Philips UCD application note

Status
Not open for further replies.
Jump to Latest
#141
stepheno said:
I would like to contact Steven who first posted the circuit of the Philips UCD. Unfortunately I am not allowed to contact him because I have not posted enough replies yet - these will come.
The design looks very sound and there is no reason to shoot it down by anyone due to selfishness or jealousy, or by someone who would like to have this thread to sleep in silence. Negative remarks will only be ignored anyhow. Can someone bring me into contact with Steven? An e-maill address will be preferred. Thank you.
Click to expand...

Hi Stepheno,

No need to contact me about the Philips UCD amp. I just came across the circuit description on the Philips site (now NXP), just after Philips published it. I wanted to notify the readers here as some had already made some guesses about component values, based on Bruno's patent description. I have no other experience with UCD than having read the threads. Although I've worked for Philips quite some years and even met Bruno once in Leuven, when he still worked for Philips, I've not started building class D amplifiers. But I'm thinking about it 😎.

Rgrds, Steven
 
#142
Originally posted by rogs
The overcurrent protection circuit for this application is not included on the main circuit diagram on page 4, nor are the components included on the demo pcb. Probably not essential for simple testing, but useful to try.
The additional circuitry is shown on page 9 --- but I can't see how it works. It looks to me as if the zener diodes D1 and D2 are drawn in reverse - surely not the same polarity for both positive and negative halves?
Or am I missing something?
Click to expand...

Just to confirm, yes they are shown backwards

Having said that, the corrected protection circuit appears to work very well - and should always be used with the Philips demo PCB, IMHO, -- especially when trying to drive into loads of 4R or less. The single ended configuration just doesn't seem to handle any DC offset very well.

BTW, has anyone tried the circuit without R14 and R15? --I haven't worked out what they are for yet (seems to perform the same with or without them! 😕
 
#144
5M6 and 3M9 to reduce hum ? -- values seem a bit high for that!

How would asymetric values help to improve PSRR, with both comparators inputs referenced to ground via 1K?

Could you give a bit more detail? -I've obviously misunderstood something here!
 
#145
psr with a simple ucd is about 50 db.
if gain is about 20 db, you need -70 db at -in to cancel.
with 1k ohm at -in and -70db = *3000 >> about 3 meg.
optimum for + and - supply depends on gain, comparator etc.,
so...test with a pot. 😉
 
#147
Start-up ... problems

Hi UcD'ers

Building on a circuit inspired by the app note and UcD in general.
It's a slightly reduced design, and the plan is to be able to configure it for either UcD or Hysteresis.

It's up and running, after some e-mailing help from Chris (classd4sure). It's running hysterisis at some 180 kHz (can get it up to more than 500 kHz) ... will try out the UcD feedback a bit later.

Problem is stat-up. I was of the impression that it would just start by it self, but I can't get the upper drriver supply charged properly, if I don't start by stopping the current source for the diff input pair! (like disconecting J3 J4 in the app note) ..... is this normal??
😕
 
#148
Re: Start-up ... problems

Baldin said:
Hi UcD'ers

Building on a circuit inspired by the app note and UcD in general.
It's a slightly reduced design, and the plan is to be able to configure it for either UcD or Hysteresis.

It's up and running, after some e-mailing help from Chris (classd4sure). It's running hysterisis at some 180 kHz (can get it up to more than 500 kHz) ... will try out the UcD feedback a bit later.

Problem is stat-up. I was of the impression that it would just start by it self, but I can't get the upper drriver supply charged properly, if I don't start by stopping the current source for the diff input pair! (like disconecting J3 J4 in the app note) ..... is this normal??
😕
Click to expand...


Hello Baldin,

1st off, why dont you build from one of chris(classd4sure) circuit? it SURE will work...

:smash:
 
#151
Re: Start-up ... problems

Baldin said:
Hi UcD'ers
Problem is stat-up. I was of the impression that it would just start by it self, but I can't get the upper drriver supply charged properly, if I don't start by stopping the current source for the diff input pair! (like disconecting J3 J4 in the app note) ..... is this normal??
😕
Click to expand...

Well the app note circuit won't start on its own unless R16 is fitted - I know, I've tried!

I've also seen it fitted with a diode in series to stop the bootstrap gate supply from sourcing current back into the +ve supply on the high side -- but that doesn't seem to make much difference actually.
 
#152
So if R16 is fitted and J3 - J4 is connected before power is turned on, it will start by it self?

I have a resistor form Vcc to the top of the gate driver as is seen with R16 in the app note, but it will not start anyway.

I have to manually stop the current source (like shorting R7) until the high side driver is fully charged? Otherwise it will not start.
 
#153
Baldin said:
So if R16 is fitted and J3 - J4 is connected before power is turned on, it will start by it self?

I have a resistor form Vcc to the top of the gate driver as is seen with R16 in the app note, but it will not start anyway.

I have to manually stop the current source (like shorting R7) until the high side driver is fully charged? Otherwise it will not start.
Click to expand...


Baldin,

try this... R16(4k7) + ANY BYV diode rated 100V... connect them up in series and feed to supply of HIGH mosfet driver......

OR

check Q15(regulator) .. maybe its DEAD
 
#155
classd_fromru said:

RX5,
VD8 in my circuit does not influence start and I don�t know why�
Click to expand...


Sorry I did not quiet get your point??

your value of R29 IS OK with those kind of supply voltages... but watch when you upper supply rail..... 🙂 that would surely heat up something....

and about "starting" oscillation, you could put some on/off switch to turn on/off manually the current source.... a delay of 2 sec(to turn ON current source) is OK enough....(if you dont have the turn-on delay circuit)
 
#156
RX5,
VD8 in my circuit does not influence start and I don’t know why…
Click to expand...

What have you included R29 and VD8 for then?

My through hole UcD circuit (based on the App circuit but modified a bit) won't start without it, but has started every time (so far!) with 'R6' fitted, whether the amp is 'on' or 'off' during startup.

Remember it will have full rail (- 12V ) across it for c. 50% of the time, so it needs to be at least 1/2 watt rating for +/- 40 volt rails, for example.

I have used 4k7 0.6 watt at the moment, but it seems to work with 10K as well -- I guess it just depends how much it has to 'pull' the high up to unbalance the comparator enough to start oscillation, and that will depend in part on the DC resistance of the load.

At least that's how I think it works 🙂
 
#158
here is my cents worth 😀

why not REMOVE R14,R15...(Im not that technically good, but what the use of these resistors anyway, I maybe wrong or right)........."beef up" the regulator section (Q15).. I dont care how you do it.... just make it MORE -hi- output current capacity.... and EXPERIMENT value for R16 + series it with a fast recovery diode... :smash:

take it from me.. who HAVE been TOYING so much with this circuit.... 😀

AND lastly, MAKE/PUT/INCORPORATE a temporary switch for the current source (R5 input)... make it a habit to power ON the amp with switch at OFF, then SWITCH ON the current source AFTER 2 secs....

I dont see WHY IT WONT(oscilation) start up.... :smash:
 
#159
RX5,
Certainly it is possible to start the comparator manually! 😀 You can use the switch if so it is pleasant more.

rogs,
I thought amplifier with this circuit (R29 VD8) will start normally. But oscillation in 1 version not started at absence of an input signal. Though this circuit there is. But I have decided to not delete this circuit for reliability. 😉

lumanauw,
1 version is prototype without delay of start and protect. 2 version its high power UcD with delay and protect, 3 - simplify low power low cost mini amp without heatsink for small speakers up to 20-30w @4ohm. Supply of 2 version may be up to +-75v with 150v mosfets.
 
Status
Not open for further replies.
Top Bottom