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Understanding how flyback transiformer works
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Understanding how flyback transformer works!

Flyback transformer is probably the biggest component in CRT television or CRT monitor.

In this article I am going to highlight few things about his component.

Technically speaking FBT is simpy a transformer just like any other transformer and the mode of operation is the same(It has the primary side and the secondary side)

Below you can see a diagram of internal structure of a flyback transiformer.





For the FBT to work it needs the support of other components and these includes:

1.Horizontal output transistor(H.O.T) Usually all transformers require alternating current(A.C) to work,In FBT this is accomplished by the H.O.T transistor.

In this circuit the H.O.T act as a switch which open and close very fast and by doing so current f
low through the pimary of the flyback to the ground and this will cause voltages to appear on the secondary of the FBT.

These voltages includes, HV, focus, screen voltages among others.  




2.Snubber capacitor. Basically the snubber capacitor is used to suppress(snub) induced high voltages by collapsing magnetic field in the flyback transiformer primary winding which could otherwise lead to destruction of the horizontal transistor(H.O.T).

That is why sometimes this capacitor is also reffered to as “safety capacitor” if this capacitor is open or is removed from the circuit it  will cause instant destruction of the H.O.T transistor.

So next time you find the H.O.T shorted you should replace it together with the snubber capacitor.

3.Damper diode. Usually this diode is inside the H.O.T transistor as you can see in the internal diagram of the H.O.T. and sometimes it is used sepately.

This is usually Fast recovery(FR) diode and therefore if it is used externally should never be replaced with a normal diode.

The damper diode is usually used to protect the H.O.T from reverse breakdown current.

Besides these components, FBT also require two essential inputs in order to function. These includes:

4.B+ supply voltage. This is usually the main voltage from the secondary output of the power supply(S.M.P.S) and it is usually DC voltage. This voltage(B+) enters the FBT and out through the H-out pulse pin to the middle(collector) pin of the H.O.T transistor.

This is usually called the primary coil of the flyback transformer.

5.Input signal. As I mentioned ealier transformers are not supposed to work with DC and therefore that is why we need to change this DC to AC.

To accomplish this we need a switch, in this case the H.O.T which switch this DC on/off very fast to generate AC.