flippineck
- Sep 8, 2013
- 358
- Joined
- Sep 8, 2013
- Messages
- 358
I have a small circuit board out of a cheap chinese LED light. Live and neutral arrive at the board from a 13A 240V UK AC mains plug. Live then passes through a fuse before arriving on one side of a 0.1uF capacitor. Neutral tracks directly across the board to the other side of the capacitor.
The capacitor has what looks like a green VDR connected across it labelled on the PCB as MOV1.
Tracks then lead from each side of the capacitor & VDR, across to two terminals of what looks like a surface mount bridge rectifier labelled as BD1.
The remaining two terminals of BD1 have another VDR connected across them, labelled as MOV2. On the PCB these points are labelled V+ and V-.
Two flying leads then exit the board and head off to the LED PCB, which is well heatsinked and has an eight-legged IC, three resistors and a capacitor on it along with an array of 15 LEDs.
Powering up the light, I measured something in the region of the mid 200's of volts across the small PCB's V+ and V- (output) points.
I had thought that the small PCB was some form of capacitor dropper power supply, and was hoping to find a low voltage output feeding the LED board. The plan was to dispense entirely with the mains power supply, just snip it out, and then power the lamps from a 12V car battery if possible somehow. Either directly or via some kind of simple replacement mini-PSU
So.. I was suprised, and as soon as I saw 200-something on the DMM display I switched everything off. Just glad I'd used my basic electrician training and started at the top voltage range on the meter and assumed from the start there was always a chance I'd encounter mains or higher where I didn't expect it!
Modifying these lamps for 12V would make economic sense to me since these lights are extremely cheap and I need loads. They're on sale at a well known high street UK chain store so I doubted they would suffer from the 'live case' problems a lot of cheap LEDs seem to.
What is the circuit on the small PCB I described? I'm figuring it's some kind of filter / rectifier / surge arrestor but not a dropper PSU. What would be the normal output from a circuit such as this, < 240V, 240V, or >240V?
I'm figuring because of the encapsulated nature of the LED board and the lack of any markings on it's eight legged chip, if it requires a high DC voltage for operation I would need to modify these units by replacing the small PCB with some kind of small boost converter with a sufficient power handling capacity, and also ensure the heatsinking were sufficient for the modified configuration.. a lot of work so I hope I can just find something on ebay that works off 12V from the get-go!
All the same, any info would be interesting..
The capacitor has what looks like a green VDR connected across it labelled on the PCB as MOV1.
Tracks then lead from each side of the capacitor & VDR, across to two terminals of what looks like a surface mount bridge rectifier labelled as BD1.
The remaining two terminals of BD1 have another VDR connected across them, labelled as MOV2. On the PCB these points are labelled V+ and V-.
Two flying leads then exit the board and head off to the LED PCB, which is well heatsinked and has an eight-legged IC, three resistors and a capacitor on it along with an array of 15 LEDs.
Powering up the light, I measured something in the region of the mid 200's of volts across the small PCB's V+ and V- (output) points.
I had thought that the small PCB was some form of capacitor dropper power supply, and was hoping to find a low voltage output feeding the LED board. The plan was to dispense entirely with the mains power supply, just snip it out, and then power the lamps from a 12V car battery if possible somehow. Either directly or via some kind of simple replacement mini-PSU
So.. I was suprised, and as soon as I saw 200-something on the DMM display I switched everything off. Just glad I'd used my basic electrician training and started at the top voltage range on the meter and assumed from the start there was always a chance I'd encounter mains or higher where I didn't expect it!
Modifying these lamps for 12V would make economic sense to me since these lights are extremely cheap and I need loads. They're on sale at a well known high street UK chain store so I doubted they would suffer from the 'live case' problems a lot of cheap LEDs seem to.
What is the circuit on the small PCB I described? I'm figuring it's some kind of filter / rectifier / surge arrestor but not a dropper PSU. What would be the normal output from a circuit such as this, < 240V, 240V, or >240V?
I'm figuring because of the encapsulated nature of the LED board and the lack of any markings on it's eight legged chip, if it requires a high DC voltage for operation I would need to modify these units by replacing the small PCB with some kind of small boost converter with a sufficient power handling capacity, and also ensure the heatsinking were sufficient for the modified configuration.. a lot of work so I hope I can just find something on ebay that works off 12V from the get-go!
All the same, any info would be interesting..
