Bench Top Power Supply from the past, opinions and some help - Page 1
Forum section: electronics / beginners

author: BeetleJuice
author_rank: Contributor
timestamp: January 17, 2021, 10:17:17 am
content: spent countless hours trying to fix my old school linear 0-30V 0-3a power supply and it never worked again. the irony is that I started modding it while it still worked from 1996.Anyway, I came across this power supply, which seems very promising, but I have some questions:1) Since i am not a power supply expert and this looks like a power supply from the past, is this worth building?the plan is for 0.7-6V - 3-30V and 0-3A, not 10A, I will keep 2 power transistors only. the switch/LEDs for 6V and 1A are fine to stay if it doesn't complicate things. but I need to use the analog meters I already have...if yes then2) can someone trim the picture/schematic since I will use the standard analog 0-30v and 0-3A panel meters? I am not sure which components should be removed.3) is the power diode 1N3209 mandatory? I have never seen such a big diode in this configuration.4) can we replace the 2N3772 with 2N3055 and the 2N6388 with TIP42?the links for the power supply:http://www.learningelectronics.net/VA3AVR/circ/ps3010/ps3010a.htmlhttp://www.learningelectronics.net/VA3AVR/circ/ps3010/ps3010b.htmlthank you all for your time

author: xavier60
author_rank: Super Contributor
timestamp: January 17, 2021, 11:02:01 am
content: The first thing that stands out is that it will have a very high dropout voltage.Including the 2 junctions inside the IC, I count 6 series PN junctions.D3 is a crude way of adding adjustable Constant Current mode to the LM723 which normally only does fixed current limiting.

author: Cliff Matthews
author_rank: Unknown
timestamp: January 17, 2021, 07:32:18 pm
content: R.I.P Tony van Roon. He was a good local electronics guru in my area.

author: Jwillis
author_rank: Super Contributor
timestamp: January 18, 2021, 01:40:59 am
content: The 2N6388 is a Darlington NPN and the TIP42 is PNP . Not interchangeable. Equivalents include ,but not restricted to , would be TIP602 ,TIP642 , MJ3001 . There are many others . The other 2N3772 transistors can be changed with 2N3055 .Analog voltage meter is not much of a problem where as the Ammeter you use may require a shunt . Most Ammeters are 75mV now which require a 75mV shunt to match the meter over 5A .The diode is still active as VS-1N3209 in the DO203AB package.

author: BeetleJuice
author_rank: Contributor
timestamp: January 18, 2021, 05:16:16 pm
content: Quote from: xavier60 on January 17, 2021, 11:02:01 amany chance to explain this CC mode?thank you for the reply

author: BeetleJuice
author_rank: Contributor
timestamp: January 18, 2021, 05:24:18 pm
content: Quote from: Jwillis on January 18, 2021, 01:40:59 amomg by bad I wasn't paying attention!the initial diagram uses ammeters. I wanna use a simple old school analog voltmeter and ammeter I already own.max current will be 3ADC, my meter is 3A DC. max volt will be 30VDC and so is my meter. the problem is that I cannot decide which resistors to remove when I remove the ammeters. the editor uses some kind of calibration for the ammeters he uses but in my case, I will not use any of them, so some resistors must go. I am afraid I will harm the voltage or the current sense if I trim the circuit.any chance you can put some x marks on the picture of the diagram?thank you

author: xavier60
author_rank: Super Contributor
timestamp: January 18, 2021, 07:56:18 pm
content: Quote from: BeetleJuice on January 18, 2021, 05:16:16 pmCC mode can be used as current limiting to minimize damage to whatever is being powered, in case something goes wrong.It can also be used for measuring low value resistors like Current Sense resistors.But in this design, some time is needed for the current setting to stabilize due to the temperature rise of D3 interacting with the setting.

author: Jwillis
author_rank: Super Contributor
timestamp: January 19, 2021, 02:57:13 am
content: Quote from: BeetleJuice on January 18, 2021, 05:24:18 pmWhat he's doing with the meters is not so much as calibration but changing the Range of the meters. The ammeter the can be ranged with the switch S3a for mA increments from 0 to 1A or 1A to 10A. The voltage meter also has a range setting with switch S2a . Which resistors to change or omit is dependent on the meters you are using . The designer explains that in part 2 . Do you want to keep the option of changing meter ranges.

author: srb1954
author_rank: Super Contributor
timestamp: January 19, 2021, 03:45:39 am
content: Quote from: Cliff Matthews on January 17, 2021, 07:32:18 pmNot sure I would describe him as a "good electronics guru". Some of his published designs are just plain wrong.

