Explain the output of the old TV flyback transformers....

[Lamont Cranston]

> It\'s just a blocking oscillator modified for regulation.

I\'m assuming this is in response the the circuit at the center tap of the secondary.
So far my experience with 60 Hz neon sign transformers is that the inductance of the secondary
limits the current to 30ma, and they have no other regulation.
With this switching style running at 20kHz, would lead me to believe that impedance limiting is
even more likely to happen.The series secondaries measure 10H, which is 1.257MΩ at 20kHz.
7.4kV / 1.257MΩ equals 6ma. That seems low in my somewhat limited experience, but I have 8 or 10 neon sign transformers
and all have 30ma impedance limited output current.
So, that 6ma is a bit confusing.
Thanks, Mikek

 

[Anthony William Sloman]

On Monday, June 19, 2023 at 2:44:44 AM UTC+10, Lamont Cranston wrote:

It\'s just a blocking oscillator modified for regulation.
I\'m assuming this is in response the the circuit at the center tap of the secondary.
So far my experience with 60 Hz neon sign transformers is that the inductance of the secondary
limits the current to 30ma, and they have no other regulation.
With this switching style running at 20kHz, would lead me to believe that impedance limiting is
even more likely to happen.The series secondaries measure 10H, which is 1..257MΩ at 20kHz.
7.4kV / 1.257MΩ equals 6ma. That seems low in my somewhat limited experience, but I have 8 or 10 neon sign transformers
and all have 30ma impedance limited output current.
So, that 6ma is a bit confusing.

In transformers, the induced current by-passes the inductance. A current flowing through the primary that is cancelled by a matching (same number of ampere turns) current in the secondaries doesn\'t generate any back EMF so it isn\'t limited by the inductance of any of the coils.

The fact that the primary-secondary couplng isn\'t perfect does impose an upper limit in practice but a couple of 0.99 or better isn\'t unknown.

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/tracir.html

That link does give the transformer equation, but doesn\'t bother with M=k .Sqr-root(L1.L2) where k is the coupling coefficient which can be anywhere from 0 to almost one. 0.99 to 0.999 is pretty typical.

--
Bill Sloman, Sydney

 

[Tabby]

On Thursday, 15 June 2023 at 21:35:40 UTC+1, Lamont Cranston wrote:

On Thursday, June 15, 2023 at 3:32:29 PM UTC-5, Tabby wrote:

I sent a question about the output to the seller, they forwarded it on to the manufacturer.
totally pointless
What is pointless? Asking for more info, or expecting to get it?
Mikek

asking a liar in writing whether they\'re lying