LED driver design

Thread Starter

qwertyio

Joined Nov 7, 2021
8
led driver.jpeg
I want to make a led driver like this but with the output current at 1A. Can someone explain what I need to change in this circuit??
 

BobTPH

Joined Jun 5, 2013
4,769
That is not an LED driver, it is a transformerless power suoply.

The output would be 15V, not 12V.

And what the hell is a 225K capacitor?

Edit: Just realized 225 probably refers to 2200000 pF, or 2.2 uF.

Bob
 
Last edited:

ericgibbs

Joined Jan 29, 2010
15,349
hi querty,
Welcome to AAC.
If you modify that circuit for 1Amp at 12V, you would have to drop the voltage from 240V down to 12V at 1Amp. That would require at least a 300Watt dropper resistor.!!!

It's not feasible or safe to use that type of circuit for 1Amp.

E
 

Thread Starter

qwertyio

Joined Nov 7, 2021
8
Hi
On top of above
they are correct

are you sure the led requires 1amp??
Actually no. I want to make a 5 watt led lamp like this.
led array.png
I want to use led smd 5730, which in the datasheet use 3.3 Volt 150mA, 0.5 watts per led.
which means if I want to make it to 5 watts, then I have to use 10 leds. The circuit can be in series (10 pieces of led) or parallel (5 pieces by 5 pieces). this also means I need 500mA for parallel or 30 volts for series. This is why I'm asking if I can make the driver output 1 mA
 

ronsimpson

Joined Oct 7, 2019
2,007
That would require at least a 300Watt dropper resistor.!!!
The circuit in #1 is a capacitor supply. The cap does the divide down with out heat loss.
(10 pieces of led) or parallel
The circuit in post #1 is much like a constant current source not a voltage source. Getting 1A from it is very hard and require a very large capacitor. If you series all 10 LEDs then you need 33V at 150mA. (which that type of supply will do) You should run the LEDs a little less than the absolute max current.

The circuit was designed by some one that does not understand the operation of the supply. The 2.2uF 400V cap limits the current into the load. So a constant current was changed to a constant voltage by a Zener and then back to current by a resistor on the LED.

Make it simple.
1637936767579.png
In the most simple version I do not have a filter cap but you can add one. In the plot the voltage across the 10 LEDs is about 33 volts. (green trace) The current is 120 or 100hz pulses averaging about 150mA. (blue trace)
1637937645694.png
Note I would use a capacitor rated for power line use. R2 will run about 1.5 watt of heat. Probably should take that down to 16 ohms to get to 1/2 watt. I used 50V diodes just to show that you do not need 1N4007 high voltage diodes because the diodes do not see power line voltages. 1N4002 = 100V would be safer. LOL
Adding a 100uF 50V cap across the LEDs will reduce the ripple.

This type of supply is dangerous and will hurt you! If you normally work on live 220V power than OK but for normal mortals this is dangerous.
---------------------------
Do you use 220V or 110V? 50 or 60hz? That will change the current! I need to know. Use a small value of C1 to get the current down a little.
Pulses of current are fine for LEDs. Some lights operate that way and people don't even know or see it.
 

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Last edited:

ericgibbs

Joined Jan 29, 2010
15,349
Hi Ron
We used to make our own Radio receivers, in the R.A.F., for 0.3Amp Valve/Tubes heater power, using 4uF 400V caps, 230Vac 50Hz.

I also recommend that he does not build this project.

E
BTW: for his original 1Amp request he would require 12uF 400V caps, cheaper to buy a ~30V 0.2A transformer, and safer.
 

ronsimpson

Joined Oct 7, 2019
2,007
I am into using old cell phone chargers to power "toys". Every one has one not in use. Safe and free. The USB type are 5V and usually in the 1 to 2A range.

