jadesteffen
New Member
I'm trying to figure out how to build a simple H-bridge to drive 2 toy motors with my 18X. All i got is 2N2222 transistors, and 1k resistors. Does anyone know any simple H-Bridges taht can be made with those parts?
H Bridges?
- Thread starter jadesteffen
- Start date
<code><pre><font size=2>
------------------------------------------> +V
| |
| |
(1)>-----|< NPN1 NPN2 >|-----<(2)
| |
| + - |
+--------(M)--------+
| |
| |
(2)>-----|< NPN3 NPN4 >|-----<(1)
| |
| |
----------+-------------------+------------> -V
</font></pre></code>
The (1) should be connected together and connected to one output pin of your controller. The (2) should also be connected together and connected to a different output pin of your controller.
A high signal at (1) will make the motor run forward (current flows,conventionlly, +v > NPN1 > M+ > M- > NPN4 > -V). A high signal at(2) will make the motor run backwards (current flows,conventionlly, +v > NPN2 > M- > M+ > NPN3 > -V).
Your transistors may get a bit hot, depending on how much current your motors draw, which depends on your supply voltage, the motor's load, as well as the characteristics of the motor's windings.
<b><i>ylp88 </b> </i>
Edited by - ylp88 on 1/16/2006 1:22:31 AM
------------------------------------------> +V
| |
| |
(1)>-----|< NPN1 NPN2 >|-----<(2)
| |
| + - |
+--------(M)--------+
| |
| |
(2)>-----|< NPN3 NPN4 >|-----<(1)
| |
| |
----------+-------------------+------------> -V
</font></pre></code>
The (1) should be connected together and connected to one output pin of your controller. The (2) should also be connected together and connected to a different output pin of your controller.
A high signal at (1) will make the motor run forward (current flows,conventionlly, +v > NPN1 > M+ > M- > NPN4 > -V). A high signal at(2) will make the motor run backwards (current flows,conventionlly, +v > NPN2 > M- > M+ > NPN3 > -V).
Your transistors may get a bit hot, depending on how much current your motors draw, which depends on your supply voltage, the motor's load, as well as the characteristics of the motor's windings.
<b><i>ylp88 </b> </i>
Edited by - ylp88 on 1/16/2006 1:22:31 AM
jadesteffen
New Member
Thanks! Just one Question. is that the Collector on the bottom 2 transistors that goes to V- ? or is it the emmiter?
Edited by - jadesteffen on 1/16/2006 1:30:36 AM
Edited by - jadesteffen on 1/16/2006 1:30:36 AM
Hi there, i suggest you use the motor driver push pull chip, i have just used it in my small robot and it works great with two motors with foward and reverse.
<A href='http:// http://www.alltronics.com/download/1330.pdf ' Target=_Blank>External Web Link</a>
Here is the data sheet, its cheep as chips two... it cost me $4.50 new zealand
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<A href='http:// http://www.alltronics.com/download/1330.pdf ' Target=_Blank>External Web Link</a>
Here is the data sheet, its cheep as chips two... it cost me $4.50 new zealand
Â
jadesteffen
New Member
thanks! I'll think about using that in future projects, but i forgot to mention this is for a presentation due thrusday. So i gotta hurry.
The 4 transistor bridge that ylp88 proposes has some problems:
The bases of the NPN transistors should not be connected directly together but instead each should have a 1K resistor connected in series with the base.
The base resistors of Q2 and Q3 are driven together by one control signal. Similarly the bases resistors of Q1 and Q4 are driven by a second control signal. Only one these control sinals may high at a time or two series connected transistors will turn on simultaneously shorting out the +V to -V supply rails.
The resulting circuit works but can only deliver about 200mA at 5V. Make sure the motors don't draw any more than that or the transistors will overheat.
Performance can be greatly increased with the following:
Separate supplies should used for the uC and the motor (highly recommended!).
The motors are likely 3V rated and therefore the motor supply should use a separate 3V battery.
