does the cell phone charger include an oscillator ?

Thread Starter

zaki.097

Joined Jun 11, 2017
3
hello
i want to build a cell phone charger and i have a small transformer so i need to increase the frequency of 220v/50hz to higher frequency and in order to do that first i rectified the 220v ac and used a 2uf capacitor then i am confused ho to have a square wive od even a sine wave and then decreased the voltage with my small size transformer to around 10 volt
so my question is that do i have to use an oscillator or what and thank you
 

Alec_t

Joined Sep 17, 2013
10,616
Welcome to AAC!
Messing with mains voltage is very dangerous, and constructing a SMPS is far from easy, particularly if you are inexperienced.
You can buy a charger for £1/$1, but it will cost more than that to build one. So why not just buy one?
 

#12

Joined Nov 30, 2010
18,167
Changing AC to DC then trying to use a transformer is self defeating. Just use a transformer on the AC.
 

WBahn

Joined Mar 31, 2012
24,981
Part of what you are trying to do, as you have described it, is a violation of the Terms of Service because it involves a direct-to-mains, i.e., "transformerless" power supply. These types of circuits are extremely dangerous unless you really know what you are doing and your set of questions indicates that you aren't there yet.

What is the voltage rating on that 2 uF capacitor you are using? Is it at least about 400 V?

Is your design and circuitry set up to ensure that 310+ V will not cause arcing at any place in the circuit?

Is your physical set up such that it is pretty much impossible to contact any part of any component that operates at anything near the mains' voltage?

If you didn't address these questions before you ever thought of hooking anything up, then you aren't ready yet to deal with these kinds of circuits -- these circuits can be lethal in a heartbeat (or permanent lack thereof).

But it is quite likely that you can achieve your goal without going this route.

Why do you think you need to increase the frequency? What to?

What is preventing you from using a transformer to step the 220 Vac down to the neighborhood of 10 Vac?
 

Thread Starter

zaki.097

Joined Jun 11, 2017
3
i do have a small size transformer and it is not rated for 50 hz for my power supply thats why i do need to change the frequency
 

WBahn

Joined Mar 31, 2012
24,981
i do have a small size transformer and it is not rated for 50 hz for my power supply thats why i do need to change the frequency
What is it rated for?

Why don't you get a transformer that IS rated for 50 Hz?

It can't be cost considerations, because you are almost certainly going to spend more in parts for what you are trying to do than simply buying a charger would cost.
 

Tonyr1084

Joined Sep 24, 2015
3,945
In the end you are charging a DC battery with a DC current. There is no need to modify the frequency. But to answer your question, 'no, cell phone chargers do not include an oscillator. They simply drop the voltage from mains voltage (be-it 120 or 240 VAC) down to the proper rectified voltage needed.

If anything, I'd take an existing charger and modify it for some other purpose. But I wouldn't undertake building one for two reasons: First, you're messing with dangerous voltages (mains) which, as others have said, can kill. The second reason would be that it's more expensive to build than to buy. Third, if you DO build, what you create is likely going to be far larger than anything on the market that you can buy. And lastly, the bought chargers already have been tested out for reliability and durability. Whatever you may create - there's opportunity for many mistakes. And it seems you're flying in the dark without instruments. Meaning that from what you're asking it does not sound (or inspire confidence) that you're competent to build such a device yet. I said "YET"!

Electronics is a wide field with lots of opportunity to learn. If I were to describe my level on a scale from 1 to 10 I'd say it's around a 2 or 3. Not that I'm trying to elevate myself above you but I don't think you're even a 2 yet. No intention to insult, and if you've taken offense, please let me offer an apology right now. I just don't want anyone getting hurt. Just about all of us here have experienced the thrill of either 50 or 60 cycle shocks. Many of us have also experienced 400 cycle (aircraft). And when you start getting into radio frequency - well, that's an area where I have zero experience; but I understand that it can be even more dangerous. Like I said, I'm hardly a 2 or 3 at this. Many here are 7, 8 and few 9's but I have yet to come across anyone here who'd accurately describe themselves as being a 10 in the electronics field.

It's OK to wonder and ask questions. That's the foundation to learning. But wisdom is knowing what to experiment with and knowing what NOT to experiment with until you're considered an expert in the basics. Sorry, I just don't see this project as something you should attempt yet.

