Let's Make Robots!

H-Bridge NPN vs. PNP

I usually make a H-bridge with 2 NPN and 2 PNP transistors but I recently noticed that there´s allot of schematics on the net showing it with 4 NPN transistors and I started wondering what´s the right/best way to do it??

 

H-bro.jpg

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.
Basic industrial training, NPN transistors can deliver more amps and are less espensive. You never see PNP transistors in power modules. I am talking old schools stuff.

That looks better. It is called a"smoke-free"  H bridge.

You have to remember that a lot of real newbies read LMR and take everythng posted as gospel an will build it.as shown.

This updated circuit would make a big dfference in a newbie deciding whether to use a'293 or build an H-bridge. 

Myc  

I´me sorry.

I´ve ben a littel unclear the simple schematics was just to show the 2 x PNP 2 x NPN vs. 4 X NPN

This is the way i use to make a H-bridge with 2 PNP and 2 NPN but if there is a better way to do it....

Min_H-bro.jpg

 

 

The problem with these simple H bridge circuits is that if both Q1 and Q4 ar turned on at the same time, they are effectively shorted to gorund. POOF! magic smoke.

This can happen when the circuit or micro is powering up and the pinouts are in defalyt status. 

 

NPN are generally more efficient but you will need the voltage at the base to be at least 0.6V higher than the emmiter voltage. This is often a problem if you are driving motors at a higher voltage than the MPU.

NPN, because then you can drive the pins high, e.g. with 5vdc. PNP requires GND. Imagine NPN as going forward, and PNP as backwards. NPN are also generally cheaper.

 NPN=Negative Positive Negative

 PNP=Positive Negative Positive

 

You can match  those up the the emitter base and collector.

I thought NPN stood for Not Pointing iN

-and-

PNP stood for Pointing iN   ...(I don't know what the last P is)

Pointing iN Punk!!

PNP is "Pointing In Proudly", but those are just mnemonics to help you remember which symbol goes with which type =D

As Krumlink mentioned, the names actually come from how the silicon is doped, either to make it have more free positive or negative charges. The same terminology is used to describe diode and other semiconductor devices too, ie: a PN diode is 2/3s of a normal BJT transistor, with one positive and one negative region sandwiched together.

Also by going "positive negative positive", you know how it controls the current, eg a PNP is controlled by negative (ground) and controls positive currents (inbetween power and transistor).

NPN is controlled by positive (5VDC) and controls negative currents (between ground and transistor).