What does the Choke (C.L.C.)  in a Tube Power Supply do?  - Page 1
Forum section: electronics / general

author: johnlsenchak
author_rank: Frequent Contributor
timestamp: September 08, 2018, 01:41:31 am
content: This guy (Mark) puts out some down right amazing tech videos !What does the Choke in a Tube Power Supply do?Blueglow ElectronicsPublished on Sep 7, 2018BG188 - An explanation of what a choke (inductor) does in a vacuum tube power supply. Choke input, capacitor input, CLC and CRC filtering explained.

author: basinstreetdesign
author_rank: Frequent Contributor
timestamp: September 08, 2018, 04:03:18 am
content: Actually I am less than overwhelmed by his explanation. By the end of the video he never actually gets around to saying what the inductor did! He showed the end result. There was no mention of its action on a changing voltage across it and what effect it would have on its current or why such action would happen. No mention of Lenz's Law. No mention of how the inductor accomplishes its purpose in concert with the other components or what the effect of deleting or changing those components would have on the circuit operation. For instance, what would happen if the capacitor immediately after the rectifier was left out? (HINT: other parts would not have a happy time of it) I will forgive the lack of any discussion on how to calculate or choose the best inductance value as that would probably be above the pay grade of his audience.But, he should at least get the basics right. It's grinding to hear @11:02 "voltage going through..." come on! Voltage does not "go through" circuit elements. It appears ACROSS elements. Current "goes through". Power is developed "within" elements.OK /rant

author: schmitt trigger
author_rank: Super Contributor
timestamp: September 08, 2018, 04:09:36 am
content: I have a 1929 Atwater Kent radio.Back on those days there were not powerful enough permanent magnets for loudspeaker use.Therefore it had an electromagnet which did double duty as a choke inductor.

author: johnlsenchak
author_rank: Frequent Contributor
timestamp: September 08, 2018, 04:25:44 am
content: Quote from: basinstreetdesign on September 08, 2018, 04:03:18 amI think he should have statedit as that the choke " acts like a inductive reactor limiting the current that passes through and also smooths out the AC component making it more direct current in nature"

author: vk6zgo
author_rank: Super Contributor
timestamp: September 08, 2018, 04:28:16 am
content: Quote from: basinstreetdesign on September 08, 2018, 04:03:18 amThat was done---it's called a "Choke Input Filter"An advantage of such a configuration is better voltage regulationQuote

author: bsfeechannel
author_rank: Super Contributor
timestamp: September 08, 2018, 02:57:18 pm
content: I'll hazard a guess."Way back when" (courtesy of Mr. Carlson's lab), linear power supplies were not designed as we do today: choose diodes with sufficient forward current, slap a large capacitor across the rails and use a voltage regulator.Rectifier tubes have considerable internal resistance, which varies with the current. You had to consider the ripple current an electrolytic capacitor would take in order to calculate its internal heat dissipation. Something we don't even think of doing today for most projects.What a choke essentially does is to smooth out the ripple current. With that you ease the stress on the filter caps, and the rectifiers work almost under constant current. Chokes can also be designed to reduce their internal impedance with the load current near saturation to compensate for the variable resistance of the rectifiers, thus improving voltage regulation.At least that's what I understand after reading the "Radiotron Designers Handbook Fourth Edition", p. 1161 to 1186.

