Check my psu board!

[JAY X]

Hi,

I have  designed a  dual psu board based on lm317/337 and some lm78xx  regulators.  The transformer will be a 10va and current draw about 200ma, dispite it is depicted a 22va trafo.. sorry.. :

All the components, included the emi filter and transformer, are on the pcb.

1. There are some 230v traces under the transformer.

1b. Important question ¿ is it important trace separation, how much? some say about 8mm between 230v traces....

2. Both grounds 230v ac ground and psu ground (first rectifier capacitor) get together with independent wires to the CHASSIS gnd point.  I know i could join both grounds together with an X2 cap.... it is another option....

attached are the pictures and schematics...

The values can't be read properly on the schematic... but after the rectifier i placed 2 x 2200uf 35v caps 2.2ohm resistor and 2200uf 35v cap. then 100nf --> lm317.  47uf/1k3.  1n4007/100R--> 100uf --> 100nf --> output idc connector.

The unregulated rail is 10ohms/1000uf35v.

The wire that gets back to the gnd pin at the IEC connector, is to join together the secondary ground to the primary ground at the gnd CHASSIS point.

The emi filter is a pcb type PREMO  PE3V

Fuse 63maT

Transformer : 10va pcb type

Any opinion is wellcome!
JAY X

 

[JAY X]

Here is the layout top layer view

The traces that go to the connector N2 L2 N1L1 , ¿¿do you think they have enough separation??. They carry 230v ac to the connector, where i attach  an ac switch which cuts neutral and live.

 

[JAY X]

and here is the psu layout bottom layer

The two vertical traces near the ground plane of the psu come from the transformer secondary and enter the rectifier bridge 4 pins SIL type.

The two horizontal traces  joins the transformer primaries. The right most pin is very near the trace going to the bridge rectifier...¿should i worry about it?...

 

[buildafriend]

Looks nice.

Respectfully, I'm wondering if mounting the toroid on the the PCB is a good idea. It's nice for space saving but it can radiate. I guess it will depend on how how strong the lines of flux are and how sensitive the circuit is.  I've been told that the 783 is superior the to the 337 but for the the bipolar supply 337 and 317 are common.

Good luck I hope this works out!

 

[Walrus]

Your relay supply may work better if you redo C18 so that its negative end goes to common, and the junction of the 10 Ohm resistor and positive of C18 go to the output connector......

 

[JAY X]

Hi,

Yes, its an error of the schematic... the cap negative goes to ground...

Respect the transformer, my main worry is to know if the 230v AC lines i places below the transformer, may affect it or the rest of the psu  due to EMI, Maybe from the EMI point of view,  it is not good practice to place these tracks below the transformer.

Besides i think they need more separation in between... like 8mm or more..  in the layout they are separated 5 or 6 mm.The circuit to which is connected the psu only draws 200ma max.

The TL783 only can supply 700ma maximum.  Both LM317/337 can supply up to 1.5 amperes each.

Jay X

 

[Samuel Groner]

See e.g. http://www.smps.us/pcbtracespacing.html for the required clearance.

I don't have time to look at your layout in sufficient detail, but the most significant coupling mechanism for HF signals is most likely through the interwinding capacitance of the transformer. The stray capacitance of PCB traces is very small in comparison.

Samuel

 

[Speedskater]

I would not connect the AC line Safety Ground/Protective Earth to the DC supply Common. I would connect it directly to the chassis near the EMI line filter.

 

[JAY X]

Hi Speedskater!

Ok, the ac safety ground near the emi filter...

But, ¿ what about the ground wire from the filter cap (the third one,  looking from top to bottom) to the safety ground..??

I think it would be better take this wire from the ground point of the regulator.... but i'm not sure.. :-\

This wire helps connecting the secondary of the transformer to AC safety ground.

Another way would be connect the primary ground to the secondary ground via an X2 capacitor. maybe 10nf.

Thank you for your help!

Jay x.

 

[Andy Peters]

Hi Speedskater!

Ok, the ac safety ground near the emi filter...

Use an AC entry module which includes the EMI filter and the switch all in one unit.

-a

 

[Speedskater]

Everything before the transformer primary goes to the chassis Safety Ground connection near the EMI filter and cord entrance.
Anything after the transformer secondary is not part of the Safety Ground.  It connects to the DC supply common/circuit common.  Yes they are galvanically connected through the chassis, but they have different tasks.
I try to avoid using the word ground, it's way too confusing.

 

[JAY X]

Hi Speedskater!


From your post: "Yes they are galvanically connected through the chassis, but they have different tasks."

So it seems that, yes, the secondary DC common should connect to the chassis ground... but in a different  way...


Jay x

 

[JAY X]

Hi All!

Finally i modified my psu design, and opted for an external EMI filter. Its safety ground lug connected to chassis with a short connection.

And i connected the secondary common from the regulators, to chassis at a separated point near the safety ground with a wire a lug and a screw.

Jay x

 

[tmuikku]

a practical point: avoid large capacitors near regulator if possible. it is hard to assembly the heat sink. many times regulators are on the pcb edge so you could possibly use larger heatsink / attach to chassis. at least access to mounting screw with screwdriver is easy

also, electrolytic cap lifetime is shorter near hot regulator.

maybe these aren't any concern to this particular pcb. just my observations along the way

 

[moamps]

If the transformer is intended for 230V primary voltage  as you stated, then you did a big mistake by connecting primaries in parallel. Also, you did a mistake with secondaries routing IMO.  And way the connector for power switch is not placed near the EMI filter?