Choosing diodes and transistors...

Thread Starter


Joined Nov 27, 2009
Hmm, seems to be something i get stuck on :confused:


So... How do I know which diode to use, and transistor to use - since there are so darn many to choose from!

I want to do a PWM project using a schematic i made a little while ago

What diode would i use between pin 7 and 2? And also I am going to need to use a transistor to power a bigger load, that would preferably have a high frequency rate too.

And for future references, how do i exactly tell what to choose?

Thanks :)


Thread Starter


Joined Nov 27, 2009
Hmm, I see the 1N4148 cropping up a few times over the internet - I take it that it is a favoured one for low power apps? :)

And thanks for your reply


Joined Apr 5, 2008

There is a lot of information on diodes in the links of this page from the EDUCYPEDIA:

There are also pages for other components over there too:

Passive semiconductors technology: Batteries Diodes Photovoltaic systems Switches Buzzers Diode types Quartz crystals Thermoelectric Capacitors General overview Relays Transformers Capacitor types Heat Sinks Resistors Transformers-RF Coils Photo diode Resistors-Nonlinear Transformer types



Joined Nov 6, 2005
Yep, diodes are pretty simple - 1N4148 for general small signal use, 1N4007 for higher power up to 1 amp rectifiers etc. (A batch of 1N4007s is almost exactly the same price as a 4002 or whatever from my supplier. You can use a 4007 in place of any other 400x but not the other way round).

Transistors are slightly more complex, but not much so.

Pick a few types you can get easily, low power say 100mA - 500mA range for general use (both PNP & NPN) and some small power like 1A - 5A range.

Same thing with FETs, small like 2N7000 and some higher power. Always look for 'logic level' types, these will work with 5V logic control as well as higher voltage, where normal ones typically need 10V or so to switch properly.

You may occasionally need some thing specialised, but for 90% of prototyping applications a handfull of devices will do.


Joined Mar 24, 2008
Other low power diodes that are good equivalents would include the 1N4454 and 1N918.

The 1N400X series is limited at 1 amp, the 1N4001 is rated at 50 volts PIV (Peak Inverse Voltage) and each one can take more voltage from there.

In many cases the 1N4001 can be used the same way the 1N4454 is, it just has better specs in terms of current.

I got lucky and found a reel of 1N4007 for a $1. It pays to keep your eyes open.