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eHam Forums => HomeBrew => Topic started by: N1AUP on January 22, 2023, 04:15:55 PM

Title: Are there any tech geniuses who can explain how this circuit works?
Post by: N1AUP on January 22, 2023, 04:15:55 PM
https://www.ameradio.com/doc/Astron%20RS-35A%2C%20RS-35M%20schematic.pdf|

I would like to start a streaming ham radio class that can teach hams some electronic basics / troubleshooting.  I'd like to start with a regulated, non-switching supply.

https://www.ameradio.com/doc/Astron%20RS-35A%2C%20RS-35M%20schematic.pdf

I know what some of this does, but would like to find an electronics expert that can help me understand how the circuit works. 

Is there anyone who can help?

Thanks
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: AI5BC on January 22, 2023, 04:29:04 PM
Now that is funny. You have no clue how a very simple circuit works and want to teach other hams.
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: W0CKI on January 22, 2023, 04:48:55 PM
Now, that’s not. Standard a hole response from BC
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: W1VT on January 22, 2023, 05:05:34 PM
The Art of Electronics by Horowitz and Hill has an excellent discussion of how the 723 regulator works.  It has been in print for decades so plenty of used copies are available.

Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: K3UIM on January 22, 2023, 05:43:42 PM
BC: I've taught a few novice classes (too many years ago) and have been asked questions that made me stop and think also. Having a license doesn't mean we know it all. It's a devil in the wood pile that we hope never rears its' ugly head. Keep on keeping on AUP!
"Red-faced" Charlie
LOL
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: AC2EU on January 22, 2023, 06:38:15 PM
It's a pretty standard circuit .
The 723 voltage regulator Ic is driving a couple of "pass" transistors to supply enough current to the load.
If this is too tricky for you, I don't know how you expect to teach others?
You might want to hit the books first.
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: AI5BC on January 22, 2023, 07:20:48 PM
It's a pretty standard circuit .

If this is too tricky for you, I don't know how you expect to teach others?
He can't, that was my point. Now he wants to teach others on the new idiot's bible, YouTube. You can't make this stuff up. 
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: K7MEM on January 22, 2023, 09:21:15 PM
IMHO, if you are going to attempt teaching, start with a much simpler power supply. The ua723 regulator has been around for a very long time. I have no problem understanding it, and have used it in designs many times. However, a power supply starts at the transformer. Start with the transformer, a couple of diodes, and some filter capacitors. For example: Basic Power Supply Design (https://k7mem.com/PS_Basic.html). Know why the parts are specified the way they are. Then branch out into regulators. I'm sure there are other web pages that discuss power supply design.
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: N1AUP on January 23, 2023, 01:17:35 AM
1.  I built a 13.8 volt DC power supply years ago.  The transformer had two pins, outputting about 18 volts.  That fed a bridge rectifier. 

This Astron has multiple pins of output on the transformer, and it appears that they are not using a bridge rectifier. 

Why?
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: G3RZP on January 23, 2023, 01:41:21 AM
I have always found the 723 to be very prone to picking up any RF that's around and going mad as result.
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: N1AUP on January 23, 2023, 02:10:41 AM
BC: I've taught a few novice classes (too many years ago) and have been asked questions that made me stop and think also. Having a license doesn't mean we know it all. It's a devil in the wood pile that we hope never rears its' ugly head. Keep on keeping on AUP!
"Red-faced" Charlie
LOL

Here's the problem with people who blithely advise you to "read the manual" or "read the textbook".

Most of this stuff was written by people who understand the topic, but are not very skilled at explaining it.  Computer books are the worst offenders.  The authors don't have any ability to comprehend where a student's understanding happens to be, and even less skill at taking that level of understanding and expanding it.  The authors assume that the student understands what they do, so much of what's there goes over the head of the person who wants to learn.  Add to the reality that too many engineers never learned to write, and you have a major problem.

