User Bartek Banachewicz | chat.stackexchange.com

Bartek Banachewicz

Dec 15, 2022 15:39

i know that this power amp IC is very picky and needs everything to be "just right"...

Bartek Banachewicz

Dec 15, 2022 15:38

there's no schematic available for this specific amplifier

Bartek Banachewicz

Dec 15, 2022 15:38

@rdtsc no tantalum caps afaict, i have the reference schematic from the datasheet and it's very similar

Bartek Banachewicz

Dec 15, 2022 13:38

it's been hard for me to test anything with the TDA in because they kept burning too easily; this one seems fine for at least a couple seconds when i power it in via the limiter, but the bulb is certainly showing some abnormal current so I'm not risking powering it for more than a couple seconds

Bartek Banachewicz

Dec 15, 2022 13:38

With the TDA removed there's +7V on standby and mute, and everything else looks fine. With the TDA in standby and mute become quite weird, and there's a -30V DC bias at the output. I haven't yet looked at that with the scope, it might be oscillations as well.

Bartek Banachewicz

Dec 15, 2022 13:36

No schematics, unfortunately, but I'm preparing to draw them.

The PSU is on a separate board. It has a 5-pin connector from the main transformer with 2 AC inputs; they get rectified, one of them is fed to a bunch of linear regulators and powers digital stuff, the other is filtered and fed directly to the TDA - no issues here, straight +/- 40V.

When working with the board I'm either powering it via a bulb current limiter or symmetric DC directly.

Bartek Banachewicz

Dec 14, 2022 11:33

Since then I've learned how easy it is to break those, and how hard it is to design a working board - but in this case I know the design is good, but I have no idea how to find the problem.

Bartek Banachewicz

Dec 14, 2022 11:32

So far I've fried 3 replacement TDAs - one that I simply put in, the other two while trying to build a functional circuit to compare to

Bartek Banachewicz

Dec 14, 2022 11:30

it's a common integrated power amplifier - I have a board from an amp that has been switched to 115V while connected to 230V which fried parts of it and I feel like I'm at a wall with this repair

Bartek Banachewicz

Dec 14, 2022 11:29

hey, is anyone here, by chance, familiar with debugging TDA7294 circuits?

Bartek Banachewicz

Mar 27, 2021 21:37

and since then I've discovered another sensor that can be programmed with I2C and seems like a perfect replacement, so... I think that story ends here for now

Bartek Banachewicz

Mar 27, 2021 21:37

that being said, I must've made a mistake somewhere, because while I programmed the sensor, it seems that something went wrong and it was programmed with wrong data

Bartek Banachewicz

Mar 27, 2021 21:36

so the slopes on either end weren't a problem at all

Bartek Banachewicz

Mar 27, 2021 21:36

that being said, I've realized my timing requirements are only stringent on the clock line, the HV line was much more lax

Bartek Banachewicz

Mar 27, 2021 21:35

@W5VO nah, that part was kinda expected - i had a resistor, just too small

Bartek Banachewicz

Mar 25, 2021 22:34

26

Q: How do I make the turn off and turn on time equal in a NPN transistor?

I have a simple NPN switch, see the diagram. I feed a 100KHz square wave (TTL) to the base of this transistor and it turns on very very fast (a few nSec) but it doesn't turn off as fast, it almost takes 2uSec for it to turn off. (I am looking at the collector of this circuit). The diode is a la...

