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History?

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It would be nice if this article included a section on the historical development of the H bridge. (also, I concur on the incorrect direction of the arrows in the diagram, and the symbol for the voltage source is incorrect, it ought to be a DC source but the circle symbol is a (still incorrect) AC source). — Preceding unsigned comment added by 202.173.167.60 (talk) 16:51, 9 February 2014 (UTC)[reply]

Arrows backwards?

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I must be tired, because it seems that the arrows showing current flow are actually drawn backwards in the 2 states of the H bridge drawing.

Does anyone else concur?

Anyway good article, thanks to the authors for their contributions.

Well... I as far as I can see, the arrows indicate the voltage, not the current... CyrilB 08:34, 8 November 2006 (UTC)[reply]
I'm pretty sure its backwards. 75.74.112.76 20:10, 18 November 2006 (UTC)[reply]
It would be backward if the arrows were representing the current, but it is the voltage ! CyrilB 19:38, 19 November 2006 (UTC)[reply]

An arrow indicates current

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Any time I have seen an arrow in a schematic it has represented current. To represent voltage a "+" on one side and "-" on the other is the convention. Very often they will be shown together such as: + -------> - (looks better if the arrow is a straight line rather than a bunch of minus signs).

Also in addition to MOSFETs and BJTs, IGBTs can be used in H-bridges.

Dsignoff 05:00, 10 February 2007 (UTC)dsignoff[reply]

Usually, the arrows that indicate current are directly on the wires, not on their side. And I put what looks like a clear label to me (V). Furthermore, in most applications, a H bridge imposes the voltage to the load, not the current, so it is not possible to presume the direction of the current in the figures of the article, while it is for the voltage. If you have an idea to make the circuit more clear, please help yourself! Usually, the direction of the voltage arrows is from minus to plus (- --------> +).
And yes, IGBT can be used too, as any other switch (e.g. relays) CyrilB 10:53, 10 February 2007 (UTC)[reply]
The only place that I know of that labels things with real current over conventional current is High School. If you study electronic engineering the standard is to use conventional current (i.e. + -------> - current flowing from positive terminal to negative terminal). America might be an exception (but I doubt it) because they seem to do everything different to the rest of the world.
Dsignoff is quite right when (he/she) says that arrows are used to indicate current. It is against standards to us an arrow to represent voltage. Your statement that it is not possible to presume current direction but it is possible to presume voltage direction is also inaccurate. Using the conventional current system, current must flow from a positive terminal to a negative terminal. If you are able to write the voltage direction, you can also write the current direction. Mathematically it is possible to have current flowing in the opposite direction but in this case the current will have a negative value and therefore obeys the previous statement. --Spuzzdawg 05:24, 16 November 2007 (UTC)[reply]
Reactive load. 207.119.56.25 (talk) 21:13, 2 July 2010 (UTC)[reply]

The arrows are wrong and so is the representation of the source. —Preceding unsigned comment added by 195.251.81.247 (talk) 16:16, 16 June 2008 (UTC)[reply]


An arrow certainly indicates current flow, but which type? Like many things there are two conventions concerning current flow. One called "electron flow" holds that current is the flow of electrons from negative to positive. The other "hole flow" maintains that current is the flow of open valences that flow in the opposite direction, from positive to negative. Both are technically correct and useful. —Preceding unsigned comment added by 64.15.95.49 (talk) 21:50, 1 February 2008 (UTC)[reply]

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I removed the link:

as it is broken. If anyone can find the new address of the file please put it back. --Spuzzdawg 05:24, 16 November 2007 (UTC)[reply]

Link seems to no longer be broken - have put it back --Spuzzdawg (talk) 14:43, 18 November 2007 (UTC)[reply]

Short-circuits and Braking

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From the article: Using the nomenclature above, the switches S1 and S2 should never be closed at the same time, as this would cause a short circuit on the input voltage source. The same applies to the switches S3 and S4. This condition is known as shoot-through.

From the Motor controller article: Both NPN or PNP transistors can be activated to cause a short across the motor terminals, which can be useful for slowing down the motor from the back EMF it creates.

There appears to be a conflict here. From what I understand, shorting across the motor terminals can be perfectly ok, depending on the circuit. Am I wrong? StevenBell (talk) —Preceding comment was added at 03:17, 22 January 2008 (UTC)[reply]

I was thinking incorrectly. Closing S1 and S2 would be bad, but closing S1 and S3 would cause a braking action.
StevenBell (talk) 17:48, 22 January 2008 (UTC)[reply]
Closing S1 and S2 would be fine if the bridge was driven by a quasi-current source, as in some types of resonant converters. Closing S1 and S3 would dissipate the mechanical energy of the system attached to the motor into the motor windings and the switches. The motor could probably take it (unless you were stopping a train), but the transistors would likely fry unless they were much beefier than otherwise necessary.
The right way to do it is to put reverse polarity across the motor. This returns the mechanical energy to the supply. In the usual case (IGBTs with antiparallel freewheel diodes) this is as simple as turning off all four transistors. If the supply cannot accept reverse current, you can shunt the motor current through a braking resistor. In large installations, this is often similar to an electric furnace.207.119.56.25 (talk) 21:36, 2 July 2010 (UTC)[reply]


Move Left and Right

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I'm a little concerned about the state table. I suppose the table is intended for use with a DC motor, in which case it makes sense. But an AC motor would stop rotating PDQ if you just left the switches on. For use as a DC to AC inverter, the switches are constantly alternating. This is required to drive an AC motor in one direction, not change directions as implied by the table. Not sure what the best way to fix this would be. -W0lfie (talk) 16:32, 14 September 2010 (UTC)[reply]

Requested move

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The following discussion is an archived discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

The result of the move request was: page moved. Vegaswikian (talk) 22:16, 15 January 2011 (UTC)[reply]


H-bridge → H bridge — The hyphen should be reserved for the adjective form of this noun compound. Sources vary, but I added a ref for the normal H bridge form. The article was originally created at H bridge, but then improperly moved by its creator in Jan. 2006. --Dicklyon (talk) 18:46, 7 January 2011 (UTC) Relisting Andrewa (talk) 15:46, 15 January 2011 (UTC)[reply]

The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

Formulas that Model H-bridge currents

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I added my derivation of equations which accurately model the H-bridges used in Vex and FRC robotics motor controllers. The link is to a blog post and discusses why some H-bridges exhibit nonlinear speeds and currents while others do not. These equations has been well vetted in the Vex and FRC robotics forums and when implemented in software produce currents that closely match actual current measurements made by members of the forums.Vamfun (talk) 06:55, 10 November 2012 (UTC)vamfun[reply]

Why "H"?

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Yes, the circuit diagram looks like an H, but any bridge could be drawn as an H: the Wheatstone bridge, the common diode rectifier bridge. Why is this one called H, but not others? 216.31.219.19 (talk) 21:06, 2 April 2013 (UTC)[reply]

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H-Bridge diagram is wrong

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H-Bridge diagram is wrong: N-channel MOSFETs are all upside down in the image added by Huor2 — Preceding unsigned comment added by 194.193.163.22 (talk) 13:18, 27 April 2020 (UTC)[reply]

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