It's rare to find someone who understands a topic, and also has the skill to properly explain and educate, and communicate.

I'm firmly convinced that engineers should spend two years studying liberal arts and especially English before spending time learning the techy stuff.  I also believe that liberal arts people should get a solid grounding in math, and tech. 

 
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: WW5F on January 23, 2023, 03:09:56 AM
You don't really learn anything until you have to teach it. 

Learned how to teach many times in my life.  Thought it would always be easy to put together a lesson plan for stuff I'd been doing my whole life until I started putting lesson plans together to teach the stuff I'd been doing my whole life.  Never realized how little I knew about what I was about to teach until I had to teach it.  So called "smart" people usually skip over a lot of stuff and assume some stuff is so obvious, it doesn't need to be stated.  This is the main reason some teachers get so frustrated when students STILL DON'T UNDERSTAND what they're saying.

First, you have to answer all the questions you raise by yourself when trying to figure something out BY YOURSELF.  Then, when light bulbs start spontaneously lighting above your brain, you realize there are things about it that are SO OBVIOUS to the person/people who originally put it together, they didn't think it was necessary to restate it.  THIS, is what you have to explain to your students.

My first impression of this astron schematic is that the transformer has two outputs.  The inside taps (lower voltage) go to a half wave rectifier, followed by a filter capacitor and then to the pass transistors.  This provides the regulated output of 13.8 volts at up to 35 amps (higher current).  The outside taps (a little higher voltage) also go through a half wave rectifier and filter capacitor and is then regulated by the UA723 (lower current) to the bases of the pass transistors (for higher current through them).  My next step would be to start looking at the specifications of the UA723 to start figuring out all the reasons for all those other little discrete components around the UA723.

But I don't fix power supplies any more and I'll never teach anything about power supplies again.

Extra vignette, supplied to you free of charge...  What I've learned about math:  You don't really learn algebra until you're in calculus.  And you don't really learn calculus until you learn its disjointed history, which started with geometry.  I'm 60 years old and didn't figure this out until a few months ago.  I think I'm now, finally, ready to start teaching calculus.
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: KF6QEX on January 23, 2023, 03:40:24 AM
"It's rare to find someone who understands a topic, and also has the skill to properly explain and educate, and communicate."

There are a lot of lousy teachers out there.
But there are also a lot of lousy students.




Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: K9CTB on January 23, 2023, 04:05:33 AM
This schematic is on the high end of basic electronics knowledge and skill course.  I'd recommend attending such a course if you want to teach this sort of circuitry on a component level.  It might be better to present it on a block-diagram level, since that's all that would be needed to pass a modern amateur radio license test.  A good (if limited) instructor could use the block diagram approach to "ignite a fire" in the student to learn more ... or to take such a basic course him or herself.  JMHO.
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: W1VT on January 23, 2023, 04:23:36 AM
One of the co-authors of the Art of Electronics is a ham, W1HFA.  I remember a memory keyer article he wrote for QST.
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: W9IQ on January 23, 2023, 04:50:59 AM
1.  I built a 13.8 volt DC power supply years ago.  The transformer had two pins, outputting about 18 volts.  That fed a bridge rectifier.

This Astron has multiple pins of output on the transformer, and it appears that they are not using a bridge rectifier. 

Why?

You probably built your supply with a full wave bridge rectifier consisting of 4 diodes arranged on the output of the transformer. That is one way to obtain full wave rectification. The other way, as shown in the linked schematic, is to use a center tapped transformer with only two diodes on its output. The result is the same but there are economic trade-offs between the two designs.

The transformer in the schematic is used to develop two separate DC voltages (often called buses). The lower voltage bus from CR101/CR102 and filtered by C5 is routed to the pass transistors for regulation as the 13.8 VDC output voltage of the supply. The higher voltage bus from CR1/CR2 and filtered by C1 is routed to the regulator circuit.

