On Fri, 25 Apr 2014 10:57:47 +0100, Daniel wrote:
On 24/04/14 23:12, Uncle Peter wrote:
On Thu, 24 Apr 2014 13:53:25 +0100, Daniel
wrote:
On 24/04/14 04:04, Uncle Peter wrote:
On Wed, 23 Apr 2014 13:08:37 +0100, Daniel
wrote:
On 23/04/14 08:02, Uncle Peter wrote:
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O.K., are you counting 1 through 6 starting at your drawings top left
pin on the coil and counting anti-clockwise??
No, sorry. Labelled now: http://petersphotos.com/temp/PSU.jpg
If so, could it be that you are forward-biasing the diode and you're
charging the cap connected to pin two of the coil?? Try re-measuring
with ohmmeter connected other way around to reverse-bias the diode.
Probably same-same with pins 5 & 6. Measure both ways.
For ones that I saw charging, I tried both ways.
I'm guessing pins 2 and 3 are not actually connected to the other
transformer windings but may or may not be connected to each other via
another winding on the transformer (0.5 ohms). Are you sure pin 3 is not
connect to anything outside the transformer??
There's quite a few connections I can't see - surface mount resistors
underneath the transformer, tracks that run underneath the chip, etc.
Pins 1 & 4 primary winding, pins 5 & 6 secondary winding plus, maybe,
pins 2 & 3 another secondary winding
If what I thought was a variable resistor is just another 280 ohm (or
1.8kohm) resister, is there actually a variable resistor anywhere in the
circuit??
I can't see anything that can be adjusted.
Is there any Brand Name and model number which might help find a circuit
diagram somewhere online?? Any info on a back panel/whatever??
No, the only markings are things like C6, R7, etc to identify components.
O.K., thanks for all this, Peter, but from what you've told me and what
I can work out, this is not a Constant Current Power Supply, it is
merely a 12 Volt Power Supply which can deliver up to approx 300mA
output Current.
That would seem very odd as it's powering LEDs without any current limiting resistor! No wonder the LEDs have a very short life!! Or are CREE LEDs self limiting?
Let's see! If you can connect a D.C. Voltmeter across the D.C. out
terminals you should, obviously, measure 12V.
Now connect a 40 ohm
resistor across the output. From Ohm's Law, R = V/I so 12V/0.3A gives 40
ohms. Voltage should remain 12V across the output terminal and output
current would be 0.3Amps, the supplies rated maximum.
Now, increase the resistance to, say, 50 ohms. I expect the output
current will have reduced (from Ohm's Law I = V/R = 12V/50 =) 0.24A,
well below the supplies Current rating of 0.3A so no problems and the
output voltage will still be 12 volts.
Now, reduce the resistance to, say, 30 ohms to try to draw more current
from the supply (from Ohm's Law I = V/R so 12V/30 gives 0.4A. Does this
happen??
18 ohms, 8.55 volts.
27 ohms, 12.45 volts.
36 ohms, 12 volts.
47 ohms, 10.8 volts.
56 ohms, 10.7 volts.
Open circuit, 12.73 volts.
27 ohms (being about a 6 watt load) seems to make the PSU happy, that's about what the CREEs draw.
But I can't explain why it drops the voltage at 47 and 56 ohms, unless it's a universal supply designed for 3 or 4 LEDs?
And why the slightly higher voltage at 27 ohms than at 36 ohms?
I'm guessing that the Supply will not supply 0.4Amps because the output
Voltage will have fallen below the 12Volts it's supposed to still be
supplying.
--
The German for nipple is "Brustwarze" - or "breast wart".