Resonant overvoltage at switch on of offline SMPS...Diode proetection?

[Flyback]

Hello,
The attached schematic shows a 24W, 230VAC SMPS being switched on at the mains voltage peak.
If D13 is not in the circuit, then the resonant overvoltage at switch on is around 630V.
Why do diodes such as D13 not exist in the schematics of offline SMPS's generally?
-The diode is a very simple way of totally getting rid of the overvoltage problem...so why does nobody do it like this?

The 630V will probably end up being quashed by a MOV or TVS if fitted, but that won't do the lifetime of the MOV or TVS any good.

(LTspice simulation also supplied)

 

[tvtech]

Hello,
The attached schematic shows a 24W, 230VAC SMPS being switched on at the mains voltage peak.
If D13 is not in the circuit, then the resonant overvoltage at switch on is around 630V.
Why do diodes such as D13 not exist in the schematics of offline SMPS's generally?
-The diode is a very simple way of totally getting rid of the overvoltage problem...so why does nobody do it like this?

The 630V will probably end up being quashed by a MOV or TVS if fitted, but that won't do the lifetime of the MOV or TVS any good.

(LTspice simulation also supplied)

Because they do bugger all and do not help reliability.
Never seen a TV SMPS or any other practical SMPS arrangement like that.

I expect a like for my input.

 

[Flyback]

If you run the simulation with and without the diode, then you can see what brilliant effect it has

 

[tvtech]

If you run the simulation with and without the diode, then you can see what brilliant effect it has

Simulation is one thing....real World is another animal altogether. Especially with SMPS....

And I expect a like for this too.

 

[ronsimpson]

In place of D13 some people use a power resistor.

 

[Flyback]

Though the power resistor, if it is to work well enough, it will need to be too dissipative, especially if it is sized to quell overvoltages which occur at mains peak voltage switch on. Simulators can be un-real, but in this case, simple LC circuits, the simulator is likely to be correct.

 

[tvtech]

In place of D13 some people use a power resistor.

LOL .

That is what I could not understand...here I am wondering about all these variations...and you nailed it first time.

Thanks Yet another Blonde moment for me

Easy to be thick sometimes

All the best,
tvtech

 

[ronsimpson]

Usually I use perfect Ls and Cs. In this case it is fine.
Some times I enter the resonant frequency for the L and C, including internal resistance.
In this case I might enter the internal resistance only.