Silicon Chip – July 2019

siliconchip.com.au Australia’s electronics magazine July 2019 63

SIL header J5 allows setting the mod-
ule’s output voltage by fitting a jump-
er shunt to one of the four possible
positions.
The current drain of the module
when operating is less than 1mA, but
this will rise if current is drawn from
any of the outputs.
Before we move on to look at the
next module, you might like to know
how easy it is to give the ML005 mod-
ule three fixed and buffered outputs of
10V, 5V and 2.5V.
Fig.3 shows all you need to do this:
a low-cost dual op amp like the LM358
or the TL072, wired as shown to pro-
vide two unity gain buffers. One is for
the 5V output of the module, and the
other for the 2.5V output. The 10V out-
put is already buffered by the op amp
inside the AD584, so it doesn’t need
any further buffering.
Note though that this buffer op
amp’s “input offset voltage” error term
will slightly reduce the accuracy of
the output voltages, although typi-
cally this figure is no more than a few
millivolts.
However, it can change with tem-
perature and time. So if you need
maximum accuracy, use a precision
or chopper stabilised op amp, which
will have offset voltages in the micro-
volt range.
So is it possible to trim the outputs
of the ML005 module, to set the output
voltages closer to nominal? Yes, it is,
using the trimming circuit shown in
Fig.4. As you can see it’s fairly straight-
forward; just a 10kW multi-turn trim-
pot connected across the output from
J3 (Vout) to J4 (0V), with a 10kW resistor
in series and with its wiper connected
to the 2.5V pin of J5 via a 3.3MW se-
ries resistor.
This allows the outputs to be ad-
justed over the range of about ±20mV;
more than enough to achieve calibra-
tion.
The trimpot should be a 25-turn
cermet unit, to allow fine adjustment
and also provide a low temperature
coefficient. The two fixed resistors
should also be metal film types. The
3.3MW series resistor can be reduced
in value for a wider adjustment range,
but its value should not be lower than
300kW as this would adversely affect
the module’s stability.

The KKmoon module

Now we turn our attention to the
module with all the ‘bells and whis-

tles’; the KKmoon (www.kkmoon.

com/p-e0555.html). It comes housed

in a laser-cut transparent acrylic case.

The case can be easily disassembled

for servicing, if needed.

The designers of this module seem

to have gone out of their way to add

every feature they could think of.

For a start, they’ve built in a

3.7V/500mAh lithium-polymer (LiPo)

battery, so the unit can be used away

from mains power.

Of course, the battery will need

to be charged when you are back in

your workshop, so they’ve built in a

charger as well, with a 5V input (mi-

croUSB socket).

Since the battery only provides

about 4.2V even when fully charged,

they’ve also included a DC/DC boost

converter to step up the battery volt-

age to around 13.5V for the AD584.

They’ve also added circuitry so

that the various voltage ranges of the

AD584 can be selected in sequence

using a single pushbutton switch and

LEDs to indicate which output voltage

is currently selected.

The circuit (Fig.5) shows the parts

they have added to provide all these

Fig.3: this circuit shows how to get multiple different reference voltages from the

ML005 module simultaneously. While you could use a low-cost dual op amp as

suggested here, the voltages would be more accurate and stable if a precision or

chopper-stabilised op amp was used.

Fig.4: it’s quite easy to connect a trimpot to the ML005 module, so that you can

adjust its output voltages to be close to the nominal values. You need a very

accurate voltmeter to do this. This will work with the output voltage set to one

of the 10V, 7.5V or 5V options.