Load regulation help.

[jep_pogi]

mga sir.
tinest ko po yung linear power supply ko gamit yung Electronic Load sa school namin.
nasa 80V 2.25 A po dapat yung output nya.

pero yung load regulation ng ckt na ito ay panget pala. or wala talaga.
kapag no load, 80V sya which is expected
pero kapag 0.5A ang kinakain ng load, bumababa na sa 70+ Volts yung output
tas pag 1.0A na ung kakainin ng load, bumababa lalo sa 60+ Volts yung output.

dapat sana regulated yung output sa 75+ Volts..
di ko pa po alam kng paano gagawin sa ckt. inaaral ko na ngayon panu ayusin ung load regulation.
pahelp po sana sa mga pwede gawin. eto yung ckt.



thank you po

[glutnix_neo]

subscribing mode muna ako, bulag eh, hehehe

[labgruppen]

i hope you gathered some data during your test. I am interested in rectified secondary voltage during your tests. Ano yung voltage sa emitter ng Q2 at no load, @0.5 Amp and @ 1 amp. Also at no load condition, your output is @80volts, higher than the total zener voltages which is supposed to be approximately 4x18 or 72 volts. So i hope you also tested the voltage at the base of Q1. these readings should help in the investigation of your problem. as-built pictures would also help.

[jep_pogi]

sir, di po kasi ako pwedeng magtest palagi dun sa electronic load e. so di ko na po ulet talaga malalaman yan. bale yung sa reference diodes, 20Volts each yung namemeasure ko so total of 4x21V = 84Volts ung nasa base ng Q1. at no load yan ha.

ngayon nagtest ako ulet, naging 85.6 to 85.8V na yung output ng supply ko. feeling ko may nasirang component nung tinest gamit ung e-load e. huhu baka kailangan mag refabricate..

yung sa collector ng Q2 at noload = 85.8V tas emitter of Q2 at noload = 85.6V

di na po ak makapagtest ulet agad sa e-load e. next week siguro ulet pwede.

[jep_pogi]

dapat po kasi di lalampas ng 82 volts yung output e. ewan ko panu umabot sa 85V. baka may nasirang diode sa bridge pero diniode test ko na ng tester ung bawat diodes sa ckt, mukhang okey naman. di ko alam panu umaabot sa 85V ung output ngayon ng ckt ko.

[jep_pogi]

umiinit din po yung mga zener diodes.. ung apat. as in mainit. hindi po sila sira pero mainit po sila tlga

[jep_pogi]

sir, sorry po sunod2.
pwede ko po ba malaman kung papaano gumagana yung regulation ng ckt na yan?

alam ko po na reference voltage yung mga zener na apat.
pero panu po nangyayari yung regulation dito?
d ko po alam kng san sa ckt kinukuha ung difference ng output sa reference.
pati kng panu nireregulate ng series pass element ung output.
yung series pass element po dito is yung MJ15025 dba?

yung nakikita ko po pala na mga regulators, yung feedback voltage ay fraction lng ng output. sa ckt na yan po e yung output voltage mismo ang fineefeedback diba? hindi na xa pinapaliit. diretso na xa sa emitter ng Q1.

[labgruppen]

your zeners are being overdriven. 18 volts lang dapat isa nyan kaya dapat 72 volts lang yung total. kindly check voltage across R2.

[labgruppen]

pwede ko po ba malaman kung papaano gumagana yung regulation ng ckt na yan?

alam ko po na reference voltage yung mga zener na apat.
pero panu po nangyayari yung regulation dito?
d ko po alam kng san sa ckt kinukuha ung difference ng output sa reference.
pati kng panu nireregulate ng series pass element ung output.
yung series pass element po dito is yung MJ15025 dba?

yung nakikita ko po pala na mga regulators, yung feedback voltage ay fraction lng ng output. sa ckt na yan po e yung output voltage mismo ang fineefeedback diba? hindi na xa pinapaliit. diretso na xa sa emitter ng Q1.

bale simple voltage follower lang yan. review the workings of transistor configured in emitter follower para maintindihan mo yung operation. treat Q1 and Q2 as a single NPN transistor. (Base=base of Q1, Emitter=emitter node of Q1 and Collector = emitter node of Q2). in emitter follower configuration, the voltage at the emitter will follow the voltage at the base. Since the voltage at the base is regulated (through the zeners) it follows that the output voltage (emitter voltage) is regulated.  In your case, it seems that your zener diodes are pulled "hard" to the unregulated voltage thus the very high output. since hindi na regulated yung node ng base ng Q1, hindi na rin regulated yung output ng power supply mo.

edit: it would have been better is you built and tested your power supply in "stages". first the rectifier and filter capacitor, then the voltage reference composed of the contant current source and zener diodes then lastly the series pass/output stage.

