Malik E. Elbuluk

University of Akron, Akron, Ohio

Scott Gerber

ZIN Technologies, Inc., Brook Park, Ohio

Ahmad Hammoud

QSS Group, Inc., Brook Park, Ohio

Richard L. Patterson

Glenn Research Center, Cleveland, Ohio

Performance of Power Converters

at Cryogenic Temperatures

NASA/TM—2001-211130

September 2001
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NASA/TM—2001-211130

September 2001

National Aeronautics and

Space Administration

Glenn Research Center

Prepared for the

Eighth International Conference on Electronics, Circuits, and Systems (ICECS 2001)

sponsored by the Institute of Electrical and Electronics Engineers

Malta, September 2–5, 2001

Malik E. Elbuluk

University of Akron, Akron, Ohio

Scott Gerber

ZIN Technologies, Inc., Brook Park, Ohio

Ahmad Hammoud

QSS Group, Inc., Brook Park, Ohio

Richard L. Patterson

Glenn Research Center, Cleveland, Ohio

Performance of Power Converters

at Cryogenic Temperatures
Acknowledgments

This work was supported by the NASA Glenn Research Center, Contract NAS3–00145, GESS Task 0020,

and by JPL’s NASA Electronic Parts and Packaging Program (NEPP).

Available from

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22100

This report contains preliminary

findings, subject to revision as

analysis proceeds.

Available electronically at http://gltrs.grc.nasa.gov/GLTRS
NASA/TM—2001-211130 1 

 PERFORMANCE OF POWER CONVERTERS AT 

CRYOGENIC TEMPERATURES 

Malik E. Elbuluk 

University of Akron 

Akron, Ohio 44325–3904 

Scott Gerber 

ZIN Technologies, Inc. 

Brook Park, Ohio 44135 

Ahmad Hammoud 

QSS Group, Inc. 

Brook Park, Ohio 44135 

Richard L. Patterson 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

ABSTRACT 

Power converters capable of operation at cryogenic 

temperatures are anticipated to play an important role in 

the power system architecture of future NASA deep 

space missions. Design of such converters to survive 

cryogenic temperatures will improve the power system 

performance, and reduce development and launch costs. 

Aerospace power systems are mainly a DC 

distribution network. Therefore, DC/DC and DC/AC 

converters provide the outputs needed to different loads 

at various power levels. Recently, research efforts have 

been performed at the NASA Glenn Research Center 

(GRC) to design and evaluate DC/DC converters that 

are capable of operating at cryogenic temperatures. 

This paper presents a summary of the research 

performed to evaluate the low temperature performance 

of five DC/DC converters. Various parameters were 

investigated as a function of temperature in the range of 

20 °C to –196 °C. Data pertaining to the output voltage 

regulation and efficiency of the converters is presented 

and discussed. 

1. POWER ELECTRONICS IN AEROSPACE 

The application of power electronics in aerospace 

technologies is becoming widespread. The potential and 

existing application areas include the International 

Space Station (ISS), aircraft and satellite power 

systems, motor drives in ‘more electric’ technology 

(MET) as applied to aircraft and Reusable Launch 

Vehicles (RLVs), starter/generators (S/G) and flywheel 

technology, servo systems embodying electromechanical actuation (EMA) and spacecraft including 

deep space probes, planetary orbiters and landers, and 

surface exploratory instrumentation. 

The aerospace power systems are typically 

interconnection of power electronic converters, 

photovoltaic (PV) solar arrays and batteries in a 

DC-based distribution system. DC/DC and DC/AC 

converters are used to provide the required output 

voltage to different loads at various power levels. 

2. LOW TEMPERATURE ELECTRONICS 

Electrical components and systems for future 

NASA space missions, such as outer planetary 

exploration and deep space probes, must operate 

reliably and efficiently in very low temperature 

environments. For example, inter-planetary probe 

launched to explore the rings of Saturn would 

experience a temperature of about –183 °C. Table 1 

shows the operational temperatures for an unheated 

spacecraft in the vicinity of each of the outer planets. 

Presently, spacecraft operating in some of these regions 

utilize Radioisotope Heating Units (RHUs) to maintain 

an operating temperature for the on-board electronics of 

approximately 20 °C [1]. RHUs require containment 

structures and thermal systems such as shutters to 

maintain the 20 °C over the course of an entire space 

mission. However, if the electronics were capable of 

operating at the temperature of the mission environment, 

the RHUs and their associated structures, and the 

thermal management systems could be eliminated, thus 

reducing the system size and weight and thereby 

reducing the development and launch costs, and 

improving reliability and lifetime [1]. 
NASA/TM—2001-211130 2 

In this paper, five low power DC/DC converter 

modules, with specifications that might fit the 

requirements of specific future space missions, have 

been selected for investigation. The specifications of 

these converters, ranged in electrical power from 10 W 

to 13 W and input voltage from 9 V to 72 V, as listed in 

Table 2. The converters were characterized in terms of 

their performance as a function of temperature in the 

range of 20 °C to –196 °C (liquid nitrogen). The 

experimental procedures along with the experimental 

data obtained on the investigated converters are 

presented and discussed [2–5]. 

