# Full wave controlled rectifier RL Load 90° Firing angle

• Physicist3
In summary, for a full wave thyristor controlled rectifier with a firing angle of 90°, the average output voltage and current will both be zero. This is true for both resistive and inductive loads, although the behavior of the current may be more complex in the latter case due to the presence of inductance. In this situation, the inductor will push current through the thyristor and back into the source, and the current will decrease with time until it reaches the thyristor's holding current and can be commutated. This may seem counterintuitive, but it is similar to the behavior of an inductor in a purely AC circuit without thyristors.
Physicist3
For a full wave thyristor controlled rectifier, if the firing occurs at 90°, the average output voltage is zero. Therefore the average output current will be zero also I assume? If considering idealised current waveforms, should all the currents also be zero (thryristors etc.) be zero or should they have some amplitude because surely if they were zero, the thyristors wouldn't latch?

Ahh

Single phase ?
with resistive load it's straightforward, instantaneous current is E/R and average of a symmetric waveform will be zero even though there is current actually flowing.

with inductive load it's more interesting. Slow your thinking down to a frame by frame movie.
We'll start at positive peak when first thyristor fires:

When thyristor fires, current begins to increase per di/dt = E/L, so a current is established during first quarter cycle.
When voltage sinewave crosses zero , current does not cease as with resistive load.
That's because you have established a current through an inductor.
Inductance now pushes current by Lenz's law in same direction, through the same thyristor and back into source. The thyristor remains forward biased due to the inductor's counter EMF..
Current decreases by same phenomenon, di/dt = E/L.

If current reaches zero(or more precisely thyristor's holding current) the thyristor can commutate.

At negative peak when next thyristor fires, current will commence(or continue) to move negative per di/dt=E/L.
And so on.

That's only a qualitative answer, i know,
The point of confusion is usually with the inductance returning power to source during part of the cycle, when current appears to flow backward through the thyristor.
But think about it with no thyristors at all, just an inductor and an AC source: - isn't that why the inductor draws no power?

Surely you're working with a textbook that derives the equations? I'd be hard pressed to find mine.

hope this helps

old jim

## 1. What is a full wave controlled rectifier RL load with a 90° firing angle?

A full wave controlled rectifier with an RL load and a 90° firing angle is a type of electrical circuit that uses thyristors to convert alternating current (AC) into direct current (DC). The RL load refers to a resistive and inductive load, which can be found in many electronic devices. The 90° firing angle indicates the point at which the thyristors are triggered to conduct and allow current to flow.

## 2. How does a full wave controlled rectifier with an RL load and a 90° firing angle work?

In this circuit, the thyristors are triggered at a 90° angle to the AC voltage waveform. This delays the conduction of the thyristors, resulting in a portion of the AC waveform being cut off. This creates a pulsating DC output, which is then smoothed out by the inductor in the load. The result is a relatively steady DC output with a lower ripple voltage compared to other types of rectifiers.

## 3. What are the advantages of using a full wave controlled rectifier RL load with a 90° firing angle?

One of the main advantages of this circuit is its ability to produce a relatively stable DC output with low ripple voltage. This makes it suitable for powering sensitive electronic devices. Additionally, the use of an inductor in the load helps to reduce electromagnetic interference (EMI) and improve power factor.

## 4. Are there any limitations or drawbacks to using a full wave controlled rectifier RL load with a 90° firing angle?

One limitation of this circuit is that it requires a higher number of components compared to other rectifier circuits. This can increase the cost and complexity of the circuit. Additionally, the inductor in the load can cause a voltage drop, reducing the overall efficiency of the circuit.

## 5. What are some applications of a full wave controlled rectifier RL load with a 90° firing angle?

This type of rectifier is commonly used in power supplies for electronic devices, such as computers, televisions, and audio equipment. It is also used in industrial applications, such as motor drives, where a stable DC output is required for precise control. Additionally, it can be used in renewable energy systems, such as solar panels, to convert AC power into DC power for storage or use.

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