49
votes
How does the switch on the back of older computer power supplies work to vary between 110 and 220 volt input?
It is a very simple trick:
simulate this circuit – Schematic created using CircuitLab
If SW1 is open, the 4 diodes work as a standard bridge rectifier. If V1 is 220 VAC you can expect a ...
- 2,191
10
votes
What does EE10 or EE15 mean for transformer cores?
EE cores are named with their dimensions.
The following is from EE10's datasheet from TDK:
As you can see, "10" here indicates the width in millimetres of a half core.
Correct Full name ...
- 17.6k
6
votes
What are the limits of transformer turn ratios?
Nothing stops one from using a transformer to generate high voltages, it's done all the time.
A couple of common applications:
Neon signs
Strobe lights
Ignition coils
Cathode ray tubes in televisions
...
- 4,565
5
votes
Help identifying possible faulty transformer
It’s a custom transformer. If it is indeed burnt up, then the simplest if tedious way to fix it would be to measure wire diameter and number of turns for each winding while you unwind. Then rewind it ...
5
votes
Accepted
What are the differences between these ferrite cores?
EC and ETD are almost identical. ER is slightly different.
EC and ETD (ETD means economic transformer design) have both circular centre leg and circular winding window. ER's winding window is not ...
- 17.6k
5
votes
Ethernet transformer
Ethernet is a digital signaling standard. Pulses must be sent and received, over a modest distance (~100m), without consuming excessive power, avoiding random errors, and tolerating ambient noise (...
- 3,017
5
votes
What are the limits of transformer turn ratios?
Specifically for pulse operation, it's winding wire length.
Roughly speaking, a wire is a transmission line (TL), whether it's wrapped in a shield like coax cable, or wound around itself like a big ...
- 3,017
4
votes
Accepted
System blocks of switching power supplies
I am aiming for a 12V/10A (120 Watts) DC switching power supply.
OK
What I think the system block should look like
1- 220V AC to some DC value this will be mainly a transformer, plus
usual filter ...
- 384k
4
votes
Accepted
LC meter fails to measure inductance of a transformer primary with the presence of opened secondary
As some pieces of information are not known, I guess only this.
You are measuring the inductor at a frequency (10 kHz or more, probably at a "high" resonant frequency) as pointed out in the ...
- 4,982
4
votes
What are the limits of transformer turn ratios?
1000:1 turns ratio also implies 1 million to 1 impedance ratio.
To drive a 1 Megohm load you need to drive the primary from something competent to drive 1 ohm.
Then you find the leakage inductance and ...
- 66k
4
votes
Doesn't the law of conservation of energy invalidate Ohm's law?
That's not how it works.
If you step up voltage to 48V, then that same 1 ohm resistor draws 48A current at 48V, not 3A.
The resistor will get 2.3 kilowatts, and you need 192 amps at 12V to provide it, ...
- 89.9k
3
votes
Ethernet transformer
Can someone tell me what is the meaning of Open circuit inductance
That's the inductance of a winding when all the other winding(s) are left open (Similarly, the inductance measured when all the ...
- 17.6k
3
votes
Best way to make a system which is both 120 and 220 Volt compatible
It's a bit hard to answer without some idea of the power involved. A two stage 1/3 HP vacuum pump is going to lead to different thinking than a small sampling pump.
If it's closer to the latter, I ...
- 332k
3
votes
Accepted
Best way to make a system which is both 120 and 220 Volt compatible
The easiest way is to make sure all your components are able to run on low voltage DC power, and then, use a listed switching power supply with a wide input range.
This will also make it easier to ...
3
votes
In a DC power-supply design, is it safe to connect the GND of the secondary side of the transformer to the AC input part?
The mains transformer input MUST NOT be connected to GNDA.
The mains transformer current should circulate between live and neutral.
The mains side safety ground is just that, for safety. It should not ...
- 142k
3
votes
Why is the LTspice transformer failing to step up?
The primary coil is 4uH with 1ohm parasitic resistance
Here's the problem.
Your input excitation voltage has a frequency of 1 Hz hence, at this frequency, 4 μH has a reactance of 25 μΩ AND, the ...
- 384k
2
votes
Accepted
Voltage mode Ethernet PHY and Current mode Ethernet PHY
Can anyone tell me the reason why the center taps of magnetics are
shorted in case of connection to a current mode PHY
They aren't shorted but connected to Vcc. This is because the PHY driver ports ...
- 384k
2
votes
Transformer copper loss
I believe this is from Electric Machiney Fundamentals, 4th Edition.
I see what is going on: the short circuit test is done by shorting the secondary coil of the transformer, not by applying a full ...
- 326
2
votes
Accepted
Can transformer secondary side noise couple back to the primary side?
Transformer coupling between primary and secondary windings is mutual and given by a coupling constant (between 0 and 1), which tells you how much of the flux going through one winding will also go ...
- 11.1k
2
votes
Can transformer secondary side noise couple back to the primary side?
The leakage flux doesn't magnetically couple the windings. The main flux does. And the noise in either winding will be reflected to the other winding via the main flux.
So yes, if the transformer ...
2
votes
Accepted
Single phase voltage (230V) without using a transformer?
Even if neutral and earth/ground are connected somewhere upstream in the electrical system, under normal conditions, the neutral wire is the conductor intended for carrying return currents and the ...
- 89.9k
2
votes
Accepted
Selection of voltage transformer and current transformer for protection in substation
We typically size CTs so at bank full load they have less than 5A in secondary (for 5A CTs like used in U.S.).
Full load current on 66 kV side of your 10 MVA bank is,
$$I_H= 1000\frac{10}{\sqrt{3}\...
- 3,300
2
votes
Is this a "gapped" ferrite transformer/choke?
Impossible to tell by inspection. Given some more context (pinout, surrounding circuit), or measurements (windings and pinout, inductance, estimated number of turns), the internal gap can be ...
- 3,017
2
votes
Accepted
Help identifying possible faulty transformer
There is nothing to identify. It is a custom transformer for the charger and likely it is not even broken.
The charger has a switching mode power supply and this is the main switching transformer. It ...
- 89.9k
2
votes
LC meter fails to measure inductance of a transformer primary with the presence of opened secondary
It’s not the best to use a “random multimeter” when doing transformer prototyping. Get a proper LC meter. Doesn’t have to be expensive, just decent enough to do L/C/R/ESR measurements at various ...
2
votes
Accepted
Phase Shifted Full bridge converter transformer design
Don't concern about the magnetizing current. Those formulas are for inductors (coupled as the case may be for flyback). Transformers for forward converters use high inductance, maybe a thin air gap ...
- 3,017
2
votes
Why is a short circuit in the secondary winding of a transformer reflected on the primary side?
First a small back step.
When Vp is applied to the primary winding, a primary current starts to flow and this causes a magnetic flux in the core, refer to the 'right hand rule' in physics texts for ...
- 515
2
votes
Ethernet transformer
In transformers, we distinguish between excitation current and magnetizing current. The excitation current represents energy passed from primary to secondary. The magnetizing current represents energy ...
- 1,611
2
votes
Do I need a resistor for my doorbell wiring?
Stepping up your voltage is a mistake.
It won't do what you want, because you misunderstand the problem.
When a smart doorbell is wired up with 2 wires, it powers itself (recharges its battery) by ...
2
votes
Accepted
Common base amplifier - no gain
The voltage gain in CB amplifiers relies on the impedance ratio of Collector to Emitter just like a negative feedback Op-Amp as the common base provides the bias current.
This means the emitter is ...
- 137k
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