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Transcript
High Temperature Electronic Systems Using Silicon Semiconductors
C. S. White, R. M. Nelms, and R. W. Johnson
R. R. Grzybowski
Department of Electrical Engineering
200 Broun Hall
Auburn University, AL 36849-5201
United Technologies Research Center
41 1 Silver Lane, M / S 129-32
E. Hartford, CT 06 108
Abstract - Many applications exist for high temperature
electronic systems. Silicon semiconductors may be utilized in
circuits operating below 200 "C. Some issues in the design and
fabrication of electronic circuits for this temperature range are
described in this paper. A hybrid version of a zero-voltageswitching solenoid drive circuit is constructed using standard
commercial components and subjected to both short-term and
long-term temperature tests. In the short-term test, the circuit
was characterized from room temperature to 150 'C. The
circuit operated at 150 "Cfor 2784 hours in the long-term test.
These tests indicate that standard commercial components exist
for operation at 150 "C. The inductor in the circuit was stable
with temperature, while the capacitors varied significantly with
temperature during the long-term test.
operation below 150 "C. Some manufacturers are beginning
to provide power devices that are rated for operation up to
175 T ; however, the devices are derated to zero operating
power at this temperature. Silicon power devices have been
tested and evaluated over the temperature range of 125 "C to
200 "C [13-181. Operating temperatures above 200 "C will
require .the use of silicon-on-insulator (SOI) technology or
materials such as S i c [1,21.
In addition to semiconductors, high temperature electronic
systems contain passive components such as resistors,
inductors, and capacitors. Commercially-available passive
components must be carefully characterized to determine
parameter variations with temperature. Inductors and
transformers are constructed using magnetic cores. The
I. INTRODUCTION
magnetics designer must understand variations in the
properties of the core materiai as a function of temperature
Interest in the area of high temperature electronics has [ 19-23]. Transformers and inductors constructed using
increased dramatically in recent years. Many papers on this permalloy and molypermalloy have been operated
subject are presented at various conferences. Technical successfully up to 200 "C [24-271. Measured inductances for
conferences such as the biennial International High the transformer of [27] were insensitive to variations in
Temperature Electronics Conference are focused on this temperature. Losses in the winding of the inductor of [25]
subject area. A reference book on high temperature increased with temperature.
electronics was recently published [l]. This interest is a
Capacitors present a challenge to the designer of a high
result of the identification of many applications for high temperature electronic system. They are utilized for timing
temperature electronics [1, 2, 31. Temperature requirements and filtering functions in power supplies, motor drives, and
for a well-logging system are described in [4]. Electronics other electronic circuits. Capacitance, due to the temperature
for automobiles must be capable of operating at high dependency of the dielectric material, and the dissipation
temperatures, depending on their location [2, 5-71. Future factor often change significantly with increasing temperature
commercial and military aircraft will require electronics [l, 281. Capacitors made with an NPO ceramic dielectric are
capable of operating at high temperatures [8, 9, IO]. very stable up to 500 "C [29]; however, capacitance values
Electronics for satellites and other spacecraft can be rarely exceed 0.1 pF or 0.22 pF. Filtering in power supplies
subjected to temperature extremes [ l l , 121.
typically requires capacitors with large capacitance values,
Like the terms 'high fiequency', 'high voltage' and 'high which are sensitive to temperature variations. Electrolytic
power', 'high temperature' has a different meaning for capacitors are unsuitable for use at high temperature;
different people.
With some exceptions, standard maximum temperature ratings seldom exceed 85 "C[ 11.
commercial silicon-based electronic devices have a
By their very nature as a dissipative circuit element,
maximum temperature rating of 85 'C. When these devices resistors have been designed and constructed to operate at
are packaged for military systems, their maximum higher temperatures than other passive components. Even
temperature rating is extended to 125 "C. The definition of though manufacturers do not qualify their resistors for high
high temperature adopted here is temperatures in excess of temperature operation, some commercially-availableresistors
125 "C. This definition does not rule out the use of standard have been tested up to 300 "C [28]. In one test, power
commercial silicon devices, which may be utilized in the resistors were operated at 300 "C for 10,000 hours at 20% of
temperature range of 125 'C to 200 'C [1,2]. For example, their room temperature power rating. With the exception of
most silicon power semiconductor devices are rated for one resistor, resistance values varied less than 4% over the
test period. Variations of resistance with temperature is a key
concern for the designer of high temperature electronic
This research was supported by the Center for Space Power and Advanced
systems.
