Electronics > Beginners
LED strip tester will it work
DarkZero:
i was wondering if my circuit for led testing will work the idea was to get delayed startup and current limiting but that the delay will start when device under test is connected
jmelson:
320 V DC power source? Are you sure this is the right value? What is the purpose of Q1? Seems like it will just be always on.
The other two transistors seem to be a current source, but the MJE13007 Darlington power transistors are optimized for saturated switching, and this looks like a linear design. I think those are a bad choice for linear operation, but look up the Safe Operating Area curves to be sure.
Jon
OOPS, I thought it was a Darlington, but the MJE13007 is NOT a Darlington, but a very low-gain plain bipolar, which is going to really not work well with the high resistor values in the original circuit.
Jon
DarkZero:
Q1 is supposed to ramp up voltage from 0 to 320v so the led doesn't burn before regulation and is supposed to do so when DUT is connected, other 2 transistors are supposed to limit current to ~ 10mA and ill power it from a 240 10VA isolation transformer.
Zero999:
Just one question: why?
Most LED strip is designed for 12V or 24V, not mains, which I presume is where the 320VDC is coming from. Whilst this circuit will limit the current and not damage the LED strip, it's still dangerous, if the LED strip isn't adequately insulated for mains usage.
Use a lower voltage <60VDC, as it's much safer.
spec:
Hi DarkZero
I can only emphasize what the other members have said about the dangers of your circuit, and if your LED strings do not need such a high voltage, it would be highly advisable to lower the voltage as much as possible.
That being said, I have had a look at your circuit and find it quite clever, but there seems to be two issues.
The constant current generator appears to be indeterminate because of the connection of R1, and there is liable to be a significant voltage drop across R3, bearing in mind the low current gain of Q1 (high voltage transistors tend suffer from low current gain, especially at low VCE). I had a go at fixing these issues and came up with the circuit shown in the attached schematic for you to have a look at.
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