[jep_pogi]

oo nga po e.. akala ko okey lang since di naman nasisira.
1.5V po yung voltage across R2.

di ko po maisip rin kng bakit naging 85V na yung inooutput ng ckt. 78 to 80V lang xa dati e.
tumaas after ikabit sa e-load.. baka may nasira na part e.

hmm so yung problem ko po pwedeng mainly dahil overdriven yung zeners.
pwede ko imeasure yung current across sa zeners pero mahirap din po gawin since kelangan nakaseries pa yung pagmeasure diba.
pero malamang mataas yung current na dumadaan sa zeners ko kaysa sa dapat padaanin sa knya.
pwede kaya mag parallel ako ng resistor sa zener reference? para lumiit ung current sa knya?
or arrange ko nlng ung constant current source which is ung sa PNP transistor at R2 na part?

thanks po

[labgruppen]

oo nga po e.. akala ko okey lang since di naman nasisira.
1.5V po yung voltage across R2.
di ko po maisip rin kng bakit naging 85V na yung inooutput ng ckt. 78 to 80V lang xa dati e.
tumaas after ikabit sa e-load.. baka may nasira na part e.

pwede kaya mag parallel ako ng resistor sa zener reference? para lumiit ung current sa knya?
or arrange ko nlng ung constant current source which is ung sa PNP transistor at R2 na part?

thanks po

another piece of the puzzle, 78-80 volts nung initial test mo pero nung pagkatapos ng test sa load naging 85 na.. baka may tinamaan na na transistor sa ckt. mo. i suggest take q1 and q2 out of the circuit and test them. while q1 and q2 are out, check the voltage of your reference. btw, yung 1.5v across r2 is too low, which means that the constant current source is not the one providing the bias for your zener string, which in turn might mean that there is something wrong with q1-q2 circuit. voltage across r2 should be around 2.7 volts. likewise, your constant current source is a around 48mA. with 48mA flowing through your 18Volt zeners, makes them dissipate around 800-900mW of power, a little too high imho for a 1watt zener.

[Born2BeWired]

The fact that you measured 85VDC at your rectifier output (Q2 emitter) at no load is already a clear indication that your transformer circuit itself is not capable supplying 2A @ 80V. I can tell you are most probably using a transformer with a secondary winding voltage rated at 85/1.414 = 60VAC with open load! (ignoring the diode drop).

You should use a transformer with a loaded secondary voltage of at least 86V @ 3A. (This will result in a no load DC voltage hovering around 120VDC)

And then check the rest of your circuit as suggested by labgruppen. Remember, as already pointed out by labgruppen, your circuit is essentially a buffered zener. Without the benefit of feedback, you are fortunate enough if you achieve a load regulation better than 2%.

[jep_pogi]

about dun sa current sa zener. oo nga po napansin ko na aabot xa almost 900mW. e 1W lagn yung zener. kaya siguro umiinit. kahit dun sa 78V plng ang output ko ay umiinit na rin ung zeners e.
dapat po ba di iinit??

sige po bukas tanggalin ko yung Q1 and Q2.
then dapat po ibahin ko yung current na iooutput ng constant current ckt ko diba?
tapos dapat 72 volts ung mameasure ko sa string ko tama po ba.

anu po bang region dapat magoperate yung series pass ko? yung series pass ay yung pinagsamang Q1 and Q2 po diba.

[jep_pogi]

sir born to be wired,

ung pinagawa ko po na transformer ay may specs na 64VAC 3A sa secondary side po nya.
yun lang ung sinabi ko na specs dun sa gumawa po.

[Born2BeWired]

That nails it down. Under spec ang transformer mo. You should replace your transformer with the sufficient rating. While waiting for your new transformer, fix the rest of the circuit. Look for an open zener along the D6-D9 chain, and check if Q1 and Q2 are still in good health. Do not operate the zener too close to their max power rating.

[jep_pogi]

anu po ba dapat specs ng transformer ko? sorry..sobrang nagulat ako na mali po yung transformer ko. para po mapagawa ko na agad..thanks po

[jep_pogi]

yung motor po na idadrive ko ay 84V ung max na pwede sa kanya. so balak ko po is 80V yung output ng supply ko.

[jep_pogi]

palitan ko po ng 110ohms ung 56ohms ng constant current part para maging 16mA to 20mA yung current through the diode string.
sir, kapag po ba nagdadraw ng current yung load, naaapektuhan ba nya yung current sa zener string? dapat po hindi diba? para constant na lang talaga yung output.
d ko po alam kng naaapektuhan ba ng output ung current through the zeners e.
mahalaga po kasi na constant lng talaga yung current nya diba.

[jep_pogi]

sir tanong pa po pala ulit. kung 72 Volts ung string ng zener, ibig sabihin ba nun 72Volts ung max na pwedeng i output ng supply ko? or okey lng na mas mataas sa 72 volts?
di ko po kasi talaga magets ung sa output part.

[labgruppen]

sir tanong pa po pala ulit. kung 72 Volts ung string ng zener, ibig sabihin ba nun 72Volts ung max na pwedeng i output ng supply ko? or okey lng na mas mataas sa 72 volts?
di ko po kasi talaga magets ung sa output part.

as i have said, voltage at emitter (which is your output) is approximately equal to the voltage at the base (actually lower). so kung 72volts yung zener string mo, yung output dapat ay di lalagpas ng 72 volts. as sir born have said, buffered lang yung zener voltage.
regarding your transformer, if i remember correctly, during the early discussions of this project i recommended 85volts 3a transformer (kulang lang ako ng 1 volt sa recommendation ni sir born). that is also the reason why your main filter capacitors (c1 and c4) are connected in series, to cope with the projected 120V dc expected with the 85vac transformer. with regards to your query on reducing the cc source to 16-20mA, compute the total current gain of q1-q2 combination and check if 16-20mA will be sufficient enough drive for full load current plus a margin.