Capacitor charging curve

Started by Sambo in sci.electronics.basics12 years ago 12 replies

I am planing to put together PIC project to measure SMD caps. I am not sure if the answer will help me for this project and how I started...

I am planing to put together PIC project to measure SMD caps. I am not sure if the answer will help me for this project and how I started wondering about it but it has been bugging me for a while ( if I was hoping to discharge through a transistor leaving .7V on it ? during repeating measurements. or was it discharging to some voltage so it coincides with the voltage reference point. ...


Question for those in the know...

Started by Dave in sci.electronics.basics8 years ago 4 replies

Hate to be obtuse, but its been nearly 40 years since I was in school, and I am now out of practice. Any idea as to how I could use a...

Hate to be obtuse, but its been nearly 40 years since I was in school, and I am now out of practice. Any idea as to how I could use a photoresistor (and sunlight) to turn off a transistor that would otherwise be conducting like crazy? Please see my post in ABSE for the particulars of what I am working with. Many thanks for any help... Dave


Common emitter as level switcher

Started by George Herold in sci.electronics.basics8 years ago 26 replies

First, I'm a transistor idiot. I wanted to change a 5V 1 MHz clock signal to 12V. I put this together, ...

First, I'm a transistor idiot. I wanted to change a 5V 1 MHz clock signal to 12V. I put this together, +12V--10kohm----+----Vout | |/ in--5V 1MHz-1kohm-+---| 2N3904 | |\> | | +--1k-+ Gnd Worked, but it took forever (~100 nS) to tur


transistor

Started by gajendra singh in sci.electronics.basics8 years ago 5 replies

is transistor used as amplifier?

is transistor used as amplifier?


Gender Inequality in Electronics

Started by Globemaker in sci.electronics.basics8 years ago 13 replies

There is a common gender inequality for electronics products. People who buy light bulbs prefer Edison bulbs over female invented bulbs. TV sets...

There is a common gender inequality for electronics products. People who buy light bulbs prefer Edison bulbs over female invented bulbs. TV sets designed by men like Farnsworth are purchased more than TV sets invented by women. Computer transistor hardware is invented by men like Shockley and Moore instead of female transistor types. The list is large where examples of toasters, ovens, heater...


Are there 22.5v. batteries?

Started by Ramon F. Herrera in sci.electronics.basics8 years ago 38 replies

I was looking at the schematics of the first transistor radio, the Regency TR-1, and noticed that it uses a 22.5v....

I was looking at the schematics of the first transistor radio, the Regency TR-1, and noticed that it uses a 22.5v. battery. http://people.msoe.edu/~reyer/regency/schematic.jpg Later models use a more normal battery such as 9v. -Ramon


LM339 Comparator input limits?

Started by Bill Bowden in sci.electronics.basics8 years ago 12 replies

The LM339 spec sheet indicates the maximum negative input voltage should not be more than -0.3 volts. The schematic shows the input connected to...

The LM339 spec sheet indicates the maximum negative input voltage should not be more than -0.3 volts. The schematic shows the input connected to the base of a PNP transistor with the collector at the negative supply terminal. So, it looks like if the input or base of the transistor goes more negative than about 0.7 volts relative to the negative supply point, the transistor will conduct like ...


Discrete Transistor Equivalents/Crosses

Started by Jim Thompson in sci.electronics.basics7 years ago 3 replies

Discrete Transistor Equivalents/Crosses for these devices... XN04401 TRXN4501 I'm search for equivalent devices that also have Spice...

Discrete Transistor Equivalents/Crosses for these devices... XN04401 TRXN4501 I'm search for equivalent devices that also have Spice models. Wringing out an _old_ discrete design :-( ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | ...


Cell phone tracking question

Started by Rusty Oxhide in sci.electronics.basics7 years ago 6 replies

I think some transistor-powered nerd might be tracking my movements by way of the emergency cell phone I carry. If I wrap my cell phone in...

I think some transistor-powered nerd might be tracking my movements by way of the emergency cell phone I carry. If I wrap my cell phone in Aluminum foil will this shield the signal from detection? Sort of a "tin-foil-hat-in-the-pocket" question? No. This is a serious inquiry. :-( Rusty Oxhide


Stretch 0.5sec pulse to 6sec

Started by amdx in sci.electronics.basics7 years ago 77 replies

I have a 4 volt pulse that is 0.5 sec long. I need a 6 sec pulse that will switch a 2n3904. The 4 volts has about a 400 ohm source...

I have a 4 volt pulse that is 0.5 sec long. I need a 6 sec pulse that will switch a 2n3904. The 4 volts has about a 400 ohm source impedance. I could use a 555, but first I need to invert the signal then drive my 2n3904 switch, so I have 2 transistors and a 555. Oh yes I could probably differentiate the 0.5 sec pulse to trigger the 555, so maybe only 1 transistor and a 555. Could ...


Temperature compensation in LTSpice?

Started by Bill Bowden in sci.electronics.basics7 years ago 5 replies

Is it possible to simulate circuit performance using LTSpice under different temperature conditions? Say you have a single NPN transistor with...

Is it possible to simulate circuit performance using LTSpice under different temperature conditions? Say you have a single NPN transistor with grounded emitter and a collector load and a resistor from base to collector so the collector voltage is about half the supply voltage. I understand the result would depend on the HFE of the transistor, temperature, and maybe not very stable. Just wonde...


