Using a darlington pair to boost your driver

As seen in this post about creating a BJT driver to control a load with a microcontroller output, there is some scenarion in which the required load current does not allow to use a simple transistor to do the job. This is due to the fact that cheap BJT for high current have usually a low DC gain.
Fortunately if you have a cheap power transistor and a cheap switch transistor you can create a configuration to boost the DC gain: The Darlington Pair.

With this configuration the gain is the product of the two gains:

We can easily simulate the circuit to create the classical Vce/Ic chart with various basis currents. In the example chart I did the lowest basis current is 0.1mA while the bigger one is 1mA. Let see the chart below:

As we can see when the basis current is 1mA, the Ic current is 3.6 A, so the current gain is about 3600 !. The drawback we can see from the chart is the Vcesat being a little higher than in a simple transistor ( this means more power the transistor should bear ) and, even if not visible from the chart, the Vbe(on) is almost twice than a regular chart. If you can deal with this limitation, and usually we can, this is probably one of the cheapest solution to drive a power load with a small current digital output.