simple H-Bridge help needed

[HolyMustard]

Hey guys i need to design a simple H-bridge that uses vcc=15V to run the a DC motor and use a 4.2V signal to drive the H-bridge forward and backward. and i've attached a pic of what i've tried so far but i've run into the problem of the top PNP transistors staying constantly on. i know it has got to do with the fact that my PNP emitter voltage is higher than my base voltage and as a result the transistor doesn't turn off.

i'm wondering if anyone could give me any advice on what i could do to the circuit to make it work?

any help would be appreciated. Thanks.

 

[Emantra]

hey check this topic, i also had problem with h-bridge which was later solved.

https://www.electro-tech-online.com/threads/need-more-help-on-h-bridge.16300/?highlight=h-bridge

 

[Styx]

you need to build a decent gate-drive (what you think is the problem is correct).

Since you are working form 15V things are alot easier, a comparator (or an OPAMP wired as a comparator) can change yr 4.5V to a 15V signal needed to drive the PNP.

or you could concider putting down a NPN with a pull-up resistor to 15V and using the collector-point as the drive for the top-PNP (it will be slow at turn-on tho, which is itself is a kind of good thing)

 

[bananasiong]

How if both the collectors of the 2N3906 are connected to GND? I don't know, but it's good to try..

 

[HolyMustard]

Thanks guys

Hey thanks guys. I used one of the H-bridge designs that was suggested to Emantra (i've attached it to see if you guys think there are any problems or disadvantages) and it works fine. I also forgot to mention that cost was a huge factor and hence i wasn't able to use the op-amp solution. also another thing is our vcc supply will vary between 15-24V. thanks for all your guys help i really appreciate it.