[Steve]

I ll try all of these fixes with my group on tuesday.
What fixes should we try first...the switching around of Q3/Q4 and
Q5/Q6 or should we try fixing the resistor values and adding the
additional ones as suggested?

When I asked someone else if swapping the transisotrs and connecting
their emmiters to drive the motor would work that person didnt even
answer and just told me to go read about transistors so according to
some thats not the solution?

Can someone explain what changes take place when you swap transistors
Q3/Q4 and Q5/Q6 and then connect their emmitters.

 

[Terry Given]

I ll try all of these fixes with my group on tuesday.
What fixes should we try first...the switching around of Q3/Q4 and
Q5/Q6 or should we try fixing the resistor values and adding the
additional ones as suggested?

When I asked someone else if swapping the transisotrs and connecting
their emmiters to drive the motor would work that person didnt even
answer and just told me to go read about transistors so according to
some thats not the solution?

Can someone explain what changes take place when you swap transistors
Q3/Q4 and Q5/Q6 and then connect their emmitters.

Hi Steve,

probably the best overall approach is the swapping of npn's and pnp's,
as it nicely avoids all the shoot-through problems inherent in the
original arrangement of Q3 - Q6, requires no extra resistors (in fact
you can throw 2 away)

One side of the H-bridge is as follows:
npn collector to V+, pnp collector to 0V
npn, pnp bases joined together, driven by Q1 collector (or Q2 for the
other side of the H-bridge)
npn,pnp emitters joined together, this is the center of the half-bridge
and connects to the motor (and the diodes, as originally drawn).

-------+------- +9V
|
/ c
+--| npn
| > e
| |
| +--------- to motor/diodes
| |
| < e
from Q1 collector ---+--| pnp
\ c
|
-------+------ 0V

this is basically a complementary emitter follower - the emitter voltage
is always 1 diode drop below the base voltage, which is either 0.2V (Q1
on) or 9V (Q1 off) and is (as another poster suggested) probably what
the original "designers" (and I use that word loosely) probably intended.

"that person" obviously didnt know much about transistors then. I
suggest you ignore everything they say.

Cheers
Terry

 

[Steve]

Thanks for all the help Terry, John, Rich and everyone else who
replied.

My group and I will try your suggestions and hopefully the circuit will
start working as it should.

 

[Terry Pinnell]

Hello,
My group and I built the following dc motor control circut:
http://forum.webzila.com/index.php?act=Attach&type=post&id=2441

I replaced the SK100 transistor with NTE262 and the SL100 with TIP110

That seems an odd choice. The circuit (duly modified as suggested by
nospam and Terry Given to correct the drawing error) will need further
changes if you use those types.

The SK100 and SL100 are a complementary pair of general purpose medium
power transistors, with max current around 500 mA and power rating of
800 mW. Plainly inadequate for your 2A motor (and presumably hard to
find), so you're obviously right to change them.

The NTE262/TIP110 are up to the job but that pair is not
complementary. And both are Darlingtons, so cannot be expected to be
straightforward replacements. Also, if you want to use Darlingtons (to
eliminate the 2N2222s?), then why not use the *pair*? IOW, either the
TIP110/115 or the NTE261/262?

 

[Steve]

Well we were going to use the pair of TIP110/115 transistors. We had no
problem finding the TIP110 at the local electronic parts store but we
couldnt locate the TIP115. So the person at the store looked the info
up on their pc and gave us the NTE262 sayings that its the replacement
for TIP115 and should be the same thing.

I know we could have ordered the TIP115 but we really couldnt wait. If
it makes a huge difference we can go back and get the NTE261 and use it
in place of TIP110 (should we do that?).

 

[Rich Grise]

That seems an odd choice. The circuit (duly modified as suggested by
nospam and Terry Given to correct the drawing error) will need further
changes if you use those types.

The SK100 and SL100 are a complementary pair of general purpose medium
power transistors, with max current around 500 mA and power rating of 800
mW. Plainly inadequate for your 2A motor (and presumably hard to find), so
you're obviously right to change them.

The NTE262/TIP110 are up to the job but that pair is not complementary.
And both are Darlingtons, so cannot be expected to be straightforward
replacements. Also, if you want to use Darlingtons (to eliminate the
2N2222s?), then why not use the *pair*? IOW, either the TIP110/115 or the
NTE261/262?

I'm wondering if the resulting 4 E-B drops in series with the motor will
have to be taken into consideration.

Thanks,
Rich

 

[James Meyer]

I'm wondering if the resulting 4 E-B drops in series with the motor will
have to be taken into consideration.

Thanks,
Rich

Even with that, the new circuit configuration will stand head and
shoulders above what they started with. This time it will work!

Jim

 

[Rich Grise]

Even with that, the new circuit configuration will stand head and
shoulders above what they started with. This time it will work!

Well, it for sure won't be making silicon popcorn!

Cheers!
Rich

 

[Terry Pinnell]

I'm wondering if the resulting 4 E-B drops in series with the motor will
have to be taken into consideration.

Yes, that's the main impact I had in mind. At the very least it will
mean increasing Vcc if the motor's full speed range is required.

 

[Steve]

Just wanted to post and thank everyone who helped out. We swapped the
transistors and removed to two 1k base limiting resistors and now the
circuit works perfectly...just like we wanted it to work.

 

[Terry Given]

Just wanted to post and thank everyone who helped out. We swapped the
transistors and removed to two 1k base limiting resistors and now the
circuit works perfectly...just like we wanted it to work.

Well done. Thanx for letting us know it worked

Cheers
Terry