PSUD (Power Supply Unit Designer)

Disabled Account
Joined 2002
Hello,
I have build some choke input power supplies where the only thing i cared about would be to get the highest number of Henry which would be limited by the current it had to support and the availabilty on the market.

It could be possible that some of these power supplies would look '' bad '' when being checked with PSUD. Most of my power supplies use a shunt power supply so the current demand should not fluctuate. The supply for the DRD amp could be a bit hard to make with regulation.

Greetings, Eduard
 
A choke input supply with a very low resistance choke, low resistance secondary and semiconductor rectifiers might ring because there is nothing to damp the LC resonance. Some resistance somewhere will damp the resonance. In many cases the necessary resistance will be provided by the choke or secondary or by using vacuum rectifiers. If not, you may need to add a big snubber.
 
Disabled Account
Joined 2002
Hello,
It shows in simulation that adding some resistance to the secondary winding or the input choke does some damping.
I am already using a tube rectifier.
The snubber should be across the total secondary winding so skipping the centre tap or across the first choke or do both snubbers have a different task?
Greetings, Eduard
 
Disabled Account
Joined 2002
Hello,
The snubber across the transformers secundary must be a serious one i will be used across the 850-0-850 ac voltage. I remember i read Morgan Jones wrote somewhere that there is a combination of a certain resistor and a certain capacitor value that will work in most of the time without '' fine tuning ''
For the cap to be placed across the reservoir capacitor are there any specs to look for? Should it just be a capacitor or an RC network?
Greetings, Eduard
 
Disabled Account
Joined 2002
I said snubber, which means RC.

Hello,
Because usually you will see people adding a small bypass capacitor on a big power supply capacitor. Sometimes adding a low esr capacitor at the output of a regulator can have bad effects. Could something similar happen to a simple power supply? And that is the reason why would use an RC instead of only a capacitor.

Yes i did work with high voltages before like a laser cutting machines that uses voltages around 20000 volts to create a beam. I always use a bleeder that will drain the power in a few seconds and to be sure i always check with a meter.

Greetings, Eduard
 
Disabled Account
Joined 2002
Hello,
In my audio documents i have an article written by Morgan Jones where he has done some test with snubbers or just caps positioned across the secondary windings on or across the diodes. HIS conclusion in most cases a 1 nF cap in series with a 1000 ohm resister across the transformers secundary is all you need.

For the 1000 ohm usually a carbon resistor will be perfect. What about the 1nF if your secondaries will be 850 volts AC? A copy and paste from another thread about PSUD:

Your amplifier is NOT a "constant current". And ideal CCSes act funny and upset simulation. A tube acts a lot more like a resistor than a CCS. If you double the voltage, the current is not the same, it at least doubles. Figure your load as-if it were a dumb resistor.

There is NO good point in modeling past the C-L-C section. The R-C droppers for the driver were figured out in 1947 and Ohm's Law has not changed.

I thought the idea behind the ccs would be to check how the supply would react to a change in the current taken by the circuit. The cap closest to the circuit will supply that demand and be ''recharged by the capacitor that is closer to the rectifier.

Rinaldo Bassi, a famous French '' audio technician '' wrote that the time constant of the last filter should be bigger than the first one so it can be recharged easily by the first stage.

Greetings, Eduard
 
eduard said:
Because usually you will see people adding a small bypass capacitor on a big power supply capacitor. Sometimes adding a low esr capacitor at the output of a regulator can have bad effects. Could something similar happen to a simple power supply? And that is the reason why would use an RC instead of only a capacitor.
A snubber is not a bypass. Most bypass caps do nothing useful; some do harm; a few do some good.

The idea of the snubber is to damp the LC resonance formed by the choke and the capacitors, if necessary. It has some similarity to the problem at the output of a regulator, because there you have a virtual inductor (the regulator output impedance) so a capacitor (which people love to add) can resonate.

In my audio documents i have an article written by Morgan Jones where he has done some test with snubbers or just caps positioned across the secondary windings on or across the diodes. HIS conclusion in most cases a 1 nF cap in series with a 1000 ohm resister across the transformers secundary is all you need.
Different snubber in a different position for a different purpose.
 
First, many thanks to duncanamps for this invaluable tool.

I have a question about entering values for a center tapped full wave rectifier.
For entering off load voltage, the help file is quite clear that you should enter one half of the total end to end voltage.
I am unclear about the impedance for the transformer secondary.
Bringing up the source impedance calculator help file states that "Winding resistance: The measured resistance of the secondary winding." Would this be the resistance from the center tap to one end just like the off load voltage or the resistance across the entire secondary?

Again, this is a great resource for the diy community!
 
First, many thanks to duncanamps for this invaluable tool.

I have a question about entering values for a center tapped full wave rectifier.
For entering off load voltage, the help file is quite clear that you should enter one half of the total end to end voltage.
I am unclear about the impedance for the transformer secondary.
Bringing up the source impedance calculator help file states that "Winding resistance: The measured resistance of the secondary winding." Would this be the resistance from the center tap to one end just like the off load voltage or the resistance across the entire secondary?

Again, this is a great resource for the diy community!


Take the impedance from the centre to one leg. In reality, your transformer is likely to be wound with two different winding resistances as the one towards the outside uses more copper for the same turns. Take the end to end and divide by 2 if you really want to get a good result.


The help file offers no guidance on that, an omission that will be fixed in PSUD 3.
 
Any movement on the 3rd version. I struggle with trying to model rectifiers not listed. The rectifier modeling feature would be a godsend.


Yes, things are happening, just very slowly. It's a whole ground up rewrite, the simulation engine is complete and is extremely accurate, unlike PSUD2.


The user interface is being sorted out at the moment, and I continue to spend time here and there when other demands permit. It's not likely I will get anything out on the streets until the Christmas break, but that's the one time of the year when I get an opportunity to do stuff like this :)