Capacitor charging curve

Started by Sambo in sci.electronics.basics15 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. ...


Common emitter as level switcher

Started by George Herold in sci.electronics.basics11 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


Are there 22.5v. batteries?

Started by Ramon F. Herrera in sci.electronics.basics11 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.basics10 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 ...


Temperature compensation in LTSpice?

Started by Bill Bowden in sci.electronics.basics10 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...


0.3V Vbe transistor?

Started by Anonymous in sci.electronics.basics9 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.basics9 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...


Transistor testing

Started by RobH in sci.electronics.basics3 years ago 15 replies

I have some BC547 transistors which I want to use in a circuit, but according to this: Hook the positive lead from the multimeter to the to...

I have some BC547 transistors which I want to use in a circuit, but according to this: Hook the positive lead from the multimeter to the to the EMITTER (E) of the transistor. Hook the negative meter lead to the BASE (B) of the transistor. For an good NPN transistor, you should see ?OL? (Over Limit). If you are testing PNP transistor, the meter should show a voltage drop between 0.


Wireless phone charger

Started by Steve Wolf in sci.electronics.basics3 years ago 5 replies

Just for fun I thought I would make a wireless phone charger. I'm not reall= y going to use it but I wanted to build it and just see if it...

Just for fun I thought I would make a wireless phone charger. I'm not reall= y going to use it but I wanted to build it and just see if it actually work= ed. The circuit uses two coils and a 2n222 transistor very simple. Well I can't really get it to work maybe I could get half a volt maybe to p= ast through induction. Then it seems to stop. I connected my meter to the r= eceiving coil to t...


2N3904 maximum ratings Vceo Vcbo

Started by Bill Bowden in sci.electronics.basics7 years ago 25 replies

Is it safe to operate a 2N3904 in a switching application with a supply voltage of 48 volts? The data sheet says Vceo is 40 and Vcbo is 60...

Is it safe to operate a 2N3904 in a switching application with a supply voltage of 48 volts? The data sheet says Vceo is 40 and Vcbo is 60 volts. When the transistor switches off, the collector to emitter voltage will be 48 and the base voltage will be near 0 through a resistor. Any problems with that? --- news://freenews.netfront.net/ - complaints: news@netfront.net ---


Transistor identification?

Started by DaveC in sci.electronics.basics7 years ago 16 replies

Help with identifying a TO-92 transistor?(at least I think it?s a transistor?) Pretty vanilla-looking with National Semi logo. Marked: NS...

Help with identifying a TO-92 transistor?(at least I think it?s a transistor?) Pretty vanilla-looking with National Semi logo. Marked: NS 444 ST 13903 (The ?NS? is the logo.) Not enough 4?s to make up a standard 2N number, and 13903 looks like a date code? Ideas? Thanks,


smps: AC or pulsed DC fed into transformer?

Started by Anonymous in sci.electronics.basics6 years ago 26 replies

It seems to me that flyback SMPSes use pulsed DC instead of AC. Is this true? For example, here, the transistor simply turns on and off,...

It seems to me that flyback SMPSes use pulsed DC instead of AC. Is this true? For example, here, the transistor simply turns on and off, providing pulses to the transformer, right? http://www.repairfaq.org/sam/smpsbd.gif Would SMPSes be more efficient if their transformers were fed high-frequency AC instead of high-frequency pulsed DC (for example, by using an H-bridge to provide a neg...


Transistor part number suffixes--215? 235? Whazzat?

Started by Phil Hobbs in sci.electronics.basics6 years ago 11 replies

So I bought a reel each of BF862-235 and BF862-215. Other parts seem to have the same suffixes, but a quick web search comes up with...

So I bought a reel each of BF862-235 and BF862-215. Other parts seem to have the same suffixes, but a quick web search comes up with nothing useful, and the datasheet links for the two types of parts go straight to the same place. I'd guess this has something to do with ROHS/halogen free/greenie-knotted-knickers-of-the-month, but don't know for sure. Wisdom? Thanks Phil Hobbs ...


Semiconductor manufacturing locations

Started by Michael Darrett in sci.electronics.basics12 months ago 4 replies

Hello, In light of the cargo ship debacle in the Pacific, I am trying to determine which companies still manufacture semiconductors in the US...

Hello, In light of the cargo ship debacle in the Pacific, I am trying to determine which companies still manufacture semiconductors in the US and Europe. I found these: https://www.thomasnet.com/articles/top-suppliers/semiconductor-suppliers-manufacturers/ https://www.bisinfotech.com/top-ten-transistor-manufacturers/ Apparently Analog Devices is headquartered in the US but it's unclea...


Why is Vbc = Vbe - Vce ?

Started by jalb...@bsu.edu in sci.electronics.basics14 years ago 8 replies

I have seen in various places the equation Vbc = Vbe - Vce for NPN and PNP transistors. It may seem obvious to others but I just don't see how...

I have seen in various places the equation Vbc = Vbe - Vce for NPN and PNP transistors. It may seem obvious to others but I just don't see how this is true. Could someone please throw me a bone? Thanks


audio amplifier output transistors

Started by Anonymous in sci.electronics.basics14 years ago 8 replies

I noticed that TR7 is PNP and TR9 is NPN here: http://www.dself.dsl.pipex.com/ampins/dipa/dpafig1.gif Then over here, TR7 is NPN and TR9 is...

I noticed that TR7 is PNP and TR9 is NPN here: http://www.dself.dsl.pipex.com/ampins/dipa/dpafig1.gif Then over here, TR7 is NPN and TR9 is PNP: http://www.dself.dsl.pipex.com/ampins/dipa/dpafig33.gif Are these correct, or in error? Also - for building audio amps "on the cheap", would TIP41C/TIP42C do for output transistors in these schematics? Thanks, Michael


Joule Thief - still not working....

Started by fungus in sci.electronics.basics13 years ago 161 replies

I just got some proper parts to start making joule thieves but I'm still having problems. The circuit is this:...

I just got some proper parts to start making joule thieves but I'm still having problems. The circuit is this: http://www.artlum.com/jt/joulethief.gif Except I have R1 and L1 one the other way around (as in the original web page at http://www.emanator.demon.co.uk/bigclive/joule.htm ) The problem is that my transistors keep on overheating and dying. Why should this be? I'm using a 2N22...


Oscillators without transistors

Started by Anonymous in sci.electronics.basics4 years ago 24 replies

Hello, What are some examples of oscillators which don't require transistors or vacuum tubes? So far I found relay oscillators and the...

Hello, What are some examples of oscillators which don't require transistors or vacuum tubes? So far I found relay oscillators and the Pearson-Anson oscillator. Does the Pearson-Anson oscillator require a high-voltage neon lamp, or would it work on LEDs as well? https://en.wikipedia.org/wiki/Pearson%E2%80%93Anson_effect Relay oscillators look neat too but I don't imagine they would la...