pmchoong,
From my record, you have not paid for the reg heatsink GB. Following link is my last announce for final call of payment on the GB thread. If I'm wrong, Pls PM me your prove of payment. Thks!
Mark
http://www.diyaudio.com/forums/grou...up-buys-related-euvls-f5x-42.html#post3759351
From my record, you have not paid for the reg heatsink GB. Following link is my last announce for final call of payment on the GB thread. If I'm wrong, Pls PM me your prove of payment. Thks!
Mark
http://www.diyaudio.com/forums/grou...up-buys-related-euvls-f5x-42.html#post3759351
So I have my F5X up and running with the regulated power supply. I listened to music for a couple hours this evening, and measured the stable bias and heatsink temperatures. With the top cover off, the amp was running with a steady bias of 1.75A.
The big heatsinks measured 58 C, and the regulator heatsinks were quite a bit hotter at 69 C. I am afraid with the cover on, the regulator heatsinks will run even warmer. The regulated output voltage is about 15.5V, so I'm dropping about 4V at the regulator. What is a safe operating temperature for the regulator sinks?
The big heatsinks measured 58 C, and the regulator heatsinks were quite a bit hotter at 69 C. I am afraid with the cover on, the regulator heatsinks will run even warmer. The regulated output voltage is about 15.5V, so I'm dropping about 4V at the regulator. What is a safe operating temperature for the regulator sinks?
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Horio,
if you lift the regulator output from 15.5Vdc to 16.5Vdc, you will reduce the Vdrop to 3V. That results in 25% less heat going into the regulator heatsinks.
The output heatsink will see that extra 1V and the heat output will increase by about 4% (keep the bias current the same).
That will get the sinks much closer in temperature.
Try a half volt adjustment and remeasure your temperatures.
I looked up the datasheet on the regulator MOSFETs and the max temperature is 150C (same as our output Fets). Seems like 70 C at the heatsinks is a bit high. What would be the easiest way up my regulated output by 0.5V to 16V? Eliminate the 1N4001 diodes (D2 & D7) in series with the 18V zener diodes?
I'm thinking a combination of lowering Vdrop to about 3.5V and lowering the bias to 1.5A might help.
I'm thinking a combination of lowering Vdrop to about 3.5V and lowering the bias to 1.5A might help.
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I can't remember the regulator circuit.
Does it use a Zener reference to set the output voltage?
If that is correct then increase the Zener reference voltage.
You can do this by selecting a different Zener, their tolerance is quite high.
Or
you can change the current through the Zener.
Or
you can add a diode in series with the Zener.
A link to the sch would help me.
Does it use a Zener reference to set the output voltage?
If that is correct then increase the Zener reference voltage.
You can do this by selecting a different Zener, their tolerance is quite high.
Or
you can change the current through the Zener.
Or
you can add a diode in series with the Zener.
A link to the sch would help me.
Post 853 is not quite right.
The Zener is the voltage reference.
The Zener does pass current. It is not zero current.
As one changes the current the Zener voltage changes.
Less current = less voltage.
More current = more voltage.
Same for the diode in series. It's voltage varies very slightly as the current is changed.
The Zener is the voltage reference.
The Zener does pass current. It is not zero current.
As one changes the current the Zener voltage changes.
Less current = less voltage.
More current = more voltage.
Same for the diode in series. It's voltage varies very slightly as the current is changed.
By no current I meant no significant current.
Please don't try to over-interprete things.
The current through the Zener is given by the difference between input voltage and the gate voltage divided by 2k. In real life it is about 1~mA.
The output voltage is given by the Zener voltage + series diode voltage - Vgs of the MOSFET at bias current.
Since the MOSFET is given, you can increase output voltage simply by raising Vg.
Whether changing Zener or diode to LED does not really matter.
You can even replace the two with a simple resisitor.
If fine adjustment is really desired (I myself won't bother), I would :
1. disconnect the regulator from the amp and connect to a dummy load (= desired voltage per rail / desired bias current);
2. use a 20k trimpot at full resistance to replace Zener + diode, slowly trim down until desired voltage is reached;
3. check gate voltage, output voltage & current for record;
4. allow to reach thermal steady state and readjust again;
5. replace trimpot by fixed resistor.
