Question 1

A common topology for DC-AC power converter circuits uses a pair of transistors to switch DC current through the center-tapped winding of a step-up transformer, like this:

In order for this form of circuit to function properly, the transistor “firing” signals must be precisely synchronized to ensure the two are never turned on simultaneously. The following schematic diagram shows a circuit to generate the necessary signals:

Explain how this circuit works, and identify the locations of the frequency control and pulse duty-cycle control potentiometers.


Question 2

The zener diodes shown in the schematic are there to absorb transient voltages resulting when the MOSFETs turn off. Explain where these transients originate from, and what might happen if the zener diodes were not there.


Question 3

Examine these check plot images from a PCB drafting program, for a control board based on this inverter circuit design. Both the top and bottom copper layer plots are shown from the perspective of the board’s top side. The six large “pads” around the periphery of the board are actually holes for mounting screws:

Assembly drawing

Top copper layer

Bottom copper layer

Mark where discrete components (resistors, capacitors, and diodes) go into the PCB, and identify which integrated circuits on the board layout are performing which functions in the schematic. Note: the square pad on each IC marks pin number 1.


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