We used to make our own Radio receivers
There was a time then radios (some) lived on the power line with out isolation. The metal chasse was directly connected to one of the power wires. (never know which one, 50:50 chance)
 

Thread Starter

qwertyio

Joined Nov 7, 2021
8
so.. the output voltage in this circuit always changes depending on the led used?
Note I would use a capacitor rated for power line use. R2 will run about 1.5 watt of heat. Probably should take that down to 16 ohms to get to 1/2 watt. I used 50V diodes just to show that you do not need 1N4007 high voltage diodes because the diodes do not see power line voltages. 1N4002 = 100V would be safer. LOL
Adding a 100uF 50V cap across the LEDs will reduce the ripple.
how do you get these values? especially for R1 and R2

By the way, I'm using 220V 50Hz
 

old_beggar

Joined Jan 29, 2021
39
It would be safest to use a transformer to reduce the (potentially lethal) voltages down to a safer level (though you still need to build it with safety in mind), then the LED control is easier - why can't you use a transformer?
 

ronsimpson

Joined Oct 7, 2019
2,007
how do you get these values? especially for R1 and R2
R1 across the capacitor is there to discharge the cap when power is missing. Its value is not important. 1M to 10M. It needs to handle 250V across the part to do not use a very small part. (no 1/4 watt)
R2 is there to remove spikes that come from the power line. It forms a low pass filter. Value is not critical. I often see a 100 ohm 1W resistor there. I changed the value down so you can use a 1W resistor at this higher current level. This type of power supply passes higher frequency energy into the load. With out R2 high frequency noise will send extra energy to the load. This is very undepictable. R2 helps strip off the HF noise. R2 is also a fuse. If the cap shorted then this resistor will open up like a fuse.
 

Thread Starter

qwertyio

Joined Nov 7, 2021
8
It would be safest to use a transformer to reduce the (potentially lethal) voltages down to a safer level (though you still need to build it with safety in mind), then the LED control is easier - why can't you use a transformer?
this is for my school project. which is where we have to make an unsafe transformerless led driver
 

ronsimpson

Joined Oct 7, 2019
2,007
this is for my school project. which is where we have to make an unsafe transformerless led driver
OK
I have a 220 to 220 isolation transformer with fuse/breaker. It makes the experimenting a little safer. It is not a good idea to connect a scope to this supply because "ground" is not ground! A battery powered meter is fine. Do not solder on the parts when it is plugged into the wall.

Do you have LT SPICE program? I posted the file.

Maybe use a 1.5uF or 1uF cap and run the LEDs at less than max power.
I use "X" or "Y" caps but probably any 400 to 1000V cap will work. Ask if you have questions.

I have sold products like this. It needs to be insulated from people! I double insulated my products to get government approval. Do not let people touch the LEDs. Put it in a clear plastic box.
 

old_beggar

Joined Jan 29, 2021
39
" this is for my school project. which is where we have to make an unsafe transformerless led driver "

Then someone at your school should know better than to endanger its students - I suggest you report them.
 

ronsimpson

Joined Oct 7, 2019
2,007
Then someone at your school should know better than to endanger its students
You are not there and we don't really know ...............
Most school projects I help with, nothing really gets build. SPICE is King and no solder was used in the making of these projects.

In school we made Radar transceivers, off line power supplies and Jacobs Ladder machines and I installed antennas 750 feet above ground, and .......
At school some people did sky diving, scuba diving, flight school, mountain climbing, some classes went to South America for the semester and played in the jungle, and ........
In school, the only ones to get hurt were drinking and driving.
 

Ian0

Joined Aug 7, 2020
4,865
View attachment 253604
I want to make a led driver like this but with the output current at 1A. Can someone explain what I need to change in this circuit??
You need a much larger value for C1 - it needs to be about 15uF (and R2, R3 and R4 need to be much smaller).
There's a few reasons that it's not usually done this way. . . .
1) Your LED luminaire that runs at 1A also draws 1A from the mains. That's 230VA. A lighting circuit is generally fused at 6A. So, you can only run 6 of these off a lighting circuit.
2) A 15uF Class-X (230V AC rated) capacitor is BIG and EXPENSIVE. It is bigger than a switched-mode supply that would run your LED at 1A, but only draw 30mA from the mains supply.

Why it is unsafe? There are thousands of LED luminaires with capacitive-dropper supplies sold every day (but probably very few that run at 1 Amp). Why is it any less safe than a fluorescent tube that uses an inductive supply?
 
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