The voltage to the pass transistors is lower in order to minimize the heat generation in those transistors. The voltage to the regulator circuit needs to be a little greater than the output voltage bus in order for the regulator to maintain control of the output voltage of the supply. There is also an advantage to having the regulator circuit on its own bus as this minimizes the fluctuation in its power supply voltage since it has its own filtering capacitor (C1) for its lower current demands.

- Glenn W9IQ
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: WB6BYU on January 23, 2023, 08:55:43 AM
I agree that it may be easier to start with a somewhat simpler
circuit to teach the basics, but understanding what the circuit
does is a good start to knowing how to simplify it.

First, always break the circuit into component blocks.  In this
case, the transformer, rectifiers and filter caps, the pass transistors,
the regulator, the over voltage protection, and the metering.

The simplest power supply might just have a transformer,
rectifiers, and filter capacitors to generate DC.  It's unregulated,
so the output voltage will vary with the load, but adequate for a
lot of less critical applications.  There are several variants:  this
uses full wave rectification with two diodes on either side of a
grounded center tap.  (Each side of the secondary delivers
current when it is positive with respect to ground.)  When the
winding doesn't have a center tap (or you need the full winding
voltage rather than half of it) then a full wave bridge with
4 diodes is used.  For low current applications, a single diode
with half wave rectification may be good enough.

The pass transistors are what adjust the output voltage up
or down as needed, controlled by the regulator.  They are
often separated from the regulator because the major
concern is heat dissipation at full current.  In this case, there
are two transistors, with emitter resistors which help to
balance the current between the two transistors (an example
of something that isn't required with a single transistor,
but improves the long term reliability of the supply).

The regulator in this case is an LM723, a common integrated
circuit with lots of features.  However, that makes it more
difficult to see exactly what it is doing without having a
data sheet handy.  A simpler regulator might just be a
single zener diode.

The metering circuit includes a voltmeter and a current meter.
Rather than running the whole current through the latter, it
actually displays the voltage drop across one of the emitter
resistors, which simplifies the required meter movement.

The overvoltage protection circuit is buried in the regulator.
It consists of zener diode CR4 along with SCR1.  When the
output voltage is high enough for CR4 to conduct, it triggers
the SCR, which short-circuits the output (like dropping a
crowbar across it, hence the name) until the regulator shuts
down or the fuse blows.  That provides protection in case one
of the pass transistors shorts, which could otherwise damage
your radio.

There are lots of other parts that aren't necessary for a simple
supply, but are added for good performance.  As G3RZP said,
the LM723 is prone to RF, so there are numerous bypass
capacitors added to reduce the problem.  There are also
extra diodes to protect the supply from damage in case there
is voltage applied to the output when the AC power is switched
off (for example, if the supply is used to charge a battery).


But the first step is always to break it down into component
blocks, then it is easier to see how the blocks work together.
There are multiple circuits that could be used for each of the
blocks, depending on the requirements of the supply.
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: AC2EU on January 23, 2023, 09:28:07 AM
There is no end to to youtube tutorials, some are good, some are bad. Why not wait and  be 100% solid on the theory, before adding to the  bad Youtubes?
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: KF6QEX on January 23, 2023, 10:26:11 AM
Have you considered starting a streaming ham radio class that can teach hams some electronics basics / troubleshooting? You could start with this regulated , non-switching power supply.

You could also add a tip jar so people can send you a few bucks.
And you could even go a step further and create a patreon account have have subscribers that pay you a few bucks every month .

Last but not least add some cool merch for sale for those loyal fans like mugs and t-shirts so they can show off their "IQ" to the world :) 

Just thinking out loud ;)




1.  I built a 13.8 volt DC power supply years ago.  The transformer had two pins, outputting about 18 volts.  That fed a bridge rectifier.

This Astron has multiple pins of output on the transformer, and it appears that they are not using a bridge rectifier. 

Why?

