It is so I can begin to work on these exercises in my quest to understand electronics. As an aside, I am gaining a great deal of admiration for the folks here and the depth of their knowledge and patience. I had started another thread about this but it got cluttered with my misunderstandings
Here are my forthcoming exercises using diodes to double, triple and quadruple AC current into DC output. I really don't want to mess around with 110v from the wall as it frightens me so, I have a circuit that works that delivers a low voltage pulsating DC signal that I want to invert into say, 25V AC, 60hz to be used for the exercises.
Question: Can i use zener diodes for this ? I have tons of them in stock. From looking at the exercises how do you know what type of diode to use ?
I have also included the inverter schematic that i had shown in another post. I have the power transistors and would like to use them.
Re the schematic, I have the output of pins 10 and 11 as I want it.
So, how to proceed ?

 

From my understanding, you want 25V AC from a DC power supply because you are afraid of mains voltages. You need AC to experiment with various circuits. You could just get a machine that generates exact waveforms, but given the cost, that is probably impractical.

Here is what I suggest: find/buy a transformer that steps your mains voltage (which you should find out exactly) to 25V. Just connect live and neutral to the primary of the transformer (use a resistor to avoid tripping breakers if necessary), maybe wrap it in an insulator like electrical tape, and connect the secondary to power whatever you are testing out. You get 25V AC at 60 Hz exactly. Just using a step-down transformer is one of the most practical and effective solutions. I would avoid using an inverter circuit unless absolutely necessary. You may be very hesitant to connect anything directly into the wall outlet, but just use use gloves, wear well-insulated shoes, and use the one-hand rule.

Also, 25V AC will hurt a lot, and would still be dangerous. If you are really, really unlucky (wires poking into you skin or dripping wet), it could even be fatal. AC is far more dangerous than DC. YOU are not only a resistor, but also a capacitor. With DC, this effect is negligible. HOWEVER, with AC, you can get much greater currents because of your capacitive properties. Just keep safety in mind, and take precautions.

 

The current available from doublers, triplers, etc will be low.

As suggested just get some transformers.

What I did was take a half dozen or so transformers I had laying around with various secondary voltages and installed them in a box (open frame mostly) with banana jacks for the secondaries. I also included a bridge rectifier and a couple fair sized caps that could be arranged in parallel or series with the flip of a switch.

That's what I use when I want to do experiments with AC. Line voltages are still present, but they're away from anything I'd normally use or touch.

 

Here are my forthcoming exercises using diodes to double, triple and quadruple AC current into DC output.

Just as a little side note you can have voltage doublers and voltage triplers and you can quadruple a voltage but using these circuits you are not doubling, tripling or quadrupling the current. The power expressed in Watts will always be the sum of the Voltage * Current so if we double one we half the other.

Voltage Doubler:

A voltage doubler is an electronic circuit which charges capacitors from the input voltage and switches these charges in such a way that, in the ideal case, exactly twice the voltage is produced at the output as at its input.

The simplest of these circuits are a form of rectifier which take an AC voltage as input and outputs a doubled DC voltage. The switching elements are simple diodes and they are driven to switch state merely by the alternating voltage of the input. DC-to-DC voltage doublers cannot switch in this way and require a driving circuit to control the switching. They frequently also require a switching element that can be controlled directly, such as a transistor, rather than relying on the voltage across the switch as in the simple AC-to-DC case.

As to any reference to mains voltage or a fear of the wall outlet I would suggest you become familiar with mains voltage and how to convert it for your purposes like the use of step down transformers, rectifiers and filter capacitors or simply get power supplies for your intended applications. With that said the design of and application of inverters becomes a world unto itself. For example which waveform would you like? Popular and inexpensive is the MSW (Modified Sine Wave). Maybe a TSW (True Sine Wave) is better suited for your application? There are also other inverter outputs but MSW and TSW are a good start:



You need to get a good understanding of the basics and work from there. Nobody I know ever learned to swim in the deep end of the pool.

Ron

 

A buddy of mine this morning suggested a variac, a new device to me. It seems like a good bet.

 

A variac won't provide line isolation and can expose you to voltages higher than 110VAC.

 

A variac won't provide line isolation and can expose you to voltages higher than 110VAC.

