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  1. AnalogKid

    Relay operations

    For the contacts, it is only when they change state from conducting to non, or vice versa. Specifically, the breaking action is the most stressful on the contact plating. ak
  2. AnalogKid

    Transistor hfe

    Not true at all. It is a classic that has been around for decades and built by tens (hundreds?) of thousands of people. Hard to find a circuit with a better pedigree. The basic regulation is not as good as a lab supply, there is no current limiting, the output noise is a bit high, blah blah...
  3. AnalogKid

    Apple vs the FBI

    A revealing question. Do you play prosecutor, judge, and jury often? What if Apple is merely keeping a promise? What if all of the disruption is being caused by nothing more than that?
  4. AnalogKid

    Apple vs the FBI

    Actually, it's been an open secret for a decades. The computing horsepower to manage a 256-bit encryption system used to be government-level technology. Now it's on your hip for $99. The math techniques have been around for almost 100 years, and the hardware for a 100,000-bit encryption key...
  5. AnalogKid

    Apple vs the FBI

    1. No. When you want a few million pieces of a custom chip *per month*, you pretty much get anything you heart desires. If you want to same a few square millimeters and milli-pennies by combining an ARM engine and its memory on one chip, then that's what you get. I haven't seen an iPhone...
  6. AnalogKid

    Transistor hfe

    1 and 2. This may be part of the source of the resistor value confusion. I don't think it is a requirement for this circuit, or even good for it, that the current through the 7812 be kept to a bare minimum level and make the transistors carry the load even for relatively small output currents...
  7. AnalogKid

    Transistor hfe

    1. You are correct. 2. I think 800 mA is unnecessarily high. For improved long-term reliability, electronic components should not be operated continuously at or above 50% of their ratings. The 7800 series of regulators is rated for 1 A continuous output current. Keeping the current through...
  8. AnalogKid

    Transistor hfe

    1. Do not eliminate R7. R7 sets the load current level at which the external transistors start to assist the 7812. 2. From the point of view of this circuit, the11015 and 11033 transistors are identical. Both have enormous gain at 5 A collector current, and approximately the same Vbe...
  9. AnalogKid

    Transistor to control resistance

    I would push back harder on Blue Sea. They sell the sensor and the monitor, so the first question is how do they recommend the two be connected? We're glad to help, but it is their problem to solve since they got your money. ak
  10. AnalogKid

    role of schottky in sw regs

    Because that is NOT the role of the diode. You are thinking of a protection diode across a relay or solenoid coil. A switching regulator is something completely different. When the switch is opened, the left side of the inductor tries to go very negative. When the voltage gets to one diode...
  11. AnalogKid

    -12Vdc Circuit design

    Note that just because a schematic says 12 V, that doesn't mean it is 12.00002836 V all the time. It might be close enough under load, driving a circuit that doesn't care about a little ripple. ak
  12. AnalogKid

    help me, signed 2 cable boxes...

    The audio portion of a cable TV channel already is in a digital format, as is the video. There might be a digital-to-digital converter to make an output that is compatible with home entertainment audio gear, but the only place there is any analog audio in that box is at the red and white...
  13. AnalogKid

    Pulse-Flash Circuit to drive 300ma LED Beacon (miniaturized)

    Some 765 kV lines run across the highway a few miles north of my house. Big puppies, 4 cables in a box. So, solar panel charges battery so a beacon runs 27/7. Are these tower strobes as on TV towers? If so, there are lotsa commercial units. Also, what about an induction coil outside the...
  14. AnalogKid

    Wien Bridge Oscillator

    Sounds like a fun project. Let us know how you do it. ak
  15. AnalogKid

    Transistor hfe

    Almost. The power dissipated in the 7812 is 0.6 W. The power dissipated in R7 is P = Isquared x R = 0.1 x 0.1 x 25 = 0.25 W As for resistor power levels, a good rule of thumb for reliability is never drive a resistor at more than 1/2 it's rating. So if a resistor is going to dissipate 4 W...
  16. AnalogKid

    Transistor hfe

    No, no, yes, no. Because the effective base-emitter voltage of a power darlington is about twice that of a non-darlington, R7 will have to increase to produce the necessary voltage drop to cause the power transistors to start conducting. The transistor gain is 1000 min at 20 A, and over 5000 at...
  17. AnalogKid

    OpAmp Circuit assistance - :(

    A couple of circuit approaches, depending on things only you know. If the power source to the opamp is greater than 10 V AND stable, then it can be divided down to form the DC offset needed to shift the output 1.75 V. Where does the 0-5V control signal come from, and what is its output...
  18. AnalogKid

    OpAmp Circuit assistance - :(

    What is the opamp part number? What is the power source for the circuit? What is the input to the circuit? "I would copy and paste the circuit I drew, but it is not legible.." You're an engineer, it says so right in your name. Make it legible and post it. ak
  19. AnalogKid

    Strange chemical reaction from PVC grommets

    Outgassing from the components affected the plastic. It's not much, but when trapped for a few years slowly works its magic. Some foam speaker cover material disintegrates after a few years. Looks fine until you touch it, then it turns to powder. All petrochemical plastics degrade over time...
  20. AnalogKid

    Working ammeter using same power source of supply

    The way the meter works is that the current being measured is put through a very low value shunt resistor, and the meter tells you the voltage across that resistor, adjusted to display the equivalent amps. At max current the voltage across the shunt resistor is too low to power the meter's...
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