You probably built your supply with a full wave bridge rectifier consisting of 4 diodes arranged on the output of the transformer. That is one way to obtain full wave rectification. The other way, as shown in the linked schematic, is to use a center tapped transformer with only two diodes on its output. The result is the same but there are economic trade-offs between the two designs.

The transformer in the schematic is used to develop two separate DC voltages (often called buses). The lower voltage bus from CR101/CR102 and filtered by C5 is routed to the pass transistors for regulation as the 13.8 VDC output voltage of the supply. The higher voltage bus from CR1/CR2 and filtered by C1 is routed to the regulator circuit.

The voltage to the pass transistors is lower in order to minimize the heat generation in those transistors. The voltage to the regulator circuit needs to be a little greater than the output voltage bus in order for the regulator to maintain control of the output voltage of the supply. There is also an advantage to having the regulator circuit on its own bus as this minimizes the fluctuation in its power supply voltage since it has its own filtering capacitor (C1) for its lower current demands.

- Glenn W9IQ
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: N1AUP on January 23, 2023, 11:11:20 AM


[My first impression of this astron schematic is that the transformer has two outputs.  The inside taps (lower voltage) go to a half wave rectifier, followed by a filter capacitor and then to the pass transistors.  This provides the regulated output of 13.8 volts at up to 35 amps (higher current).  The outside taps (a little higher voltage) also go through a half wave rectifier and filter capacitor and is then regulated by the UA723 (lower current) to the bases of the pass transistors (for higher current through them).  My next step would be to start looking at the specifications of the UA723 to start figuring out all the reasons for all those other little discrete components around the UA723.]

I think a lot of the other components are crowbar stuff to deal with pass transistor failure.

I had no idea that current handling had something to do with voltage on the base of the pass transistors.  I thought pass ts were rated on current, and that was it.  The one I built used a 7812 with diodes on the center pin to raise the voltage to 13 plus volts.  That device drove a T03 pass transistor to handle the higher current.


[/quote]
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: AC2EU on January 23, 2023, 11:44:57 AM
Quote
I had no idea that current handling had something to do with voltage on the base of the pass transistors.  I thought pass ts were rated on current, and that was it.  The one I built used a 7812 with diodes on the center pin to raise the voltage to 13 plus volts.  That device drove a T03 pass transistor to handle the higher current.

It doesn't.
The second sentence is more like it.
Simply put, the 723 regulates the voltage , but has very limited out capability. There is even a 'buffer' transistor to provide enough current to drive the pass transistors.
The pass transistors are in "common collector" configuration AKA "emitter follower, which has voltage gain of about 1 , and  approx beta ( transistor) current gain.
Voltage is determined by the 723.
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: N1AUP on January 23, 2023, 11:54:09 AM
Just talked to the Astron guy.  I'm not a genius yet, but he helped explain some things.

https://elektrotanya.com/PREVIEWS/power_supply/power_supply_vegyes/23432455/egyeb/astron_rs-35m_rs-35a_sch.pdf_1.png

Apparently, the heavy tap off the transformer provides the heavy current for running radios and stuff.  The diodes on the output convert the AC off the transformer to DC, and the filter capacitor removes the ripple. 

The lighter tap provides electricity to do the regulation stuff associated with the 723.  Pin 10 of the 723 drives Q2, which provides voltage from that secondary tap to the base of the heavy transistors that regulate the output of the supply.  I'm guessing the 723 itself lacks enough oomph to do that directly to the output transistors, so they use a transistor in between to handle that increased need.  The 70 amp supply has two  transistors inline with pin 10 before attaching to the heavy duty output transistors. 

He also mentioned that they way that the heavy transistors are controlled is by the 723 applying varying voltage to the bases of the heavy transistors.  He suggested attaching a VOM to the base of those transistors, and varying the load on the supply.  He said that you'd see the voltage applied to the base changing to keep the output voltage consistent.

