I need to protect a number of 24V stepper motor drivers from cable disconnects as described in "Adding diodes to easy driver stepper motor driver". This means using eight Schottky diodes with a forward voltage <= 400 mV at >= 1.5 A in a bridge rectifier configuration, as follows:


simulate this circuit – Schematic created using CircuitLab

I will be designing PCBs for these and then soldering all components by hand. SMD components are fine.

However, I need to protect 20 stepper drivers and I would prefer to avoid dealing with hundreds of discrete diodes if I could just buy one or two ICs per stepper driver. I have found ICs containing eight diodes at a time, arranged in a dual bridge-rectifier configuration, but only with much higher forward voltages at lower currents. They seem to be for different purposes entirely.

My best guess is that I am searching incorrectly, and such a product likely exists but I don't know the correct name or terminology. What is the correct name for an IC consisting of some multiple of two (two, four, etc.) Schottky diodes arranged in this configuration as protection circuitry?

  • \$\begingroup\$ Why do you need the diodes ? The driver IC you refer to has diodes built in. Why do you need VF < 400 mV ? \$\endgroup\$ – jp314 Jan 27 '16 at 3:14
  • \$\begingroup\$ In response to a user question during a webinar, the designers of the particular driver IC from ST Microelectronics that I will be using recommended the use of diodes to protect the driver IC in the event that a cable is disconnected or broken. The idea of wanting VF <= 400 mV is to ensure that these diodes conduct before any internal diodes in the IC. \$\endgroup\$ – JohnSpeeks Jan 27 '16 at 4:26
  • \$\begingroup\$ That IC - powerSTEP01 - also has body diodes in the power MOSFETs. If those can't clamp the signals, there is something wrong with the IC. \$\endgroup\$ – jp314 Jan 27 '16 at 5:01
  • \$\begingroup\$ There's also the issue of the motor being turned manually. In their October 22 Webinar on the powerSTEP 01 (registration required) at 38:18, someone asked "Is any additional protection required to prevent damaging the PowerSTEP01 if it is unpowered and the motor is turned manually effectively acting as a generator?" ... \$\endgroup\$ – JohnSpeeks Jan 27 '16 at 5:24
  • \$\begingroup\$ The answer was: "It is usually best to put some external diodes to ground and to the VBus, and we would want to use a Schottky diode because the Schottky diodes have a lower forward drop so that if the motor does start acting as three-phase generator, those diodes will carry the current and feed it back to the DC bus... Putting external Schottky diodes to ground and to the supply, so that would be a total of eight diodes, two on each line, will prevent that problem because the lower drop Schottkys will carry the current instead of the body breakdown diodes of the internal MOSFET." \$\endgroup\$ – JohnSpeeks Jan 27 '16 at 5:25

A google image search for "schottky diode array" led me to this part: http://www.ti.com/lit/ds/symlink/sn74s1051.pdf might be what you're looking for.

  • \$\begingroup\$ The word "array" was what I was missing in my searches. While that particular part won't handle the voltages I need, this has now opened up a large number of options--at least one of which I am sure will work! \$\endgroup\$ – JohnSpeeks Feb 17 '16 at 14:13
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    \$\begingroup\$ Excellent. glad I could help. \$\endgroup\$ – mhz Feb 18 '16 at 9:50

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