120vac LED light bulb

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gary350

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I am curious about the circuitry of this LED light bulb. I assume it has a voltage step down circuit? What step down voltage does the circuit board need? What voltage does each of these 16 LED lights need? Circuit board has 2 parts I have never seen metal things with metal pin sticking straight up from the center?

I had no trouble melting off the round bulb part. I have not been able to get the rest of the light apart it is very thick plastic it took soldering gun a while to melt a small dent in the side. Circuit board will not come out.





 
The two metal parts are connectors. That is where the 120 Vac from the lamp socket enters the board. L is for line, the bottom tip contact. N is for neutral, the threaded body contact.

There are more parts on the bottom side of the board. BD probably stands for Bridge diode, a 4-diode assembly common in power supplies. U1 probably is the switching power supply controller and high voltage switching transistor all in one. Power Integrations is a big name in these components. The round silver thing in the middle is an aluminum electrolytic capacitor.

ak
 
Hmm, 16 LED at (if around 120V A/C) ... rectification can result up to 130 or so volt. LED should be around 8 or 9 V drop each. The full bridge rectifier and capacitor result a DC Voltage and the "Chip" is a current limit regulator with an external resistor or resistor divider to set the current value that the IC limits across the LED's. The D-pack IC usually have a relatively low voltage of about 6V or 7V DC, tho that by manufacturer can vary without any details on the IC And should be at the end of the LED string in series. That MELF resistor (F1) may be the discharge resistor for the removal of voltage from the capacitor, or the larger SMD resistor (R3). The R1 may be the current limiting resistor for the IC.

The wires are pin clipped from the base plate, which is aluminum or similar (heat sink). The L (Load) and N (Neutral) leads are push insert connectors. Those can be carefully opened from the sides with a small flat blade screwdriver (sunglasses repair kit) and the wires extracted.


That LED bulb does appear to be a decent design.
 
BP5131D is an example LED driver that may be similar to that bulb. Or a close example. This one can handle some voltage tho. Some other types not so much.
 
Corrections to post #3:

Rectification results in (120 x sqrt2) - 2 x Vf = 168 V peak, not 130 V.

White LEDs have a Vf around 4 V.

L stands for Line, not load.

F1 is a fuse.

ak
 
168v / 16 LEDs = 10.5v each LED. If LEDs are 4v each = 64v total what keeps them from burning up.? If LEDs are in series 104v has to get dropped. Capacitor in center says 200v 10uf.
 
Unless you know the part number of U1, my guess is that it is not a linear regulator. The underside of the pc board contains the rest of the components of a switching power supply.

ak
 
The bulb probably does not have a switching power supply. Rather, it probably has a capacitive dropper, with U1 being a current regulator chip. Check out Big Clive on YouTube - has had done autopsies on dozens of bulbs, complete with schematic diagrams and clear explanations of how each bulb works. If you really want to understand how LED bulbs work, check out Clive's videos.

A capacitive dropper circuit is similar to using a series resistor to drop voltage, but a capacitor's reactance (rather than the resistance of a resistor) is the key element. Little power is lost in a capacitive dropper.
 
JonSea said:
capacitive dropper circuit
Click to expand...
There is no high voltage capacitor in the top of the PCB. But like mentioned many time we need to see the other side of the PCB.
OR
We need to see the part number for U1.
Also nice to know what is written on C1, the large capacitor in the center of the board. (what voltage)
 
As I suggested, watch some of Big Clive's videos. He has dissected a large number of similar LED bulbs. A capacitive dropper is often in the base, not on the circuit board with the LEDs.

Sunbeam bulbs are sold at The Dollar Store - i.e., they cost a buck a piece. They are going to be made as cheaply as possible. It's extremely unlikely there is a switching power supply hidden in that bulb.
 
Here are a few examples. Looks like the first one has the same current regulator chip.



 
An obvious concern here is if the bulbs are dimmable or not?, presumably a non-dimmable bulb has a SMPSU inside, so keeps the brightness constant, where a dimmable one will be a simple capacitive dropper and brightness will be subject to input voltage.
 
Nigel Goodwin said:
presumably a non-dimmable bulb has a SMPSU inside, so keeps the brightness constant,
Click to expand...
Some switching power supplies are dimmable. They keep the LED current constant but if they find the power line has a dutycycle then they turn off the LED current to match.
 
I doubt that U1 is a switch mode device. If it were, it would probably need more than 3 pins.
 
Let's start with what we know. Sunbeam is a brand sold at the Dollar Store for, you guessed it, a buck.



This is the same bulb Gary has, with the identical model number.



This is a 9 watt bulb, rated for 120VAC only. Therefore, based on the price point and voltage rating, a switcher is extremely unlikely.

The package the bulb comes in echos the same 120VAC, 60 Hz rating.



So what's inside? What we see on top of the lamp PCB is everything in this bulb.



The black chip to the left is a bridge rectifier. The silver object in the center is an electrolyte cap, the value of which is cut off.



The chip to the right is an RM9003A, a constant current LED regulator.

 
There's another cue above the capacitor. The terminals are marked L (for Line) and N (for Neutral).



And on the back side of the aluminum circuit board.....



And nothing inside the base.



The only heat sinking beyond the circuit board is a Coke-can-thick layer of aluminum inside the fairly thick plastic housing.

The RM9003A circuit diagram is shown here - a line-voltage-input constant current regulator. This bulb adds an electrolytic cap to reduce flicker.

 
Here's the data sheet for a virtual clone to the RM9003A from Diodes Inc.

There's no reason the bulb shouldn't work on 50Hz or DC power, and with the possible exception of the electrolytic cap, on 240 volts as well.

These are pretty neat devices which automatically reduce the current to the LEDs when they get too hot.
 
JonSea said:
These are pretty neat devices which automatically reduce the current to the LEDs when they get too hot.
Click to expand...
That explains why at night, my solar garden light (that is indoors) turns off when I turn on the LED room light then turns on after the cheapo Chinesy light heats up. Before I noticed the solar light detecting less light, I thought the dimming was my vision adjusting to the brightness which happens.
My LED light has 72 surface-mounted LEDs and is rated at 120VAC/0.25A which is 30W and it is way too bright.
 
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