Electronics with funds from NASA grant NCC3-511, Auburn University,
and the Centers' industrial partners.
0-7803-4943-1/98/$10.000 1998 IEEE
967
Standard commercial passive components and silicon
semiconductors have been operated at high temperatures.
The operation of two different dc-dc converters was
evaluated up to 200 "C [24, 251. Losses in the active and
passive components and the converter efficiency were
measured as a function of temperature. The H-bridge section
and the transformer for a 100 W dc-dc converter were
operated at 200 "C for 1000 hours [26]. A 500 W version of
the same converter was tested for approximately 3500 hours
at 200 "C [ 271. The efficiency of both converters remained
constant during the test period. For all four converters, all
filter capacitors were located outside of the test chamber
because of the difficulty in locating capacitors with large
capacitance value capable of operation at 200 'C. In
addition, the MOSFETs utilized in the converters were
operated well below their current rating at 25 "C to reduce the
conduction losses to keep the junction temperature as close as
possible to the ambient temperature. Paralleled MOSFETs
were used in the 500 W converter to keep the conduction
losses low at this power level.
The design, fabrication, and testing of a solenoid drive
circuit for operation at 150 "C is described in this paper. This
circuit regulates current flow in a solenoid and is constructed
using standard commercial silicon-based components. The
test temperature was restricted to 150 "C to prevent melting
of the components in plastic packages. The test results are
utilized to identify design issues for power converters at
temperatures up to 150 "C. The next section of this paper
contains a description of the solenoid drive circuit. This is
followed by a list of the parts selected and the procedure for
constructing a hybrid version of the circuit. The paper
concludes with a discussion of the test results.
linearly until it reaches V,. At this point, the fi-eewheeling
diode is forward biased and interval t2 ends. The source V,,
inductor L,, and capacitor C, now form a resonant circuit.
The voltage v,-(t) and current ixt) are described by the
following equations
Yc ( t )= vs
+ Z,I,
sin wt
if ( t )= Io cos wt
(1)
(2)
The capacitor voltage starts at V,, reaches a peak value of
Vs + &Io, and is zero at the end of interval ts. When it starts
to go negative, the diode in antiparallel with the MOSFET
turns on clamping the voltage across the MOSFET at zero.
The current if is now negative and flows through the
antiparallel diode. The MOSFET is turned on before current
if reverses direction, so it is turned on under zero voltage.
Current if continues to increase until it reaches Io and the
freewheeling diode turns off. Because of the zero voltage
turn on, this circuit is referred to as a zero-voltage-switching
(ZVS) solenoid drive circuit.
11. SOLENOID DRIVE CIRCUIT
A hard-switched solenoid drive circuit is shown in Fig. 1.
The solenoid is modeled by the inductor LD. The current
flowing through the solenoid is regulated by the MOSFET
switch. When the current flowing through LD, the MOSFET,
and the sense resistor reaches some current level Io, the
MOSFET is turned off. It remains off for a fixed period of
time and is then turned back on. A control circuit senses the
voltage across the sense resistor to determine when the
MOSFET should be switched off.
The resonant switch concept [30-321 can be utilized to
convert the circuit of Fig. 1 to a soft-switching drive circuit.
This is accomplished by adding an inductor L, in series and a
capacitor C, in parallel with the MOSFET as shown in Fig. 2.
The operation of this circuit is described in the literature, but
will be reviewed briefly. With the MOSFET on, current
flows through LD,L,, the MOSFET, and the sense resistor as
shown in interval tl in Fig. 3. When this current reaches
some value Io, the MOSFET is turned off, which marks the
end of interval tl. Current is now diverted fi-om the switch to
capacitor C,. Assuming that the current is constant at IO
during interval t2, the voltage across the capacitor increases
Fig. 1. Hard-switched Solenoid Drive Circuit.
