Half wave rectifier

hyytg

Joined Nov 19, 2023
2
What will be the output of the half wave rectifier if the
secondary winding of the transformer is open?

Joined Jul 18, 2013
28,026
Zero??
Why??

hyytg

Joined Nov 19, 2023
2

MisterBill2

Joined Jan 23, 2018
16,514
If there is an open circuit, that implies directly that current can not flow. If no current can flow then all of the voltage drop will be across the open segment.

Joined Jul 18, 2013
28,026
@hyytg It is very unusual for a transformer secondary to go open. These generally consist of heavier windings, unless it is H.V. output.

Tonyr1084

Joined Sep 24, 2015
7,547
What will be the output of the half wave rectifier if the
secondary winding of the transformer is open?
Welcome to AAC.

Let's start at the end. Zero volts. Why do I have zero volts? Assuming a transformer and a rectifier - either the transformer has failed open or the rectifier has failed open.
As Max said, if the secondary is open then there's no circuit. A circuit is like a circle. Both words come from the Latin word we translate as circle and circuit. If the circle is broken then you no longer have a circle - or circuit. An open circuit (broken circle) means something has become disconnected. Either by a broken wire or a failed component. Since a transformer is a set of wires coiled around an iron core - a broken wire means no current can flow. The open circuit can even be in the primary. But like Max also said
It is very unusual for a transformer secondary to go open.
Rather, transformer windings may overheat and destroy the insulation of the wires that make up the transformer. Primary and secondary are wound on separate bobbins so it's extremely unlikely you would get a short from primary to secondary. But rather, the primary coil OR the secondary coil Could go short. A short circuit means the current pathway has found a shortcut back to the origin of the current. Hence a short cut or a short circuit. That's a more likely failure of a transformer.

Start by fully diagnosing the problem, assuming you're experiencing a problem. Is there power going TO the transformer? If so - is there current flowing through the primary coil? If there's no power then you've found the problem. If there's power but no current flowing then you've found the transformer to be bad. IF there's power and current flowing through the primary AND a voltage present on the secondary then the transformer is good. Something else is wrong. Likely it's the diode.

Diodes can fail in two ways: They can fail OPEN or they can fail SHORT. A shorted diode will act like just another wire allowing current to flow in both directions. An open diode will not pass any current through it, nor will a voltage be present.

Hope this helps.

ElectricSpidey

Joined Dec 2, 2017
2,628
An open diode will not pass any current through it, nor will a voltage be present.

Technically you are correct. (no current equals no voltage)

But, considering most people use emf and voltage interchangeably, most will say that voltage will appear across an open diode.

Tonyr1084

Joined Sep 24, 2015
7,547
Here's where my head is: If the diode is good you get the below sine wave. If the diode is open you get no sign wave.
And as before mentioned, if the diode is good but the transformer is bad - you get no sine wave. The line is open somewhere. Either in the transformer or in the diode. A failed open diode will not present a voltage at the cathode end.

Now: A shorted diode will present a full sine wave because as far as the circuit is concerned, there is no rectification, just a current path.

MisterBill2

Joined Jan 23, 2018
16,514
Really, we have no clue as to the context of the question. In many transformers a thermal fuse is embedded within the windings. This is done because it allows a cheaper construction using worse quality materials while still reducing the chance of starting a fire. So the very first step in actual diagnostics is to disconnect the mains power and measure the primary and secondary winding resistance.
Because of the poor quality of such transformers, the thermal sensor will on many occasions fail at a lower temperature. Bypassing the ermal sensor is often possible, which restores the product to a useful life. At that point adding an external fuse is a good idea, but seldom added.

Joined Jul 18, 2013
28,026
My findings so far with Thermal fuses have only been fitted in the primary side, the OP said the secondary is open.

ElectricSpidey

Joined Dec 2, 2017
2,628
I thought the question was academic.

MisterBill2

Joined Jan 23, 2018
16,514
But IS that secondary open, or has the output just gone dead?? It would not be the first incorrect diagnosis on this forum. An ohm meter will answer the question quite accurately. OR is this a case of we only get "the information we need."
And I am also wondering what the voltage should be. Like Max stated some are bigger wire than others.

Tonyr1084

Joined Sep 24, 2015
7,547
What will be the output of the half wave rectifier if the
secondary winding of the transformer is open?
we have no clue as to the context of the question.
Seems clear to me. Asked. Answered. Since then there has been some elaboration on various scenario's. Mentioning a thermal fuse is a good point. A transformer with no output CAN be dead on the primary side or the secondary. There are lots of possibilities. But the question is what's the output on an open secondary.

Joined Jul 18, 2013
28,026
There are lots of possibilities. But the question is what's the output on an open secondary.
What would you expect?

Tonyr1084

Joined Sep 24, 2015
7,547

MisterBill2

Joined Jan 23, 2018
16,514
Actually, for some transformers there is a fair amount of capacitance between the primary and the secondary, and so, depending on the location of the break, a high impedance ac input on a DVM may show quite a few secondary volts, relative to some common neutral, if the open winding is not connected to a load. Not enough to be useful, but enough to confuse the analysis.