author: srb1954
author_rank: Super Contributor
timestamp: January 19, 2021, 04:09:49 am
content: Quote from: BeetleJuice on January 17, 2021, 10:17:17 amI don't think this PSU design is going perform well down at 0.7V output. This circuit configuration of the 723 regulator is only recommended for output voltages down to 2V, below which the 723 error amplifier is working outside its recommended operating range.Also, with diode D2 in circuit the temperature stability of the output voltage will be poor for lower output voltages. The diode should be replaced with a 2k2 resistor to set the minimum error amplifier input voltage to around 2V and preserve the good temperature stability of the 723 regulator.

author: BeetleJuice
author_rank: Contributor
timestamp: January 20, 2021, 12:29:04 am
content: i know the cc function , what i cant understand is how "D3 is a crude way of adding adjustable Constant Current mode to the LM723". any chance to explain how D3 works?

author: BeetleJuice
author_rank: Contributor
timestamp: January 20, 2021, 12:43:27 am
content: i would like to make it without the range adjust.maybe s1s2 and leds could stay just to have a "low voltage low current mode"i am going to use analog meters ,a volt meter and an ammeter i already have (0-30v , 0-3 a).but i cant decide which resistors are for the voltage/current sense and which for the range adjust , so i might harm the circuit.can you tell me which resistors can go?my guess:R17 R18 R19 R20 and M2 can go and an analog ammeter can be used in series with the outputR24 R25 R26 R27 and M1 can go too and a standard voltmeter can go to the output.

author: xavier60
author_rank: Super Contributor
timestamp: January 20, 2021, 02:12:40 am
content: Quote from: BeetleJuice on January 20, 2021, 12:29:04 amCurrent sensing is done with one NPN BJT inside of the LM723, B-E on pins 2 and 3.With D3 bypassed, the current limit threshold would be about 0.6V divided by the CS resistance, about 4A.The voltage drop across D3 adds to the voltage drop across the CS resistance, allowing the current limiting to be set from zero and up.It's crude because it adds to the already high dropout voltage and changes in D3's temperate with changing load will interact with the CC setting.This won't matter for some applications.

author: Jwillis
author_rank: Super Contributor
timestamp: January 20, 2021, 07:32:13 am
content: Quote from: BeetleJuice on January 20, 2021, 12:43:27 amOK . First you need to know if your ammeter is internally shunted some are not and require an external shunt to operate . If it has an internal shunt then yes you just put it in series with the output between D3 and L1 . Omit R15 through R20 , R10 and 11 (Shunt resistors) , and S3a switch . If your meter requires a shunt , place shunt in place of R10 and R11 and connect your meter to the shunt accordingly . Voltage meter is installed parallel to out put and omit R22 through R27 and S2a switch.

author: BeetleJuice
author_rank: Contributor
timestamp: January 21, 2021, 03:42:28 pm
content: if we need a max amperage of 3 amps do we have to use the D3?Quote from: xavier60 on January 20, 2021, 02:12:40 am

author: BeetleJuice
author_rank: Contributor
timestamp: January 21, 2021, 03:50:57 pm
content: R15 R16 and R22 R23 can go too?also Current sense resistors can go? how does the lm723 count the amps if current sense resistors are not present?my meter is an analog minipa ms-52 0-3 ADC, i dont know if it has a shunt inside.it has just a +/- plug at the back of the meter ,you have to respect the polarity or the needle goes the other side.i think all analog meters have a shunt inside and they are "millivoltmeters"?can you guess the value of C8? should i keep this capacitor if all meters are gone?ZD1 ZD2 and D1 D2 are mandatory?sorry to bother you and thank you for the reply!Quote from: Jwillis on January 20, 2021, 07:32:13 am

author: Jwillis
author_rank: Super Contributor
timestamp: January 21, 2021, 10:24:18 pm
content: I can't confirm if model MS-52 3A requires no shunt.Only this listinghttps://www.ebay.ca/itm/DC-Panel-Mount-Meter-3-Amp-DC/193649183828?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D6c5e6084847d4dc8b0f33110209a86fc%26pid%3D100675%26rk%3D3%26rkt%3D15%26mehot%3Dnone%26sd%3D123702060362%26itm%3D193649183828%26pmt%3D0%26noa%3D1%26pg%3D2380057%26brand%3DUnbranded&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3A89f28b25-5c13-11eb-ad28-fa62ecfd17f1%7Cparentrq%3A2621575f1770ad4d75347ee4ffa9e92c%7Ciid%3A1says it doesn't .Sorry your correct on R10 and R11 they are required for current sense.I misread the schematic.ZD1 regulates the LM723 supply voltage at V+ to 39V keep that in place.ZD2 is 5.6V reference for the error amplifier for accurate voltage regulation .D1 and D2 are protection diodes.C8 I believe is for transient response. 10uF to 47UF would probably be enough.

author: xavier60
author_rank: Super Contributor
timestamp: January 22, 2021, 08:38:14 am
content: Quote from: BeetleJuice on January 21, 2021, 03:42:28 pmD3 is not needed for fixed current limiting.