TDA2030 output dc decoupling capacitor rating - Page 1
Forum section: electronics / beginners

author: hozone
author_rank: Regular Contributor
timestamp: September 04, 2022, 09:10:40 am
content: Hello,I'm building a single supply TDA2030 amplifier.I've a question on the output dc decoupling capacitor voltage rating.Let's suppose the datasheet values are used, and supply voltage is 24V (see attached schematic).I'm talking about the 2000uC cap in series with the speaker.What's the voltage rating I should use here?thanks!

author: iMo
author_rank: Super Contributor
timestamp: September 04, 2022, 09:17:39 am
content: 50V or 63V

author: hozone
author_rank: Regular Contributor
timestamp: September 04, 2022, 09:31:16 am
content: Thanks!Can I ask you how did you get this result?

author: wraper
author_rank: Unknown
timestamp: September 04, 2022, 09:33:52 am
content: 25V is more than enough. In practice there will be 12V on the cap unless you try to amplify some very low frequency signal.

author: Ian.M
author_rank: Super Contributor
timestamp: September 04, 2022, 09:38:06 am
content: The output can swing from near 0V (ground) to near +Vs, and the speaker provides a DC path to ground, so the capacitor needs a voltage rating greater than +Vs, even though on average it only has +Vs/2 across it. A 25V rated capacitor would be the lowest sane choice.However, assuming an 8 ohm speaker load, the TDA2030 can deliver nearly 8W (Its rated for 8W into 8 ohms at 28V +Vs), so the AC current through the capacitor can be nearly 1A, and thus the capacitor needs a ripple current rating of over 1A at all audio frequencies. Higher voltage rating capacitors generally have larger can sizes and a larger can generally increases the ripple current rating, so Imo's preference for a 50V or 63V rated capacitor is justifiable.Also, if the capacitor is mounted anywhere near the TDA2030 heatsink or other significant heat source a 105 deg C temperature rating would be advisable.

author: wraper
author_rank: Unknown
timestamp: September 04, 2022, 09:47:50 am
content: Quote from: Ian.M on September 04, 2022, 09:38:06 amFirst of all real music is not like amplifying sine. Therefore average actual power will be lower. Secondly, high frequency components in sound contain only a small fraction of power. Thirdly, basically any 2200uF 25V cap has more than 1A ripple current rating at 100/120Hz, and with increasing the frequency, ripple current rating rises.QuoteCapacitor will be approximately at half of +Vs unless you try to amplify something below audible frequency.

author: hozone
author_rank: Regular Contributor
timestamp: September 04, 2022, 09:53:48 am
content: Thanks all!

author: Zero999
author_rank: Super Contributor
timestamp: September 04, 2022, 10:50:27 am
content: Quote from: wraper on September 04, 2022, 09:47:50 amYou're right about the average power and frequency content of music, but incorrect about the ripple current rating increasing with frequency. At high frequencies, the losses due to skin effect increase, causing more power to be dissipated inside the capacitor, which would reduce its ripple current rating. This doesn't matter in this application because the power at high frequencies is low, as you've correctly stated.QuoteYes that's true. In theory, you could use a capacitor with a voltage rating of1/2+Vs, but the capacitor could be subject to higher voltage transients i.e. during power up, or when something is connected to the input, whilst the power is on. I'd recommend a minimum voltage rating of +Vs - 2V, because the amplifier's output stage will drop a couple of volts, so it would cover the transients and it's always good to allow some headroom for reliability.Quote from: hozone on September 04, 2022, 09:10:40 amI'd recommend:C3 & C5 = 35VCB = 22µF 25VC1 = 1µF 25VC2 = 2.2µF 25V because it's easier to find than 2µF.C7 = 220nF 25V2000µF can be 2200µF 25V again because it's easier to find.Higher voltage ratings are obviously fine and you'll probably find it's easier to get small capacitors ≤2.2µF in 50V, than 25V.

