Where to add dimmer in ac led bulb?

[alex ezorsky-lie]

My goal is to build a dimmable led light of 75-100w in the cheapest and easiest way possible for video lighting.

As an experiment I bought this $30 75watt AC bulb from amazon. Its crazy bright but of course not dimmable (it flickers if attempted). My thought was that I could add a dimmer to the built in driver. Also if I could add an optional dc input that would be awesome too.

I took it apart and tested the output voltage and current leading to the LED’s and its 75v and .83 amps. Being that I am a novice with real circuitry I am at a loss as to where in this little ac-dc driver I could add a dimmer with the least complexity. My instinct is to do it on the output leads since thats the only part I understand but considering the board itself is already regulating voltage I figured there might be a more elegant solution. Also not sure how or where I could put dc input leads without frying things.

Thanks!

(the little plug is for the fan)

 

[Bluejets]

cheapest and easiest way possible for video lighting

For what you want to do, this statement becomes null and void.

 

[Audioguru]

There are three identical circuits on the circuit board.
The IC is made by SI of China.The datasheet for the IC shows a circuit and the IC has two pins and three resistors that are not explained. A dimmer is not shown.

 

[Bluejets]

This one explains to a degree.
I'd say 3 drivers for 3 internal LED arrangements.
Could be paralleled for current. Who knows.
With the 3 bridges on the V- output it looks like it might be.
Board say 1506x3-150W.....??
Mostly chip is a mosfet.
Fairly standard chip design these days for LED drivers.

https://datasheetspdf.com/pdf/1112308/SISemiconductors/SIC9554A/1

Would be simpler to arrange say 3 or 4 (or whatever) smaller LED lights and switch them in and out for dim effect.

 

[hevans1944]

My goal is to build a dimmable led light of 75-100w in the cheapest and easiest way possible for video lighting.

As an experiment I bought this $30 75watt AC bulb from amazon. Its crazy bright but of course not dimmable...

Your "experiment" is a colossal FAIL.

Lessee... you want a dimmable, bright, LED light (presumably white) with 75 - 100 watts power input capability. Plenty of those available. Choose a reliable manufacturer (Cree would be my first choice) or take a chance on an Asian import, your choice. Cheap is not always better. Be sure the LED you purchase is mounted properly on a heat sink of the appropriate size. Make sure you purchase a programmable constant-current DC power supply with a DC control input to power the LED. Use the $30 light to illuminate something else, like maybe your work bench.

 

[WHONOES]

The simple way to dim LED's is with PWM (Pulse Width Modulation).

 

[alex ezorsky-lie]

This one explains to a degree.
I'd say 3 drivers for 3 internal LED arrangements.
Could be paralleled for current. Who knows.
With the 3 bridges on the V- output it looks like it might be.
Board say 1506x3-150W.....??
Mostly chip is a mosfet.
Fairly standard chip design these days for LED drivers.

https://datasheetspdf.com/pdf/1112308/SISemiconductors/SIC9554A/1

Would be simpler to arrange say 3 or 4 (or whatever) smaller LED lights and switch them in and out for dim effect.

In the datasheet there is a pin for Radj, do you think putting a pot there could dim? I would definitely say the 3 circuits are for parallel because there are only 2 wires going to the led panel.

Thanks!

 

[Harald Kapp]

Without a thorough analysis of the circuit design it is imho not possible to modify this lamp.

In the datasheet there is a pin for Radj,

This resistor is for adjusting the overvoltage protection of the IC. It is not intended to control the LED current.
You'd use R_ISEN tlo adjust LED current (datasheet, page 6). However, you't have to adjust the value for all three circuits simultaneously if, as suggested, the drivers are in parallel.

Could be paralleled for current. Who knows.
With the 3 bridges on the V- output it looks like it might be.

Looks like the design is originall meant to drive three LED strings (3 V- pads visible) and the bridges are an option, possibly to save cost.

this $30 75watt AC bulb from amazon

For a tad more you can get an LED videolight with dimmable brightness and changeable
color temperature.

 

[alex ezorsky-lie]

Without a thorough analysis of the circuit design it is imho not possible to modify this lamp.

This resistor is for adjusting the overvoltage protection of the IC. It is not intended to control the LED current.
You'd use R_ISEN tlo adjust LED current (datasheet, page 6). However, you't have to adjust the value for all three circuits simultaneously if, as suggested, the drivers are in parallel.

Looks like the design is originall meant to drive three LED strings (3 V- pads visible) and the bridges are an option, possibly to save cost.



For a tad more you can get an LED videolight with dimmable brightness and changeable
color temperature.

Awesome thanks for your reply!
1. I totally understand why folks are suggesting I just buy video lights that do what I want. But just to be clear this light puts out about 7,000 lumens. Here is a video light of about the same price and it puts out only 1,300 lumens. If anyone can find me a light even close to this price with dimming and near 7,000 lumens I would love to see it.

2. I'm also getting a learning experience out of this.

 

[Harald Kapp]

this light puts out about 7,000 lumens. Here is a video light of about the same price and it puts out only 1,300 lumens.

That one is similar to what I had in mind. I have one of that kind and I'm satisfied. But you have an argument there concerning the max. intensity.

I'm also getting a learning experience out of this.

In that case you'll learn a lot more by building your own video light from scratch. As hop mentioned in post #5 buy a decent bare high power LED (like this one: 100 W for the price of 13 € - o.k., 100 W may be a bit over the limit ).
Then build an LED Driver from one of the many available chips.
Use an off the shelf power supply (the LED from my example requires 30 V ... 34 V at 3 A). to avoid having to deal with mains voltage directly. With the operating voltage in said range, you may also consider operating the Light from batteries. Agreed, you'll net hefty ones, but you'll be independent from a mains outlet. This could even be optional: mains or battery operated, whatever comes in more handy.

 

[dave9]

You want something warmer than 5600K color temperature and higher CRI. Just because someone makes some junk and markets it towards the video light market, does not make it suitable for a video light.

As is often the case, cheapest and easiest will yield the worst result and not by only a little bit.

 

[Harald Kapp]

Another issue you will experience with a single high lumen source is hard shadows due to the point source character of the light. You may be better of creating the high light intensity by using more small lamps arrayed over a larger area (as in the video lamp only using higher brightness LEDs). Mix LED lamps of different color temperature (bluish and yellowish) and you'll be able to adjust overall color temperature. LEDs with CR >= 95 % are available.

 

[dave9]

Since it is a single point, you could probably, effectively dim it 2 steps by just (switch) disconnecting 1 or 2 of the 3 circuits so only 1 or 2 of the 3 series of LEDs is powered. I mean switch them off at the input to the power circuit, not the output to the LEDs in case the circuit needs a load to be stable.