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I have some questions on bridge rectifiers and how they work/output current and voltage, see details for full info. Answered

If I use a bridge rectifier to convert AC 110V into "DC" 110(154V), I'm guessing the amperage rating on the rectifier is how much current will be available to use vs the voltage being output as well? The reason I put 154 volts is because peak voltage is 110ac times 1.4. I'm using this for LEDs, just to provide some more info. The bridge rectifiers I have are rated at 200V and 1.5A.?


Phil B

9 years ago

Someone used LEDs on alternating current by calculating how many LEDs would be required to dissipate 110 volts (more like 117 volts). They wired together two banks of LEDs, each bank in series. They connected the banks of LEDs in opposite polarity. One of them took care of one half of the sine wave, the other took care of the other half. There was no need for a separate rectifier. Although blinking, the LEDs would appear to be "on" continuously. LEDs that are "on" continuously actually are not. They pulse to reduce heat and power consumption, but still appear to give a solid light. I wish I could say I thought of this idea, but it was someone else's and I read it.

Oh my god!! This is awesome!! I could use this info for sure on another project!! Never even thought about this.

Electronics are cool !!

That's exactly how LED "Christmas light" strings are setup. May not be the most efficient, but it works.

You can also add a bridge rectifier to LED christmas lights to make them about twice as bright because they light up during both parts of the AC cycle. If you add a capacitor (make sure it's a HV type such as from a PC power supply) they get even brighter because they're running at a continuous ~150V... but probably won't last as long.

you will find voltage reduce's by .6v per each diod it pass through in a full wave bridge it passes through 2 in each direction so its (120 minus 1.2v) and as for current. the max current of yours is 1.5A so it wont burn out a diode untill you draw more than that through it. you should select the bridge you need after you know the resistance of the load you are to power not the other way around.. p.s use RMS values to calculate the current too.

Would a full wave bridge rectifier work ?

If you're not using a capacitor on the output of the bridge rectifier you should consider the voltage to be 110VDC. If you are using a capacitor, several things should be considered but mainly that the voltage rating of the capacitor must be at least 160VDC else you risk smoke and possible explosion! Be Aware! LED's have to have the current through them limited! For instance: Let's say you want to light 10 LED's. Wired in series, each one drops about 1.7 volts so the total voltage dropped by the LEDs is 17 volts. 110VDC minus 17 volts equals 93 volts that must be dropped by a resistor that will limit the current to about 20mA. That is 93 divided by .020 equals 4650 ohms, 4.7K. Next the wattage for the resistor must be determined 93 times .020 equals 1.86 watts or a 2 Watt minimum resistor. If you use a capacitor then your calculations should be made using 155 volts instead of 110. Have Fun!

remember that the AC voltage (without accounting for rms 1.4 factor) is approximately the same as the rectified and averaged (smoothed dc voltage - since an AC waveform isnt power for the full sine wave. you want a 200v rectifier for 110ac, and it will output approximately 110v dc after it's smoothed with caps. 110v @ 1.5 amps is 150 watts++ of leds. Thats a LOT of leds.

Sounds to me like the bridge rectifiers will handle the voltage, but you shouldn't draw more than 1.5A from them regardless. Still 1.5A @ 154V is quite a lot of power for LEDs - how many?
The voltage drop over the silicon will be the same for a fixed current regardless of the input voltage - power dissipated in the rectifier is proportional to IR2 even if it's 12V input for example.