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There 7408 is used to drive Mosfets (I have IRFZ44n instead of TIP122). Its input is limited to 5.25V (not so much high volt to drive mosfets).

I want to provide higher volt pulse to Mosfet-Gate to make Mosfets turn-on fully. Is it really better idea to do this?

So I want to use L293 instead of 7408. Is it suitable to use.

Is it better to use co-amplifier (single-741, Dual-LM833, Quad-LM3900) instead of 7408?

OR is there any other better option.

enter image description here

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  • \$\begingroup\$ First, get proper low inductance motors, which typically means those with a low coil voltage rating - say below 4 volts - today these will all but invariably be bipolar. Then get a 12v, 18v or even 24v supply. Then get a proper chopping stepper module rated for that supply. \$\endgroup\$
    – Chris Stratton
    Commented Oct 14, 2017 at 16:23
  • \$\begingroup\$ I have following two motors taken from photocopier scrape shop for $0.50/each: \$\endgroup\$
    – user1958898
    Commented Oct 15, 2017 at 5:20
  • \$\begingroup\$ 1. KH56KM2U014 A02 2. KH56JM2U014 A06 I contacted manufacturer but it answered: "Unfortunately they are Custom products and we can't deliver their data/specification to you. Because we have a NDA contract with customer and we can't tell to other third party directly." I also searched these motors in company catalog, I could not find them. So I can only calculate winding resistance, HOW to calculate A/phase, Volt and Inductance mh/phase? \$\endgroup\$
    – user1958898
    Commented Oct 15, 2017 at 5:26
  • \$\begingroup\$ What is the motor power voltage? What is the maximum current? How is it not obvious this information should have been supplied in the first place? There are FETs that turn on well with only 5 V gate drive, but without proper specs it is impossible to tell whether any of the are suitable. \$\endgroup\$
    – Olin Lathrop
    Commented Oct 7, 2018 at 13:05

1 Answer 1

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5V logic is not nearly enough to turn on those MOSFETs sufficiently. Vgs threshold has a max value of 4V, so they may be barely on with a TTL high signal. 10V or 12V on the gate would be much better.

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  • \$\begingroup\$ Thanks for your expert reply. Yes, I also think so. So which is better alternative of 7408 in above schematic. Please mention the name. Big thanks \$\endgroup\$
    – user1958898
    Commented Oct 15, 2017 at 5:30
  • \$\begingroup\$ In above circuit, 7408 is AND gate IC with max VCC 5.25V. CD4081 is also AND gate IC with max VCC 18V. Is CD4081 better alternative to 7408? Please suggest most suitable component for this application, whether CD4081 or other. \$\endgroup\$
    – user1958898
    Commented Oct 15, 2017 at 6:50
  • \$\begingroup\$ Can I use this circuit (i.sstatic.net/r3Pbe.png), If it is suitable, please modify it for 12v input instead of 24v. \$\endgroup\$
    – user1958898
    Commented Oct 15, 2017 at 7:56
  • \$\begingroup\$ Waiting the reply..... \$\endgroup\$
    – user1958898
    Commented Oct 16, 2017 at 11:40
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    \$\begingroup\$ @user1958898 this is not a design service. Your image circuit will work though you need to calculate the right resistances for 12V. \$\endgroup\$
    – Trevor_G
    Commented Oct 16, 2017 at 13:11

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