Question about Duncan PSU designer

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Hi,
I have been trying to learn how to to use the Duncan PSU designer.

I have a design that is using a bridge rectifier and the help files say that I should use a transformer value of one leg as the input value.

In other words, if I have a transformer that inputs 120vAC and outputs 200vAC that I should set the transformer value as "100". That seems straight forward.

I was reading about the using the Source Impedance Calculator and that is where I have a question. What voltage do I use in the Source Impedance Calculator for the "Off-load Voltage" input? Would I use the "200vAC" value or half of that?

Thank You.
 
Here are some illustrations to help explain the nature of my question:

Duncan-psu-help-01.gif

This is the help file note that indicates that bridge rectifier designs should use the value of one leg of the transformer as an input value.


Duncan-psu-help-02.gif

This is the help file note that does not specify how to input the voltage value in the "Source Impedance Calculator" when, or when not, using a bridge rectifier.

edit-transformer-01.gif

This is a screen shot of the "Edit Transformer Properties" where I have used a value of 100 for a transformer that outputs 200 volts because the design uses a bridge rectifier.

source-impdedance-calc.gif

This is a screen shot of the "Source Impedance Calculator" where I have used a value of 200 for a transformer that outputs 200 volts.

edit-transformer-01b.gif

This is a screen shot of the "Edit Transformer Properties" after I have used an output value of 200 in the "Source Impedance Calculator" and pressed OK. It appears to update the value in the "Edit Transformer Properties" to 200.

This leads me to believe that I should use one leg in the "Source Impedance Calculator" as well, but I was hoping that maybe someone would have some specific knowledge about how the Duncan PSU designer is intended to work.

I can not find a contact at the Duncan Amps website so it seems like the only way to learn more is to ask publicly and hope someone who knows the answer will see the question.

Thank You!
 
Last edited:
A bridge rectifier has 4 diodes and is fed by two tapping of a single winding.

A full wave rectifier has 2 diodes and is fed by all three tappings of a centre tapped winding.

Most HV gear use a full wave rectifier, especially if the rectifier is a tube/valve version.
 
Hi Merlin,
Thank you for the Designing a PSU with Duncan Amps PSUD II pdf.

Hi Andrew,
Thank you for the explanation. If I understand correctly a "bridge" rectifier is a sub set of possible "Full Wave" designs.

I've used bridge rectifiers in many tube guitar amplifiers I have built.

Here is a document I have refered to in the past: http://www.hammondmfg.com/pdf/5c007.pdf

This is the first time I have attempted to "design" or model a PSU for a tube preamp before soldering up an assembly. In the past I have copied traditional designs and tweaked them on the bench. I am new to using the Duncan PSUD II application and that is why I have a specific question about using it.
 
PSUD II is a little non-precise in this.

1. Full-wave rectifier in PSUD II means and only means the rectifier configuration with two diodes being fed from the ends of a center-tapped HV winding and the center tap being the ground.

In this configuration, only the voltage of one half-winding has to be used.

2. Although a bridge rectifier is also 'full-wave' with respect to its physical principle, it has to be simulated differently, choose 'bridge rectifier' then. The schematic shown in PSUD II tells you if the right one is selected for your application.

For bridge rectifier configuration, the full winding voltage has to be used.

Regards,
Andreas
 
Hi Rundmaus, Thank you for explaining this clearly.

I was actually coming back to thank Andrew for inspiringing me to refresh my memory by looking at the Hammond page I linked too.

It reminded me that Half Wave and Bridge rectifiers with a capacitor input load have output voltage of approximately V (Avg) D.C.= 0.90 X Sec.V A.C while a Full Wave with center tap is approximately V (Avg) D.C.= 0.45 X Sec.V A.C and so I was beginning to deduce that Duncan PSUD II did treat Full Wave and Bridge differently.

You have all been very helpful.

Thanks very much.
 
Hi Rundmaus,
I was just returning to ask a question about this and what I am observing with PSUD II.

Thanks for your comment.

