The simplistic Salas low voltage shunt regulator - Page 90 - diyAudio
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Old 29th July 2009, 06:27 PM   #891
iko is offline iko  Canada
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Quote:
Originally posted by Salas
How will V1 fair for early HF phase turn if you substitute IRF9510s in the sim?
Improvement. But now it needs compensation at high freq, because as it is it oscillates. Probably a small cap on B-C pins of the NPN driver would do.
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Old 29th July 2009, 07:10 PM   #892
Salas is online now Salas  Greece
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Standard stuff. You make it lighter for Ciss, it opens, but it gets more dangerous and ups impedance. Nahh, I prefer it conservative as it is V1. Better go V2 for more open, so we do it in the drive department.
I wonder if it is the phase turn or the better drive that gives an audible edge to V2. We can bump on reacting circuits up high though, like closed loop small phone amps or little class A amps. Depends on synergy.
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Old 29th July 2009, 09:12 PM   #893
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@ikoflexer
thanks for explanation, appreciate your efforts.
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Old 29th July 2009, 09:14 PM   #894
anatech is offline anatech  Canada
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Hi Salas, ikoflexer,
Good looking project you have on the burner here. Howdy from a neighbor.

Hi stormsonic,
Quote:
For trimmer I will recommend multiturn type. With ordinary trimmer it is difficult to set shunt current.
I'd say that a multi-turn trimmer is the last thing you want in there. Remember that both the contact area and pressure are lower than a standard trimmer. If you are going to pass any current through it at all, it's important to stay away from multi-turn types.

Will they work? Probably.

Will they reliably work? Don't know, but not from what I have seen and I'm not a betting man.

The proper way to reduce the range of a control is to use fixed resistors. You probably want to set a minimum resistance, so one fixed is needed right there. Then you just figure out what adjustment range you want and split that between the fixed resistances and the total resistance of the final fixed resistor. If someone wants a different adjustment range, they only need to change the fixed resistors. No biggie and the home constructor can exercise their noodle some.

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Old 29th July 2009, 10:11 PM   #895
iko is offline iko  Canada
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Chris, I moved the resistor that sets the current out of the main current path. In this position there's only about 7-8mA (depending on the jfet Idss) passing through the resistor, so a trimmer would be ok you think?

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Old 29th July 2009, 10:35 PM   #896
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anatech, it will pass only few mA, depends on Idss od JFET bellow trimmer. Edit: J2 on Iko's shematic above.

For example, let's say 6 mA.
VLED=1.85V (for 3 mm red LEDs, I am using)
Trimmer value formula: (Vbias-VLED1-VLED2) / Idss = (4.5V-1.85V-1.85V) / 0.006 A = 133 Ohm

You will need 133 Ohm resistor, to set Vgs to 4.5V.
Looking at datasheet for IRFP9240, if you have Vgs at 4.5V and Vds is 5V, then you are shunting approx. 1.5A

6 mA accross 133 Ohm will result into 0.798 voltage drop on resistor. With 0.798 V and 0.006 A you will dissipate 0.0048W on trimmer

If you want to shunt less, then you should reduce Vgs, let's say to 4V. (4V-1.85V-1.85V) / 0.006 A = 50 Ohm
6 mA accross 50 Ohm will result into 0.3 voltage drop on resistor. With 0.3 V and 0.006 A you will dissipate 0.0018W on trimmer

But I agree with you, with fixed resistor you will eliminate possible problems.
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Old 29th July 2009, 11:28 PM   #897
AndrewT is offline AndrewT  Scotland
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the maximum current that a trimmer track can pass is determined by the maximum power the whole track can dissipate.
A 400mW 1k pot can pass sqrt(p/r) = sqrt(0.4/1000) = 0.02A = 20mA.

This is the maximum.
I recommend that you never pass more current than would exceed 50% dissipation.
This reduces the usable current to <=14mA for a 1k 400mW pot and <=20mA for a 500r 400mW pot.
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Old 30th July 2009, 03:30 AM   #898
grenert is offline grenert  United States
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Default Resistor function in V1

There have been a number of different renditions of the V1 regulator. Some of these have a resistor between the zener and Q3 (the BC550), but some do not. What is the function of this resistor? Is it to drop the voltage from a reference that is too high?

Thanks for the explanation!
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Old 30th July 2009, 03:40 AM   #899
Salas is online now Salas  Greece
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It is a base stopper resistor to improve on oscillation guard. Its a bit better transiently without, but in some layouts a good measure.

Another thing you may saw is having two resistors on the left if with a vbe (transistor) controlled ccs or one and a jfet.
It is effectively one resistor split in two for creating a middle point so to bootstrap the CCS transistor with a capacitor. This is a Douglas Self trick. Now in some of Ikoflexer's iterations, one jfet local ccs is simulating a much bigger resistor in place of one of the pair but keeps the current adequate for a bit better performance still. If short on jfets, the two resistors are OK enough though.
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Old 30th July 2009, 04:06 AM   #900
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Use single main resistor with a higher value single turn pot in // or, just add the resistor across the pot pins.
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