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need more help on H-bridge

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audioguru

Well-Known Member
Most Helpful Member
Those darn DOC's that need to be fiddled with to get them to display! :(

When Q1 turns on, it will turn on Q4. If the load is a DC motor then its "stalled" current will try to flow until it gets up to speed.
Q2 works similarly with Q6.

If an input is low then Q3 or Q5 is turned on, but not very well.
 

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eblc1388

Active Member
This is a graphic respresentation of how the circuit works. Red arrows indicate current direction.
 

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Emantra

New Member
thanks for the reply

the problem that i am facing right now is that, i couldnt find the transistor NTE262 and TIP110, are there any other transistor that i can use.

what i have to do is that i have to take a voice signal which is processed using the voice recognition tools and if the right voice is there, then to run the motor to open the door or close.

so r there any other transistor that can help me.

also i have attached on the jpg format hope that this wont create any problem viewing.

thanks for any reply
 

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eblc1388

Active Member
the problem that i am facing right now is that, i couldnt find the transistor NTE262 and TIP110

You need to find and replace them with transistors of similar or higher voltage, current and gain.

For your circuit, the original transistors have the following characteristic:

Both are TO220 darlington transistor
NTE262: PNP, 100V, 4A, 65W, hfe=2500 at 4A
TIP110: NPN, 60V, 2A, 50W, hfe>1000

The data of most transistors are available on the web so you can look up the data on whatever transistors are available in your local shop before buying them.

also i have attached on the jpg format hope that this wont create any problem viewing.

Its a little late after the same circuit has been posted 3 times already. :cry:
 

Emantra

New Member
thanks for the reply

but my mentor told me to use 2 555 timer at the output of the h-bridge and then to connect to the motor.

since i dont see any logic behind using the 555 timer at the output.

so is it good to use the 555 timer at the output of the h bridge to control the movement of the motor. if it can be use they can any one tell me about the why and how can they be used
in the h-bridge.

thanks for any reply
 

eblc1388

Active Member
uncle_sam said:
but my mentor told me to use 2 555 timer at the output of the h-bridge and then to connect to the motor.

Perhaps your mentor has good reasons to do so. But there is only one way to find out.

You can print out the GIF I posted and bring it along to the mentor. The GIF also showed the connection for the motor.

Ask him why he would consider the circuit is not adaquate enough to drive a motor and why using two 555s would be better. Ask him for the reasons and satisfy yourself that his reasons are good. I would like to hear them too.

uncle_sam said:
since i dont see any logic behind using the 555 timer at the output.

Me too. I myself think using two 555s is a lousy idea.
 

Emantra

New Member
i'm sory for misleading u guys

well the actual thing was that my mentor wants to connect the 555 timer at the input of h-bridge that is at piont at A & B, n he told that by doing so the performance of the H-bridge can be increased.

so what u guys think about it

thanks
 

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Styx

Active Member
I dont like, you cannot ensure that the two 555 timers are syncronised.
adminidly with this design you cannot get shoot-throughs (be it demanded or switching).

However, doesn't the 555 have an inverted output? - not to sure years since I used one.


If it doesn't use the 555 (a good way to generate PWM) and then via an inverter chip/gate pass the output though the inverter.

You now have a NON-INVERTED and INVERTED PWM, feed these two signals into each input will do the job
 

Emantra

New Member
Styx said:
I dont like, you cannot ensure that the two 555 timers are syncronised.
adminidly with this design you cannot get shoot-throughs (be it demanded or switching).

Well that was what i was thinking that the two 555 timer cant be synchronized once

Styx said:
If it doesn't use the 555 (a good way to generate PWM) and then via an inverter chip/gate pass the output though the inverter.

You now have a NON-INVERTED and INVERTED PWM, feed these two signals into each input will do the job

Well Styx i couldnt understand what have u tried to says
Can u be little more detailed

thanks for the reply
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Using two 555's like that is a complete receipe for disaster! - it's bound to turn all four transistors on at the same time, blowing all four transistors, and possibly causing other damage as well (depending on the supply).