Fig. 2. ZVS Solenoid Drive Circuit.
968
multitude of standard commercial parts available for use in
thick film hybrid design.
A discrete prototype of the ZVS solenoid circuit was
constructed and tested in the laboratory. The hybrid version
was then laid out based on the prototype. Surface mount
components were utilized in the hybrid. The manufacturing
process and parts used in the production of the hybrid circuit
are described in this section. Concerns over the effects of
temperature on the commercial surface mount components
and over the choice of interconnect composition is also
discussed.
A circuit schematic for the hybrid version of the ZVS
solenoid drive circuit is shown in Fig. 4, and a complete parts
list is given in Table 1. The control circuit is based on three
components: an AD820 operational amplifier, an LM3 11
comparator, and an LMC555 timer. With the exception of
the sense resistor, all resistors were 5% Panasonic thick film
chip resistors. The sense resistor was a 1% Panasonic thick
Fig. 3. ZVS Solenoid Drive Circuit Waveforms.
film chip resistor. The fi-eewheeling diode used was a
In the hard-switched solenoid drive circuit, the current Schottky diode fi-om Vishay-Liteon capable of carrying 3
flowing through LDis regulated by varying the on-time of the amperes continuously.
The capacitors used were ITW Paktron, Inc. model ST and
MOSFET with a constant off-time. The same approach is
SS
capacitors and were chosen because of their temperature
employed in the ZVS circuit. The off-time is set so that the
characteristics.
The manufacturer's specifications indicated
MOSFET is turned on while the capacitor voltage is clamped
at zero and before current if reverses. From (l), zero voltage that the capacitance changes a maximum of 8% at an elevated
switching is achieved if ZoIo is greater than V,. Large temperature of 125 "C. The resonant capacitor was formed
variations in either Io or Zo can result in the loss of zero by connecting two 220 nF capacitors in parallel for an
voltage switching. Note fi-om (3) that Z, depends on both L, equivalent capacitance of 440 nF. The resonant inductor was
and C,. Variations in L, and C, with temperature may cause a surface mount inductor manufactured by Coilcraft, Inc. and
Z, to fall below the minimum value for zero voltage has an inductance of 68 pH.
The layout of the ZVS hybrid circuit was done using the
switching. In addition, the time required for the capacitor
layout
and design package Magic [33]. A total of four layers
voltage to reach zero, designated t,also depends on L, and
was
utilized:
two conductor layers, a dielectric layer for
C,. Setting (1) equal to zero and solving yields
crossovers of the conductors, and a solder layer for the
mounting of the surface mount components. Two different
philosophies were used in the design of the power section and
the control section of the circuit. Because the power section
needed to support a peak current of 2 amperes, the conductor
Recall that the off-time for the MOSFET is selected such that traces were made wide to reduce resistance and minimize i2R
it is turned on after the capacitor voltage is clamped at zero losses. The minimum width of the traces in this branch was
and before current if reverses. If the off-time is adjusted at 140 mils. The selection of this width was dependent on the
room temperature to fall within this time window, then zero size of the surface mount components and the smallest pad
voltage switching may be lost if either L, or C, drift with size to be used in that section. The majority of ground traces
were also made with this design philosophy and have a
temperature and time at temperature.
minimum width of 70 mils. The choice of line widths for the
control section did not depend heavily on current carrying
capacity, as the maximum current flow in this section is on
111. HYBRID FABRICATION
the order of a few hundred milliamps. Therefore, a minimum
The ZVS solenoid drive circuit was fabricated using thick line width of 20 mils was chosen for the control section. The
film hybrid technology.
Thick film substrates and layout of the ZVS converter is shown in Fig. 5 . The "F's"
connections are excellent for moderate temperature and crosses shown in the layout were used for orientation and
applications such as 150 "C. The hybrids have very low alignment of the thick film screens during the printing
parasitic values, which can allow the circuitry to be very process.
compact for use at high 6-equencies. In addition, there are a
vc A
969
3.0 kfl
[email protected]
-
-
Fig. 4. ZVS Hybrid Circuit Schematic.
Table 1. Parts List for Solenoid Drive Circuits.
