DRC1746_15 Datasheet, PDF (5/8 Pages) Analog Devices – HIGH POWER OUTPUT HYBRID DIGITAL TO SYNCHRO RESOLVER CONVERTERS

- ANALOGDEVICES FAX-ON-DEMANDHOTLINE
Page 1~
>55
"'1--.".
135
I' ,."
,
~ 115
i 105
~_{.. ...~_..}
~;<J> III
~_x
75
..
16S
145
1JS
I' ^1:>5
~ 116
c^~r:
i
:_.":_.:
I
%
DRC1745/DRC1746
~........_...
'"
OBSOLETE ..
D.D
0.2
D.4
D.O D."
1.D 1.2
u
1.0
1.8 2.0
NOTE,
LOAD POWER - VA
1. _81E",~ TEMPERATURE 21'1:. NO HEAT SlftK,
2. TEMPERATuRE MONITORED WITH WORST CASE DIGITAL 'NNT '46'.
3. TEMPERATURE MEASURED ON HOTJEST PART Of; CASE
Figure 4. Case Temperature for Resistive Loads
As can be seen from Figures 4 and 5, it will be necessary to
provide heat sinking when driving significant loads in order to
keep the temperature of the case below its 12S.C maximum.
The converters have been designed with a flat metal base to
facilitate mounting on heat sinking materials. Special thermal
management, utilizing direct eutectic bonding, has been employed
in the output stage to minimize thermal resistance to:
Angle
0°,90°
6Junctionlcase = less than IrC/watt
45". 135° eJunctionlcase = less than 6°C/watt
Consequently the internal junction temperatures do not exceed
.. _0.0
D.'
D,O ...
1.0 1,2 1.4 1.6 1.8
2.0
LOAD POWER - VA
NOTE,
,. AMIIIENT T'£MPERATUBE 21'(;.",0 HEAT SINK.
2. TEMPERATURE MONITORED WITH WOBS, CASE DIGITAL INPUT ,...,.
J. TEMPERATURE MEASURED ON HOTIEST PART DF CASE.
Figure 5. Case Temperature for Inductive Loads
Therefore
iZ""i = v'700T + 49002 = 4950 Ohms
Therefore, the load presented by the control transformer is:
9023
4950x4 = 1.23VA
Adding to this value O.25VA for the STMl683 gives a figure of
1.48V A total.
In the case of a resolver control transformer the same exercise
must be performed but it is not necessary to multiply by 3/4.
Some resolver manufacturers quote rms input current and in
case header temperature by more than 20°C when using pulsating _{this case the load will be the product of the input current and}
power (even under worst case pure inductive load conditions.
the rms voltage used to drive it. The 0.25VA must be added if
The maximum permitted junction temperature is 15S.C).
the STM1683 transformer pair is used.
CALCULATING THE LOAD
The following describes how to calculate the load.
In the case of synchro control transformers, fIrst determine the
value of ZIO' This impedance is normally quoted by the synchro
manufactUrer.
The load presented by the control transformer will be:
3 V2
4 x iZ '
wbcr~V2is the rms signal input voltagc.
When the STM1683 output transformer pair is used, it is necessary
[0 add O.25VA to the calculated figure to allow for transformer
magnetizing current. For the STMI663 output transformer a
figure ofO.30VA should be added.
For example, assume that a 90V rms signal, 400Hz synchro
control transformer is to be driven by the DRCl745 in conjunction
with the STM1683/412 output transformer pair. (The STM1683/
412 boosts the 6.8V rms signal from the DRCl74S to the 9OV
rms required by the control transformer.)
Zso for the control transformer is quoted as:
700 + j4900
DRIVING CAPACITIVE LOADS
Syncbros and resolvers often employ capacitive tuning to minimize
power dissipation. Tbis tuning can be on tbe load itself or (pref-
erably for best accuracy) on the primary of the transformer
driving the load. Full tuning modifies the load to appear resistive
at the reference frequency, bUt it appears progressively more
capacitive at all frequencies above.
Since the converter is an active negative feedback device, it is
essential to include a low value resistor in series with each tUning
capacitor to prevent highly dissipative output stage oscillation.
This resistor must not be less than 3.30. A value of 5.6n is
recommended when referred to the oUtput of the DRCl74S1
DRC1746.
The DRC1745 and DRC1746 can readily drive capacitive inputs
up to IOOnF at the converter output terminals withoUt special
precautions. However, please consult the factory when extreme
lengths of screened cable or any other cases of high capacitance
are to be driven. For example in the case of step-up transformers
where the effective capacitance to be driven is:
Ceft = nlCt.
Where CL is the capacitive load.
REV. A
-5-