3. EXPERIMENTAL SETUP 

The converter modules listed in Table 2 were 

characterized as a function of temperature from 20 °C to 

–196 °C in terms of the output voltage regulation, 

efficiency, and input and output current distortions. At 

any given temperature, these properties were obtained at 

various input voltages and at different load levels; from 

no-load to full-load conditions. The tests were 

performed using an environmental chamber utilizing 

liquid nitrogen as the coolant. A temperature rate of 

change of 10 °C/min was used throughout the 

experiment. The converters were first tested at room 

temperature then at successive test temperatures with 

20 °C decrement, down to –196 °C. At every test 

temperature, the device under test was allowed to soak 

at that temperature for a period of 30 minutes before any 

measurements were made. After the last measurement 

was taken at the lowest temperature, the converters were 

allowed to stabilize to room temperature and then the 

measurements were repeated at room temperature to 

determine the effect of one thermal cycle on the 

converters. 

4. RESULTS AND DISCUSSIONS 

During the investigations, data was generated for 

both steady and dynamic states. In this paper, only data 

pertaining to the steady state efficiency and voltage 

regulation of the tested converters are presented and 

discussed. More detailed results are reported in 

references [2–5]. 

Figures 1 through 5 show the output voltage and 

efficiency of the modules versus temperature for four 

conditions of input voltage and output load levels. These 

conditions include minimum input voltage under light 

and heavy loads, and maximum input voltage under light 

and heavy loads. For all modules, an offset in the output 

voltage occurs at both light and heavy loads due to the 

voltage drop in the wiring leads connecting the output 

terminals of the module to the electronic load where the 

output voltage was actually measured (a resistance of 

about 70 mΩ). 

 At a given load, the output voltage of module 1 

maintains a steady value from room temperature to 

–120 °C. For temperatures beyond –120 °C, the 

converter begins to show loss in regulation. For 

example, the output voltage increases slightly when the 

input voltage is 36V but decreases drastically when the 

input voltage is 12V. As expected, the output voltage 

drops slightly when the load is increased. The effect of 

temperature on the efficiency of converter module 1 

under different input voltage and load conditions is also 

shown in Figure 1. In general, the efficiency drops as the 

temperature is lowered with the heavy load condition 

having a higher efficiency than that of a light load. For 

the same loading, the efficiency is higher as the input 

voltage is decreased. For a given input voltage, the 

converter has lower efficiency when the load level is 

low. 

Module 2 shows reasonable performance to –80 °C, 

but shows complete loss of voltage regulation for 

temperatures below –80 °C, as shown in Figure 2. It did, 

however, continue to operate with no regulation down to 

–196 °C. Similar trend was observed in the efficiency 

behavior with temperature. 

The output voltage of module 3 does not exhibit 

any dependence on either the input voltage or the test 

temperature at low loads as shown in Figure 3. At heavy 

loads, it does however decrease slightly upon lowering 

the test temperature regardless of the level of the input 

voltage. In general, the efficiency of this converter 

exhibits a slight decrease with decreasing temperature. 

This reduction becomes apparent at temperatures below 

–60 °C, as shown in Figure 3. 

Module 4 showed excellent output voltage 

regulation with temperatures down to –120 °C, as shown 

in Figure 4. The only exception is at –120 °C where at 

minimum input voltage and light load condition, the 

output voltage increased to over 4 volts. In addition, this 

module ceased to operate for temperatures below 

–120 °C, but regained operation once its temperature 

rose above –120 °C. The efficiency of this module held 

relatively steady values at heavy load to –60 °C and then 

dropped off as temperature decreased down to –120 °C. 

Module 5 showed relatively good output regulation 

down to –120 °C, as depicted in Figure 5. Beyond that 

temperature, the output voltage seems to slightly 

increase as the temperature is decreased further. Its 

efficiency, however, exhibits a gradual decrease as 

temperature is decreased. Although this module ceased 

to operate for temperatures below –180 °C, it regained 

operation once its temperature rose above –180 °C. 
NASA/TM—2001-211130 3 

5. CONCLUSIONS 

Five low power, DC/DC converter modules were 

evaluated as a function of temperature in the range of 

20 °C to -196 °C. Data pertaining to the output voltage 

regulation and efficiency of the tested converters were 

presented and discussed. 

Test results obtained on the modules have shown 

that they operated as expected within their 

manufacturer’s specified temperature range as well as 

with reasonably good performance down to 

temperatures between –80 °C and –100 °C. For 

temperatures below –100 °C, performance was either 

out of range, erratic, or non-existent. 

