Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Higher current NPN transistor with same characteristics as a BC337

Status
Not open for further replies.

danrogers

Member
Hi all, as title really. I have used lots of BC337s in the past (T092) case which are good for 800mA. I need something similar but to be able to PWM 1A+ LED's but I'm not sure what would do it?
 
Personally I'd use a MOSFET rather than a BJT for currents > 800mA. Much less wasted power (=heat).
 
In general, those "bigger" transistors like TIP31 or BD135 have lower hFE than small ones. Therefore you must pay attention for producing enough base current to the transistor.
 
1A LEDs are generally running from a low voltage like a few volts. A FET (like Alec_t said) would give much better energy efficiency.

However if you are running a chain of 1A LEDs from a 12v or 24v supply etc it might be worth just using a NPN transistor, although the right FET choice would probably still be better.
 
Tip122

a darlington version of the tip31 with a much higher gain, the thing to be aware of is vbe is higher, but still just the job for switching leds from a micro.
 
The TIP122 is common and easy to use as it needs very little base current, but a TIP122 passing 1A will drop very close to 1v across Vce, which is 1 watt dissipated. That's enough to need a heatsink, heats up the enclosure unneccessarily and wastes as much power as a 1W LED.

Even a small cheap 8A rated NFET at 1A will only drop 0.05v to 0.1v at 1A and won't need a heatsink etc.
 
Last edited:
Yep ok I have to agree with that.
It was a few years into my electronics bashing before I started to use fets.
What do you think roman an IRF540
 
If you use an NPN transistor as a low-side switch (emitter directly to ground), it will be fully saturated as long as the base voltage is at least [Vbe] above the voltage present at collector. When fully saturated, the Vce loss will be minimal, often less than 0.1V so it won't heat up much. For example, if you control the transistor by a microcontroller i/o pin, it will give 5V and that's most likely more than enough to saturate the transistor in low side.
 
I dont think that counts for a darlington, looking at the vce sat for it on the data sheet it says its 2v, so at 1 amp that'd be 2 watts dissiation, for a switch 2 trannys a bc547 followed by a tip32 would dissipate less heat, or as roman says a fet.
 
Yep ok I have to agree with that.
It was a few years into my electronics bashing before I started to use fets.
What do you think roman an IRF540

It's funny people are reuctant to use FETs, I find myself doing that from time to time. Generally with digital and micro situations FETs are even easier to use than say an NPN as you don't need a base resistor, just connect the digital output pin to the FET gate.

I guess most of it is people use what they have got and what they know best. I've been trying to stock up some common FET types so I can just reach for them like my favorite bipolar transistor types (I normally buy in the 100's).

I don't know the IRF540 but at 1A there must be a lot of common FET types. Mostly it depends ont he package that the OP wants to use. I would just buy something common that is good for 8A or so to drive a 1A load, and have a lot of small SOT-89 etc SMD NFETs good for 8A. Most of my TO-220 NFETs are overkill for a 1A LED and rated for 40-60A.
 
thanks all for the help.

The scope has now changed slightly! I'm using TLC4950's to run the LED's and they sink so I'm going to need a PNP transistor that can switch about 800mA and also one that will handle a few amps. Any suggestions?

Thanks
 
For reasons stated above, personally I'd use a P-MOSFET :)
 
Might be time for a schematic so we can see the whole thing.
 
real simple at the moment, set up following the example here https://playground.arduino.cc/Learning/TLC5940

breadboard-arduino-tlc5940.png



I just now need to drive transistors with the ouputs. Is there a way I can use the BC337's that I have?
 
Last edited:
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top