H-Bridge Driving me MAD, help needed

[burners]

After I went home last night I did some testing and found out where I was getting confused with the transistors / MOSFETs.
The transistors I have only need around 2.8V to be fully saturated, I didn't know the FETs would be different and that the Gate Threshold was the voltage at which the FETs just started to turn on.
I did play with the 520's more last night and I noticed no difference when I applied 4-10 Volt to the gate, In other words I received the same power through the FET. This is likely because the motor I am using draws very little current.

Another thing I never noticed before is this
If I apply voltage to the Base of one of my transistors power will flow, if I take it away it will stop
If I apply voltage to the Gate of one of my FETs power will flow, if I take it away it will continue to flow until I change the Gate to Gnd or Pos depending on if it is a NPN or PNP.
This sheds new light on the FET H bridge and tells me that the Gate's can NEVER FLOAT, they must be pulled high or low even when not in use.

I do understand the PNP issue I was having also, I recreated the circuit and I noticed when I hooked the PNP Base to the Micro-Controller it would NOT SHUT OFF, If I understand correctly it is because the transistor needs +12 on the Base when the transistor is to be off, the Micro only supplies +5 volt which isn't enough to shut the transistor off. So now I understand what you mean when you say the top (PNP) transistors are not shutting off.

OK So here are the transistors I would like to use
101 NPN
106 PNP

These are the matches equivalents of each other.

Thanks for helping me out.

 

[audioguru]

"101 and 106" are meaningless numbers. Maybe you mean TIP101 and TIP106 darlington power transistors invented by Texas Instruments.
Their max allowed current is 8A so they are pretty big. But you said your load's current is small so smaller transistors could be used instead.

Each darlington has a voltage loss of about 0.8V to 1V at low current so your load will get only 10V when the supply is 12V.
If you use Mosfets instead then the load will get the full 12V.

 

[ericgibbs]

hi burners,
This is one option, the TIP's are an overkill for such a small motor.

 

[burners]

"101 and 106" are meaningless numbers. Maybe you mean TIP101 and TIP106 darlington power transistors invented by Texas Instruments.
Their max allowed current is 8A so they are pretty big. But you said your load's current is small so smaller transistors could be used instead.

Each darlington has a voltage loss of about 0.8V to 1V at low current so your load will get only 10V when the supply is 12V.
If you use Mosfets instead then the load will get the full 12V.

Sorry I was referring to the parts I posted yesterday so I didn't think I needed to put the TIP before the numbers.
I only have the TIP's I posted and the IRF MOSFETS and I think the MOSFETS will be harder to control since I need up to 10V to turn them fully on.

 

[burners]

hi burners,
This is one option, the TIP's are an overkill for such a small motor.

Cool I will check this out when I get a minute, I only have the TIP's and MOSFETS I posted but maybe I will put in another order soon. I just need to find another cheap place like Futurlec. I love Futurlec prices but my last order took 1 Month to ship and another Month to arrive. Waiting 2 Months for an order blows, but most other sites are a rip off. Solarbotics is OK but pricey, Adafruit and Sparkfun are major rip offs and Digikey has everything but still pretty pricey.
For example I needed some 3 pin Molex headers, the same kind that are used for a 3 pin PC fan. Digikey had about 10 to choose from but none were exactly what I wanted and they wanted like $1.80 each. Futurlec had the exact connectors in vertical and horizontal for .08 Cents each !!!

 

[ericgibbs]

hi,
If you can find some old PC or other electronics pcbs from a dumpster you can usually find various connectors and other bits.

You have to shop around for components, some of the suppliers should be wearing a highway man's mask.!

I hope the cat is going to approve of the new design, if not, get him/her to post a new spec.

 

[burners]

Well for now I am just trying to learn the H Bridge. I think for the final design I might go a different route. Like an integrated circuit style H Bridge or maybe a DPDT Reed Relay.
I don't think it needs to switch from forward to reverse that fast, I mean the faster the better to keep the toy fun but I could sacrifice a little too.

What are some other methods to get this done? Remember the Voltage is 12 V but the motor draw very little current. Maybe I can put a meter on it when I get home tonight

 

[ericgibbs]

Well for now I am just trying to learn the H Bridge. I think for the final design I might go a different route. Like an integrated circuit style H Bridge or maybe a DPDT Reed Relay.
I don't think it needs to switch from forward to reverse that fast, I mean the faster the better to keep the toy fun but I could sacrifice a little too.

What are some other methods to get this done? Remember the Voltage is 12 V but the motor draw very little current. Maybe I can put a meter on it when I get home tonight

hi,
A simple way would be a couple of 5V relays that could be controlled by the logic IC, that would give you OFF,FWD and REV [ at full speed]

 

[burners]

Is there anything I can use in place of the 74LS07? Maybe something a little more simple? Like less pins or something in a different package like a TO-220 style or anything?

 

[ericgibbs]

Is there anything I can use in place of the 74LS07? Maybe something a little more simple? Like less pins or something in a different package like a TO-220 style or anything?

hi,
Do you have a dual OPA or comparator IC, say an 8 pin DIL.???

 

[burners]

hi,
Do you have a dual OPA or comparator IC, say an 8 pin DIL.???

Nope
Just a few micro's and standard parts like caps, transistors, resistors, diodes, trim pots etc...

 

[ericgibbs]

Nope
Just a few micro's and standard parts like caps, transistors, resistors, diodes, trim pots etc...

hi,
For this simple app I would go for a couple of 5V coil SPDT relays, low current coils are available.

 

[burners]

hi,
For this simple app I would go for a couple of 5V coil SPDT relays, low current coils are available.

How about some Reed Relays?

 

[ericgibbs]

How about some Reed Relays?

Providing the contacts can carry the motor switching current they will be OK, a couple of change over relays.

 

[burners]

Anyone got a good hookup on a US parts supplier with prices like Futurlec but better shipping speed?

 

[ronv]

Try Mouser, nice database and catalog.

 

[burners]

Try Mouser, nice database and catalog.

You know I have heard that but requested a catalog and never received it. I will check the site again.
I also thought they were in another country.

 

[burners]

Would buying one of these solve my issues

ZXMHC10A07T8TA Diodes Inc. / Zetex MOSFET Small Signal

L6202 STMicroelectronics Motor / Motion / Ignition Controllers & Drivers

 

[burners]

Or this one, this one says is has a built in Gate Logic, is that what I need?

L6205PD STMicroelectronics Motor / Motion / Ignition Controllers & Drivers

 

[ericgibbs]

Or this one, this one says is has a built in Gate Logic, is that what I need?

L6205PD STMicroelectronics Motor / Motion / Ignition Controllers & Drivers

hi,
The ZXMHC is only the drivers, you would still need level shifters for the logic inputs.

The L6202 looks ok, it should drive the small motor and its logic level compatible, its puuurrrfect for the cats toy mouse.

The L6205PD is a serious overkill for a mouse toy motor, its also a dual bridge