Please - have a good day. And don't hurt yourself.
 

Thread Starter

zaki.097

Joined Jun 11, 2017
3
In the end you are charging a DC battery with a DC current. There is no need to modify the frequency. But to answer your question, 'no, cell phone chargers do not include an oscillator. They simply drop the voltage from mains voltage (be-it 120 or 240 VAC) down to the proper rectified voltage needed.

If anything, I'd take an existing charger and modify it for some other purpose. But I wouldn't undertake building one for two reasons: First, you're messing with dangerous voltages (mains) which, as others have said, can kill. The second reason would be that it's more expensive to build than to buy. Third, if you DO build, what you create is likely going to be far larger than anything on the market that you can buy. And lastly, the bought chargers already have been tested out for reliability and durability. Whatever you may create - there's opportunity for many mistakes. And it seems you're flying in the dark without instruments. Meaning that from what you're asking it does not sound (or inspire confidence) that you're competent to build such a device yet. I said "YET"!

Electronics is a wide field with lots of opportunity to learn. If I were to describe my level on a scale from 1 to 10 I'd say it's around a 2 or 3. Not that I'm trying to elevate myself above you but I don't think you're even a 2 yet. No intention to insult, and if you've taken offense, please let me offer an apology right now. I just don't want anyone getting hurt. Just about all of us here have experienced the thrill of either 50 or 60 cycle shocks. Many of us have also experienced 400 cycle (aircraft). And when you start getting into radio frequency - well, that's an area where I have zero experience; but I understand that it can be even more dangerous. Like I said, I'm hardly a 2 or 3 at this. Many here are 7, 8 and few 9's but I have yet to come across anyone here who'd accurately describe themselves as being a 10 in the electronics field.

It's OK to wonder and ask questions. That's the foundation to learning. But wisdom is knowing what to experiment with and knowing what NOT to experiment with until you're considered an expert in the basics. Sorry, I just don't see this project as something you should attempt yet.

Please - have a good day. And don't hurt yourself.
thank you sir fo your answers
sir why they don’t put the transformer directly into the main voltage instead they rectified it then there is 2 bjt transistors also in the secondery they rectified it again
 

Alec_t

Joined Sep 17, 2013
10,616
Because the mains frequency is low (50/60 Hz) and would require a big transformer, whereas a SMPS has a switching frequency of several hundred kiloHertz so would require a tiny transformer by comparison.
 

ian field

Joined Oct 27, 2012
6,539
i do have a small size transformer and it is not rated for 50 hz for my power supply thats why i do need to change the frequency
Most modern chargers are SMPSU and frequently are capable of operating from anything between 85 - 265V.

You could probably feed it DC at anywhere within that voltage range and it would work.
 

AnalogKid

Joined Aug 1, 2013
8,231
But to answer your question, 'no, cell phone chargers do not include an oscillator.
Yes, they do.

The world consumes billions of small chargers (wall warts) per year for cell phones and other devices, and the vast majority are switching power supplies with an input power line rectifier, storage capacitor, high frequency oscillator, power switching device, fully isolated transformer, secondary rectifier, output filter, and feedback mechanism. Not bad for $2.

ak
 

#12

Joined Nov 30, 2010
18,167
There's still a *FEW* iron cored transformer chargers about that don't.
They're rapidly becoming extinct though.
I have a few iron core wall warts, but they are so old that it's difficult to read the manufacturing date codes on them.:D
 

WBahn

Joined Mar 31, 2012
24,981
Some of them don't. I've seen Julian calendar date codes.:eek:
Good point.

I got curious about why it is called "Julian" since, in my experience, it is generally the last digit of the year followed by the three digit day of the current year. I didn't think that any ancient calendars counted days since some year-defining event, but maybe.

So Google to the rescue!

What I've always thought of as "Julian dates" really aren't -- just a related concept. An actual Julian Date is the number of whole solar days + fractional day since noon (Universal Time) 01 JAN 4713 BC on the Julian calendar. It's used primarily for astronomical observations, which makes sense. I vaguely recall having seen this before, so I probably ran across it years ago and proceeded to forget it. Gotta love Google!

FWIW: The current Julian Date is 2457917.
 
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