■ PHOTO 1. This mechanical assembly
is designed to restrict the flow of liquid
when the solenoid is inactive. When
the solenoid coil is energized, the
solenoid plunger will retract, removing
the blockage element which will allow
liquid to flow.
1. PROTOTYPE LED IS CHICAGO MINIATURE MOUSER
PART NUMBER 606-4302H1-12V
■ SCHEMATIC 2. This is just how easy it is to
employ a MOSFET to act as a high-voltage/
high-current electronic switch component. If
you’re still thinking about hooking up those
20 LEDs all at once, here’s your ticket.
■ PHOTO 2. This is really rough, but it works
just fine. I added the LED to provide a visual
indication of the status of the solenoid
valve. When the solenoid valve is energized,
the LED illuminates. The LED only draws
10 mA and places no significant extra load
on the ZVN4306G.
duty requirement as far as the ZVN4306G is concerned.
As a test, I decided to run the solenoid continuously
until the magic smoke appeared. As it turned out, the
solenoid got much hotter than the ZVN4306G, which
retained its magic smoke. So, we can actually get away
without attaching an external heatsink to the ZVN4306G.
I lashed up a prototype of the MOSFET buffer in Photo
2. Note that I used a specialized Chicago Miniature LED in
the prototype. The prototype LED contains a built-in current
limiting resistor. I like to use these LEDs in prototypes and
for debugging as they can simply be soldered into the
circuit as-is. These LEDs also come in
five-volt versions. The available colors
are red, amber, and green. You can
get these specialized LEDs from
Mouser. The LED is used here to provide a visual indication of the state of
the solenoid valve. When the solenoid
is energized, the LED illuminates. The
Chicago Miniature LED only draws
13 mA and does not introduce any
significant load to the ZVN4306G.
The ZVN4306G in the sink configuration can provide buffered control for
a brushed DC motor or a relay coil with
ease. However, even with the
ZVN4306G’s high-voltage and high-current capabilities, you
may find that your application needs some additional horsepower. Fortunately, we can take the basic ZVN4306G-based
I/O concept we have been discussing and amplify it by
employing a heftier MOSFET switching element. That’s
exactly what Werner von Braun did. He took the Redstone
Rocket concept and amplified it to create the Saturn booster.
In this case, our ZVN4306G is the Redstone Rocket
and the IRLI2910 is the Moon Rocket. The IRLI2910 is a
logic-level gate drive power MOSFET. If you keep it cool,
the IRLI2910 can pass up to 31A at voltages up to 100V.
The IRLI2910’s Gate-Source threshold voltage lies between
1.0V and 2.0V and when you turn it on with 5V, the
Drain-Source resistance falls to .030Ω.
An interesting feature of the IRLI2910 is the way it is
packaged. The IRLI2910 is completely insulated with a
moulding compound that electrically isolates the device
from the heatsink while providing a very high thermal
transfer characteristic. To use the IRLI2910, simply drop it
into our ZVN4306G circuit as the electronic switching
component instead of the ZVN4306G.
The words that I speak in the Design Cycle column are
■ PHOTO 3. Teamwork — that’s what this is all about. This shot
shows the IRLI2910 poised in its modest heatsink alongside
of a gaggle of ZVN4306G devices. The IRLI2910’s job is
to control a 35V @ 5A DC motor. The ZVN4306G crew is
handling solenoid, relay coil, and solid-state relay duties.