Bartek Banachewicz

Mar 25, 2021 22:34

and actually, i think i just found a dupe

Bartek Banachewicz

Mar 25, 2021 22:28

a bit smaller it would seem but still

Bartek Banachewicz

Mar 25, 2021 22:28

and uh that one also has a delay

Bartek Banachewicz

Mar 25, 2021 22:28

i tried with the 5V line where I just have one transistor

Bartek Banachewicz

Mar 25, 2021 22:28

umfh

Bartek Banachewicz

Mar 25, 2021 22:27

0

Q: Transistor turns off only after a delay

I'm building an IC programmer (for the AS5043 sensor) that requires two voltage levels; 5V and 7.5V. I decided to control those with two PNP transistors. I'm controlling them from a 5V microcontroller. The programming scheme requires a 2us pulse for each bit. For the 7.5V line, I made an NPN driv...

transistors npn pnp programmer

Bartek Banachewicz

Mar 25, 2021 22:27

posted Q anyway

Bartek Banachewicz

Mar 25, 2021 22:26

whatever is happening at the base of Q2 just follows that

Bartek Banachewicz

Mar 25, 2021 22:26

@rdtsc base of Q3

Bartek Banachewicz

Mar 25, 2021 22:10

@rdtsc I have a resistor across PROG to discharge it and simulate the "load". That's why it tapers off like that, which makes sense, but it doesn't explain why the pulse is much longer than the control one.

Bartek Banachewicz

Mar 25, 2021 22:06

@rdtsc but why does it behave like that?

Bartek Banachewicz

Mar 25, 2021 22:02

eh time to post a question I gues

Bartek Banachewicz

Mar 25, 2021 22:02

I am 99% sure this is a simple mistake

Bartek Banachewicz

Mar 25, 2021 22:00

so for some reason it needs an extra 1.8us to get back off

Bartek Banachewicz

Mar 25, 2021 22:00

i mean i guess that's probably expected

Bartek Banachewicz

Mar 25, 2021 22:00

that offset stays constant at about 1.8us btw

Bartek Banachewicz

Mar 25, 2021 21:58

i don't understand what's causing it to stay open for so long

Bartek Banachewicz

Mar 25, 2021 21:57

that's what i thought - but what I'm observing is the blue line

Bartek Banachewicz

Mar 25, 2021 21:52

the one thing I'm fairly confident about (and you can actually see) is the 2us control pulse I'm generating

Bartek Banachewicz

Mar 25, 2021 21:51

I wouldn't know if it's a problem with my transistor selection or the circuit or...

Bartek Banachewicz

Mar 25, 2021 21:51

they seem to have been produced by a lot of companies with roughly similar parameters

Bartek Banachewicz

Mar 25, 2021 21:48

they're labeled "8050SS D 06F"

Bartek Banachewicz

Mar 25, 2021 21:47

the voltage after R3 seems to be high for way longer (and again, I understand next to nothing about transistors...)

Bartek Banachewicz

Mar 25, 2021 21:46

but observed no such change

Bartek Banachewicz

Mar 25, 2021 21:46

> The first circuit will turn off the PNP a little faster

Bartek Banachewicz

Mar 25, 2021 21:46

6

A: Is one circuit better than the other to drive the PNP transistor?

In most applications it doesn't matter. The first circuit will turn off the PNP a little faster, which would only matter in high speed switching, like if the load was being PWM controlled. Here is yet another topology to consider: This only works if V+ is about a Volt or more higher than the...

Bartek Banachewicz

Mar 25, 2021 21:46

i altered the circuit according to this answer

Bartek Banachewicz

Mar 25, 2021 21:45

i thought for this purpose it really won't matter, i think they're rated to like 1A and 100MHz

Bartek Banachewicz

Mar 25, 2021 21:45

@rdtsc i think so, they're just random PNPs i had laying around

Bartek Banachewicz

Mar 25, 2021 20:41

oh and their simplified schematic only shows one PNP, but I presume that's an oversimplification?

Bartek Banachewicz

Mar 25, 2021 20:39

i don't particularly like either output but the HV one is significantly worse

Bartek Banachewicz

Mar 25, 2021 20:37

the scope pic is at 5V btw, but it works the same at 7.5

Bartek Banachewicz

Mar 25, 2021 20:35

this is the driver circuit i made

Bartek Banachewicz

Mar 25, 2021 20:35

Bartek Banachewicz

Electrical Engineering