I
Part Designation
AD820
~~
ERJ-14YJ102
ERJ-14YJ302
ERJ-14YJ390
103J25SS 18 12
103J25SS1812
224J50ST1812
,D05022P-683
~
1 k Resistor
3 k Resistor
390 ohm Resistor
0.01 micro Farad Capacitor
0.01 micro Farad Capacitor
0.22 micro Farad Capacitor
68 micro Henry
Current limit (Zener Diode)
Discharge Resistor
Inverter Resistor
555 Discharge Capacitor
555 Control Capacitor
Resonant Capacitor
Resonant Inductor
After the screens were allowed to cure, the first layer was
printed on a 40 mil thick alumina substrate with a MPM TF100 Screen Printer. The conductor paste used was palladiumsilver based from the Dupont Corporation, paste number
9476. After printing, the paste was then dried at 150 "C for
15 minutes in a BTU Engineering Transheat DR85405 oven.
The paste was then fixed at 850 'C in a Watkins Johnson 8Zone Firing Furnace with a firing time of approximately 45
minutes. The dielectric layer was then visually aligned and
printed, and the drying and fKing process was repeated. The
dielectric used in the design was paste number 5704 from
Dupont. The dielectric layer was printed and fired twice to
assure that proper isolation of the overlapping conductor
traces was maintained. The second conductor layer was then
aligned, printed, dried, and fired. The fmal step was to print
Panasonic
Panasonic
Panasonic
ITW Paktron
ITW Paktron
ITW Paktrou
Coilcraft, Inc.
-55 to
-55 to
-55 to
-55 to
-55 to
-55 to
-40 to
125
125
125
150
150
125
85
the solder layer with a eutectic TinLead paste, Heraeus paste
number SC3401HTPL. The surface mount components were
immediately hand placed, and the hybrid was placed in a
Dima SMT Systems SMRO-0252 IWConvection Reflow
Furnace to reflow solder. The final circuit is shown in Fig. 6 .
The power, ground, and load inductor connections were hand
soldered.
The parts for the ZVS solenoid drive circuit were shown
previously in Table 1 with their ratings. Because most of the
temperature ratings of the components were below the target
ambient temperature of 150 'C, several concerns were noted.
The most predominate concern was with the capacitors that
were of type ST and SS. The manufacturer's temperature
specifications indicated that the capacitance of these
components changed by more than 5% at 125 'C. With these
970
capacitors utilized in timing functions, the effects of
capacitance changes could negatively affect the operation of
the converter.
The eutectic Sn/Pb solder, with a melting point of
approximately 183 '(2, was also of concern. With a test
temperature of 150 T , there was a possibility of the solder
reflowing because of the additional heat produced by the
operating components. If this were to occur, the connection
of the components could be weakened and the circuit could
operate improperly or fail.
IV. EXPERIMENTAL RESULTS
The power, ground, and load connections were manually
soldered to the hybrid of Fig. 6 along with connections for
probing the resonant capacitor voltage, the load current, and
the output voltage of the LM311 comparator. The load
inductor was fabricated using a Magnetics, Inc. ferrite core
part number P-41206TC and 80 turns of 26 AWG magnet
wire. After the hybrid and the load inductor were placed in
an oven, the control circuit was energized at 12 volts. A
separate power supply was connected to the power section of
the hybrid and also set to 12 volts. The hybrid operated for
15 minutes at a particular temperature before any
measurements were taken. All waveforms were recorded
using a Tektronix TDS744A oscilloscope. In addition,
waveform characteristics such as average value and peak
value were determined using this oscilloscope.
A. Short-Term Testing of the ZVS Hybrid
Fig. 5. Magic Layout of ZVS Hybrid.
Fig. 6 . ZVS Hybrid Solenoid Drive Circuit.
The waveforms for an oven temperature of 30.1 "C are
shown in Fig. 7a. It can be seen that the converter operates
properly with a small spike in the resonant capacitor voltage
corresponding to the gating of the MOSFET. The off-time
for the MOSFET was adjusted such that it was not gated
when the antiparallel diode was conducting, but just after
current if reversed and started to charge C,. The average load
inductor current was measured to be 2.02 amperes, and the
peak capacitor voltage was measured to be 32.4 volts. The
frequency of the converter was taken from the LM3 11 output
voltage and was measured to be 21 .lo6 kHz.
