The circuit exemplified in figure 8 is suggested by National Semiconductor and is based on an enhanced power transistor, which is the LM195. This transistor can provide a maximum output current of 1 A and consists of a Darlington with additional elements. The base excitation current is only 3 µA and it has a switching time of 500 ns with a saturation voltage of 2 V. The base can be excited by voltages of 40 V without problems. In this application we have an RC power oscillator that operates at a frequency of 1MHz. The LM195 housing is TO-3, and a TO-220 equivalent is the LM395T.
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