Updating the transistor connections:
– Disconnect the PNP transistor base from the TIP42 drive transistor emitter.
– Connect the NPN transistor base to the TIP42 collector.
– Move the 100-ohm resistor (R15) from between the TIP42 emitter and the output to between the collector and –Vcc.
By implementing these changes, you’ll successfully convert a complementary amplifier to a quasi-complementary NPN amplifier.
PNP Quasi-Complementary Amplifiers
Converting to Quasi-Complementary PNP Amplifier
We’ve successfully converted the amplifier to a quasi-complementary PNP design. To achieve this, I applied the same modifications as before, but with a twist on the 0.22-ohm resistor (R16) that polarizes the NPN transistor by moving it from between the NPN transistor emitter and the output to between the new PNP transistor emitter and +Vcc.
Modify the transistor connections:
– Disconnect the NPN transistor base from the TIP41 drive transistor emitter.
– Connect the PNP transistor base to the TIP41 collector.
– Move the 100-ohm resistor (R14) from between the TIP41 emitter and the output to between the collector and +Vcc.
With these changes, you’ll have a functioning quasi-complementary PNP amplifier.
Adapting Amplifier Designs to Suit Local Availability
Sometimes, we come across an ideal amplifier design, only to find that it uses transistors that are scarce or unavailable in our local market. Alternatively, we might stumble upon affordable transistors of a different polarity than the one required by our chosen amplifier design. In such situations, knowing how to convert a complementary amplifier to a quasi-complementary design can be incredibly useful. This skill allows us to adapt the circuit to work with the available transistors, saving us time and money. For instance, I once found myself in a situation where PNP transistors were significantly cheaper than their NPN counterparts. By modifying the circuit to use only PNP transistors, I was able to build the amplifier I needed while staying within my budget.
Acquiring this knowledge not only helps us overcome component availability issues but also enhances our understanding of amplifier design and printed circuit board modification. To illustrate this, buy my PDF file that showcases the same amplifier in three different configurations—complementary, quasi-complementary NPN, and quasi-complementary PNP—is available at the end of this article.