The uController should use a conventional 4.5V (or 5V) supply. The two supplies are joined together on the GND and -V terminals.
The input signals should switch between GND (OFF) and 5V (ON). The ON signal is greater than the 3V motor supply which drives the base of the top NPN (emitter follower)above +V thereby saturating the emitter collector voltage. This reduces the wasteful voltage drops in the h-bridge transistors and develops more useful voltage across the motor winding.
The 4 transistor h-bridge can (and therefore will) fail if the two inputs are driven high simultaneously.
It is easy to make the bridge smokeproof by adding two more NPN transistors (Q5 and Q6). Q5 collector is connected to the base the Q3 and Q6 collector to the base of Q4. The emitters of Q5 and Q6 are connected to -V. The bases of Q5 and Q6 should have a series resistor with an ideal value of 10K but 1K is fine too.
The base resistor of Q5 is driven together with the base resistors of Q1 and Q4.
The base resistor of Q6 is driven together with base resistors of Q2 and Q3.
Moreover this protection circuit now adds a brake feature to the bridge.
Now when both inputs are driven high, the bridge will brake the motor rotation by turning on Q1 and Q2 but turning off Q3 and Q4.
When both inputs are low the motor can freewheel (no brake).
When one h-bridge input is low and the other high, the motor will turn forward or reverse.
wilf
The bases of the NPN transistors should not be connected directly together but instead each should have a 1K resistor connected in series with the base.
The base resistors of Q2 and Q3 are driven together by one control signal. Similarly the bases resistors of Q1 and Q4 are driven by a second control signal. Only one these control sinals may high at a time or two series connected transistors will turn on simultaneously shorting out the +V to -V supply rails.
The resulting circuit works but can only deliver about 200mA at 5V. Make sure the motors don't draw any more than that or the transistors will overheat.
Performance can be greatly increased with the following:
Separate supplies should used for the uC and the motor (highly recommended!).
The motors are likely 3V rated and therefore the motor supply should use a separate 3V battery.
The uController should use a conventional 4.5V (or 5V) supply. The two supplies are joined together on the GND and -V terminals.
The input signals should switch between GND (OFF) and 5V (ON). The ON signal is greater than the 3V motor supply which drives the base of the top NPN (emitter follower)above +V thereby saturating the emitter collector voltage. This reduces the wasteful voltage drops in the h-bridge transistors and develops more useful voltage across the motor winding.
The 4 transistor h-bridge can (and therefore will) fail if the two inputs are driven high simultaneously.
It is easy to make the bridge smokeproof by adding two more NPN transistors (Q5 and Q6). Q5 collector is connected to the base the Q3 and Q6 collector to the base of Q4. The emitters of Q5 and Q6 are connected to -V. The bases of Q5 and Q6 should have a series resistor with an ideal value of 10K but 1K is fine too.
The base resistor of Q5 is driven together with the base resistors of Q1 and Q4.
The base resistor of Q6 is driven together with base resistors of Q2 and Q3.
Moreover this protection circuit now adds a brake feature to the bridge.
Now when both inputs are driven high, the bridge will brake the motor rotation by turning on Q1 and Q2 but turning off Q3 and Q4.
When both inputs are low the motor can freewheel (no brake).
When one h-bridge input is low and the other high, the motor will turn forward or reverse.
wilf
Although I applaud making an H bridge for it's educational benefits,the L293D is THE industry standard approach for modest power motors & just HAS to be considered ! I recall it's arival was akin to the 555 (1972)whereby zillions of discretes were done away with. Crucial hence you feature it at your presentation...
jadesteffen
New Member
Thanks a ton guys! Now i just need to wait for the beam group to aprove my membership...
waiting...
man this is taking forever...
are the resistors in the H-bridge needed? cause oi only have 5...
Edited by - jadesteffen on 1/16/2006 8:13:28 PM
waiting...
man this is taking forever...
are the resistors in the H-bridge needed? cause oi only have 5...
Edited by - jadesteffen on 1/16/2006 8:13:28 PM