Electronic – Switching 60V with 3.3V microcontroller at 50kHz – 1MHz

mosfetswitch-mode-power-supplyttl

I'm playing around with some switching mode power supply things. For this reason, I'd like to switch the input voltage with a microcontroller, from the PWM output or other output pins.

The specifics:

  • Input voltage: 4V – 60V
  • Switching input signal: 3.3V (LVTTL)
  • Maximum switching speed: 50kHz – 1MHz (as high as I can easily get it)
  • Required current tolerance: 1.5A or 15W

There is no supply voltage besides the 3.3V signal.

I am looking for suitable components to do this as simply as possible. For me, simple means as few components as possible, and as few requirements on both the inputs and outputs of the components – I do not wish to impose any driving requirements to the microcontroller, or restrictions on how the switch can be used, or similar things. But I'd want the components to be suitable for a high efficiency switching mode power supply.

I know it can be done with a combination of n-MOSFET and a p-MOSFET and a couple resistors. I know it can also be done with a gate driver IC and a n-MOSFET, although I have been unable to locate one that would only require 3.3V supply voltage (and a boost pin?). I know I do not want a solution that would force some minimum off-time rate on the MOSFET to charge a capacitor, but I might be convinced otherwise. In theory, the most direct solution would be a 3.3V compatible solid state relay or analog switch, but the actual solid state relays available do not seem very suitable.

But, primarily I am just interested in learning more about the problem space here and the possible solutions.

Clarifying schematic stolen from another question:

enter image description here

  • Vin = 4V – 60V
  • Controller = 3.3V signal, toggling at, for example, 250 kHz
  • Q1 = the component, or the set of components I wish to find

So, strictly, the question is simply: what do I need in place of Q1?

(Note that this is just an example schematic, not exactly the sort of circuit that I wish to build.)

Best Answer

The 2N6782 N-channel FET is rated at 100v drain to source at a maximum 3.5A and 15W max power. I picked a through-hole part because the surface-mount part would be difficult to solder by hand.

To drive the FET, you can use the LT4440-5, which takes a logic level in and can drive an N-channel MOSFET switching up to 60 or 80V depending on the version. The supply current is negligible, only a few µA. The driver only comes in a surface mount part (SOT 23-6 or MSOP).

The only drawback is it requires a supply voltage (VCC) between 5 and 15V (thanks to the OP for pointing out this variant of the LTC4440 with a lower minimum supply voltage). Since you have only a 3.3v supply, you could use either a voltage doubler or a simple boost converter (such as the MIC2141) to supply the VCC voltage.

Both the driver and voltage doubler/boost converter should only require a few ma (if that) from your 3.3v rail.

The FET and driver should work up to 1 MHz, maybe a little higher.

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