Basic question about transistor operation

Started by Imagineer in sci.electronics.basics7 years ago 4 replies

Hi everybody, could someone explain to me something very basic: the simplest transistor has 3 legs: gate, drain and source. If I were to...

Hi everybody, could someone explain to me something very basic: the simplest transistor has 3 legs: gate, drain and source. If I were to ap= ply voltage to the gate (above threshold), the transistor "opens" and now c= urrent between the source and the drain can flow. I have simulated it in LT= Spice and also tested the same in a lab - and the drain current always prop= ortional to the gate v...


Soldering newbie

Started by M. Hamed in sci.electronics.basics7 years ago 51 replies

I am not new to soldering. I have some soldering experience. I have built a= radio kit with no soldering problems whatsoever. I have made little...

I am not new to soldering. I have some soldering experience. I have built a= radio kit with no soldering problems whatsoever. I have made little boards= for things like transistor amplifiers for my crystal radio. I have little = surface mount experience, but in a moment of extreme courage, my boss let m= e rework about 50 PCBs at once when he was on vacation. That involved solde= ring a lit...


Question for the group..

Started by Dave in sci.electronics.basics7 years ago 27 replies

I have an automatic battery charger which is totally non-functional, apparently not sensing when it is connected to a load, and the first thing...

I have an automatic battery charger which is totally non-functional, apparently not sensing when it is connected to a load, and the first thing I note about it is that it makes prodigious use of the 2N3904 transistor on its main control board. And one of these (2N3904) has an odd characteristic- it measures .676 VDC from emittor to collector, rather than the typical OL that the others m...


Transistor as a current limiter

Started by Lauri Alanko in sci.electronics.basics7 years ago 103 replies

Hello. I need to wire some leds, and I figure that a transistor for each series is a good way to ensure that the leds get constant...

Hello. I need to wire some leds, and I figure that a transistor for each series is a good way to ensure that the leds get constant current, with the additional benefit that I can run PWM through the base of the transistor to control the brightness. However, I'm unsure about the best way to do this. The most common design I see is this: V1 ---- LOAD ---- \Q1-> ---- R1 ---- GND


Low-voltage rail for transistor bases?

Started by Lauri Alanko in sci.electronics.basics6 years ago 5 replies

Hello. When power transistors are used as switches, the base current can be significant, as the saturation beta may be as low as 10. On the...

Hello. When power transistors are used as switches, the base current can be significant, as the saturation beta may be as low as 10. On the other hand, the base _voltage_ need only be at Vbe(sat), and any additional voltage needs to be dropped by e.g. a resistor. Given the high currents, this voltage drop may be a significant loss. This suggests to me that ideally the base of a low-side ...


Darlington pair is two stage current amplifier

Started by Patrick Chung in sci.electronics.basics6 years ago 1 reply

Darlington pair is actually two stage current amplifier. Now, there is new...

Darlington pair is actually two stage current amplifier. Now, there is new tutorial: http://www.cirvirlab.com/index.php/tutorials/107-darlington-pair-or-darlington-transistor-simula tion.html and new online simulation: http://www.cirvirlab.com/simulation/darlington_pair_or_darlington_transistor_online.php


0.3V Vbe transistor?

Started by Anonymous in sci.electronics.basics6 years ago 4 replies

A friend wanted to make a DC-DC converter for his daughers' science project, which involves making an LED torch out of a hand-held Peltier...

A friend wanted to make a DC-DC converter for his daughers' science project, which involves making an LED torch out of a hand-held Peltier tile. I suggested he look into the Joule Thief, which he did. He says it works, but he'd prefer for it to work at 0.3V instead of 0.7V. I then remembered the germanium transistors. When he asked where to find one, I realized they're so old they don't ...


MOSFET switching an inductive, high-frequency load

Started by Don Gilmore in sci.electronics.basics6 years ago 8 replies

Guys: I'm an ME working on a project where I must switch voltage to a small coil = on and off at a fairly high frequency (around 25 kHz) with...

Guys: I'm an ME working on a project where I must switch voltage to a small coil = on and off at a fairly high frequency (around 25 kHz) with a MOSFET transis= tor. The DC resistance of the coil is very low (about 1 ohm), but the impe= dance is much higher because of the frequency (about 100 ohms). I'm switch= ing 24 Vdc. Should I specify the max. pulsed current of the transistor based...


4 transistor discrete opamp (LTspice problem or circuit problem?)

Started by Bill Bowden in sci.electronics.basics6 years ago 9 replies

Why doesn't this discrete 4T opamp run in LTspice at higher frequencies? It looks ok at 1Khz, but I get a 5 meg oscillation at 10K or more....

Why doesn't this discrete 4T opamp run in LTspice at higher frequencies? It looks ok at 1Khz, but I get a 5 meg oscillation at 10K or more. There are no oscillations with the input disconnected. Version 4 SHEET 1 880 680 WIRE 128 -112 32 -112 WIRE 192 -112 128 -112 WIRE 400 -112 192 -112 WIRE 512 -112 400 -112 WIRE 400 -96 400 -112 WIRE 32 -64 32 -112 WIRE 128 -16 128 -32 WIRE 128 ...