As I said, I'm not a genius at this, but it is really cool to understand what's going on in the box, and if something does break, how you can troubleshoot, and make repairs.

There are voltages at various points on the schematic.

Plus, also found this, which provided more information.

https://www.repeater-builder.com/astron/astron-repair/astron-repair.html



Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: N1AUP on January 23, 2023, 11:58:15 AM
Have you considered starting a streaming ham radio class that can teach hams some electronics basics / troubleshooting? You could start with this regulated , non-switching power supply.

You could also add a tip jar so people can send you a few bucks.
And you could even go a step further and create a patreon account have have subscribers that pay you a few bucks every month .

Last but not least add some cool merch for sale for those loyal fans like mugs and t-shirts so they can show off their "IQ" to the world :) 

Just thinking out loud ;)




1.  I built a 13.8 volt DC power supply years ago.  The transformer had two pins, outputting about 18 volts.  That fed a bridge rectifier.

This Astron has multiple pins of output on the transformer, and it appears that they are not using a bridge rectifier. 

Why?

You probably built your supply with a full wave bridge rectifier consisting of 4 diodes arranged on the output of the transformer. That is one way to obtain full wave rectification. The other way, as shown in the linked schematic, is to use a center tapped transformer with only two diodes on its output. The result is the same but there are economic trade-offs between the two designs.

The transformer in the schematic is used to develop two separate DC voltages (often called buses). The lower voltage bus from CR101/CR102 and filtered by C5 is routed to the pass transistors for regulation as the 13.8 VDC output voltage of the supply. The higher voltage bus from CR1/CR2 and filtered by C1 is routed to the regulator circuit.

The voltage to the pass transistors is lower in order to minimize the heat generation in those transistors. The voltage to the regulator circuit needs to be a little greater than the output voltage bus in order for the regulator to maintain control of the output voltage of the supply. There is also an advantage to having the regulator circuit on its own bus as this minimizes the fluctuation in its power supply voltage since it has its own filtering capacitor (C1) for its lower current demands.

- Glenn W9IQ

This is not about making money.  It's trying to help people make the move from being appliance operators to having some understanding of what's in the box, so if it breaks, you can fix it. 

It's not likely that people are going to be able to understand and fix a Kenwood 890, but it is possible with an astron supply.

If you're not interested, don't read.  There are lots of posts about lots of other things.

Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: KH2BR on January 27, 2023, 07:55:24 AM
There is nothing better then building a basic power supply and learning from your experiences.
Then you can get a data sheet for the voltage regulator, study its design and implement it into your project. You cant just jump in and teach the astron right away, thats to complex. Small steps !!
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: KD6VXI on January 27, 2023, 11:57:15 AM
Have you considered starting a streaming ham radio class that can teach hams some electronics basics / troubleshooting? You could start with this regulated , non-switching power supply.

You could also add a tip jar so people can send you a few bucks.
And you could even go a step further and create a patreon account have have subscribers that pay you a few bucks every month .

Last but not least add some cool merch for sale for those loyal fans like mugs and t-shirts so they can show off their "IQ" to the world :) 

Just thinking out loud ;)




1.  I built a 13.8 volt DC power supply years ago.  The transformer had two pins, outputting about 18 volts.  That fed a bridge rectifier.

This Astron has multiple pins of output on the transformer, and it appears that they are not using a bridge rectifier. 

Why?

You probably built your supply with a full wave bridge rectifier consisting of 4 diodes arranged on the output of the transformer. That is one way to obtain full wave rectification. The other way, as shown in the linked schematic, is to use a center tapped transformer with only two diodes on its output. The result is the same but there are economic trade-offs between the two designs.

The transformer in the schematic is used to develop two separate DC voltages (often called buses). The lower voltage bus from CR101/CR102 and filtered by C5 is routed to the pass transistors for regulation as the 13.8 VDC output voltage of the supply. The higher voltage bus from CR1/CR2 and filtered by C1 is routed to the regulator circuit.

