keantoken said:I'm multiposting, Mooly style.
Something's getting hot... Hot enough for me to smell... How much current does it take to heat up those small black transistors?
- keantoken
I use two 220pF caps to stabilize my regulator.
In a real amplifier such stabilizing compenastion may need more cap values.
further, there are most probably several other ways, than the way I use
to get regulator stable.
See my posted schematic above. For those 2 x 220 pF.
Now, as with any other amplifier using negative feedback with high gains
... the higher the gain .. the more capacitance may be needed to compensate VAS.
Actually I have used as high values as 1-2.2 nF in some such real life regulators I have built.
regars, lineup
I see...
At any rate this latest version seems to WORK. I don't know if it works WELL. But I guess that testing will be for another day, when I feel up to it.
Right now I've got another project going, an extremely high-Z MC pickup. I just smoked a 22ohm resistor. Pretty soon I'll be able to tell what I'm smoking by the smell, or maybe even taste.
Luckily my three remaining 2N5088s are still alive.
- keantoken
At any rate this latest version seems to WORK. I don't know if it works WELL. But I guess that testing will be for another day, when I feel up to it.
Right now I've got another project going, an extremely high-Z MC pickup. I just smoked a 22ohm resistor. Pretty soon I'll be able to tell what I'm smoking by the smell, or maybe even taste.
Luckily my three remaining 2N5088s are still alive.
- keantoken
keantoken,
The last circuit you posted should work quite well (except the input voltage is way too large). Good for you.
You could simplify the circuit be eliminating Q1 and moving the zener diode to where the collector and emitter of Q1 were connected. I would also increase R1 to 220 ohms. You want R1 to be small enough to bias the zener off its knee, but making it too small just wastes power.
In general zener diodes are not precision devices. Except for zeners in the 6.2 volt range, their temperature coefficient is large as well.
Rick
The last circuit you posted should work quite well (except the input voltage is way too large). Good for you.
You could simplify the circuit be eliminating Q1 and moving the zener diode to where the collector and emitter of Q1 were connected. I would also increase R1 to 220 ohms. You want R1 to be small enough to bias the zener off its knee, but making it too small just wastes power.
In general zener diodes are not precision devices. Except for zeners in the 6.2 volt range, their temperature coefficient is large as well.
Rick
Thank you.
Through reading some things on this forum about CCSs, I've pretty much come to that conclusion. According to tests that were made, IR LEDs are best to keep a CCS stable when biased at about 20mA. I'm not sure what exactly is involved with switching LEDs out for zeners...
But at any rate, my reason for using Q1 as I did was so that minimal current would be running through the zener. That and from looking at the model, this zener has about 150pF of junction capacitance! So I think using Q1 is beneficial in the way that it increases the sensitivity of the zener, and makes total junction capacitance not more than the Cje of Q1.
Also, what if this oscillates horribly? What do you think would be the best way to prevent oscillation?
- keantoken
Through reading some things on this forum about CCSs, I've pretty much come to that conclusion. According to tests that were made, IR LEDs are best to keep a CCS stable when biased at about 20mA. I'm not sure what exactly is involved with switching LEDs out for zeners...
But at any rate, my reason for using Q1 as I did was so that minimal current would be running through the zener. That and from looking at the model, this zener has about 150pF of junction capacitance! So I think using Q1 is beneficial in the way that it increases the sensitivity of the zener, and makes total junction capacitance not more than the Cje of Q1.
Also, what if this oscillates horribly? What do you think would be the best way to prevent oscillation?
- keantoken
Keantoken,
As I explained, you should have a few mA (3 mA) through the zener to get it off the knee. Please elaborate on your comments regarding capacitances. How does the capacitance of D1 increase the sensitivity of Q1?
I simulated the circuit I described and it has a little "peaking" in frequency response, but it is stable. A transient analysis also show this.
Rick
As I explained, you should have a few mA (3 mA) through the zener to get it off the knee. Please elaborate on your comments regarding capacitances. How does the capacitance of D1 increase the sensitivity of Q1?
I simulated the circuit I described and it has a little "peaking" in frequency response, but it is stable. A transient analysis also show this.
