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N-Channel MOSFET High-Side Drive: When, Why and How?

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I had previously shown how to drive N-channel MOSFETs in low-side configuration. You can find the tutorial here: http://electel.blogspot.com/2016/12/low-side-mosfet-drive-circuits-and_23.html I’ve been requested to write a tutorial/article regarding high-side MOSFET drive. So, here I’ll talk about N-channel MOSFET high-side drive. Let’s first look at the common low side configuration.  Fig. 1 - N-channel MOSFET configured as low-side switch Now let’s look at a MOSFET configured as a high-side switch. Fig. 2 - N-channel MOSFET configured as high-side switch You can quite easily see the difference between the high-side configuration and the low-side configuration. In the low-side configuration, the load is connected between the drain and +V, while the source is connected to ground. Thus, the gate drive is referenced to ground. So by applying a voltage of >7V (for Power MOSFETs) or >4V (for Logic Level MOSFETs), the MOSFET can be fully turned on. Now let’s talk about the high-si...
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Using the SG3525 PWM Controller - Explanation and Example: Circuit Diagram / Schematic of Push-Pull Converter

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PWM is used in all sorts of power control and converter circuits. Some common examples include motor control, DC-DC converters, DC-AC inverters and lamp dimmers. There are numerous PWM controllers available that make the use and application of PWM quite easy. One of the most popular of such controllers is the versatile and ubiquitous SG3525 produced by multiple manufacturers – ST Microelectronics, Fairchild Semiconductors, On Semiconductors, to name a few. SG3525 is used extensively in DC-DC converters, DC-AC inverters, home UPS systems, solar inverters, power supplies, battery chargers and numerous other applications. With proper understanding, you can soon start using SG3525 yourself in such applications or any other application really that demands PWM control. Before going on to the description and application, let’s first take a look at the block diagram and the pin layout. Pins 1 (Inverting Input) and 2 (Non Inverting Input) are the inputs to the on-board error amplifier. If you a...
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Using the TLP250 Isolated MOSFET Driver - Explanation and Example Circuits

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I’ve already shown how to drive an N-channel MOSFET (or even an IGBT) in both high-side and low-side configurations in a multitude of ways. I’ve also explained the principles of driving the MOSFETs in these configurations. The dedicated drivers I’ve shown so far are the TC427 and IR2110. Some people have requested me to write up on MOSFET drive using the very popular TLP250. And I’ll explain that here. The TLP250, like any driver, has an input stage, an output stage and a power supply connection. What’s special about the TLP250 is that the TLP250 is an optically isolated driver, meaning that the input and output are “optically isolated”. The isolation is optical – the input stage is an LED and the receiving output stage is light sensitive (think “photodetector”). Before delving any further, let’s look at the pin configuration and the truth table. Fig. 1 - TLP250 Pin Configuration Fig. 2 - TLP250 Truth Table Fig. 1 clearly shows the input LED side and the receiving photodetector as well...
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