How can I calculate inductance for these inductors.

[Oneminde]

Okay fellas.
Electronics is fairly new to me and there are things I do not understand, but I want to learn. Right now I am facing some difficulties in fully understanding how I should proceed when calculating the values.
Its two DC-DC Transformer converters. One is located in a protection board after the Preamplifier, and the other type is located on the Power amplifier board.

This is a car amplifier. I have included schematics and general information for the amp that is related to the components in question.

Information:
Response Bandwidth: 5-100 kHz (but in reality it is 5-20kHz)

Amplifier Output details:
300 W - 4 Ohm - 2 ch.
600 W - 2 Ohm - 2 ch.
1000 W - 1 Ohm - 2 ch.

Low Pass Frequencies: 50-200 Hz
High Pass Frequencies: 50-200 Hz
Bass Boost Frequency: 40 Hz
Bass Boost Gain: 0 to +10dB
Output Power: Total 2000 Watt
Distortion Factor: 0.02%

Power is supplied through twin 70A resettable circuit breakers.

300W / 14.4V = 20.8(21)A
600W / 14.4V = 41.6(42)A
1000W / 14.4V = 69.8(70)A
 
***
Protection Board.
Looking at the Primary input of the DC-DC Transformer Converter, it looks like it is 12V from the battery which is regulated by the 2SC3074 TOSHIBA Transistor, here also referred to as Q871, 872 Inverter to 9.3V (?). On the secondary side, we see some Low Forward Voltage drop Diode followed by  16V and 80V capacitors - there is also one 0.45 uH inductor.

This is the first part in question. What values or power rating dictates the value for this ?

Power amplifier.
The DC-DC Transformer Converter or Inductor primary side shows: B+, 1 x 160V capacitor and 5 x 16V capacitors., while the secondary shows: 1 x 100V and 2 x 63V capacitors., from there we can see B+ 58V and B- -57.8V (116,8V total). There is one inductor for the B+ and one for B- side.

This is the second part in question. What values or power rating dictates the value for this ?

Download the attachment and view in full size or open in new window for fine details.

[T3sl4co1l]

1. You mean L851?

2. Voltage rating isn't very clear, and I don't see any 100 or 160V on the secondary (left) side.  To what are you referring?

Tim

[Oneminde]

1. You mean L851?

2. Voltage rating isn't very clear, and I don't see any 100 or 160V on the secondary (left) side.  To what are you referring?

Tim

Sorry for the late reply.

1. The L851 is indicated as 0.45 uH, so that is not an issue. The T851 DC-DC Transformer value is. Not sure what to use - value that is - to calculate. I have included a larger and cleaned up image of that "Protection Board"

2. Voltage specs is now more visible for "Protection Board" and "Amp Board" - see attachement.

[T3sl4co1l]

The film caps are higher voltages just because film capacitors aren't available in low voltages.  Depending on how modern this design is, they could've used aluminum polymer instead (which have comparable performance to films, but with much lower voltage ratings and much higher capacities).  Or, they just needed one or two such caps, in particular locations.

The transformers will be defined more by saturation flux density than inductance.  Likely for all of them, the permeability is high, so that the inductance is large enough not to matter (very little energy storage).  The inductance will also have a large tolerance on it, and vary significantly with current.

The turns ratios will simply be the voltage ratios (sadly, this design has neither voltage regulation nor current limiting, a very dangerous design indeed), and the required flux needs at least this many turns:
N = Vpk / (4 * F * Bmax * Ae)
Where Ae is from the transformer core's datasheet, Bmax is the desired peak flux density (Bmax must be < Bsat, usually 0.3T for ferrite), and F is the switching frequency.  (It looks like the uPC494s are wired for about 80kHz oscillator frequency, which is divided internally to 40kHz output frequency. R968 and C928 are the frequency setting components, and Fig.1 in the datasheet http://www.ti.com/lit/ds/symlink/tl494.pdf gives the frequency vs. component values.)

An important question: why do the transformers need to be replaced or reconstructed?  If you're building from scratch, this isn't the best design to work with.

Tim

[Oneminde]

An important question: why do the transformers need to be replaced or reconstructed?  If you're building from scratch, this isn't the best design to work with.

Tim

"If you're building from scratch, this isn't the best design to work with" - Good question. It started with several people saying that this is one of SONY's best amplifier, and for me who is not an expert yet, it certainly looks like a beefy construction. This date back to 1999 so the design is a bit older. But so far I like it, but should I ?

Well, I do not have the amp and the missing value in the schematics is the transformer / inductors.

[T3sl4co1l]

Given the general build quality, the amount of circuitry (including protection, preamp and so forth) and the adherence to ratings, I don't doubt that this is a quality Sony product.  (As opposed to a cheap Sony product, for which it's important to remember: neither term is exclusive.  Sony is a huge company and makes both consumer and professional equipment!)

But, as with ALL automotive power amplifiers I have seen, they commit the cardinal sin: neglecting filter inductors, leaving off current mode protection, assuming that the 12V input won't do anything sudden and dangerous.

