simple h bridge

[hypersnapper]

Hello. can you comment if this is my hbridge plan? I am driving simple small toy dc motors. I will be using this schematic.

**broken link removed**

What happens if I will use BD646 PNP silicon power darlingtons instead of low current transistors like 8550?
https://www.electro-tech-online.com/custompdfs/2011/01/bd646.pdf

also on NPN if I use this BDW46 NPN darlington silicon power transistor instead of 8050.
http://www.datasheetcatalog.org/datasheet2/d/0ktoqfy3rda5g46g3h8t5yuutuky.pdf

What will happen? Aside from the comparison on the size. Thank YOU

 

[audioguru]

Without knowing the current drawn by the motors then you are just guessing about if the circuit will smoke or not.
I have some simple toy motors that draw 3A from 4.2V. If I used your circuit then the power transistors would have a max voltage drop of 2V so the motor would get only 3V and the 100 ohm resistors must supply a base current to the output transistors of 300mA so must be 8.2 ohms each.

Your PWM won't work because nothing turns off Q1, Q4 and Q5 quickly unless the PWM frequency is very low.

 

[hypersnapper]

Ola audioguru, stalling current is 600mA. Neglect the pwm thing. I'm not using it. I connect it to the ground. Does it matter if I use this circuit? even with transistors with high Ic like what I stated above?

Sorry, i can't really get what you mean with max voltage drop and also the base current to the output transistors

 

[audioguru]

All transistors have a spec on their datasheet called "saturation voltage" which is their max voltage loss when they are turned on hard.
The voltage loss is about 0.8V for many power transistors when their collector current is 600mA and their base current is 60mA.
The max base-emitter voltage is also listed on the datasheets which is about 1.0V for a power transistor as above. So your 100 ohm resistors must be reduced to 47 ohms for the output transistors to saturate well with 600mA.

 

[hypersnapper]

thanks so you mean. for example I use these transistors and their Vce is 5v ea, then I'll lose 10v? considering my supply is 9v. I got no voltage left at the end?

 

[audioguru]

The transistors need to "saturate" when used as a switch. Then the base current must be 1/10th the collector current.
The current gain (a fairly high number) of the transistor is called hFE and is when the transistor is a linear amplifier, not a switch, and its collector to emitter voltage (Vce) is at least 5V as listed on its datasheet.

In an H-bridge, two transistors are turned on. Each one has a saturation voltage loss. The max saturation voltage loss is shown in the datasheet and is about 1V at 600mA for each transistor. Then with a 9V supply and a total saturation loss of 2V the motor gets only 7V.

 

[3v0]

Seems to be missing diodes to protect the transistors when the motor is switched off.

 

[cr0sh]

I don't understand the need for a third PWM pin - you should be able to just tie the low-side transistors to ground, then PWM whichever directional control pin...?

 

[hypersnapper]

Thank you for all your comments im learning so many. Godbless all