Unusually, the first resistor I looked at was a 5W 15R8!
Anyway, I hooked that up with croc leads in parallel with R101, giving 4R5.
The results are strange though;
AC in = 17.3V
DC before R101 = 21.2V
DC after R101 = 19.9V
Voltage across R101 = 1.3V
Current across R101 = 288mA
So, less voltage drop and less current?
Do you use enough ccs leds like four greens?
Yes, I wasn't precise with my notes. Sorry. I measured the value across the parallel resistors as well as calculating - the parallel resistor is on longish croc test cables>
Battery in multimeter is good.
Anyway. despite my inexactitude the story is the same.
4 greens equals more voltage drop across the CCS.
That in turn requires more voltage to be available at the input to ensure the CCS is actually operating in constant current mode.
This points to ignoring the warning repeatedly made that this style of CCS+SHUNT regulator MUST have adequate voltage at the input.
A normal DCB1 requires at least 5V across the CCS. we have recommended a 14Vac or 15Vac transformer for this 10Vdc supply so that 7Vac is maintained across the CCS in worst case operation.
A high current, 4green led, 14Vdc regulator will require a much higher AC voltage than 15Vac.
18Vac might do it, if the regulation and the smoothing capacitance are optimised.
But a high regulation transformer combined with a lowish value of smoothing capacitance may require as high as a 20Vac transformer.
That in turn requires more voltage to be available at the input to ensure the CCS is actually operating in constant current mode.
This points to ignoring the warning repeatedly made that this style of CCS+SHUNT regulator MUST have adequate voltage at the input.
A normal DCB1 requires at least 5V across the CCS. we have recommended a 14Vac or 15Vac transformer for this 10Vdc supply so that 7Vac is maintained across the CCS in worst case operation.
A high current, 4green led, 14Vdc regulator will require a much higher AC voltage than 15Vac.
18Vac might do it, if the regulation and the smoothing capacitance are optimised.
But a high regulation transformer combined with a lowish value of smoothing capacitance may require as high as a 20Vac transformer.
and yet I have a positive regulator using 15VAC that works fine?
I haven't ignored anything but recognise the shortcomings in my theory knowledge so I have simply followed the build guide, which seems the sensible thing to do, it states;
"Transformer...Calculate minimum 5VDC in more than DC out."
As I have more than 21V DC going into the CCS I thought I had met that criteria, or am I missing something?
Grateful for any guidance.
Ray
merlin, my dummy load is 47R 10W. My target load is around 350mA. at 14.75V the dummy load represents a load of 313mA.
Ray
A little more on the transformer. I'm using a toroid from Avel-Lindberg's Y23 range; mine is 50VA, dual 0-15V secondaries, dual 0-115V primaries, stated regulation is 11.8%. In addition, our mains voltage is always closer to 240V than 230V.
AC into the BIB modules measures 17.3V (measured on the positive regulator under load).
As it was mentioned earlier, I'm using 10,000uF smoothing caps.
Ray
AC into the BIB modules measures 17.3V (measured on the positive regulator under load).
As it was mentioned earlier, I'm using 10,000uF smoothing caps.
Ray
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Salas and Andrew T,
As a sparky that is often on the phone assisting other tradies onsite to find and rectify faults, I am constantly amazed at your abilities to see the issue and offer rectification advise so well without actually testing the device yourself. Give yourselves a pat on the back guys, really great support!
Laters
Drew.
As a sparky that is often on the phone assisting other tradies onsite to find and rectify faults, I am constantly amazed at your abilities to see the issue and offer rectification advise so well without actually testing the device yourself. Give yourselves a pat on the back guys, really great support!
Laters
Drew.
Thanks Andrew. Pet's mail made me think that perhaps I had come across as disrespectful, which wasn't my intention at all. As you say, I was just trying to understand.
Anyway, good news.
I stood away and thought through what I was seeing. One of the things I was seeing was a significant difference in value of the resistor chain in the sensing circuit, plus I couldn't get the voltage to more than around 12V on the 'faulty' negative unit. I tested the resistor and preset and found that the preset was faulty; at least it didn't measure to the value written on the outside! So, I swapped the preset out and bingo!; I can now adjust the voltage correctly and I'm measuring the expected current across R101/201.
It was nothing to do with R201, the negative mosfet or the transformer voltage, which are all unchanged.
The lesson I learned; measure presets before use (I already measure ordinary resistors with my DVM before use).
Anyway, thanks to yourself, Salas and merlin for your support.
Frustratingly, work is beckoning now so although I'm very close to being able to make the final hook-ups, testing and setup of my DAC it will have to wait until later.
Ray
I've already taken your point on board Andrew. The I/V stage I'll be powering can run on between 12-15V so I'm thinking it might be sensible to adjust the BIB modules down to a lower operating voltage so there is more 'headroom' across the CCS.
Ray
Naut,
Pet's mail made me think that perhaps I had come across as disrespectful, which wasn't my intention at all. As you say, I was just trying to understand.
Not at all, was just saying exactly what was said, find it amazing these guys with the support and being able to visualise the circuit, if you aren't in the problem solving game, many people cannot do it on the fly, just wanted to pass on my respect to these guys, so no, no fault was intended on my part that was sideways pointed at you.
Good sideways thinking on your part to look at it as a whole, nicely done. Glad that's sorted, off to the next stage for you!
Laters,
Drew.
Pet's mail made me think that perhaps I had come across as disrespectful, which wasn't my intention at all. As you say, I was just trying to understand.
Not at all, was just saying exactly what was said, find it amazing these guys with the support and being able to visualise the circuit, if you aren't in the problem solving game, many people cannot do it on the fly, just wanted to pass on my respect to these guys, so no, no fault was intended on my part that was sideways pointed at you.
Good sideways thinking on your part to look at it as a whole, nicely done. Glad that's sorted, off to the next stage for you!
Laters,
Drew.