MOSFET Driver

270

06:22:46

A MOSFET gate driver in totem-pole configuration to both push and pull charge to/from the gate.

published 8 years ago

2ctiby

8 years ago

But is it better for having the extra parts http://everycircuit.com/circuit/5926121943334912

npandolfi

8 years ago

Yes it is, for high frequency, large gate capacitance applications. You usually see dedicated driver ICs with to-247 packages because the charge they need pushed in and pulled out is quite significant.

2ctiby

8 years ago

Yes, but what are the stated figures of the in and out charge time so that we can compare them to a simple pull-down resistor for comparison in a similar situation? I mean... Is it that they are produced because it is economically sensible to save wasted current due to the necessity of a low pull-down resistor value to gain speed of discharge, or does the totem really win in terms of speed?... just wondering for interest.

npandolfi

8 years ago

The totem pole is a better 'buffer' so to say. If we load down the circuit that is sourcing the signal, it is going to negatively affect the frequency response of the circuit. By using a dedicated gate driver IC, we provide a high impedance input for the signal to get pushed to the gate, similar to an op-amp's inputs. The less we use the signal to drive a complex impedance (gate capacitance), the better the signal is preserved in its original state. It's all about encapsulation of different stages of a circuit.

npandolfi

8 years ago

Also, this isn't the right resource to get numerical data. This resource (everycircuit), is used to understand the concept of certain designs. If you want to know more, google it. Read application notes...

2ctiby

8 years ago

If you had read application notes that you mention, then I think you will find that your1M Ohm pull down resistor should not be there in your totem pole setup.

npandolfi

8 years ago

Have you designed working products before? That resistor is a fail-safe to ensure that the MOSFET is off by default...

2ctiby

8 years ago

See Fairchild AN-6069 Figure 14 and the last sentence just above that figure 14 https://www.google.co.uk/url?sa=t&source=web&rct=j&url=https://www.fairchildsemi.com/application-notes/AN/AN-6069.pdf&ved=0ahUKEwiz6-yuzNDXAhUoJ8AKHTn_BJUQFggxMAA&usg=AOvVaw1UdK5Yz9rnH3vkLjOvG1Mc

npandolfi

8 years ago

The resistor is a FAIL-SAFE. In theory, it makes no sense. When working with high powered electronics, you never want a delicate power switch to be on if it wasn't SPECIFICALLY meant to be on. That means that if the primary stage melted itself out and disconnected, the MOSFET would be guaranteed to turn off regardless. In fact, the pull down resistor should even be a smaller value. Ill change it.

npandolfi

8 years ago

Figure 14 doesn't even mention anything about practical usage. That is a concept design. Notice no part numbers. Notice no specifics.

npandolfi

8 years ago

I'm done with this thread.

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