The oven temperature was increased in steps up to 150 T ,
and measurements recorded after a 15 minute wait at each
temperature. Waveforms for 84.9 'C and 150 "C are shown
in Figs. 7b and 7c. The peak value of the resonant capacitor
voltage and the average load current were measured to be
32.0 volts and 1.848 amperes at 84.9 "C and 30.4 volts and
1.6 amperes at 150 "C.
The peak value of the resonant capacitor voltage, the
average load current, and the frequency of operation of the
ZVS hybrid are plotted as a function of temperature in Figs.
8a, 8b, and 8c. It can be seen in Fig. 8a that the peak
resonant capacitor voltage decreased as the temperature
increased. Recall fiom (1) that the peak value of the
capacitor voltage is V, + ZoIo. Z,is related to L, and C, as
shown in (3) and will vary with temperature if either L, or C,
are temperature dependent. Both the resonant inductor and
capacitor were characterized as a function of temperature,
and the results plotted in Figs. 8d and 8e. These values were
obtained with a standard LCR meter; each data point was
recorded after a 15 minute wait at a particular temperature.
Note that both the inductance and capacitance increased with
temperature. Z,decreases about 6% from 30 "C to 150 T ;
approximately the same drop is observed in the peak
capacitor voltage over the same temperature range.
97 1
Both the average load current and fiequency of operation
decreased with temperature as seen in Figs. 8b and 8c. With
the exception of one data point, the decrease in the average
load current looks linear. The fiequency of operation leveled
off around 125 "C. The decrease in these two quantities can
be attributed to the LMC555 timer in Fig. 4, which is
configured as a monostable multivibrator. The width of the
output pulse for this timer configuration depends on the value
of capacitance and resistance connected to the 'Discharge'
and 'Threshold' pins. An increase in the value of capacitance
connected to these pins would increase the off-time of the
converter, thus decreasing the frequency.
. . . . . . . . .
:
*d&"d
j..
..
t i :
I..
.
t
. . . . . . . . . . ._
f" . . . . . . . . . . . . . . . . . . . . .
:
J
I
.
.
,
, , .
,
.
3
Fig. 7c. ZVS Hybrid Waveforms at 150 "C.
Ch 1: 10 Vldiv, Ch 2: 5 Vldiv, Ch 4: 1 Aldiv, 20 ysldiv
Peak ResonantCapacitor Voltage Vs. Temperature(Vs=12 volts)
5' 35.0
v
...
5
..... .....
.........
..
. . . . . . . .
34.0
> 33.0
5... 32.0
3
. . . . . . . . .
5 31.0
U
V' . . .cti2. .5.0.0.v.. . . . . . . . . . . . . . . . . . . . . . . .
....
/ . . . . , . . _ . I . .
I 30.0
M 2O.O)lS: Chl :I 600mVj
10:OmVQ
.
_ . ! . _ . .. . . . / . . _ . ! _ _ . _ / . . . . ! . _ . .
29.0
28.0
25.0
36.2
55.5
Fig. 7a. Z V S Hybrid Waveforms at 30.1 "C
Ch 1: 10 Vldiv, Ch 2: 5 Vldiv, Ch 3: 1 Aldiv, 20 psldiv
74.7
N.8
114.9
134.9
150.0
Temperature (degrees C)
Fig. 8a. Peak Resonant Capacitor Voltage vs. Temperature.
Average Load Current Vs. Temperature (V,=12 volts)
21
n
s 2
I
1.9
U
p
2
1.8
1.7
e!
5
1.6
1.5
25.0
(91E1 lO.OmV?
f.
.
I
36.2
55.S
74.7
94.8
114.9
134.9
Temperature (degrees C)
v. . . ' C ~ 2 .s..dd
.
v'. . . . . . . . . . . . . . . . . . . . . . . .
M 20.0~C
~ h: l f
600mV1
1
Fig. 8b. Average Load Current vs. Temperature.
Fig. 7b. ZVS Hybrid Waveforms at 84.9 "C.
