Switch Applications and Realization in Power Electronics

A set of 15 vocabulary flashcards covering single-quadrant switch realizations, active versus passive switches, diode and transistor i-v characteristics, and buck converter switch implementations.

Ideal SPST switch

A single-pole single-throw switch containing power terminals $1$ and $0$, defined such that the voltage $v$ is zero in the on state and the current $i$ is zero in the off state, sometimes including a control terminal $C$.

Passive switch

A switch that does not contain a control terminal $C$, whose operating state is determined entirely by the waveforms $i(t)$ and $v(t)$ applied to its power terminals $0$ and $1$.

Active switch

A switch whose conducting state is determined by a signal applied to a control terminal $C$, rather than directly depending on the waveforms $v(t)$ and $i(t)$ across its power terminals.

Ideal diode

A passive SPST switch requiring v(t) \ble 0 and i(t) \bge 0, which is off ($i = 0$) when $v < 0$ and on ($v = 0$) when $i > 0$, capable of blocking negative voltage but not positive voltage.

SPST switch distinguishing features

The two primary features used to characterize an SPST switch: its control method (active vs. passive) and the operating region it occupies within the $i\text{-}v$ plane.

Active switch operating states (BJT and IGBT)

Operating states in which the off state blocks positive voltage (v \bge 0 with $i = 0$) and the on state conducts positive current (i \bge 0 with $v = 0$), with poor or nonexistent reverse-conduction and reverse-blocking capabilities.

Power MOSFET switch characteristic

An active switch characteristic that blocks positive voltage (v \bge 0) and normally conducts positive current (i \bge 0), with the unique capability to conduct current in the reverse direction.

Synchronous rectifier

A power converter application exception in which a power MOSFET is operated to conduct current in the reverse direction rather than being restricted to i \bge 0.

SPST switch realization rule

The principle that an SPST switch can be realized using a transistor or diode provided that its required operating points in the on and off states lie on the device's $i\text{-}v$ characteristic.

Single-quadrant switch realization

A switch implementation using semiconductor devices capable of conducting current of only one polarity and blocking voltage of only one polarity.

Buck converter switch A operating points

Switch operating requirements wherein the device must conduct positive inductor current ($i_A = i_L$) when closed and block positive voltage ($v_A = V_g$) when open, realizable using a transistor such as a BJT, IGBT, or MOSFET.

Buck converter switch B operating points

Switch operating requirements wherein the device must conduct positive inductor current ($i_B = i_L$) when closed and block negative voltage ($v_B = -V_g$) when open, realizable using a diode.

Freewheeling diode

A diode configured to automatically turn on and maintain a continuous path for inductor current when an active transistor switch turns off.

Inductor turn-off voltage equation

$v_L(t) = L\thinspace\frac{di_L(t)}{dt}$, which becomes sufficiently negative when turning off the transistor causes $i_L(t)$ to decrease, thereby forward-biasing and turning on the freewheeling diode.

Buck converter operating polarity constraints

The conditions requiring $V_g$ to be positive so the diode remains reverse-biased when the transistor is on ($v_B = -V_g$), and $i_L$ to be positive so the transistor conducts in the forward direction and the diode can be forward-biased upon turn-off.