Rick
If I may talk like a textbook for a minute (sorry, it's easiest for me to explain this way. I'm not trying to act professional),
Looking at Q1 like an amplifier, Q1 will increase the current swing when D1 starts to conduct (as well as slew rate). Since the input (zener) and output (collector) paths are kept separate, the amplifier operates at open-loop gain, if you neglect the rest of a circuit working as NFB. The high parasitic capacitance of D1 theoretically will degrade the performance of the circuit since it will bypass the NFB (if you now look at D1 as the NFB for the rest of the circuit) and will make Q3 act at open-loop gain. So since Q1 has a Cje of say, for a 2N5088, 14p, this means that the parasitic capacitance ('looking' into the emitter of Q1) can be no larger than 14pF. This was what I was trying to say.
I think if anything, the stopper with the above is the enormous Cje of the 2N3055. This makes optimizing for HF stability pointless.
At any rate, my theory with Q1 is that it will increase the slope of the zener knee to a point that it is useful. Biasing the zener elsewhere than this point can make the circuit vulnerable to parasitic fluctuations like temperature, and can cause less stability in output voltage. Also, I'm assuming that the voltage drop across the zener will wander with temperature if given a specific bias point, eg 3ma, while the actual point where the current begins to rise should be more solid. I don't know if this is correct.
As a note, I uploaded that version because it was the only one that was stable. If I change any of the components in the sim, it will ring like ****. This is why I was asking about oscillations. If the circuit is this sensitive to components, I don't know if I want to risk relying on simulation.
- keantoken
Keantoken,
Try this.
Version 4
SHEET 1 1104 680
WIRE -96 16 -144 16
WIRE 48 16 -96 16
WIRE 144 16 48 16
WIRE 176 16 144 16
WIRE 464 16 176 16
WIRE 544 16 464 16
WIRE 672 16 544 16
WIRE -96 48 -96 16
WIRE 48 48 48 16
WIRE 464 48 464 16
WIRE 176 96 112 96
WIRE 288 96 176 96
WIRE 672 96 672 16
WIRE 288 144 288 96
WIRE 464 144 464 128
WIRE 544 144 544 16
WIRE 144 160 144 16
WIRE 48 176 48 144
WIRE -144 192 -144 16
WIRE 288 240 288 208
WIRE 432 240 288 240
WIRE 464 240 464 208
WIRE 464 240 432 240
WIRE 544 240 544 224
WIRE 544 240 464 240
WIRE 672 240 672 176
WIRE 672 240 544 240
WIRE 144 288 144 240
WIRE 224 288 144 288
WIRE 144 304 144 288
WIRE 48 352 48 256
WIRE 80 352 48 352
WIRE -144 432 -144 272
WIRE 48 432 -144 432
WIRE 144 432 144 400
WIRE 144 432 48 432
WIRE 288 432 288 336
WIRE 288 432 144 432
FLAG -96 48 0
FLAG 432 240 out
SYMBOL npn 224 240 R0
SYMATTR InstName Q1
SYMATTR Value 2N3055
SYMBOL npn 80 304 R0
SYMATTR InstName Q2
SYMATTR Value 2N2219A
SYMBOL pnp 112 144 R180
SYMATTR InstName Q3
SYMATTR Value 2N2907
SYMBOL zener 304 208 R180
WINDOW 0 -53 44 Left 0
WINDOW 3 -124 -1 Left 0
SYMATTR InstName D1
SYMATTR Value BZX84C12L
SYMBOL voltage -144 176 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 24
SYMBOL res 160 0 R0
SYMATTR InstName R1
SYMATTR Value 230
SYMBOL res 32 336 R0
SYMATTR InstName R2
SYMATTR Value 1k
SYMBOL res 128 144 R0
SYMATTR InstName R3
SYMATTR Value 500
SYMBOL cap 448 144 R0
SYMATTR InstName C1
SYMATTR Value 100µF
SYMBOL res 528 128 R0
SYMATTR InstName R4
SYMATTR Value 500
SYMBOL res 32 160 R0
SYMATTR InstName R5
SYMATTR Value 100
SYMBOL current 672 96 R0
WINDOW 123 24 116 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value2 AC 1
SYMATTR InstName I1
SYMATTR Value PULSE(.5 1 0 .1u .1u 4.9u 10u)
SYMBOL res 448 32 R0
SYMATTR InstName RESR
SYMATTR Value .1
TEXT -144 -40 Left 0 !;op
TEXT -144 -16 Left 0 !;ac oct 100 100 1meg
TEXT -144 -64 Left 0 !.tran 0 20u 0
TEXT 96 -16 Left 0 !.options plotwinsize=0
Try this.
