![]() ![]() These high-side driver ICs are enormously popular in, shall we say, cost-sensitive power supply applications, because they are much cheaper than any form of isolator and at least appear to be much easier to use. ![]() The latter IC essentially lets the driver for the high-side gate follow the potential of the source/emitter of the switch being driven while level-translating the control signal up to that same potential. To drive the upper switches requires either an isolator or a level-translating (aka “high-side”) driver IC. The sources/emitters in the upper switches, however, do swing violently with each state change, and their potential with respect to the negative rail is undefined when off, and not even fixed when on, since the voltage across the load will vary as well (due to, say, the back EMF of a traction motor changing with RPM). high dV/dt) will be coupled back through them. The lower switches in a half-bridge all have their sources/emitters referred to “ground” (more correctly, the negative rail), which makes it easy to control them directly, and with little worry that noise from rapid voltage swings (i.e. For example, to turn on a MOSFET or IGBT, its gate needs to be made more positive than its source or emitter, respectively, by about 10 V. In cases where isolation isn’t required for safety reasons, it still might make the circuit more reliable to use it, such as driving the gates of the switches in a totem-pole or bridge circuit. ![]() Any power converter for EV applications (charger, inverter, DC/DC converter, etc) that is either supplied by the mains or a >48 V battery pack will pretty much require strict isolation between its power (high-voltage) and control (low-voltage) circuits. Of course, the cheapest (though not necessarily the easiest to use) option is not to use an isolator at all, so the first consideration is whether one is even necessary, either for the circuit to operate, for safety, and/or to minimize electrical noise problems. ![]()
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