Identification of AC side of LED driver please

woodersd · May 12, 2021

I have a replacement LED driver for a lighting circuit that had normal halogen G4 bulbs. The forum has already put me onto the right track by explaining that the LED do not draw enough current to allow the original transformer to operate, so thank you for that.

However, my problem is I have removed the board from the casing and now cannot work out which side is the AC inlet and which side is the DC output. (Sarky comments accepted as what a pillock).

[ElectriciansForums.net] Identification of AC side of LED driver please

Any guidance would be very much appreciated please?

Woodersd

littlespark · May 12, 2021

Well that was a daft thing to do....

is there no markings on the board as to what is in and out? On the bottom?

maybe someone else can confirm, but would the black component with the yellow tape be some form of transformer, being the first component from the 230v side?
I wouldn’t want to test that theory myself

SJD · May 12, 2021

A photo of the top of the board only doesn't really help, as the components could be wired in any order, but a photo of the PCB tracking underneath might.

MJPD29 · May 12, 2021

Maybe the clue would be on underside. Out of interest why did you remove it?

DPG · May 12, 2021

Judging by that big orange safety-rated capacitor on the right, I would say the top-right connector is the input.

However, I would want to be more certain before applying power. Maybe get the device number from the IC and the opto isolator. The data sheets for these will probably give the answer for definite.

Lucien Nunes · May 12, 2021

Agreed, the end with the yellow capacitor is the AC input, i.e. the board is rotated 180° relative to the cover in the first pic.

There are various clues. The transformer, C5 and U2 are the three components that straddle the isolation barrier which therefore lies almost straight across the board. U2's LED (pins 1 & 2) must face the output side and its phototransistor towards the input. The main IC, the MOV and the MKP capacitor must be on the input side. The 220μF 35V electrolytic is the output smoother, etc.

would the black component with the yellow tape be some form of transformer, being the first component from the 230v side?

It is indeed the transformer, however in a typical SMPSU it is electrically nearer the output, especially in a larger unit with power factor correction. The incoming AC is filtered (to keep the noise in), rectified, boosted by the PFC converter and smoothed to give the DC bus voltage. This is chopped at high frequency and fed into the transformer primary. On the secondary side of the transformer it merely needs to be rectified and smoothed to provide the output DC.

In a tiny unit like this or a wall wart, all the control electronics are on the primary side. All they require from the secondary side is the voltage feedback via the opto-isolator.

Timbo · May 13, 2021

@Lucien Nunes you are an amazing fount of knowledge!

Lister1987 · May 13, 2021

Timbo said:
@Lucien Nunes you are an amazing fount of knowledge!

Ah but does he sport a impressive purple beard like bigclivedotcom and have an unhealthy obsession with spirits and sodastream?

Lucien Nunes · May 13, 2021

No beard (never had one), no Sodastream (had one in the 90s), significant interest in certain spirits (not the ghostly kind).

DPG · May 13, 2021

Wasn't it Davesparks who had the purple beard?

Timbo · May 13, 2021

Lucien Nunes said:
No beard (never had one), no Sodastream (had one in the 90s), significant interest in certain spirits (not the ghostly kind).

These might interest some, significantly ?

woodersd · May 14, 2021

Lucien Nunes said:
Agreed, the end with the yellow capacitor is the AC input, i.e. the board is rotated 180° relative to the cover in the first pic.

There are various clues. The transformer, C5 and U2 are the three components that straddle the isolation barrier which therefore lies almost straight across the board. U2's LED (pins 1 & 2) must face the output side and its phototransistor towards the input. The main IC, the MOV and the MKP capacitor must be on the input side. The 220μF 35V electrolytic is the output smoother, etc.

It is indeed the transformer, however in a typical SMPSU it is electrically nearer the output, especially in a larger unit with power factor correction. The incoming AC is filtered (to keep the noise in), rectified, boosted by the PFC converter and smoothed to give the DC bus voltage. This is chopped at high frequency and fed into the transformer primary. On the secondary side of the transformer it merely needs to be rectified and smoothed to provide the output DC.

In a tiny unit like this or a wall wart, all the control electronics are on the primary side. All they require from the secondary side is the voltage feedback via the opto-isolator.

Perfect. Thank you so much.

Identification of AC side of LED driver please

woodersd

littlespark

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SJD

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MJPD29

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DPG

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Lucien Nunes

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Timbo

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Lister1987

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Lucien Nunes

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DPG

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Timbo

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woodersd

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