Using a resistor has the disadvantage in that if the mains voltage or transformer secondary voltage changes, it will also change your output voltage.
A Zener and a diode in series is much less sensitive.
Of course you can also use a precision voltage reference, such as what Davide tried with the TL431.
Hope this helps.
Patrick
Please don't try to over-interprete things.
The current through the Zener is given by the difference between input voltage and the gate voltage divided by 2k. In real life it is about 1~mA.
The output voltage is given by the Zener voltage + series diode voltage - Vgs of the MOSFET at bias current.
Since the MOSFET is given, you can increase output voltage simply by raising Vg.
Whether changing Zener or diode to LED does not really matter.
You can even replace the two with a simple resisitor.
If fine adjustment is really desired (I myself won't bother), I would :
1. disconnect the regulator from the amp and connect to a dummy load (= desired voltage per rail / desired bias current);
2. use a 20k trimpot at full resistance to replace Zener + diode, slowly trim down until desired voltage is reached;
3. check gate voltage, output voltage & current for record;
4. allow to reach thermal steady state and readjust again;
5. replace trimpot by fixed resistor.
Using a resistor has the disadvantage in that if the mains voltage or transformer secondary voltage changes, it will also change your output voltage.
A Zener and a diode in series is much less sensitive.
Of course you can also use a precision voltage reference, such as what Davide tried with the TL431.
Hope this helps.
Patrick
no significant to me means <<1µA
try reducing the set 1mA to 500µA. The Zener reference voltage will change.
Try increasing the set 1mA to 2mA. The Zener reference voltage will change.
All these currents from 100uA to 10mA are very significant.
A typical 18V Zener, like BZX79B18, has a part-to-part variation of +/-0.4V.
It also has a differential resistance at 1mA of 50R.
This means that if the current is increased from 1mA to 2mA (or decreased from 1mA to 0mA for that matter), the Zener voltage changes by 50mA.
I do not consider 50mA significant, considering the norminal voltage of 18V, and the tolerance voltage of +/- 400mV.
It also has no significance to the performance of the F5X amplifier itself.
Patrick
It also has a differential resistance at 1mA of 50R.
This means that if the current is increased from 1mA to 2mA (or decreased from 1mA to 0mA for that matter), the Zener voltage changes by 50mA.
I do not consider 50mA significant, considering the norminal voltage of 18V, and the tolerance voltage of +/- 400mV.
It also has no significance to the performance of the F5X amplifier itself.
Patrick
Instead of stating this you could have answered some of his concerns/question.
The regulator MOSFET is supposed to drop about 3V at 4A bias per balanced channel.
So it should be dissipating 12W by design, which is quite a bit less than the 32W as in the amplifier.
With a Rthjc of about 1°C/W, the temperature difference between heatsink and MOSFET junction is 12°C.
So even with a heat sink at 70°C, the junction temperature is a harmless 85°C, quite a bit lower than my design limit of 100°C.
(You should allow a few °C drop across the Kerafol also.)
The design limit has been discussed in detail in the article at Linear Audio, which you can download for free.
MOSFETs for the amplifier dissipate 32W each, but they have a larger substrate.
So with a Rthjc of 0.83°C/W, and heat sink at 58°C, the junction temperature is about 90°C, again lower than the design limit.
In Horio's case, you are dropping too much voltage across the regulator.
I would raise it by say 1V.
That should make you feel more comfortable, even though there is no real problem.
Patrick
So it should be dissipating 12W by design, which is quite a bit less than the 32W as in the amplifier.
With a Rthjc of about 1°C/W, the temperature difference between heatsink and MOSFET junction is 12°C.
So even with a heat sink at 70°C, the junction temperature is a harmless 85°C, quite a bit lower than my design limit of 100°C.
(You should allow a few °C drop across the Kerafol also.)
The design limit has been discussed in detail in the article at Linear Audio, which you can download for free.
MOSFETs for the amplifier dissipate 32W each, but they have a larger substrate.
So with a Rthjc of 0.83°C/W, and heat sink at 58°C, the junction temperature is about 90°C, again lower than the design limit.
In Horio's case, you are dropping too much voltage across the regulator.
I would raise it by say 1V.
That should make you feel more comfortable, even though there is no real problem.
Patrick