Darlington circuit

One transistor can feed its amplified signal directly to another, and this is called the Darlington circuit, named after its innovator. If each transistor has a gain of about 100, the overall gain is about 10,000. They can be bought in a single... 

Figure 6.16 Circuit symbol for a two-junction transistor or power Darlington...

Figure 10. Diode/Darlington-transistor circuit of a series (OEM) charger [39].

The second alternative is an electronic load. This device is a circuit that has a controllable switch (typically a Darlington configured pair of bipolar transistors or a MOSFET) that can be modulated to conduct any level of current the user desires. An example of an electronic load circuit is presented in this chapter. The electronic load will be constructed piece by piece and tested separately. When all the pieces are constructed and simulated, the whole sum of the electronic load can be assembled and tested as a unit. 

One problem, or should we say challenge, in designing this type of circuit is to ensure that the Darlington pair transistors are not overstressed by causing them to dissipate too much power. The maximum power the transistor can dissipate decreases with increasing collector-emitter voltage. 

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