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    1. · Registered
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      Discussion Starter · #31 ·
      You can use this or similar for low-side MOSFET if we talk about a simple PWM controller for brushed DC motor. If you build a controller with regen or for BLDC/ACIM motor you should have a half-bridge or even 3 of them. So you have low- and high-side MOSFETs. Gate and source of the last one is under high voltage so you need to use either opto-isolated driver or one that I mentioned ( many similar available). The IRS2186 can handle bridges up to 600V

      In case of half-bridge be better to use a driver which has both low- and high-side output because many of such ,first, has a circuits to prevent to open both low and high FETs at a time and , second, have a small delay to open a low side which can handle pass-through current.

      OK I'm sold.
      Where to attain IRS2186?
      I'm really trying to avoid using a microcontroller as I thing it's unecessarily complex for a PWM circuit.

      I was thinking of this one. 200 ma output, dual output. Fed into an IRS2186 and then fed into a MosFet array. Sink the hell out of it all and schottky the output and pray.

      http://www.ebay.ca/itm/5-x-TL494CN-...ltDomain_0&hash=item2c6321ddbd#ht_2543wt_1043
       
    2. · Registered
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      OK I'm sold.
      Where to attain IRS2186?
      I'm really trying to avoid using a microcontroller as I thing it's unecessarily complex for a PWM circuit.

      I was thinking of this one. 200 ma output, dual output. Fed into an IRS2186 and then fed into a MosFet array. Sink the hell out of it all and schottky the output and pray.

      http://www.ebay.ca/itm/5-x-TL494CN-...ltDomain_0&hash=item2c6321ddbd#ht_2543wt_1043
      That's a very good price for five of these ICs. But there may be additional shipping and international tarrifs, so watch out for that.

      Actually, a microcontroller such as the PIC16F684 can give you a PWM drive and a control input with only a properly bypassed 5 VDC power supply and the signal from the throttle pot. It's a 14 pin DIP (or SOIC-14) and costs about $1. I can supply the code to get you started, and all you need is a programmer like a PICkit 3. Or a PICkit 2, and I have an extra one I'll sell you for $30 which is about 1/2 price.

      If you are serious about building a PWM for a vehicle you WILL need more than the TL494, and the PIC can provide everything you need. It's a lot easier to build the hardware with all the bells and whistles and then program the PIC as you add the features.

      Hoping and praying and massive heatsinking will not make your parallel MOSFETs reliable if you exceed the SOA. The damage occurs too quickly for the heat to be transmitted through the substrate and tab and the heat sink. The weakest MOSFET will be destroyed first. If you are lucky, it may short out and save its comrades, but it will supply full voltage to the motor and the current will probably be enough to vaporize the leads. Then its buddies will take turns letting out the magic smoke until you have a real mess.

      The IRS2186 is available from DigiKey for about $3.40/1:
      http://www.digikey.com/product-detail/en/IRS21864PBF/IRS21864PBF-ND/1300606

      It's a good half-bridge driver with 4A gate drive but you really don't need the high side unless you want to do dynamic braking or regen. You CAN do that with the PIC, not the TL494.

      A good low side driver is the TI http://www.digikey.com/product-detail/en/UCC27321P/296-13672-5-ND/509704 which has 9A drive and also about $3.28.

      Isolation is not absolutely necessary but for an EV it's a good idea. In that case there are some high speed optoisolators such as:
      http://www.digikey.com/product-detail/en/HCPL0501R2/HCPL0501R2CT-ND/3041742
      It's about $2 in an SOIC-8 package and has about 500 nS propagation delay. The driver will then provide about 50 nS rise/fall gate drive. You may find you actually need to add a bit of delay to avoid overshoot and inductive spikes. You will need a good scope to see these transients, at least 40 MHz and 100 MHz or better is ideal.
       

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