Ch 1: 10 Vldiv, Ch 2: 5 Vldiv, Ch 4: 1 Ndiv, 20 psldiv
972
150.0
j
Convertds Operating Frequency Vs. Temperature (V.=l2 volts)
21.6
21 4
21.2
h
N
21
20.8
$ 206
20.4
20.2
& 20
19.8
19.6
19.4
2
E
5
25.0
36.2
55.5
74.7
94.8
114.9
134.9
150.0
Temperature (degrees C)
fust. The peak resonant capacitor voltage, average load
current, and frequency of operation variations with
temperature are similar to those in Figs. 8a, 8b, and 8c. The
converter was turned off and allowed to cool to room
temperature before beginning the long-term test. It was reenergized at Vs = 24 volts, and the oven temperature was
slowly increased to 150 "C. The converter remained at this
temperature to evaluate the effects of temperature over time.
It operated for a total of 2,784 hours and 20 minutes at I50
"C. Several interruptions in operation occurred, and a list of
run times and suspected causes of failure are recorded in
Table 2.
Table 2. Long-Term Test Results for 150 'C
Fig. 8c. Frequency vs. Temperature.
Resonant Inductor Value Vs. Temperature
73.5
- 7 3
b 72.5
n
g 71.5
Run Time
1344 hr 20 min
1082 hr 15 min
122 hr
235 hr 45 min
Suspected Cause of Failure
Power Supply Failure
Unknown
555 Ouput Latch-Up
555 Ouput Latch-Up
2784 hr 20 min
Total Run Time
,g
X
e
.-
-8
2
71
70.5
U
5
70
69.5
22.2
40
M)
80
1w
120
140
Temperature (degrees C)
Fig. 8d. Inductance vs. Temperature.
Resonant Capacitor Value Vs. Temperature
240
230
h
la
5 220
0
5
.-
210
0
fam
U
190
180
22
40
60
80
LOO
I20
140
Temperature (degrees C)
Fig. 8e. Capacitance vs. Temperature.
B. Long-Term Testing of the ZVS Hybrid
After short-term characterization at 12 volts, the hybrid
was allowed to cool 24 hours in preparation for long-term
testing at temperature. The power section was operated at 24
volts for this test. Short-term characterization of the
converter operating at this supply voltage was performed
The converter had operated for over 1,300 hours before an
error occurred in the power supply for the power section.
This error was cleared by turning the power supply off to
reset it. The power supply was turned back on, and the
converter immediately responded to the source voltage and
continued to operate at 150 'C. The converter then operated
for an additional 1,082 hours before an undetermined failure
occurred. The power supplies for the control circuit and the
power section were reset, but the converter did not respond.
The oven temperature was gradually decreased to room
temperature, and the converter was removed to probe its
signals. The converter responded immediately to the power
supplies at room temperature before any probing was
performed. As a result, it was placed back into the oven to
observe how it would respond to a temperature increase. The
converter continued to operate as the temperature was slowly
increased to 150 'C.
The converter ran for an additional 122 hours before
failure and was taken out of the oven for probing. The 555
timer's output was found to be latched high. As a result, the
inverter's output was latched low preventing the MOSFET
lkom being gated on. The output to the 555 was momentarily
ground, and the converter began to hnction again. The
converter was again placed into the oven, and the temperature
was increased to 150 'C. The converter hctioned for an
additional 235 hours before the 555 timer's output latched
again. The momentary grounding procedure was repeated,
and the converter was placed back into the oven. As the
temperature was increased, the converter failed at 85 "C. The
555 timer failed permanently as it continued to latch up even
at room temperature. Long-term testing of this converter was
concluded at this point.
973
Waveforms at the end of 48 hours at 150 "C are shown in
Fig. 9a. Note that the capacitor voltage is not resonating to
zero, so zero voltage switching is not occurring. In fact, the
condition for ZVS operation is not satisfied at room
temperature when V, = 24 volts. Fig. 9b is an oscilloscope
trace after 936 hours. The resonant capacitor voltage in this
figure shows a distinct difference in its appearance &om that
in Fig. 9a. The resonant capacitor voltage begins to rise
again before the switch is turned on; it rises to approximately
8 volts as compared to 4.5 volts in the converter after 48
hours. The capacitor voltage resonates to zero after 2498
hours as seen in Fig. 9c.
