Electronics Forum / Basics / August 2004

I've got a power supply that has 2 470uF 400V filter caps in series. The
power supply puts out 400VDC.
Now if I change the caps to 1000uF 400V, what will happen? Will the output
voltage of the supply change?

Greetings! I'd like to power my external PC speakers with my computer
instead of using the bulky AC wall transformer/adapter that they were
shipped with. The wall adapter is rated for +9VDC @ 1A. When I measured the
output with a DMM, I get +12.5 Volts, so I presume the voltage goes ...

I'm looking for a circuit that will protect a lead acid battery against
excessive discharge - i.e. cut off the supply to the main circuit when the
voltage from the battery goes below about 11V. Ideally, once the circuit
has switched off, the protection circuit shouldn't use any ...

Can someone help me design a simple dual voltage power supply.
I  have some IC's that require 5V and others that require 3V (actually a
battery  operated device that I am interfacing to). I want to build a power
supply that can power both devices.

I know things are ALWAYS changing for the computer itself, but I
figure television /CRT technology is pretty much matured.
You can get a 19" CRT for $200 today that has a completely flat tube.

I was curious if anyone knew of a vendor who makes/sells high voltage
LEDs.  I have a 25 volt power supply, and for various reasons don't
want to step down the voltage to ~12 volts with a voltage regulator.
If it helps, or makes a difference, I'm looking for an IR led with a

How do you calculate the voltage peaks of voltage coming out of a full-wave
rectifier tube?
If 230V 50Hz AC has voltage peaks approx 1.41 times the average voltage, the
voltage peaks seen by the rectifier tube would also be like that. But what

Before I begin I should say that we are pretty familiar with most
basic electronics but are really stumped here.
What we are looking for is a circuit that would use very little power-
be battery operated and as small as possible. The idea is to a mic

I have a problem using a PNP 2N3906 transistor as a high side switch. I'm
plugging a 18V line to the emitter, with a 3.3k pull up resistor from the
18V line from 2 9V batteries to the base of the transistor. The collector of
the transistor is going to a 12V power regulator (so the ...

I've been interested in learning about electrical engineering for some
time now.
I know a little bit about the basics from physics, but a refresher
would not be unwelcome.

I plan to use two Yuasa NPO.8-12 12v 0.8Ah gelcells for portable radio
amateur  rig..
I will use them in France where power is 50 Hz. I see that chargers
available here in Canada always specify 60 Hz.

Talk about a hard-to-find chip!  We're trying to find the pinouts of this
TTL chip made by Texas Instruments: SN74118.  A web search indicates it's
some type of RS latch, but for testing purposes the pinout would really
help.

I'm trying so hard to imagine of such a transistor circuit when it is driven
into saturation."The collector-base pn junction acquires a forward voltage
bias even though there is still a reverse current flowing through it", I'm
trying to visualize it, how can a foward voltage applied ...

very interesting group, but how can u teach novices and explain circuits
without drawings?

Just have a techniacl question. Over the passed 2 days I'm trying to
think of a way to build a power suppyly for may magellan sportrak
map(gps) which needs 3.8vdc-4.2vdc that will be converted from cars
12vdc. What is the best way to put that power supply togther ueseing