I try to explain in my germlish:
A L-input-choke has to withstand much harder conditions.
The best is to make a simulation with the fantastic PSUD - tool from DuncanAmps and you will see whats going on.
Regards,
Hilmar
A L-input-choke has to withstand much harder conditions.
The best is to make a simulation with the fantastic PSUD - tool from DuncanAmps and you will see whats going on.
Regards,
Hilmar
In a choke-input filter the choke has to withstand much higher average current, so it needs thicker wire and a bigger air gap to avoid saturation and overheating.
A choke in a choke-input filter has exactly the same average current as a smoothing choke in a cap input filter, but it also has a significant AC current/AC voltage which increases heating and can cause lamination hum. If you put current at two different frequencies (one of which may be DC) through a resistance then the heating powers add. (If at the same frequency then you have to add voltages, taking account of phase, and then calculate power).
Does anyone make "swinging chokes" or chokes for LC filters anymore?
I've always just overrated, for example using a 200mA choke in a 80mA class A circuit.
Back "in the day" I've seen modifications to Dynaco 70s, part of it dropping the B+ voltage by using that tiny 1.5H unit as a LC filter. Not something I would recommend, but it seemed to work.
Just an aside, I used to own a big HP 0-500VDC/200mA regulator. The first choke in the power supply had an electric fan blowing on it.
I've always just overrated, for example using a 200mA choke in a 80mA class A circuit.
Back "in the day" I've seen modifications to Dynaco 70s, part of it dropping the B+ voltage by using that tiny 1.5H unit as a LC filter. Not something I would recommend, but it seemed to work.
Just an aside, I used to own a big HP 0-500VDC/200mA regulator. The first choke in the power supply had an electric fan blowing on it.
Last edited:
I've been looking in to this, and noticed Electraprint will wind them for you. I didn't find any 'off the shelf' options.
I use a swinging choke from an old Motorola transmitter in my ps. Mostly to drop the B+ to a useable level.
When using a C input choke for L input PS, how much overrate does the choke has to be ?
Is there an equation or a general rule ?
Two issues for overrating: heating in the windings, and core saturation. You can get a figure for heat from the RMS current given by PSUD2. Core saturation is a matter of peak current, although a little saturation may do no harm. You would need to know whether the stated choke performance for DC is limited by heat or flux. A well-designed choke will probably have equal limits on each.
Focusing only on current handling, what would be a suitable percentage range of overrate for a C input choke ?
Let's say the DC current draw is 100mA in a L-input PS.
What is the max mA that the C-input choke needs to be able to handle ?
Let's say the DC current draw is 100mA in a L-input PS.
What is the max mA that the C-input choke needs to be able to handle ?
Many say a factor of 2 is the rule of thumb, but a more accurate answer really depends on the manufacturer, and what AC voltage and current you're running the choke at. If you model the power supply in PSUD2 you can find the RMS current at your operating point, then ask the manufacturer if the choke can handle that.
For example, I am getting away with using a Hammond 159ZL (10ADC) choke as L1 in the 10V, 10A choke input filament power supply for my 833 amps, even though it's only rated for 10A. PSUD gives me an RMS current of 10.97A, and when I spoke to Hammond they told me that anything under 120% of the rating will be OK in terms of core heating. The choke does buzz a little but drilling out the metal bracket around the core and putting six bolts through it has tamed that, and mounting it on rubber washers has made it silent outside the chassis. Going to a 20A rated choke was not an option due to size, but with a little work I was able to make the smaller choke work because of the low voltage of the supply.
I bought Choke input Chokes from China work very well, also from Indonesia; Sowter also makes them.
Phil
Phil
Looking at the current (mA) figures for the first choke in PSUD, I see a very high spike of current at the first half of a second.
RMS is 15mA and the top of the spike is 200mA.
Lets say the choke can run safely at 50mA, in general, can chokes handle this kind of current spike ?
RMS is 15mA and the top of the spike is 200mA.
Lets say the choke can run safely at 50mA, in general, can chokes handle this kind of current spike ?
What happens to the voltage in the sim?
It's possible to specify the input choke of a choke input filter so that it will saturate on the turn-on current surge. This will leave the choke's DCR as a resistor so no inductive high voltage spike.
If you're into the details, do a search of the Audio Asylum for old posts by VoltSecond. Lots of detail.
It's possible to specify the input choke of a choke input filter so that it will saturate on the turn-on current surge. This will leave the choke's DCR as a resistor so no inductive high voltage spike.
If you're into the details, do a search of the Audio Asylum for old posts by VoltSecond. Lots of detail.
