INDEX

L298
Stepper motor driving with ULN2003
Stepper motor diriving with L293D
Another  motor driving circuit
 

This is an ideal H-bridge using 4 transistors. This circuit is called H-bridge because, it has a shaped of 'H' with central limb as motor. A transistor become saturated when Vbe>.8V and in cut off when Vbe<.5V (normally). Suppose I1=12v(logic HIGH of a digital circuit) then transistorQ1 is cut off
Vbe1=Vb1-Ve1= 12-12=0V . So transistor Q1 is in saturation because it is a PNP transistor. When I1=0v(logic LOW) Vbe1=0-12v =-12V , it is in saturation. When I1=0V Vbe3=0-0=0V make Q3 in cut off. When I1=12V then Q3 is saturated. When I1=HIGH and I2=LOW then Q3 and Q2 are ON
and the current flow in one direction while I1=LOW and I2= HIGH Q1 &Q4 become ON and current flow in other direction. When I1=I2=LOW, then Q1 and Q2 are ON and motor get's braking. When I1=I2=HIGH then Q3,Q4 become ON and the motor gets normal stopping. So this is not an ideal H-bridge because when you apply (1,1) then the motor is not braking. Now you try to make it ideal H-bridge so that when (1,1) come motor will brake and (0,0) the motor will stop. Try to make and see
the circuit in next  page