author: strawberry
author_rank: Super Contributor
timestamp: September 04, 2022, 10:56:07 am
content: 150k better 10k less sensitive circuit and better high frequency response

author: iMo
author_rank: Super Contributor
timestamp: September 04, 2022, 11:26:53 am
content: Quote from: hozone on September 04, 2022, 09:31:16 amWith your 24V Vcc and the inductive load, with all possible transient effects you may imagine, I came to conclusion it should be 2x higher than the Vcc.. Your amp will work longer, I bet

author: Zero999
author_rank: Super Contributor
timestamp: September 04, 2022, 12:34:20 pm
content: Quote from: strawberry on September 04, 2022, 10:56:07 amSorry that's meaningless. Please explain.Quote from: imo on September 04, 2022, 11:26:53 amHow did you arrive at that insanely high figure? It's not true. The amplifier's low output impedance, the Zobel network formed by R4 and C7 damp any transients and failing that D1 and D2 clamp the output to the supply voltage. A voltage rating of 25V is sufficient.

author: wraper
author_rank: Unknown
timestamp: September 04, 2022, 12:55:34 pm
content: Quote from: Zero999 on September 04, 2022, 10:50:27 amTake any capacitor datasheet with ripple current frequency coefficients. Usually it's about 1.5-2 times higher for 100kHz than for 120Hz. Example:http://www.samwha.com/electric/product/list_pdf2/RD.pdf

author: Zero999
author_rank: Super Contributor
timestamp: September 04, 2022, 01:57:41 pm
content: Quote from: wraper on September 04, 2022, 12:55:34 pmYou're right. I was wrong about the ESR, which decreases at higher frequencies, up to a point when it becomes flat. The skin effect isn't important because most of the ESR is due to the ions in the electrolyte.https://www.nichicon.co.jp/english/products/pdf/aluminum.pdf

author: iMo
author_rank: Super Contributor
timestamp: September 04, 2022, 03:41:17 pm
content: QuoteImagine a mountaineer (alpinist/climber) who wants to climb K2 and who orders on Ali a 700N rope as his net weight is 70kg

author: Zero999
author_rank: Super Contributor
timestamp: September 04, 2022, 03:51:07 pm
content: Quote from: imo on September 04, 2022, 03:41:17 pmWhat an absurd analogy.

author: wraper
author_rank: Unknown
timestamp: September 04, 2022, 03:57:59 pm
content: Quote from: imo on September 04, 2022, 03:41:17 pmImagine that SMPS use 16V caps for 12V output and it works just fine (unless it's a cheap garbage with garbage design, made from garbage components). In this case there is about 2x margin when 25V output cap is used. Also you completely misrepresent situation. Rope stopping 70kg in fall will experience way more than 700N of force. While this cap will not. This cap is basically a level shifter, not some component which could experience so called voltage transients because it holds no energy. Capacitor is resisting voltage change across it. How much energy do you think is stored within a speaker to be able to charge a 2000uF cap above +Vs? Why it will do so in one direction only, why it won't charge capacitor to voltage of opposite direction?

author: strawberry
author_rank: Super Contributor
timestamp: September 04, 2022, 04:24:22 pm
content: THD will be x2 no mater how low ESR issome Grundig amp used additional feedback after el.capacitor

author: hozone
author_rank: Regular Contributor
timestamp: September 07, 2022, 06:09:16 am
content: Thanks all! I've finally used a 2200uF 50V salvaged from an old gear. I will not use this amp that much, it will be just a practice guitar bass amp I'll use a low volume.

author: mariush
author_rank: Super Contributor
timestamp: September 07, 2022, 08:50:17 am
content: You should go with TDA2050, as it's less picky about input voltages, it can run with lower input voltage (but of course, the total output power is less the lower the input voltage).They can still be bought from lcsc.com, but made by asian companies (HGSEMI or Unisonic UTC for example).The clones may differ from original parts by lacking or having weaker protections (ex no short circuit protection or weaker over voltage protections)The datasheets have example circuits just like the TDA2030 datasheet has and it's just as easy to make amplifier.Also see this but they use split power supply design here :https://diyaudioprojects.com/Chip/DIY-TDA2050-Hi-Fi-Chip-Amplifier/other linkshttps://www.eleccircuit.com/tda2050-amplifier-stereo-35w-75w/https://www.circuitbasics.com/tda2050-diy-amplifier-build-guide/

author: hozone
author_rank: Regular Contributor
timestamp: September 07, 2022, 11:49:33 am
content: Thanks.Indeed I'm thinking about the TDA2050 too, the decoupling there it's 1000uF.What I wanted to know with my post here was not strictly referred to the TDA2030 but was more a question on the decoupling cap. I just take the TDA2030 as example cause I've one here and I'm "playing" with that.I have a single supply trafo laying around here... that's the reason for the single rail, but I prefer dual rail design.

