66 Silicon chip Australia’s electronics magazine siliconchip.com.au
The reference outputs of that module
seemed to be just as stable and clean
as those from the other two.Trimming the AD584LH
The output measurements of the
AD584LH-based module were a little
disappointing, so we decided to try it
out with a trimming adjustment adap-
tor. Fig.7 shows the adaptor circuit
connected to the AD584LH module.
The components were fitted to a
small piece of ‘stripboard’, with the
25-turn trimpot at one end and a 4-pin
SIL socket at the other, to mate with
pin header P2 on the module.
Using this simple adaptor we were
able to adjust the 10.00497V output
of the module down to 10.00003V at
26.4°C, with no increase in the appar-
ent noise level.used to make the measurements, but
they were shown as 10.004V, 7.503V,
5.003V and 2.501V; again within the
AD584LH specs and also quite close
to the figures we measured.
Our measurements for the noise lev-
els from each module are somewhat
higher than the AD584 specs would
lead you to expect, although they’re
still quite low.
This might be due to a shortcoming
in the millivoltmeter used to make the
measurements as its resolution below
1mV is rather poor.
We were interested to see if there
was any adverse effect on the output
stability or noise levels of the KKmoon
module outputs as a result of its use of
Mosfets to control the output voltage
and that high-frequency DC-DC boost
converter, but we couldn’t find any.ming adaptor like that shown in Fig.4
to this module.
Trying them out
When we received the three mod-
ules, we put them through their paces.
In each case, we applied power and
allowed the module to warm up and
stabilise for about one hour.
At the same time, we also switched
on our very accurate Yokogawa 7562
6-1/2 digit DMM, and allowed it to sta-
bilise as well. We then measured the
four different DC voltage levels from
each module, along with the noise lev-
els, as shown in Table 2.
Overall, the output voltages from
each module were within the specifi-
cations given by Analog Devices for the
AD584 version used in that module.
In fact, the measured output volt-
ages from all three modules were all
within the specs given for the superior
AD584LH device, with those for the
ML005 and the KKmoon modules ac-
tually tighter/better than those for the
module using the actual AD584LH.
How surprising!
The box for the KKmoon module
came with a stick-on label listing the
actual output voltages for that module
as measured at 23°C using an Agilent
34401A DMM. These were shown as
10.00393V, 7.50163V, 5.00292V and
2.50014V. Our measured figures were
quite close to these, as you can see.
The ML005 module didn’t come
with any equivalent figures, but the
module using the AD584LH device
had a similar stick-on label on the
sealed plastic bag it was packed in.
This “high-precision” module did
not state the meter that had been
Fig.6: the “high precision” voltage reference uses the more accurate
AD584LH chip. Otherwise, it’s a pretty basic module, with a linear
voltage regulator, power indicator LED and four different output
sockets (P1-P3 and P5). With the exception of the 10V/7.5V outputs at
P1 and P2, the others must be connected to very high impedance loads
(eg, the inputs of CMOS or JFET-input op amps) to avoid inaccuracy.Fig.7: the voltage reference can also be trimmed with the addition of just four
components. As this is the most stable of the references describe here, it would
make sense to adjust it to be as close to the nominal voltages as possible. It
should then remain accurate in the long term.