Does anyone (especially R.G.) know if it is going to be continued?
Yes, it is. Meanwhile, any specific question?
Well, not really specific. I just try to get into this.
A few times you mentioned that you have to 'chose' a drain/source current. So a possible question would be from which range I can chose.
As you might see on my question there are a few things I didn't understand and so it's hard to be specific.
He(we) probably is looking forward to the "Cut to the chase, where's the schematic" section. I know we'd all like to see what your take on the MosFet booster is. It'd be hard to beat the SHO though :wink: .
Regards
RDV
QuoteA few times you mentioned that you have to 'chose' a drain/source current. So a possible question would be from which range I can chose.
Ah. OK.
You're entirely correct - you have to know a reasonable value to choose, and it's not always obvious what could be a reasonable value.
The "reasonable" comes from things other than just the circuit or the gain desired. It's usually from external stuff, and most often "reasonable" gets set by a whole set of things limiting your choices.
On the high current end, you'd like to not start fires (literally) or melt the parts down, so you have to look at power dissipation. The TO-92 plastic package is only good for about 100mW of power dissipation, so at a rough estimate, you can't have more than 0.1W/9V = 11ma through the device if some of the voltage is not eaten up in a resistor. Since there will (usually) be a resistor in either the source or drain or both with about half the power supply across it/them, you can usually do maybe 22ma of current through the device and still have it not overtemp.
This same thing applies to resistors. 1/4W resistors are good for 250mW at a 100C surface temperature - that means, water boils on the surface if you go to full rated power. Usually we limit that to half dissipation to keep from branding ourselves with resistors, so 1/4W resistors are run at no more than 125mW, similar to the transistor. Again, you come up with no more than about 25ma.
A 9v battery is good for maybe 165ma-hr, so if you pull 25ma, the battery is drained in a bit over six hours. Not good. Battery drain sets a lower practical limit of a few milliamps per transistor stage. It's a soft limit, but one to worry about.
On the low side, you are hamstrung by the need to have big resistors to drop voltage through. If you use 1M (that is one volt per microamp) resistors, you'll wind up with a few uA through the resistors to get a few volts across them. That's OK, and laudable for low power, but the high resistance is prone to RF and hum pickup, and the parasitic capacitances can be a problem.
As a matter of experience, I skip worrying about the limits because I've been down the path so often. For typical 9V powered effects, I kind of automatically use half to a few milliamperes of drain (or collector) current unless there is some other reason I have to change.
Did that help?
QuoteA few times you mentioned that you have to 'chose' a drain/source current. So a possible question would be from which range I can chose.
Ah. OK.
You're entirely correct - you have to know a reasonable value to choose, and it's not always obvious what could be a reasonable value.
The "reasonable" comes from things other than just the circuit or the gain desired. It's usually from external stuff, and most often "reasonable" gets set by a whole set of things limiting your choices.
On the high current end, you'd like to not start fires (literally) or melt the parts down, so you have to look at power dissipation. The TO-92 plastic package is only good for about 100mW of power dissipation, so at a rough estimate, you can't have more than 0.1W/9V = 11ma through the device if some of the voltage is not eaten up in a resistor. Since there will (usually) be a resistor in either the source or drain or both with about half the power supply across it/them, you can usually do maybe 22ma of current through the device and still have it not overtemp.
This same thing applies to resistors. 1/4W resistors are good for 250mW at a 100C surface temperature - that means, water boils on the surface if you go to full rated power. Usually we limit that to half dissipation to keep from branding ourselves with resistors, so 1/4W resistors are run at no more than 125mW, similar to the transistor. Again, you come up with no more than about 25ma.
A 9v battery is good for maybe 165ma-hr, so if you pull 25ma, the battery is drained in a bit over six hours. Not good. Battery drain sets a lower practical limit of a few milliamps per transistor stage. It's a soft limit, but one to worry about.
On the low side, you are hamstrung by the need to have big resistors to drop voltage through. If you use 1M (that is one volt per microamp) resistors, you'll wind up with a few uA through the resistors to get a few volts across them. That's OK, and laudable for low power, but the high resistance is prone to RF and hum pickup, and the parasitic capacitances can be a problem.
As a matter of experience, I skip worrying about the limits because I've been down the path so often. For typical 9V powered effects, I kind of automatically use half to a few milliamperes of drain (or collector) current unless there is some other reason I have to change.
Did that help?
This helps indeed!
I'm making little steps, though... :wink: