Halogen lamp PSU keeps burning fuse !!

[kc8adu]

Re: Halogen lamp PSU keeps burning fuse !!

42v=36v system.
230vac will blow it up as you found.

[budm]

Re: Halogen lamp PSU keeps burning fuse !!

Filter caps are rated at 50vdc, so at 36VAC (about 50V on the cap after the bridge) is still too high.

[SM-Piyes90]

Re: Halogen lamp PSU keeps burning fuse !!

Filter caps are rated at 50vdc, so at 36VAC (about 50V on the cap after the bridge) is still too high.

So its rather 24 v rectified to 36 volts , makes sense i guess .

[budm]

Re: Halogen lamp PSU keeps burning fuse !!

24VAC Input x 1.414 - two Vf drop of the rectifiers = around 33VDC.

[stj]

Re: Halogen lamp PSU keeps burning fuse !!

maybe not.
the caps may be in series.
we cant see the tracks on top of the board.

*i* think this is a lamp ballast for an aircraft or boat with a 42v input that will probably already be DC.

you could email the maker with the part number on the sticker & ask.

[budm]

Re: Halogen lamp PSU keeps burning fuse !!

If it is made for DC there will be no 4 rectifers diodes on that board.
Post 29 shows the bottom side as I requested but I did not trace out the connection yet, I can see that the filaments are connected in series.
Easy enough verify if the caps are connected to the Bridge out put + and -, also easy to check if the caps are in series or in parallel.

[SM-Piyes90]

Re: Halogen lamp PSU keeps burning fuse !!

You are right stj .

Just checked the bottom tracks and also powered it up with 24 AC , i get 16 volts on each capacitor that are in series, also the IC is getting around 15 volts .

But why they have used 50 v caps if its only for 16 volts ? maybe its not 24 volts.

[budm]

Re: Halogen lamp PSU keeps burning fuse !!

So if you check the resistance + of one cap is connected to the - of the other cap?
- to - of each cap shows <1 Ohm?
So far it looks like bridge drive are the two MOSFET in series and another half bride are the two caps.

[SM-Piyes90]

Re: Halogen lamp PSU keeps burning fuse !!

So if you check the resistance + of one cap is connected to the - of the other cap?
- to - of each cap shows <1 Ohm?
So far it looks like bridge drive are the two MOSFET in series and another half bride are the two caps.

Nop only from + to - thats <1ohm .

[budm]

Re: Halogen lamp PSU keeps burning fuse !!

See an108 app notes in post 48, that is more likely is what is being used on you board.

[SM-Piyes90]

Re: Halogen lamp PSU keeps burning fuse !!

See an108 app notes in post 48, that is more likely is what is being used on you board.

I have just took a look at it . it appears that the mosfets are switching the half rectified voltage .

[budm]

Re: Halogen lamp PSU keeps burning fuse !!

This is what I see based on your pictures, but since it is double-sided board I cannot see top traces too well on the top side.

[SM-Piyes90]

Re: Halogen lamp PSU keeps burning fuse !!

Yes bro , you got the idea .
Its just that input voltages that needs to be known exactly , because i don't grasp a 50 v cap having only 16 volts .

[budm]

Re: Halogen lamp PSU keeps burning fuse !!

If you look at the app notes AN108. You will see the two caps are in series and they are connected to the + AND - of the power supply so the Voltage at the center point will be half of the power supply voltage.
Cap voltage rating will usually be twice the running voltage for safety margin, same for rectifier diode rating, you will want it to be at least twice the Voltage or more.
The voltage on the cap will not at 16V when the circuit is running.

[SM-Piyes90]

Re: Halogen lamp PSU keeps burning fuse !!

Exellent BUDM . i guess i need to read more about the smps designs.

[stj]

Re: Halogen lamp PSU keeps burning fuse !!

the cap voltage in that design may be irelevant (providing they arent too low),
the caps may have been chosen to handle the current, they probably have pretty high ripple rating.