transistor with pwm

69-cat

Member
Just asking, it may have been covered before but what is the best transistor to use with a PWM output?
Dave
 

inglewoodpete

Senior Member
qty 4, 5mm LEDs
Just an NPN small signal transistor that can handle the voltage you need to power 4 LEDs in series. Don't forget to include a series current-limiting resistor.

What's a small signal NPN in your country? 2N2222? Where I am I'd use a BC548.
 

zorgloub

Member
Good evening,
For trying various models on my CNC drivers, which of course on MosFET, the use of a transistor faces the problem of switching frequency. I ended up opting for a dedicated PWM driver.
Obviously, for LEDs, this technical constraint does not matter much.
Think also about drivers type ULN2803, ...
 

Circuit

Senior Member
The ULN2803 drivers are obsolete now and much better stuff is available.
The ULN2803 is far from obsolete; it is commonly available and is listed in Texas Instruments site as being "active". ST also list the chip as "active" and available in four different packages. Neither manufacturer appears to list the device as "end-of-life" or "not recommended for new designs" and supplies appear plentiful (RS can let you have 1900 next day!).
I do agree, however, that more recent MOSFET-base equivalents such as the TBD62083APG ( https://uk.rs-online.com/web/p/power-switch-ics/1445314/ ) offer some advantages and indeed I have just taken a delivery of these chips which are actually cheaper than the ULN2803. For many purposes, though, the ULN2803 is a robust and reliable old workhorse.
 

69-cat

Member
It stinks that MOST of the electronic stores are gone! We have one in our area about 45 minutes away but 95% of the stuff I get comes from Tayda or Mouser. Back on topic.....the 2n7000 works great!
Dave
 

AllyCat

Senior Member
Hi,

Yes the 2N700 and its equivalent "European" BS170 is an excellent small, general-purpose Logic-Level FET, always worth having a few in your "spares" box. But don't try to use them with a PICaxe supply rail of below about 3.3 volts, whilst bipolars like the BC548 or BC337 can be used down to the lowest PIXace Vdd (say 1.8 volts).

Cheers, Alan.
 

westaust55

Moderator

Billo

Senior Member
Good evening,
For trying various models on my CNC drivers, which of course on MosFET, the use of a transistor faces the problem of switching frequency.
I doubt a PICAXE will threaten the speed capability of a 2N2222, 2N3904 or 2N7000. There is no real need to get very fancy here.
 
Top