Powering COBs with AC and bridge rectifier

BobCajun

BobCajun

Well-Known Member
I recently was looking at some LED string lights and noticed they have some that run from AC without a full driver, just a small rectifier on the cord. So I did a little research about powering LEDs by converting 110 ac to 110 dc with a full wave bridge rectifier and it looks pretty simple. In theory, you could run 3 CXB3590s on 110v. I guess you would need a current limiting diode (CLD) on it to keep it at a certain current.

Being that the drivers are actually more costly than the COBs they power, it would make a drastic reduction in price if all you needed was a few cheap components costing a few dollars. A 200v bridge rectifier costs less than $5. There's actually a company in Korea that sells AC COB floodlights, so apparently it's possible. Maybe they use special COBs though. Admittedly, a simple rectifier probably wouldn't produce the smoothest light around, but for plant growth it might not matter. Might need to put a heat sink on the rectifier though.
 
dandyrandy

dandyrandy

Well-Known Member
Current limit is the problem. Also using a linear device to regulate current isn't as efficient as a pwm driver. Hence the cost of the driver. It's basically a switch mode supply with current limit. Lot's of electronics inside.
 
BobCajun

BobCajun

Well-Known Member
dandyrandy said:
Current limit is the problem. Also using a linear device to regulate current isn't as efficient as a pwm driver. Hence the cost of the driver. It's basically a switch mode supply with current limit. Lot's of electronics inside.
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Yeah but would it work? Regular CLDs only handle very low current but something like this might work for regulating a current around 1-2 amps.
 
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dandyrandy

dandyrandy

Well-Known Member
Sure. You could use a Variac and a bridge rectifier. That circuit is a linear regulator. Series type. You have to remember if you have 2 amps of current and have to drop 3 volts across a device in linear mode p=e×i. 3 × 2 gives you 6 watts of heat.
 
BobCajun

BobCajun

Well-Known Member
dandyrandy said:
Sure. You could use a Variac and a bridge rectifier. That circuit is a linear regulator. Series type. You have to remember if you have 2 amps of current and have to drop 3 volts across a device in linear mode p=e×i. 3 × 2 gives you 6 watts of heat.
Click to expand...
I think a capacitor would need to be added to stabilize the voltage. That means it would burn out within a couple years but otherwise the voltage might be too variable. The idea is mostly to avoid a transformer but avoiding capacitors would also be nice. Maybe have to settle for buying the pre-built AC floodlights. The company is in Korea though.

Apparently you have to use the number of LEDs that comes close to the mains voltage x sqrt 2, to allow for the upper voltage variation. So you would need 4 COBs instead of 3, I guess, because it's 156v
 
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C

churchhaze

Well-Known Member
guod said:
no rectifer , done by the cobs itself
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You'll probably want to stick a smoothing cap on there... and scrap the whole idea all together.

Edit: Derp.. I just realized the futility of putting a smoothing cap before the bridge rectifier... :dunce:
 
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