The voltage to the pass transistors is lower in order to minimize the heat generation in those transistors. The voltage to the regulator circuit needs to be a little greater than the output voltage bus in order for the regulator to maintain control of the output voltage of the supply. There is also an advantage to having the regulator circuit on its own bus as this minimizes the fluctuation in its power supply voltage since it has its own filtering capacitor (C1) for its lower current demands.

- Glenn W9IQ

This is not about making money.  It's trying to help people make the move from being appliance operators to having some understanding of what's in the box, so if it breaks, you can fix it. 

It's not likely that people are going to be able to understand and fix a Kenwood 890, but it is possible with an astron supply.

If you're not interested, don't read.  There are lots of posts about lots of other things.

Typically when someone is wanting to make videos, but doesn't know the subject they are talking about, they are on youtube......  Attempting to monetize their supposed 'channel'.



I'm still trying to figure out what you are trying to accomplish.  Let's say someone walks you through the basics of a basic 723 based supply with pass transistor(s).  Then let's say someone in your class asks a question you didn't know the answer to.

Now what?  Hold on class, let me ask QRZ????

Teachers are supposed to be masters of their subjects, if not at least have a thorough understanding of it's operation and hopefully it's theory.  Coming on a website asking people to teach you how a circuit works so you can teach others.....  huh??????


Seriously, don't get mad at people for questioning your motive(s) here.  What you are purporting to do is a great idea, teaching people electronics and getting them interested in the hobby.

Unfortunately for you, you don't know what you're talking about!


--Shane
WP2ASS / ex KD6VXI
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: N7EKU on January 27, 2023, 08:31:11 PM
Hi N1AUP,

For teaching any subject, you need to be at least a couple levels above the one you are trying to teach.  The example Astron power supply is not that complicated, so experts are not really needed.  But it is obviously above your current level.

When I wanted to learn about radio and electronics, I bought ARRL's "How to Become a Radio Amateur" and read through the whole book about five times, taking notes and thinking about the examples in the book.  Then I bought the next more advanced book, "Understanding Amateur Radio" and did the same thing with that book.  I also read through the old ARRL "Antenna Book".

If you do this, you will have a good basis to understand many circuits.  This doesn't really cover op amps, or digital electronics, but those subjects can be added later.  With this knowledge you can start building and troubleshooting simple circuits like power supplies with different kinds of regulation, with or without pass transistors, crowbar circuits etc.

Getting you hands dirty first and making measurements to make sense of schematics is really important too.  I think ARRL still makes a nice "Hands On..." series that would be worth doing for sure.

73

Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: WT1V on January 28, 2023, 09:15:15 AM
Do the simple stuff first. The xfmr has 2 full wave rectifiers: one goes to the regulator transistors Q101 & Q102 then to the output and the I and V meters, the other to the 723 IC regulator.  Googling the 723 IC you will find it is a regulator and is supplied be the other full wave rectifier. The output goes to Q2 to control the pass transistors. That leaves the other circuitry. The output voltage line also goes to pin 3 of the 723 and Q1 and then to the SCR.  So the SCR gets triggered when the output line gets too high and shorts the output.  So I'm guessing the 723 has internal short circuit sensing and shuts down when the SCR is triggered.
73 wt1v
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: AC2EU on January 28, 2023, 12:58:31 PM
There is so much "noise pollution" on the net already. I hope N1AUP will reconsider contributing to it.

Besides, how are you "helping" the Ham community if you provide inaccurate information?
Title: Re: Are there any tech geniuses who can explain how this circuit works?
Post by: KM4AH on February 01, 2023, 01:11:51 PM
I don't know. My father built mill houses for Cone Mills and kitchen cabinets at night until he was 40 years old.  Then in 1963 they hired him to teach carpentry at the new consolidated high school.
He said he didn't know how much he didn't know about the subject until he had to teach it.