Diodes with RL loads. Freewheeling Assume ideal diode (zero reverse rocvery time, zero voltage drop) An antiparallel diode known as the freewheeling diode must be connected across the load to provide a path for the inductive current to flow.

Diode rectifiers Learn performance parameters of rectifiers and power converters Study effects of load inductance on load current L R D1 D2 Vs

First neglect the freewheeling diode

From The diode current is found using the Laplace transform method: Note that the diode conduction time is longer than half-period The waveform is nonsinusoidal but periodic.

Now with the freewheeling diode

Recommended reading ● Chapter 1 ● Sections and examples in those sections, the rest are optional) ● Sections 3.1 to 3.3, example 3.2

Single phase full wave rectifier Full wave rectifier with centre tapped transformer

Full wave bridge rectifier

Single phase full wave rectifier with large inductive load

Single phase full wave rectifier with RL load T /2

For a steady state solution, require i0 (0)= i0 (T)= I0. Then I0> 0 guarantees that the current flows continuously.

Download Matlab code fwr.m, (also requires fun_fwr.m). Load, source and diode currents (E=10V).

Load, source and diode currents (E=0.6Vm)

E=10 V

E=120 V Load voltage Source voltage Load current

Conclusion ● An inductive load can make load current flow continuously if voltage ratio is below the critical value ● E=0 guarantees continuous current ● If L=0, any E>0 will cause current interruptions ● References: Section 3.4 and examples in that section

Three phase bridge rectifier

(Note 30 deg phase shift).  0

Single phase rectifier 3 phase rectifier Performance:

3phase rectifiers with RL load E

Condition for continuous load current Largest critical value of the EMF ratio is substantially higher (95.5% vs 63.6%)