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Regulator Rectifier Technical Guide

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How do regulator rectifiers work?​

Modern motorcycle regulator rectifiers are considered plug and play devices. But how do regulator rectifiers work?

A regulator rectifier works as an analogue to digital converter. By combining a voltage regulator, with a bridge rectifier.

This is required on a motorcycle as the stator outputs AC electricity. Whereas the battery and electronics require DC electrical power.

Lamberts Bikes, Analog and Digital Signals

The bridge rectifier converts the incoming AC stator voltage into a DC ripple. Stopping the voltage from going negative.

Then the voltage regulator smooths out this DC ripple with a capacitor. After which, the voltage regulator monitors the DC output via on a feedback loop.

Combining bridge rectifier and voltage regulator circuits creates a power source that is now suitable for the battery and other electrical parts.

Now we have a basic understanding, let’s discover more about how regulator rectifiers work….

What is a Bridge Rectifier?

Originally patented in 1896 by Polish electro-technician Karol Pollak. The bridge rectifier has been an essential part of AC to DC conversion for over a century.

In technical talk, it’s purpose is to provide the same output polarity for either input polarity.

An animation of a bridge rectifier:


The bridge rectifier animation highlighted, shows how this is achieved with 4 simple diodes.

A diode is an electronic device that only allows current to flow in one direction. And so, you can think of them as a one-way valve for electrons.

In the bridge rectifier animation, you can see that the voltage polarity on the input is alternating between positive and negative. Whereas, the voltage polarity on the DC output side remains the same.

DC ripples

The pulsing on the DC output is known as DC ripple. This can be seen by plotting the DC ripples against time on a graph…

Input – Sinusoidal signal

Lamberts Bikes, Bridge Rectifier DC Ripple, Sinusoidal Signal
Sinusoidal input signal to a bridge rectifier (voltage against time)

The above graph in Red shows the AC current coming from the motorcycle stator. Nothing really to see here – just an AC waveform.

Output signal – Half-wave rectified

Lamberts Bikes, Bridge Rectifier DC Ripple, Half Wave Rectified
Half wave rectified output signal from a bridge rectifier (voltage against time)

Above is a Green graph that illustrates the effect of half wave rectification. This is what happens when you put AC through a single diode. This is not to be confused with the bridge rectifier example given above.

With half wave rectification, the negative side of the AC wave is simply chopped off. Consequently, half wave regulator rectifiers have a much lower potential power output than full wave versions.

Lower budget motorcycle regulator rectifiers often use half wave rectification. This is because there are fewer component required during manufacture; helping to keep production costs low.

Output signal – Full-wave rectified

Lamberts Bikes, Bridge Rectifier DC Ripple, Full Wave Rectified
Full wave rectified output signal from a bridge rectifier (voltage against time)

Finally, above is a Blue graph that illustrates full wave rectification. Rather than being ‘chopped off’, it can be seen that the negative side of the waveform has been inverted. Providing additional power to be utilised!

To make this DC ripple useful for batteries and electronics, all that needs to be done is to smooth out the ripple and regulate the outgoing voltage…

DC Ripple Smoothing with a Capacitor

This section covers how capacitors are used to smooth out the DC ripples from a rectifier. Along with what effect half wave rectifiers have on this smoothing process.

A graph showing ripple smoothing with a capacitor:

Lamberts Bikes, DC Ripple Smotthing with a Capaictor

The Red line of the graph shows the charging and discharging of a capacitor.

As the voltage increase then the capacitor charges up.

As the voltage decreases, then the capacitor slowly discharges its energy. This prevents the voltage from falling back to zero as quickly as the supply. Hence the smoothed ripple effect.

The output voltage no longer matches the original DC ripple. Such smoothing out effect has been created by the capacitor slowly discharging. Which makes it much easier to regulate a constant DC voltage.

How Does a Voltage Regulator Work?

This is where it gets somewhat complicated. Without a solid understanding of electronic engineering, it can be difficult to grasp the details. So, let’s keep it simple and look at the fundamental concept.

Smoothing DC

Lamberts Bikes, Bridge Rectifier DC Ripple

The key to the voltage regulator is the capacitor. This is the source of the smoothed DC voltage.

However, to function properly the regulator needs a supply too.

Therefore, the voltage regulator needs to maintain a high enough voltage inside the capacitor.

Regulating Voltage

Via a feedback loop, voltage regulator continuously monitors their own output voltage. Either done internally or with an external voltage sensing wire (Vsense).

The regulator controls the amount of energy being sent to the capacitor. This directly affects the amount of energy stored within the capacitor. But it’s a delicate balance!

Store too much energy and it may blow the device. Inversely, store too little and there might not be enough power to meet demand.

Voltage regulators therefore constantly vary power being sent to the capacitor in order to keep up. This is analogue control at its best!

Format and Design

Lamberts Bikes, Voltage Regulator Formats
Common format designs of compact voltage regulator semiconductor devices

Most voltage regulator’s come in the form of a small solid-state device. They monitor their own output voltage.

If the voltage climbs too high, these devices will dump any excess input power to ground. This excess energy is dissipated as heat. Therefore, motorcycle regulator rectifiers are sold inside a large alloy heat sink.

Also, this method of feedback control is also very effective for protecting against over voltages and surges. If the voltage suddenly climbs sky high, the regulator will detect the increase and limit the amount of energy flowing to the capacitor. When the energy flow is restricted enough the device, simply turns off.

Learn more…

Want to learn more about regulator rectifiers? Don’t miss Lamberts Bikes motorcycle regulator rectifier data library.

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