Darlington circuit

Darlington Transistors are electronic circuits that consist of a pair of bipolar transistors (bi polar) are connected in tandem (series). This series connection is used to obtain reinforcement (gain) is high, because it results in the strengthening of the first transistor will be strengthened further by the second transistor. The advantage of the Darlington circuit is the use of a smaller space than the ordinary transistor circuit with two forms of the same configuration. Strengthening of electric current or gain of a Darlington transistor circuit is often written with the notation β or HFE.

With the configuration of HFE darlington then be obtained by:

HFE = hfeQ1 * hfeQ2

The main difference between Bipolar and Unipolar are:

- Bipolar

• currents in the coil can be berbolak forth to change the direction of motor rotate 
• only one motor winding and energized with alternating directions

- Unipolar

• currents flowing in one direction, and change direction depending on the rotary motor winding (coil) current-carrying

• a separate winding in 2 sections and each section is only passed current in one direction only.

Bipolar type weakness is that the driver circuit is more complex, because it must be a current in 2 directions (back and forth) through the same coil. The core circuit is actually a stream buffer that serves to strengthen the currents that move the MCU logic and stepper motors. This buffer is formed by using two NPN bipolar transistor in a Darlington configuration for result in a current amplifier (HFE) is high.