That being the caveat worth consideration. A Variac while a useful tool on the bench will not provide any isolation from the AC mains it is connected to.

Ron

 

Don't be afraid of AC mains. Give it due respect it deserves.

Go to a second hand store and buy inexpensive AC adapters. You can get different output voltages such as 6VAC, 9VAC, 12VAC. Be aware that the output voltage with no load attached will be higher than what is written on the label.

Similarly, you can get unregulated DC output wall adapters.

You want to select wall adapters with DC or AC outputs with actual transformers to provide you with isolation. Transformer adapters will be heavier than simple DC switching power supplies. You can tell the difference immediately from the size, shape, and weight of the adapter.

 

Quite the learning experience reading the replies.
Still undecided as to which way to go.

Many thanks

 

Still undecided as to which way to go.

What is it that you were planning to do with this AC generated from the voltage multipliers?

 

What is it that you were planning to do with this AC generated from the voltage multipliers?

Nothing other than to satisfy the requirements of the exercise book. Though there might be further exercises that could use them. I will cross that bridge at the time.
However, I expect that when I get the doubler, tripler, etc working, I will be poking around with my meter and maybe scope, to see what things look like.
Hence my caution of high voltage on a breadboard. I know for sure that I will be measuring currents and perhaps waveforms.
If I get ambitious and get a scope in the near future, I will see if I can figure out a way to clean up a waveform, whatever that entails.
More hands on learning.

Oh yeah, my original question was what kind of diodes to use for the bridge circuits ? Zener ok ?

 

NO

 

Let's say you want to learn how a voltage doubler, tripler, or any cascaded multiplier works.
All good and dandy.

In reality, there are not a lot of times (applications) when you would want to use such a circuit. The one legitimate case would be if you wish to build a high-voltage supply for a geiger tube for detecting nuclear radiation. Are you planning on doing that?

Thus, where are you planning on using a voltage doubler circuit?

 

Let's say you want to learn how a voltage doubler, tripler, or any cascaded multiplier works.
All good and dandy.
Thus, where are you planning on using a voltage doubler circuit?

I am doing none of these. My project satisfies exercise pages 101 and 102 in " Getting Started in Electronics " by Forrest Mims.
Plus I need the breadboarding practice.

 

NO

Ah hah. Looking again at the schematic, I now remember that the zener has a sorta backwards z on it.

And I thank you for causing me to focus closer.

 

May be missing some thing in all of this. But isn't AC coming from the mains through a step down transformer going to be just as dangerous as the same voltage coming from your converter? But the step down transformer will have a much better/accurate sine wave.

 

Let's say you want to learn how a voltage doubler, tripler, or any cascaded multiplier works.
All good and dandy.

In reality, there are not a lot of times (applications) when you would want to use such a circuit. The one legitimate case would be if you wish to build a high-voltage supply for a geiger tube for detecting nuclear radiation. Are you planning on doing that?

Thus, where are you planning on using a voltage doubler circuit?

Even then, there are much better ways to get high voltage (like a Marx generator). But given the dangers, it is really NOT recommended. As suggested before, just us a step-DOWN transformer. What you should do is find an old computer charger and take it apart (make sure it is disconnected, discharge caps first). You can usually just take out a few screws to access the insides. Computer chargers generally output ~15-25 VDC. Just so you know what you are working with, google the charger and try to find schematic, or at least google some part numbers. There is probably a step down transformer that converts 120V to 20ish V. Look for the transformer (it should be obvious if there is one). Just take out caps, diodes, and other stuff, and you now have a good AC output. Make sure that you do not mix up primary and secondary, as this will lead to 5-6x the voltage, and will be extremely dangerous.

 

If you just want to play around with these circuits for learning purposes, just buy a simple 12 volt AC mains powered transformer.

It will be perfectly safe.

Buy a bunch of 1N4001 diodes, the cheapest garden variety - and have at it.

Feels like this thread went way off the rails with complicated ideas.

 

Read the top of the page of the book even starting at 12 volts them voltage doublers can hurt you if you fear a transformer
you better fear them more some of those put out 300 volts DC after doublers and with more then you need to stop your heart in mA

 

Feels like this thread went way off the rails with complicated ideas.

Welcome to AAC.