Version 4
SHEET 1 1104 680
WIRE -96 16 -144 16
WIRE 48 16 -96 16
WIRE 144 16 48 16
WIRE 176 16 144 16
WIRE 464 16 176 16
WIRE 544 16 464 16
WIRE 672 16 544 16
WIRE -96 48 -96 16
WIRE 48 48 48 16
WIRE 464 48 464 16
WIRE 176 96 112 96
WIRE 288 96 176 96
WIRE 672 96 672 16
WIRE 288 144 288 96
WIRE 464 144 464 128
WIRE 544 144 544 16
WIRE 144 160 144 16
WIRE 48 176 48 144
WIRE -144 192 -144 16
WIRE 288 240 288 208
WIRE 432 240 288 240
WIRE 464 240 464 208
WIRE 464 240 432 240
WIRE 544 240 544 224
WIRE 544 240 464 240
WIRE 672 240 672 176
WIRE 672 240 544 240
WIRE 144 288 144 240
WIRE 224 288 144 288
WIRE 144 304 144 288
WIRE 48 352 48 256
WIRE 80 352 48 352
WIRE -144 432 -144 272
WIRE 48 432 -144 432
WIRE 144 432 144 400
WIRE 144 432 48 432
WIRE 288 432 288 336
WIRE 288 432 144 432
FLAG -96 48 0
FLAG 432 240 out
SYMBOL npn 224 240 R0
SYMATTR InstName Q1
SYMATTR Value 2N3055
SYMBOL npn 80 304 R0
SYMATTR InstName Q2
SYMATTR Value 2N2219A
SYMBOL pnp 112 144 R180
SYMATTR InstName Q3
SYMATTR Value 2N2907
SYMBOL zener 304 208 R180
WINDOW 0 -53 44 Left 0
WINDOW 3 -124 -1 Left 0
SYMATTR InstName D1
SYMATTR Value BZX84C12L
SYMBOL voltage -144 176 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 24
SYMBOL res 160 0 R0
SYMATTR InstName R1
SYMATTR Value 230
SYMBOL res 32 336 R0
SYMATTR InstName R2
SYMATTR Value 1k
SYMBOL res 128 144 R0
SYMATTR InstName R3
SYMATTR Value 500
SYMBOL cap 448 144 R0
SYMATTR InstName C1
SYMATTR Value 100µF
SYMBOL res 528 128 R0
SYMATTR InstName R4
SYMATTR Value 500
SYMBOL res 32 160 R0
SYMATTR InstName R5
SYMATTR Value 100
SYMBOL current 672 96 R0
WINDOW 123 24 116 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value2 AC 1
SYMATTR InstName I1
SYMATTR Value PULSE(.5 1 0 .1u .1u 4.9u 10u)
SYMBOL res 448 32 R0
SYMATTR InstName RESR
SYMATTR Value .1
TEXT -144 -40 Left 0 !;op
TEXT -144 -16 Left 0 !;ac oct 100 100 1meg
TEXT -144 -64 Left 0 !.tran 0 20u 0
TEXT 96 -16 Left 0 !.options plotwinsize=0
keantoken,
Good question: What does the 100-ohm resistor do?
The answer is nothing useful and it could be deleted. Actually, the simulator had problems with a 2N2222 as Q2 and I was trying some things to overcome it. (It's a problem with the 2N2222 model.) Increasing the 100 ohm resistor would help, but again, the 2N2222 is at fault.
Rick
Good question: What does the 100-ohm resistor do?
The answer is nothing useful and it could be deleted. Actually, the simulator had problems with a 2N2222 as Q2 and I was trying some things to overcome it. (It's a problem with the 2N2222 model.) Increasing the 100 ohm resistor would help, but again, the 2N2222 is at fault.
Rick
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