Your transformer is almost as bad as the cheap Chinese one I have that has an output of 18V without a load and it drops to 9V with a low current load. It gets hot even with no load because it is cheap and does not have enough turns or its core is made of rice.
I have a unregulated power supply from a transformer that gives out a peak voltage of 61V after the rectifier (unloaded). With a 1A load the voltage goes down to 41.5V peak. I am powering a very large LED, 32V @1A and will be using A NCL30160 to do so, but its max input voltage is 40V (lower would be better). What kind of pre-regulator should I use? A series pass transistor or a LM317HV? I dont care what happens after the 40V, its just so the chip wont fry. Adding on another SMPS in front of the LED regulator would be too costly.
To re-iterate:
Vin Min:41.5V Peak DC (1A Load)
Vin Max: 61V Peak DC (no Load)
Iout Max:1A
Voltage needed: 40V (lower would be better since I wouldnt stress the chip out).
I know there are other solutions (ie TI) but I would rather not spend $2.50 a chip.
Haha I never seen a rice-core transformer!It gets hot even with no load because it is cheap and does not have enough turns or its core is made of rice.
Hi Overclocked,
In fact, you probably don't need an LM317HV or NCL30160: just drive the LED directly from the SMPS. An SMPS with a current limit of 1A should do the job. Most SMPSs will not take more than 30 to 40V input, so the 60V peak from the transformer would need to be sorted, but I can't see that as being a major problem., and if the LED would be connected all the time, there is not a problem anyway.
In my experience those SMPS modules are really $5, use cheap components, and take a month to get here if I order from china. The NCL30160 is the SMPS for the LED (Buck converter).
Sounds like it would be easier just to get another transformer, or for the price of a new transformer, I could get a 36V Offline SMPS and be done with it. To the scrap bin with these transformers!
I have found the cheap SWMPs OK; there is not much to them.
Wise move going for another transformar, but if you could give more details of the transformer you have maybe something coulod be done. I should have checked what the NCL30160 was- my bad.
what arrangement do you have: bridge and resovour capacitor? what bridge/rec diodes. What value reservour cap. presumably the mains is 60hz where you are?
The windings of a transformer use their inductance to transfer power from primary to secondary and to keep the current low when there is no load. If there are not enough windings or if the iron core is too small then the primary is almost simply a piece of wire that gets hot because it has a high current in it.Haha I never seen a rice-core transformer!
Did you mean less size core or not pure material can produce heat?
Considering such a POOR Quality Transformer, That Shunt Regulator will cause the transformer to OVERHEAT Really Bad.
Hi Spec, Thanks for the circuit, but why did you choose to go with a shunt regulator instead of a series pass regulator?
Hi again Overclocked,
I am doing the detailed analysis of your requirement and really need the following information:
(1) what is the circuit of the transformer rectifier and reservoir capacitor? Is it one secondary winding and bridge. two windings and two diodes, or even half wave rectification.
Never got that fair. Part spec was the last thing on my mind. 3A, 1000V for my 24VRMS system.(2) what bridge/rec diodes are you using? The part number would be ideal.
Lets switch gears and use the 24VRMS system I mentioned above. I plan on using one 6800uF Cap @50V. Calculated it out to give out less than 3% ripple.(3) most important, what is the value of the reservoir capacitor?
Low ESR. 68mOhm(4) is the reservoir capacitor a lage low esr type or just an ordinary capacitor?
No. There is a smaller onboard capacitor on the LED driver though. Its worth noting that if the LED is off, main power will also be off. The LED will be on for ~8hrs a day, 7 days a week. So basically there will be a switch controlling main power to the transformer.(5) are there any impedences (resistors thermistors etc) in the primary or secondary of the transformer?
60Hz, 120VRMS(6) what is the frequencu of your mains supply 50 or 60Hz?
I calculated peak from RMS from my voltmeter (Vrms*1.414).(7) when you say that the voltage with 1A drain is 41V5 peak, how did you measure that: with a scope or a DC voltmeter. A DC voltmeter would measure mean not peak.
Never filtered it, I was concerned with how much my unknown transformer could supply. Again, this was salvaged from something a long time ago and has been sitting in my junk box. Cost was a factor since I dont have much money these days. If I had a larger resistor, I would let it sit around to see if it heats up at all at the current I need, BUT I have to keep in mind that if I want to use it (which I probably wont), the capacitors will have to be rated for 120V, which will be quite expensive. So I'll just use a 36V Offline power supply for That LED system.(8) If you measured with a scope could you say what the peak to peak ripple voltage was at 1A drain?
Hi Overclocked,
The top contender, which I have just finished in hand sketch form, is the PMOSFET serial preregulator.
Nice talking to you- especially your presentation of data.
spec
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