Power Conversion Circuits

This circuit uses an 8038 waveform generator IC (integrated circuit) to produce a “sawtooth” waveform, which is then compared against a variable DC voltage from a potentiometer:

The result is a pulse waveform to the base of the power transistor, of the same frequency as the sawtooth waveform. Normally in circuits such as this, the frequency is at least several hundred Hertz.

Explain what happens to the brightness of the lamp when the potentiometer wiper is moved closer to V, and when it is moved closer to ground.

This circuit generates a pulse of DC voltage sufficient to energize the neon lamp, every time the switch is opened:

Describe the principle of operation for this simple circuit, and also how it could be modified to produce continuous high-voltage DC power.

Hint: how does a common AC-DC power supply circuit convert pulses of rectified DC into a relatively “smooth” DC output?

The schematic diagram shown here is for a “buck” converter circuit, a type of DC-DC “switching” power conversion circuit:

In this circuit, the transistor is either fully on or fully off; that is, driven between the extremes of saturation or cutoff. By avoiding the transistor’s “active” mode (where it would drop substantial voltage while conducting current), very low transistor power dissipations can be achieved. With little power wasted in the form of heat, “switching” power conversion circuits are typically very efficient.

Trace all current directions during both states of the transistor. Also, mark the inductor’s voltage polarity during both states of the transistor.