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When in general is it easier, even preferable, to use a dual isolated gate driver on an H-bridge with IGBT power transistors, rather than separate high side and low side drivers; what if any are the guidelines?

For example, I want to use an IGBT H-Bridge module as the main component of a switch in a 12V DC circuit to an array of electromagnets whose polarities require periodic alternation at a rate of around 4 to 8 Hz only (with the aim of creating a rotating magnetic field). In that case, would a dual gate driver for each half of the H-bridge -- such as an ISOdriver from 'Silicon Labs' etc. -- with a bootstrap circuit* be simpler and more straightforward than using separate HS/LS drivers, or even superior? *Vgs 15V required.

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    \$\begingroup\$ An isolated driver on a 12 volt DC power rail is just not needed. At 4 Hz, you'll be lucky to get bootstrapping circuits to work very well. \$\endgroup\$
    – Andy aka
    Jan 22 '21 at 17:33
  • \$\begingroup\$ @Andy aka Can you explain briefly why an isolated gate driver is not necessary. The specs for the H-bridge tell me the gate needs 15V, so a gate driver is surely needed, isn't it? As you might have guessed, I'm not experienced in electronics; just a bit of basic theory. \$\endgroup\$
    – jeremiah
    Jan 22 '21 at 17:44
  • \$\begingroup\$ Please explain you think it needs to be isolated. \$\endgroup\$
    – Andy aka
    Jan 22 '21 at 18:28
  • \$\begingroup\$ @Andy aka Sorry for delay; I'm also isolated. I don't know why one needs an isolated as opposed to an ordinary old-fashioned garden variety gate driver; and it is extremely difficult, for me anyway, to find reliable info on it on the internet. The first advice I received at AAC was to use an isolated high side driver for my H-bridge. Your initial comment confused me a bit, that's all, the way toddlers can be confused about nearly anything. I'm an electronics toddler. A few short phrases of direction may be very valuable. \$\endgroup\$
    – jeremiah
    Jan 23 '21 at 13:29
  • \$\begingroup\$ @Andy aka The other thing is the bootstrap: I'd have thought intuitively that low frequency switching would favour the use of a capacitor/diode set-up -- but again, just toddling. Thanks for any help. \$\endgroup\$
    – jeremiah
    Jan 23 '21 at 13:29
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If you need continuous (or very long, aka low frequency) high side drive, isolated makes it easier since you can more easily use a floating gate drive supply. Also works if it is not a half-bridge and is just a high-side switch with no low-side switch.

Separate high-side/low-side drivers tend to be made with boostrapping caps and diodes for the high side supply which is cheaper but cannot do 100% duty cycle. In this scheme, the high-side REQUIRES a low-side switch so it must be a half-bridge. The low-side of the half-bridge must periodically turn on (usually through normal operation) to allow a current path to refresh the bootstrap cap. They can be adapted for continuous gate drive with charge pumps and such which is more complicated but cheaper than a floating supply.

Note: a half-bridge is one half of an H-bridge. The 'H' in H-bridge is the shape of the circuit and does not stand for "half".

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  • \$\begingroup\$ ''The requirement of..?'' Yes I understand about H-bridges and that the gates of all 4 IGBTs in this case require gate drivers: 2 HS and 2 LS. My question was intended mainly to determine whether it is generally preferable to use these drivers as separate components, or to incorporate HS/LS drivers in a dual driver for each half of the full bridge. Now I see that this is complicated by the necessity for the HS and LS of the half bridge to be operating alternately; I'd thought these dual drivers might be used for the HS/LS IGBTs in opposite corners of the H-bridge. Sorry, thanks. \$\endgroup\$
    – jeremiah
    Jan 23 '21 at 14:12
  • \$\begingroup\$ @jeremiah Oh I think that was just a snippet that got left behind when i was reordering things. You can just ignore it. \$\endgroup\$
    – DKNguyen
    Jan 23 '21 at 19:36

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