How exactly the source current of Q1/Q2 returns to the negative of C3 filter cap? I can't see a path for GND on the layout.
Ok - I see.I have 2 holes left and right to connect 2 thick wires to the ground so that ground is as as close to MOSFETs
Hi,
This is why usually a single sided PCB layout is not sufficient to make a reliable high currrent high frequency switching circuit.
Just a connection from A to B may work in simulation and in a schematic, where the connecton is considered to have zero impedance.
But on a real circuit there is ohmic resistance and - sometimes even worse - impedance caused by stray inductance.
The signals become dirty, with overshoot and ringing. Peaks of high voltage may occur. Switching speed becomes slow and discontinous which causes increased heat in the MOSFET.
Usually every semiconductor manufacturer for power switching devices provides and application notes and other informations on how to design a suitable PCB layout. They explain what you need to take care of. --> Read through them.
My recommendations to try to make your circuit working:
* A thick wire from C5_GND tor R3_GND
* a 30V MOV across each MOSFETs drain-source. Very short connections.
* C9 will cause a lot of current during switching transitions. Decrease it´s value and/or include a series inductance .. combined with a sutable RC combination to suppress LC resonance effects..
* Add 100nF ceramics capacitors directly at each supply pin to GND pin of each IC. Short wiring.
* add a (big) bulk capacitor at the input of your 7805. It´s more important than big capacitors at the output.
*****
Genrally:
* read throuch standard PCB design rules: especially distance of trace to outline.
* use useful isolation distance: reduce the distance with your low voltage signals
* use useful isolation distance: increase the distance with your high voltage signals. Proper saftey distance for 230V AC to other non related voltages is >6mm!! (area of D3..D6)
(Don´t use GND around these high voltage signals.)
* be sure to use resistors with enough voltage rating plus safety margin for R8, R9
Klaus
- - - Updated - - -
Hi,
Ok - I see.
Mind: shorter signal paths are better than thicker wires. (high frequency impedance is about independent of wire gauge)
***
I also recommend to have all three transformer primary windings connections on your PCB. This enables twisted wiring, which reduces stray inductance. Additionally you may connect a fast capacitor to GND.
Klaus
There´s no need to eliminate jumper wires. This is not the target.i tried to eliminate jumper wires
In my eyes: You never had a true "ground plane". You had a copper pour. But this far away from being a GND plane.And this is a design without ground plane
In my eyes: You never had a true "ground plane". You had a copper pour. But this far away from being a GND plane.
With a GND plane you never have current loops in the length of 150mm, and the return path is usually exaclty on the opposite side (layer) of the current carrying traces, which means the enclosed area is very small.
This results in
* stable signals
* low EMI
* good EMC
Klaus
I do not like the look of that C9 across the secondary, it
seems prone to take a -lot- of charge at 2u*200V and
will reflect a very low impedance to the primary on every
switching edge.
The only possible thing it could be good for is EMI / snubber
duty, but snubbers always have a series R.
Easy enough to lift one lead and see if stuff quits stinking.
It normally works but the transformer has to be split bobbin type to achieve higher leakage inductance.
I have seen couple of such designs. Temperature will be slightly in the higher side and efficiency will be lesser.
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