I am a bit confused. The Hammond page indicates that a bridge rectifier with a capacitor input load has these characteristics:

http://www.hammondmfg.com/pdf/5c007.pdf

V (Peak) D.C.= 1.41 X Sec.V A.C.
V (Avg) D.C.= 0.90 X Sec.V A.C.

I was imagining that I would be concerned with the Average because, to my way of thinking, more or less, DC without any ripple is "averaged" and the 120vAC input is a RMS value. My gut instinct was that I would need for example, a 140vAC output to build a 120vDc supply.

I was noticing that the PSUD II graphing displays the curves as reflect the 1.41 factor rather than the 0.9 factor and so I have begun to wonder what I'll encounter in real life when I assemble a circuit.

The PSUD II suggests that I can use a transformer with a 100vAC secondary to get a 120vDC supply.

One reason I am trying to think through this carefully is that I intend to commission a custom wound transformer and while it is reasonably priced it will only seem reasonably priced if I get it close to right the first time and don't have to reevaluate and order a second one after I learn I have made a gross mistake.

I will appreciate any tips about how I should be thinking about this.

Thank You.
 
Last edited:
I have been reading the Hammond page I've mentioned and it indicates that a bridge rectifier with a choke input load has these characteristics:

http://www.hammondmfg.com/pdf/5c007.pdf

V (Peak) D.C.= 0.90 X Sec.V A.C.
V (Avg) D.C.= 0.90 X Sec.V A.C.

I guess I just don't know what the terms peak and average mean... I had assumed that peak was the MAX voltage at the transformer output before the circuit loaded it down and it settled at something below the peak as an average.

The fact that Hammond mentions both specifications, Peak and Avg, with both choke and capacitor input load has gotten me confused when I consider the ideas that have been shared here.


Here is the basic question I am asking; If I build this circuit on a test board:

PSUD-1.gif


will I measure and observe something close to the voltages shown here with my VOM or will the real life voltage be much lower?

PSUD-2.gif


I am trying to end up with something like 100-110vDC at a 40mA draw so right now I am hoping I can take the results of the PSUD II at face value and try to buy some parts and build a test set up and be close enough to be able to tweak some values and get where I need to be.

Thank You.
 
Last edited:
Yes, that is what you will get.

whyvoltage said:
I guess I just don't know what the terms peak and average mean... I had assumed that peak was the MAX voltage at the transformer output before the circuit loaded it down and it settled at something below the peak as an average.
No. Hammond are referring to the peak/average of a full-wave (but unsmoothed) rectified AC sine wave. A cap input PSU (as you have) gives the peak value, which then reduces a little under loading. A choke input PSU gives the peak value with no load, and then the average value with some load and a gradual reduction as load increases. As I said, do some reading on PSUs and all should become clear.
 
psu designer ii headaches

I also am learning how to use psu designer and i think i pretty much have it worked out.

The question I wanted to ask is a very simple one which may appear a little sillly but.

What i was wondering is in the result box should i be paying attention to RMS or Mean voltage when adjusting resistors.

my example is i am trying to design a simple power supply for tone control which has 2x 12ax7's

for the B+ i am getting Mean:261.49v and RMS:265.83v at a current of 4.8ma
if i were to build this circuit and it happened to draw exactly 4.8ma which voltage should i be able to read in the circuit, the mean or RMS.

also the graph line is ending at around 285v is this possibly the voltage i would get in circuit.

for a dc heater supply off the same transformer I am getting Mean:12.514 Rms:12.603 plus the graph on this one is not a thin line but a block of red stretching from about 10.5--15v

these were achived with the simulate set to 5000ms and reporting delay of 0



I have been playing with diptrace plus psu designer for many days now and starting to get a little upset with both of them.

hope you can help

warm regards from
sydney australia
gary
 
the DC has a ripple on it.
The mean (or average) is what your voltmeter will read.
The Power in the varying DC is a little higher, it is the rms value. Only true rms reading instruments read this.

But neither of these matter to the circuit using the supply.

The lowest voltage, on the varying DC, is the voltage that causes voltage or current clipping.
Subtract half the ripple peak to peak from the mean to get a fair indication of the minimum voltage on your supply rail.

When ripple is very low, this correction of half the peak to peak is generally ignored.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.