I can't believe anyone would tell you to do it that way!, perhaps you misunderstood?.
 

Styx

Active Member
Nigel Goodwin said:
Using two 555's like that is a complete receipe for disaster! - it's bound to turn all four transistors on at the same time, blowing all four transistors, and possibly causing other damage as well (depending on the supply).

I can't believe anyone would tell you to do it that way!, perhaps you misunderstood?.

Yes using two 555 is a very bad idea, but as I stated, this topology is the safest one for it to accedently done two.

The phase-legs are in a PUSH-PULL configuration, thus only one transistor per leg will be on => no problem.

IF one input LOW and other HIGH => normal operation
IF both inputs LOW => both upper PNP will be ON, this provides a zero-voltage loop around the top
IF both inputs are HIGH => both lower NPN will be NO, this provides a zero-voltage loop around the bottom

uncle_sam:
What I mean is take a 555 as the source of your PWM.
Now the H-bridge takes two inputs (as you can see), these inputs should be the complement (ie inverse) or each other. IF they are not you end up with the zero-loop configuration I just mentioned. This isnt bad and in some cases extreamly beneficial.

Anyway so you need an inverted PWM signal? Use an inverter/NOT gate.
so you have one PWM from the 555, feed it into the NOT gate and you end up with !PWM.

feed the !PWM into one input and PWM into the other input and it will work fine
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Styx said:
Yes using two 555 is a very bad idea, but as I stated, this topology is the safest one for it to accedently done two.

The phase-legs are in a PUSH-PULL configuration, thus only one transistor per leg will be on => no problem.

Sorry, I didn't realise the H-bridge was as horrible as it is :lol:

It's going to lose a LOT of voltage to the motor in that configuration.

I would suggest connecting point B to the collector of Q1, and feeding a single 555 in to the base of Q1 (point A). This will give sensible PWM to the H-bridge, but still leave the horrible losses!.
 

Emantra

New Member
Hi all,

thanks for the reply

Well i came up with this new idea about using the SL74LS86 IC of XOR gate. Then the output of the XOR gate is feed into the 555 timer to provide the logic to the appropriate input of the H-bridge and also time the operation of the circuit.

I dont know if this idea will work or not it just came to my mind that this might work, so how u guys feel about it?

Any comment will be appreciated
 

Styx

Active Member
the XOR chip seems reduntant. As I stated use the output of the 555 (which you are still using) and invert it to make the 2nd signal

Nigels method to make the inverted signal is perfect for this situation (supprised I didnt spot the natural inversion from the BJT)
 

eblc1388

Active Member
....and if the right voice is there, then to run the motor to open the door or close.

Logic inverting one signal to get another has one minor disadvantage. The motor will never stop.

You will need two independant input signals to start/stop the motor.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
eblc1388 said:
....and if the right voice is there, then to run the motor to open the door or close.

Logic inverting one signal to get another has one minor disadvantage. The motor will never stop.

You will need two independant input signals to start/stop the motor.

By providing a 50/50 mark/space ratio the motor won't move - it's rather crude and nasty!, but it works 8)
 

Styx

Active Member
Well it will kinda hover around 0speed.

IF you want to lock it (as long as it doesnt have to support much torque) turn on both upper (or both lower) switches, this will provide a zero-volt loop and for a machine it will lock it into position.
 

Emantra

New Member
With much of the discussion with my mentor we fianlly came to a final idea about using one 555 timer and an inverter making it 1 PWM and 1 !PWM.

Thanks for all ur suggestion guys.

Well we thought that just using dc motor in the H-bridge might work, but as u guys told we might face a new problem here. Coz I thought that we could rotate the motor in forward or the backward direction through the H-bridge, and also to stop by the voice command.

If it didnt then how can we do it?

Thanks for any reply
 
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