I Don't Understand

[petehall347]

Re: I Don't Understand

looks like a connector block ..
p.s there seems to be a stray bare wire melted into the wire nut .

[EasyGoing1]

Re: I Don't Understand

That looks to be non-isolated constant current power supply (HOT chassis, so I hope you are using scope without the safety connected which is dangerous or connect this board to isolation transformer), what are the P/N of IC U1, U2?

Look at the attached image ... the power comes in through that ... im assuming thats an isolation transformer?

U1
BP2326A
16D30A
DEG26 or OEG26 or CEG26

U2
BP5602
16C14A
BRG23

[i4004]

Re: I Don't Understand

OK, so when I said there was nothing on the underside of this board, I made a mistake ...

offcourse you did, there were no semiconductors on the top side, so nothing to rectify mains ac etc.

that small smps pos(like "cheap chinese piece of shit") has no power and that's why it starts to pulse as soon as you (over)load it, and it doesn't take much.

can you power it from pc psu?

[i like the signature signature, used to have same thing at another forum...]

[stj]

Re: I Don't Understand

recap that psu - the small ones anyway.

[budm]

Re: I Don't Understand

That looks to be non-isolated constant current power supply (HOT chassis, so I hope you are using scope without the safety connected which is dangerous or connect this board to isolation transformer), what are the P/N of IC U1, U2?

[EasyGoing1]

Re: I Don't Understand

Hey Budm,

What do you think about replacing this circuit with a capacitive dropper as STJ suggested?

[EasyGoing1]

Re: I Don't Understand

I do not understand the 'ORIGINAL CIRCUIT', what is the ORIGINAL CIRCUIT? The power supply module? You should also shows the bottom side of the board so we can see how the output section is setup, it may be setup as constant current source already.
So the second picture shows ripple (5V P-P) riding on top of 12.5VDC. at what test point is that?
15V source (based on you scope showing 5V per division with compensation with x10 PROBE) with 400 Ohms so the max shorted current will be 15V/400 Ohms = 37.5mA so how many LED's are connected in series with that resistor?

ORIGINAL CIRCUIT = Driver circuit installed in the lamp from the factory ... the "original" ... no modifications, and no additions to the output etc.

OK, so when I said there was nothing on the underside of this board, I made a mistake ... I was thinking of my other thread about the flashlight circuit ... this one does have stuff on the bottom ... here is the picture... I reversed one of the images so that the components line up properly ... you'll see what I mean ...

I have NINE LEDs in series but only 4 are working now ... here are the exact LEDs that I'm using:

[budm]

Re: I Don't Understand

I do not understand the 'ORIGINAL CIRCUIT', what is the ORIGINAL CIRCUIT? The power supply module? You should also shows the bottom side of the board so we can see how the output section is setup, it may be setup as constant current source already.
So the second picture shows ripple (5V P-P) riding on top of 12.5VDC. at what test point is that?
15V source (based on you scope showing 5V per division with compensation with x10 PROBE) with 400 Ohms so the max shorted current will be 15V/400 Ohms = 37.5mA so how many LED's are connected in series with that resistor?

[EasyGoing1]

Re: I Don't Understand

Is it really pulsing? What is the ON time and OFF time of the pulse being applied to the LED's?

So this is kind of interesting ... here is the voltage with the stock circuit powering the new LEDs with no other modifications:



and here is the same exact thing with an added 400Ω resistor in series



it definitely pulses on and off with the resistor in series ... by the way I tested this earlier with my ammeter and it still draws 170ma even with a series resistor in place and even when it flashes...

And are you using that constant current source circuit as you have shown to drive the LED's?

NO I canned that circuit.

What did you use to limit the current to the LED's? Just remember that LED is current device, you have to manage the current flowing through it, you do not hook them up to constant Voltage source and hoping it will not blow up, you use constant current source to drive LED.
That power supply board looks like capacitive dropper type.
Are there any parts on the bottom side of the board.

I am well aware that LEDs are a current sourcing device and that exceeding the rated current is bad juju and I know that you should never run them without a limiting resistor OR a constant current power supply.

and NO there is nothing on the underside of the board.

