What is a Class E chopper?

A Class E (four-quadrant) chopper is a full H-bridge built from four controlled switches and four anti-parallel diodes — effectively two Class C legs. It can apply both voltage polarities and carry both current directions, so it drives a DC motor in all four quadrants: forward motoring, forward braking, reverse motoring and reverse braking. It is the standard front-end of a fully reversible DC drive.

How does a Class E chopper reach all four quadrants?

The H-bridge can set the output voltage positive or negative (by which diagonal pair conducts) and the anti-parallel diodes let the current flow either way. Combining +/- voltage with +/- current covers all four quadrants of the voltage-current plane, so the same circuit both drives and brakes the motor in either direction of rotation.

What is the difference between Class E and Class C or D choppers?

A Class C chopper is one leg giving Quadrants I and II; a Class D chopper is a different two-quadrant arrangement giving Quadrants I and IV. A Class E chopper uses two legs (a full H-bridge) to combine both and reach all four quadrants.

Class E Chopper Simulator (Four-Quadrant DC Chopper)

Q: What is the average output voltage of a Class E chopper?

With bipolar (two-level) PWM the diagonal switch pairs apply +Vs and -Vs, so the average output voltage is Vo = (2D - 1) * Vs, where D is the duty of the +Vs interval. At D = 0.5 the average is zero; above 0.5 it is positive (forward) and below 0.5 negative (reverse). The load current can be either sign, giving four-quadrant operation.

Class E Chopper Simulator — Four-Quadrant DC Chopper

An advanced, physics-accurate simulator of the Class E (four-quadrant) chopper — a full H-bridge of four switches and four diodes (two Class C legs) that drives a DC motor in all four quadrants: forward and reverse motoring and forward and reverse braking. With bipolar PWM the output swings ±Vs so the average Vo = (2D−1)·Vs, and the current can be either sign. Vary the duty D, frequency, source, motor (with signed back-EMF) and device model; read the live bidirectional current, a four-quadrant map and the ripple spectrum, and export the data — all validated against Vo = (2D−1)·Vs.

Class E chopper circuit diagram (power circuit): a full H-bridge with four controlled switches and four anti-parallel diodes (two Class C legs) driving an R-L-E DC-motor load in all four quadrants — forward and reverse motoring and braking — Figure 3: Class E chopper — power circuit. A full H-bridge — two Class C legs. Diagonal switch pairs apply +Vs or −Vs and the diodes carry either current direction, so the drive reaches all four quadrants.

Chopper control

Duty cycle D 0.50

Vo = (2D−1)·Vs · full H-bridge, bipolar PWM (diagonal pairs)

Chopper frequency 500 Hz

DC source

Source voltage Vs 220 V

Load — DC motor (R-L-E)

Resistance R 1.0 Ω

Inductance L 20 mH

Back-EMF E 100 V

Motor back-EMF ∝ speed. E > Vo makes the current fall (light load / DCM).

Device model

Switch drop V_sw 0.0 V

Diode drop V_f 0.0 V

On-resistance R_on 0 mΩ

Ideal (0,0,0) matches the Vo = D·Vs theory exactly.

Protection ratings

Switch V rating

Current rating

Drives the protection-margin check (peak device voltage = Vs, peak current).

Sampling & display

Sampling rate 600 pts/cycle

Time window

Run speed (DSO) 1.0×

Show sample points

Presets

Waveforms to display

Switch state Output voltage v₀ Load current i₀ Source current i_s

Waveforms — steady state four-quadrant

switch v₀ output i₀ load i_s source Vs / avg

LIVE

Four-quadrant operating map

Q1 Forward motoring — Vo > 0, Io > 0.

Vo = — V
Io = — A

Class A operates in Quadrant I only.

Ripple spectrum analysis

Harmonics shown 16

Output-voltage ripple / distortion (relative to |DC|)—

FFT of the output voltage — ripple harmonics at multiples of the chopper frequency f_c. Raising the frequency or inductance lowers the current ripple. Toggle to the load-current spectrum above.

Measurements

Live accuracy check — simulation vs closed-form theory

Average output

Load current

What is a Class E (four-quadrant) chopper?

A Class E chopper is a full H-bridge — four controlled switches with four anti-parallel diodes, effectively two Class C legs. By choosing which diagonal pair of switches conducts it can apply +Vs or −Vs to the load, and the anti-parallel diodes let the current flow in either direction. Combining both voltage polarities with both current directions gives full four-quadrant operation: forward motoring, forward (regenerative) braking, reverse motoring and reverse braking. It is the standard power stage of a fully reversible DC-motor drive.

Output voltage & four-quadrant operation

Vo = (2D − 1) · Vs · Io = (Vo − E) / R (either sign)

With bipolar PWM the diagonal pairs apply +Vs for a fraction D of the period and −Vs for the rest, so the average is Vo = (2D−1)·Vs: zero at D = 0.5, positive (forward) above and negative (reverse) below. The motor back-EMF E then sets the current direction — below Vo the machine motors, above it the machine brakes. Move the duty and the signed back-EMF to visit all four quadrants. This simulator integrates the real R-L-E load and compares the measured average to (2D−1)·Vs.

Advanced options in this simulator

Duty & signed back-EMF: sweep the duty through 0.5 and set the back-EMF sign to reach forward/reverse motoring and braking.
Device model: switch and diode drops with on-resistance; the accuracy check stays locked to Vo = (2D−1)·Vs.
Four-quadrant map: the operating point can land in any of the four quadrants.
Ripple spectrum & export: FFT of voltage/current and CSV/report/PNG export.

The five chopper classes

Class	Quadrants	Average output	Use
Class A	I (V+, I+)	Vo = D·Vs	Forward motoring (step-down)
Class B	II (V+, I−)	Vo = (1−D)·Vs	Regenerative braking
Class C	I & II	Vo = D·Vs	Motoring + braking
Class D	I & IV	Vo = (2D−1)·Vs	±V, one current direction
Class E	I–IV	Vo = (2D−1)·Vs	Full four-quadrant drive

Explore the others: Class A, Class B, Class C and Class D chopper simulators. For the full theory see the Class E chopper tutorial.

Applications

Fully reversible DC-motor drives — rolling mills, cranes, hoists, mine winders, electric traction and servo drives — where the machine must run and brake in both directions with smooth, fast transitions between quadrants.

Frequently asked questions

What is the average output voltage of a Class E chopper?

With bipolar PWM, Vo = (2D−1)·Vs. It is zero at D = 0.5, positive (forward) above and negative (reverse) below.

Why is it a four-quadrant chopper?

The H-bridge sets the voltage either polarity and the diodes carry either current direction, so the operating point can reach all four quadrants.

How do I reach each quadrant?

Set the duty above or below 0.5 for forward/reverse voltage, and set the back-EMF below or above the output for motoring/braking — the four combinations give the four quadrants.

How is it built?

As a full H-bridge — four IGBTs/MOSFETs with anti-parallel diodes, equivalent to two Class C legs.

Power4All · Class E (four-quadrant) chopper interactive simulator. All waveforms are produced by numerical integration of the actual circuit and validated against closed-form theory.