixed to output ON state (OE = High), Current limit reference voltage setting = 100% (ATT1 = Low, ATT2 = Low) ,Chopping frequency : 37kHz (RCHOP = 43k ).

Voltages required by this LV8741V current-control DC motor driver are from 9.5 to 35 volt for motor power and from 2.7 to 5.5 for logic power supply .

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Stepper Motor Generator

Any stepper motor can be used as a generator. In contrast to other generators, a stepper motor produces a large induced voltage even at low rotational speeds. The type used here, with a DC resistance of 2×60 Ω per winding, can generate more than 20 V when turned by hand, without any gearing. The circuit diagram for a ‘hand-cranked torch’ shows how you can use a stepper motor as a generator. A supplementary circuit stores the energy. Two bridge rectifiers, each made up of four 1N4148 diodes, charge the 4700µF capacitor. The super-bright (white) LED is driven either via a 390-Ω resistor (Power Light), or via 22 kΩ in series with 390 Ω. In the latter case, the LED is not as bright, but it stays on longer.

You must restrain yourself when cranking the dynamo, since in the ‘bright’ setting it is possible to exceed the rated LED current of 20mA, while in the ‘long’ setting it is possible to exceed the rated capacitor voltage of 25 V. If necessary, adjust the value of the LED series resistor. The lamp is bright enough for reading in complete darkness. The stepper motor generator is thus ideal for spies, thieves and children who want to read under the bedcovers. You could also keep it handy in your hobby room, in case of a short circuit.

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