The peak value of the resonant capacitor voltage was
measured during the long-term test and is plotted in Fig. 10.
This voltage increases with time due to changes in the
capacitance of the resonant capacitor. At the beginning of the
test, this capacitance was measured with an LCR meter and
had a value of 438 nF. The capacitance had decreased to 335
nF at the end of the long-term test. The inductance of the
resonant inductor was also measured using an LCR at the end
of the test and found to be 68 pH. Z, increased with time
because the inductance remained essentially constant, while
the capacitance decreased significantly. Recall that the peak
value of the resonant capacitor voltage is directly
proportional to Zo.
In addition to measuring the resonant capacitor and
inductor, the capacitors connected to the 'Discharge' and
'Threshold' pins of the 555 timer in Fig. 4 were also
measured using the LCR meter. The 0.01 pF capacitor
connected to the 'Discharge' pin had a value of 0.0242 pF at
the end of the test. The capacitance of the 'Threshold'
capacitor was found to be 0.00097 pF.
1:I I I
. . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . .
....
. .......... ......
............
....
,
-. . . . . . . . . . . . . . . . . .
-
....... .....
Fig. 9b. ZVS Long-Term Test (936 hours)
Ch 2: 20 Vldiv, Ch 3: 5 Vldiv, Ch 4: 1 Aldiv, 10 jddiv
. . ' !. . . .
i . . .
.
.... ....
i
1;:
.
iI I I
.... :....:.... : .....
.
:
-
f
. i
....
-
j
m
, . , i
........
I
...............
i
j-.
'
+'
-
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I
i - J-.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fig. 9c. ZVS Long-Term Test (2498 hours)
Ch 2: 20 Vldiv, Ch 2: 5 Vldiv, Ch 4: 1 Aldiv, 10 psldiv
.;
.-$.
.+
..........
.-If. . . .
..........
. . . . : , . . . ! . . . . , . .
:oti:;
I
..........
g&
... .
:f
.L..
:f.
..
::
I
:I
..
Peak Reasonant Capacitor Voltage Vs Time at IS0 degrees C
-L
8
56
54
52
>
E
50
.
I
D
3 48
U
:
1 46
'
. . . . . . .+. . . . . .: . . . : . . , . : . . . . , . . . .
ov
0.ops C h 2 /
If00%2
M2
8 4 4
42
0
72
675
936
1104
1272
1344
1968
2160 2308 2498 1522 2523
Time (ius)
Fig. 9a. ZVS Long-Term Test (48 hours)
Ch 2: 20 Vldiv, Ch 3: 5 Vldiv, Ch 4: 1 Aldiv, 20 psldiv
Fig. 10. Peak Capacitor Voltage vs. Time at 150 "C
974
V. CONCLUSION
Many applications have been identified for high
temperature electronics. Temperatures in excess of 200 “C
will require semiconductors fabricated using silicon-oninsulator technology or materials such as Sic. Silicon-based
semiconductors can be utilized in electronic circuits operating
below 200 “C. In addition to semiconductors, electronic
systems contain passive components such as resistors,
inductors, and capacitors, which must be capable of operation
at elevated temperatures.
The design, fabrication, and testing of a ZVS solenoid
drive circuit for operation at 150 ‘C has been presented in this
paper. A hybrid version of the circuit was constructed using
thick film technology and standard commercial components.
The hybrid was subjected to short-term characterization fkom
room temperature to 150 “C and to long-term characterization
at 150 ‘C. The circuit operated for a total of 2784 hours at
150 “C. The test results can be utilized to identify issues in
the operation of high temperature electronic systems.
Standard commercial components can be operated at elevated
temperatures. Operation of one circuit at 150 ‘C does not
demonstrate a sufficient level of reliability. Improvements in
component materials and packaging will help to achieve
higher reliability. Resistor and inductor technology exist now
which are very nearly stable with temperature. Capacitors,
on the other hand, tend to be sensitive to variations in
temperature. The circuit designer must be aware of these
variations, because they are often utilized in timing and
filtering hctions.
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