[budm]

Re: I Don't Understand

Is it really pulsing? What is the ON time and OFF time of the pulse being applied to the LED's?
And are you using that constant current source circuit as you have shown to drive the LED's?
What did you use to limit the current to the LED's? Just remember that LED is current device, you have to manage the current flowing through it, you do not hook them up to constant Voltage source and hoping it will not blow up, you use constant current source to drive LED.
That power supply board looks like capacitive dropper type.
Are there any parts on the bottom side of the board.

[EasyGoing1]

Re: I Don't Understand

It is rated at 150mA max with proper thermal management that you can force through it before it is damaged but how much current are you forcing through it, the current source will force what ever current it can force through the device, the device will not limit the current, so when you force more current than the LED can handle that is when you blow them up. You can have 150mA LED that you can force less than 150mA or more than 150mA through it.
So did you actually measure the current flowing through the LED. You need to understand how the device functions. Look at the graph of Vf VS If to see what the effect of current it has on the Vf.

So of the 9 series LEDs that I put in this lamp after removing the stock LEDs ... only 4 work ... but after reading your message, I threw an ammeter on it and it's drawing 170ma ... so I obviously fried the other LEDs and I'm over driving these ... of course that 170 is basically an RMS because we already know that the signal pulses so they are seeing much higher current at any given time ...

Here is a pic of the circuit that came with the lamp this is what Im using to drive these LEDs ... by the way I have a bunch of these LEDs as a got pack of 100 for $7 on Amazon...

[budm]

Re: I Don't Understand

It is rated at 150mA max with proper thermal management that you can force through it before it is damaged but how much current are you forcing through it, the current source will force what ever current it can force through the device, the device will not limit the current, so when you force more current than the LED can handle that is when you blow them up. You can have 150mA LED that you can force less than 150mA or more than 150mA through it.
So did you actually measure the current flowing through the LED. You need to understand how the device functions. Look at the graph of Vf VS If to see what the effect of current it has on the Vf.

[EasyGoing1]

Re: I Don't Understand

So you are forcing 150mA through the LED.
But what is the current rating? The Vf rating of 3V is at what current being forced through the LED?

The LEDs are rated at 3V, 150ma - per the datasheet.

[budm]

Re: I Don't Understand

150ma with 9 of them in series ... my voltage source is AC 120 with not much space to mount a circuit in so I need the circuit to be as small as possible ... the circuit that is in the lamp now has a small transformer and a bunch of surface mount components ... OH the LEDs are rated at 3 Volts.

So you are forcing 150mA through the LED.
But what is the current rating? The Vf rating of 3V is at what current being forced through the LED?

[EasyGoing1]

Re: I Don't Understand

capacitive dropper??

Never heard of that till now ... looks simple enough...

[stj]

Re: I Don't Understand

capacitive dropper??

[EasyGoing1]

Re: I Don't Understand

That LM317 is set up as 139mA (1.25Vref/9 Ohms) constant current source not as Voltage regulator.
The LED is current device, the Vf will vary with the If and temperature.
So what is the spec of the LED and how many LED are you going to put in series? Lets start with that first.
Then you also need to consider the power lost and power dissipation for the constant current source circuit.

150ma with 9 of them in series ... my voltage source is AC 120 with not much space to mount a circuit in so I need the circuit to be as small as possible ... the circuit that is in the lamp now has a small transformer and a bunch of surface mount components ... OH the LEDs are rated at 3 Volts.

[PeteS in CA]

Re: I Don't Understand

Speaking more generally, oscilloscope pictures are easier to interpret if the amplitude and time scales are included, and also where the zero volts reference is.

The LM317 is being used as a constant current source. It will source whatever current will cause a 1.25V difference between pins 2 and 1 in the OP diagram. It is still a dissipative method, so the IC may need a heatsink, and if the voltage across pins 2 and 3 is high enough, the IC may power limit.

[stj]

Re: I Don't Understand

why not just use a real led driver from LT ??
https://www.analog.com/en/products/p...driver-ic.html

[budm]

Re: I Don't Understand

That LM317 is set up as 139mA (1.25Vref/9 Ohms) constant current source not as Voltage regulator.
The LED is current device, the Vf will vary with the If and temperature.
So what is the spec of the LED and how many LED are you going to put in series? Lets start with that first.
Then you also need to consider the power lost and power dissipation for the constant current source circuit.