For a project I need to design a dual H bridge to drive two motors with the specs provided below:

Output speed: 150±10%rpm

No_load Current: 200mA (Max)

Stall current: 4500mA(max)

Stall torque: 9.5kgNaN

Rated speed: 100±10%rpm

Rated torque: 3000gNaN

Rated Current: 1200mA (Max)

Noise: 56dB

Working voltage: 9V

Outside Shaft Length: 14.5mm

Shaft End Play: 0.05-0.50mm

Screw Size: M3.0

Dia. Of Shaft phi4mm, D3.5

encoder: 2 pulses/circle

We will be over driving the motors at 12V instead of 9V.(Marked as Vcc on the schematic)

The logic chips are powered by the Vcc pin which is coming from the header which will be either 5 or 3.3V, but the ground is shared across logic and power sections. The choice of mosfets isn't finalized but they will be sufficiently rated for the job(Currently considering IRF4905 for the high side and IRFZ44N for the low side). I've already designed an H bridge with a lot of safety features and logic circuit to prevent shorting out the mosfets, but I thought I share the design with you ... maybe someone finds a flaw or recommends some better components that I can use. Here is the schematic diagram of the driver:

schematic diagram


Edit: Please just comment on my design and don't go off topic. It's not about buying an off the shelf bridge with better design, we are doing a robotics project for fun and would like to build everything ourselves.

  • \$\begingroup\$ include the PCB layout in your question. And sketch in your understanding of the high-current fast-switching loops. \$\endgroup\$ Jul 22 '18 at 21:54
  • \$\begingroup\$ Your specifications are not that exotic that you need to build one yourself. There are very good H-bridges driver ICs out there which can do what you have designed and better. e.g. You have no short/high current detection or over heating shut down. Also those have a built-in charge pump so they can use NMOS on the high side. \$\endgroup\$
    – Oldfart
    Jul 22 '18 at 22:30
  • \$\begingroup\$ If rated current is 1.2A motor stall current 4.5A @9V implying 2 ohm DCR thus for 9W output power and 40W stall/start power with MOSFET efficiency of say 90% of 90W then is RdsOn<= 20 milliohm true? 2 pulses/ rev at 150 RPM seems rather low ?? For encoder. \$\endgroup\$ Jul 22 '18 at 22:38
  • \$\begingroup\$ You say you're driving the motors with 12V, which your schematic denotes as "Vcc". Does that mean you're also powering the 74HCxx logic that tolerates a 2.0-6.0 V supply with that? Only the MC14081 will tolerate a supply that high. Your sch doesn't specify a part-number for the MOSFETs, so we can't verify their suitability to the job. The logic gates aren't showing Vcc/Gnd, which is bad practise. \$\endgroup\$
    – Techydude
    Jul 22 '18 at 23:28
  • 1
    \$\begingroup\$ You need to call your two VCC voltages something different, because when you go to route your board they will be the same net. \$\endgroup\$
    – Tyler
    Jul 23 '18 at 0:40

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