author: CaptDon
author_rank: Super Contributor
timestamp: September 07, 2022, 01:09:23 pm
content: With a single ended supply one of the things sadly missing here is a 'turn-on delay relay' for the speaker!!! This thing will thump the speaker while charging the capacitor to idle state. A relay circuit with delayed turn on which will allow the capacitor to equalize through perhaps 33 ohms for 2 to 4 seconds prior to switching the output over to the speaker would be a nice 'add-on'. The relay coil should also be wired through an extra set of contacts on the power switch so that when switched off the relay immediately opens the speaker path. Some of these amplifiers tend to break into uncontrolled oscillations as the power supplies decay and can damage sensitive tweeters. 2000 or 2200uf at 16vdc is very common and more than enough safety margin. I am surprised at the published ripple current ratings vs. frequency? My experience is that capacitors start to show a series inductance at higher frequencies although maybe not so much below 100khz and when new? As an amplifier designer and builder since the 70's there are 'just good enough' designs and there are 'this thing will live forever' designs often achieved with only a 10% increase in cost over a weak design. As for the THD thing due to the coupling capacitor....Even the highest caliber set of 'audiophool' ears couldn't tell if this amp was a single supply with speaker coupling cap or dual supply without the cap...Except for the turn-on thump!!!

author: hozone
author_rank: Regular Contributor
timestamp: September 07, 2022, 05:54:33 pm
content: So clearI think mine can be called a "just good enough" designSee attached just for curiosity (this is the TDA2050 version).

author: mariush
author_rank: Super Contributor
timestamp: September 07, 2022, 08:11:55 pm
content: I'd be more comfortable with 50v rated electrolytic after that transformer.If you have a 230v - 20v AC transformer, you have to account for the voltage at idle (low power consumption) and also for the voltage you may have at 2-3 am in the morning when power consumption in your building or around you is very low.I have personally measured 245-250v AC in my mains sockets in the middle of the night, which is still legal, as the mains voltage is 230v +/- 10% or maybe -5% / +10%.For the capacitance, you can estimate with the formula C = current / [2 x ac frequency x (Vdc peak - Vdc min) ] but usually 2200uF is good for around 1A of current with reasonably small voltage drop.IF that transformer was only used for the 9v, then assuming vdc peak = 20v x 1.414 - 2 x ~ 0.8v = ~27v and your Vdc min is around 12v (9v + regulator drop + some safety margin) and your current is around 0.3A (more than enough for relay and the ics) then you'd need C = 0.3 / (100 x (27-12)) = 0.3 / 1500 = 0.0002 Farads or 200uF so even a 220uF would be plenty, and a 470uF would be overkill.Not sure why you'd have R3 at 3.3 megaohm and R43 at 1 megaohm, values seem a bit high to me but maybe I don't get it.

author: hozone
author_rank: Regular Contributor
timestamp: September 08, 2022, 08:03:01 am
content: Thank you!Good to know about the capacitance formula ( C = current / [2 x ac frequency x (Vdc peak - Vdc min) ] ), I have never used it, now I have a new tool in my swiss army knife35V was a copy and paste error, indeed I've put 50V - updated schematic attached. (also I've notice now 220V transformer and 230V AC input typo error, I will fix it later). Also 7809 could be 78L09.About the 3.3M and 1M, the first value comes from the Tillman preamplifier design (http://www.till.com/articles/GuitarPreamp/), it's for the input impedance of the bass guitar. Second one it's "stolen" from the 1wamp design from Electrosmash.com (see attached).

author: Zero999
author_rank: Super Contributor
timestamp: September 08, 2022, 09:22:29 pm
content: Quote from: CaptDon on September 07, 2022, 01:09:23 pmThere won't be much of a power on thump. CBcharging via RA||RBgiving a of time constant 1.1s.t =RA||RB*CB= 100k/2*22µ = 50k*22µ = 1.1sThe time constant of R2 & C2 is much shorter: t = C1*R2 = 2.2µF*4k7 = 10.34msWhen the power is initially applied. CBwill take a long time to charge up, so the voltage on the non-inverting input will rise slowly. C2 will charge a little quicker, creating a blip and the difference amplified, creating a small blip on the output. The simulation shows a 450mV pulse which peaks at 52ms, which will not be barely audible.

author: hozone
author_rank: Regular Contributor
timestamp: September 09, 2022, 06:17:57 am
content: Once again I made things simpler than it was. Thank you for taking me back to reality