LED driver directly from 230VAC ?

[Externet]

Hi all.
Do you know of another brand of current regulator to drive LEDs directly from 240VAC ? I cannot find the one I saved its datasheet now. This is similar from ON semiconductor :

:

 

[D.A.(Tony)Stewart]

Any low dropout CC circuit can be put in the correct polarity on the high side of DC or the low side.
An LM317-ADJ is the simplest with Rs to define current. However this requires you to match the supply voltage to the sum of all Vf's within 10% for example, then the heat dissipated in the LDO rises with this error in voltage drop raises the temperature and must be kept cooler than 85'C for reasonable reliability.

 

[BradtheRad]

Current regulation with 2 NPN. Reducing supply voltage by half alters current through led only slightly.

 

[Externet]

Thanks. Shifting a bit the subject; on post #1:
1.- can the bridge rectifier be replaced by one single diode ?
If yes,
2.- Will the circuit work more 'relaxed' on lower voltages from a single diode ?
3.- can that diode in place of the bridge rectifier be a LED as the ones on the right side of the circuit ?

 

[BradtheRad]

According to specs the CCR is only made for current in one direction. The same could be true of any current regulating circuit. The full diode bridge prevents current in the opposite direction through the circuit.

Moreover ordinary led's lack tolerance for high reverse voltage. It's risky even to assume we can put many many in series. To test an led's reverse voltage could destroy it. It's a good idea to install a safety diode in series rated for the highest expected reverse voltage.

There's nothing wrong with building two identical circuits so one operates during each half of the mains cycle. Using a current regulating circuit in each direction.

 

[D.A.(Tony)Stewart]

The base can be biased from 1 or 2 LEDs above the collector.

1 diode will flicker badly, 4 will operate at twice the frequency but can be 1 part called a diode bridge.

 

[Externet]

The full diode bridge prevents current in the opposite direction through the circuit.

Thank you. A single diode instead of the full bridge also prevents current in the opposite direction, does it ?

 

[KlausST]

Thank you. A single diode instead of the full bridge also prevents current in the opposite direction, does it ?

Yes.
Indeed I did not expect this question from a 20 years member of an electronics forum.

Klaus

 

[dick_freebird]

I've got "night light" bulbs which have this scheme.
The "CCR" is a chip resistor. Since line voltage is pretty
stable (in the USA) there's little value in a LDO or even
any attempt at line regulation. Who cares if the bulb
looks like 3W or 5W when the "4W equivalent" is fiction to
begin with?

Single diode will make more flicker than a FWB.

 

[D.A.(Tony)Stewart]

1.- can the bridge rectifier be replaced by one single diode ?

It "can" but half the time off means 50% luminous intensity and power and slower eye flicker, yet common in older cheap Xmas string lights.​

2.- Will the circuit work more 'relaxed' on lower voltages from a single diode ?
If 50% less power and more than twice the flicker effect is relaxed, maybe.
3.- can that diode in place of the bridge rectifier be a LED as the ones on the right side of the circuit ?
No. LEDs cannot withstand more than 5V Peak Inverse Voltage before the leak towards avalanche failure.

1. The CCR circuit will likely have a maximum P=VI dissipation at ambient temperature when the line is 10% above nominal for V is the voltage drop from the peak voltage.
2. If insufficient LEDs are in series, the CCR circuit will overheat from excess V drop.
3. Even a FW bridge will flicker since the LED fades out 15% below the peak voltage thus those with a ACDC light controller can achieve the brightest effect without overstressing the current at low duty factors with continuous current.
4. Normally LEDs are rated to only a maximum rating of only 50% over nominal current for rated power dissipation and assumes adequate method of cooling.

 

[Externet]

Thanks.

" ... 3.- can that diode in place of the bridge rectifier be a LED as the ones on the right side of the circuit ?
No. LEDs cannot withstand more than 5V Peak Inverse Voltage before the leak towards avalanche failure. "

What is the peak inverse voltage on the LEDs at right of the CCR on the circuit, and what is the peak inverse voltage of the diodes at the left of the CCR in that same post #1 circuit, which are not a full bridge rectifier but a paralleled series of two ? Which by the way; would produce flickering ?

 

[D.A.(Tony)Stewart]

All LEDs =-5V max
Diodes may be 1kV or more if selected

 

[KlausST]

What is the peak inverse voltage on the LEDs at right of the CCR on the circuit, and what is the peak inverse voltage of the diodes at the left of the CCR in that same post #1 circuit

Often I ask myself similar questions.
Then I open the datasheets ... and get the answers.

Klaus