The only safe way to build a switching supply is with some means of monitoring and controlling the switch current, and switching that current into an explicit inductance.

The uPC494s are wired for maximum duty cycle, except during startup, when they rise, v-e-e-e-r-r-y-y, s-l-o-w-l-y, to mitigate inrush.

If the secondary side goes shorted, it explodes.

If the primary side surges, it explodes.

If the primary side voltage varies, the secondary side has no regulation (not that regulation is really necessary for a linear amplifier).

Will it ever die?  Not necessarily.  But that doesn't excuse bad design decisions.  It's particularly disappointing, having seen some rather novel power supply designs from other Sony departments, e.g. http://seventransistorlabs.com/Monitor/index.html the resonant SMPS with saturable reactor control.

If this is a "build from scratch" kind of thing, you'll have no end of trouble trying to debug the power supply itself, and inevitably having it fail many times (filling up half a bucket with burnt transistors).  And then building the amplifier side, and having it fail many times, taking out the SMPS in the process (and filling up another bucket and a half with transistors lacking magic smoke).

Not that kilowatt power levels are all that easy to work with in the first place.  You really need a good understanding of circuits to build one of those.

(This is an example of how a '494 might be used, in a more safe manner: http://seventransistorlabs.com/tmoranwms/Circuits_2010/12-24_Converter.png It has a current sense resistor on the switches, which feeds back to the controller.  The transformer is wound for extra output voltage, so it can be PWM'd down to the required level, and filtered with an inductor.  The feedback and compensation loops are all wrong, but again, this is just an example.  There are plenty of much better controllers out there, with fast current control, stable operation, and fail-safe by nature.  Or you can build your own out of comparators and stuff -- which is a rather laborious process, but there's perhaps no better instruction than seeing the contents of one of these chips in action on the macro scale.)

Tim

[Oneminde]

@ Tim

For me who have no more than a basic understanding of electronics, what I read was a love story. There is passion in your thoughts and you clearly know what you are talking about. I have nothing to add. So maybe this is to complicated at the moment and maybe - since I don't spend hours every day learning - will remain to complicated. Sometimes that is the most important thing one can realize.

This is not the only amplifier of interest, I think Mosconi/Gladen makes great stuff as well as Audison and Hertz, maybe even JL Audio and Ground Zero (amplifiers).

I spend my days learning architecture, that is my passion and while I am interested in electronics, I don't think I will be that interested like you are. I am grateful for your input, but maybe I should let this one go.

[T3sl4co1l]

Someone's probably said: Wisdom is not just knowing what you're capable of, but also being able to admit what you're incapable of.

Tons of audio amps out there -- I'd suggest sticking to basic linears, either powered by mains and good old fashioned iron, or off the automotive 12V (in which case it'll be around 50W tops, for a bridged mode amp at 4 ohms).

Tim

[Oneminde]

Someone's probably said: Wisdom is not just knowing what you're capable of, but also being able to admit what you're incapable of.

Tons of audio amps out there -- I'd suggest sticking to basic linears, either powered by mains and good old fashioned iron, or off the automotive 12V (in which case it'll be around 50W tops, for a bridged mode amp at 4 ohms).

Tim

- How come you say: in which case it'll be around 50W tops ?

[T3sl4co1l]

Well, if you have a 12V DC supply, how much power can you get into 4 ohms?

Tim

[Seekonk]

12V implies car.  Since this thread has never gone above dribble I would like to talk about hearing loss.  Even with hearing aids my wife can only understand me if she can see my lips move.  I can't begin to understand the isolation she feels.  What you are doing is a lot of fun now but is it worth it?  Might as well stick ice picks in your eyes too.

[Oneminde]

Well, if you have a 12V DC supply, how much power can you get into 4 ohms?

Tim

Well, that depend on the amperage and what things are rated at. Ex: 300W at 12V = 25A. And the speaker watt depend on resistance, what it draws or how much power it like etc. There are subwoofers that like 500W or more, on a 12-14.4 vdc system. Usually measured in dB sensitivity with 1 watt input measured at 1 meter from the speaker (efficiency).

@Seekonk
Yeah I've pretty much concluded with the fact that this build is not going to happen and that is okay.

[T3sl4co1l]

Well, if you have a 12V DC supply, how much power can you get into 4 ohms?

Tim

Well, that depend on the amperage and what things are rated at.

No, I mean without a DC-DC converter, just a linear (rail-to-rail), bridged amplifier.

Tim

[Oneminde]

No, I mean without a DC-DC converter, just a linear (rail-to-rail), bridged amplifier.

Tim

I have absolutely no idea

[T3sl4co1l]

Well, what's the peak voltage on a sine wave, when it's delivering P watts into a 4 ohm load?

And, what's the peak (undistorted sine wave) voltage from such an amplifier?



Tim

[Oneminde]

Well, what's the peak voltage on a sine wave, when it's delivering P watts into a 4 ohm load?

And, what's the peak (undistorted sine wave) voltage from such an amplifier?



Tim

That must be measured.

[T3sl4co1l]

Measure what?  You've got all the parameters, just put them together.

Tim