author: coppercone2
author_rank: Super Contributor
timestamp: September 08, 2018, 03:20:48 pm
content: It's actually a good idea IMO if you are doing a nut and bolts design with no care for size or cost or weight.If you power your supply from a capacitor and limit current with a fuse or active element any kind of semiconductor failure (unless your current regulator is working) you will get a monstrous current pulse that will cause arcing because the capacitor has low ESR.The consequence of the heavy component is that you might not get a regulator that blows up, instead it will fry nicely without visible damage, in the time it takes for the fuse to open. Also the semiconductors will protect eachother better with a lower current since there wont be a plasma bridge that is as bad, so you may limit damage to less or a single component with more probability.If you put inductors at the input of the capacitor then you get inrush current control to the capacitor and the diode bridge is better protected. I have made a few threads about inrush current from mains if you switch in at the right time,it appears you can get between 50-2000 amps peak, depending on your home wiring. If you keep switching on a capacitor with a massive inrush the diodes will get hammered and the capacitor will be degraded.But you do get a resonance that you need to either accept or somehow dampen. It will change because electrolytics won't keep their value well.Also think about the CIC vs ICI filter configuration when making this choice (T or Pi filters (if you draw it, it looks like Pi with LCL and a T with ICI).. but keep the resonance in mind.Also keep in mind ICI / CIC filters are mirroredThe norm is obviously active inrush control or relay switched inrush control combined with fuses. movs, gdt and nonlinear devices to handle surges, and to handle the nonsurge filtering in a manner less related to inrush control, rather then to try to use the filter for both tasks. By surge I mean the input impedance of the circuit becoming extremely low / amplitude increasing at expected input frequencies, not transients which I define as high energy at frequencies not supposed to be there ever.But look, with no load to dampenI used 5 ohms for the inductor (high) and 0.5 ohms for the electrolytic.If you just have a wire rather in a inductor, the resonance will be non issue because the capacitor is large and has a ton of parastics but the wire inductance is tiny and pretty perfect in comparison . But you get like a 200A spike vs a 5A spike. A semiconductor will fail nicer if you trim that 200A down. Obviously you can set it to whatever you want to make acceptable response and resonance and everything.The main problem is load impedance of the power company and your home (if you don't have a transformer). If you have a transformer and you feel comfortable with the worst case surge being like 10X the transformer current, then you are OK.Since you have a transformer, that will reduce the inrush current to something like 10-20 times the transformer rating in the scales we are typically dealing with (but check my other threads to see what people wrote).Also, this solution is not liked because it wastes power and creates a voltage drop. The less you use it the more efficient it is. The quality of current nonlinear protection designs is good enough that you probably should not do it under normal circumstances, but I find it interesting.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 08, 2018, 04:04:59 pm
content: Besides reducing ripple, the choke also improves the power factor. For this reason old PC power supplies from the 1990s quite oft had a similar positioned choke - though at the input of a switched mode power supply. So if you look for a suitable choke those PFC chokes might be worth a look.Back then electrolytic caps where relatively expensive and also considered limited lifetime - though the early one usually lasted longer than expected. Chokes get more effective and increase in cost less than linear with higher power. So for a high power circuit the choke can be also cheaper. Another advantage of the choke compared to a larger capacitor is, that the choke does not need an extra bleeding resistor to remove stored energy fast.The effect on inrush current limiting can be less than the simple simulations as there is possible saturation.

author: floobydust
author_rank: Super Contributor
timestamp: September 08, 2018, 04:26:49 pm
content: As Kleinstein says there was an era where filter capacitors were small yet expensive so large chokes were incorporated. Copper and iron were low cost back then.Since the choke is a component with energy storage, it does lower ripple by providing current during the valleys in the input pulsing DC.Tube rectifiers such as 866 and 5U4 did not like high peak currents from large filter capacitors.So you would see first a small 2uF-40uF filter capacitor used, in a C-L-C filter and then the larger cap. to lower the rectifier peak currents.I've used big chokes in power supply L-C filtering, 5-10H and 500-1kVDC. There, the choke acts like a constant-current source during valleys in the input pulsing DC, and actually helps regulation.But big, heavy, expensive by today's standards.

author: james_s
author_rank: Super Contributor
timestamp: September 08, 2018, 05:32:12 pm
content: Quote from: schmitt trigger on September 08, 2018, 04:09:36 amYeah that was pretty much standard up into at least the 1940s. I have a couple different Philco radios from the late 30s that have the same arrangement.

author: SeanB
author_rank: Super Contributor
timestamp: September 08, 2018, 06:47:02 pm
content: Beware of those chokes in older PC power supplies, they often were fake parts, consisting of an iron core 9 because that is the cheap part) and then a single turn of wire looped through, as the copper is the expensive part, then encapsulated in plastic to hide the fact.