In all cases, the temperature range for which these 

modules were designed and specified does not include 

the severe temperature range for which they were 

subjected to in this investigation. Additional testing 

taking into account long-term evaluation and thermal 

cycling may reveal the potential for extending the 

operational temperature range and/or improving their 

performance at these very low temperatures through 

component screening and/or modification to the module 

design. 

REFERENCES 

1. R.L. Patterson, A. Hammoud, J.E. Dickman, S.S. Gerber, 

and E. Overton, “Development of Electronics for Low 

Temperature Space Missions,” 4th European Workshop 

on Low Temperature Electronics, Noordwijk, The 

Netherlands, June 21–23, 2000. Also NASA/TM—2000-

210235. 

2. M. Elbuluk, S. Gerber, A. Hammoud, and R. Patterson, 

“Characterization of Low Power DC/DC Converter 

Modules at Cryogenic Temperatures,” Proceedings of 

IEEE IAS Annual Meeting, October 2000, Rome, Italy. 

3. M. Elbuluk, S. Gerber, A. Hammoud, and R. Patterson, 

“Efficiency and Regulation of Commercial Low Power 

DC/DC Converter Modules at Low Temperatures,”

Proceedings of 35th Intersociety Energy Conversion 

Engineering Conference (IECEC), August 2000, Las 

Vegas, NV. 

4. S. Gerber, A. Hammoud, R. Patterson, and M. Elbuluk, 

“Performance Evaluation of Low Power DC/DC 

Converter Modules at Cryogenic Temperatures,”

Proceedings of IEEE 2000 Power Electronic Specialists 

Conference (PESC’2000), Galway, Ireland. 

5. M. Elbuluk, S. Gerber, A. Hammoud, R. Patterson, and 

E. Overton, “Low Temperature Performance of High 

Power Density DC/DC Converter Modules,” NASA EEE 

Links, Electronic Packaging and Space Parts News, 

Vol. 4, No. 1, January 1998. 

Table 1. Typical operational temperatures 

of an unheated spacecraft.

Mission Temperature °C 

Mars –20 to –120 

Jupiter –151 

Saturn –183 

Uranus –209 

Neptune –222 

Pluto –229 

Table 2. Converter module specifications and evaluations 

Converter Specifications GRC Evaluations 

Module Input 

Voltage 

(V) 

Output 

Voltage

(V) 

Power 

(W) 

Operating 

Temp 

(°C) 

Observations and Comments Temp at which 

module ceased to 

operate (°C) 

1 9–36 3.3 10 –40 to 60 Vo

 dropped to 2.4 V at –140 °C; chip functioned 

down to –160 °C. 

–160 

2 36–72 3.3 10 –40 to 85 Vo

 lost regulation at –100 °C; converter still 

functioned to –196 °C. 

–196 

3 18–36 3.3 10 –40 to 70 Chip worked very well down to –120 °C. Input 

current oscillations occurred at all temperatures 

under heavy loading. 

–120 

4 18-36 3.3 13 -40 to 85 Oscillations in input current started at –80 °C. -120 

5 9-36 3.3 10 -40 to 85 Oscillations in input current observed at –140 °C 

under heavy loading. 

-180 
NASA/TM—2001-211130 4 

Figure 1. Voltage regulation and efficiency of module 1 versus temperature 

Figure 2. Voltage regulation and efficiency of module 2 versus temperature 

Figure 3. Voltage regulation and efficiency of module 3 versus temperature 

-200-180 -160 -140-120-100 -80 -60 -40 -20 0 20 40

Tem p erature (°C )

2 0

3 0

4 0

5 0

6 0

7 0

8 0

9 0

Efficiency (% )

-200-180 -160-140 -120-100 -80 -60 -40 -20 0 20 40

Tem p erature (°C )

0

1

2

3

4

Output Voltage (V )

36Vin/0.5A out

12Vin/0.5A out

36Vin/2.5A out

12Vin/2.5A out

-200 -180-160 -140-120 -100 -80 -60 -40 -20 0 20 40

Tem p erature (°C )

0

1 0

2 0

3 0

4 0

5 0

6 0

7 0

8 0

9 0

Efficiency (% )

-200 -180-160 -140-120 -100 -80 -60 -40 -20 0 20 40

Tem p erature (°C )

0

1

2

3

4

5

6

7

8

9

1 0

O utput V oltage (V )

72Vin/0.5A out

36Vin/0.5A out

72Vin/4.0A out

36Vin/4.0A out

-200-180 -160 -140-120-100 -80 -60 -40 -20 0 20 40

Tem p erature (°C )

2 0

3 0

4 0

5 0

6 0

7 0

8 0

9 0

Efficiency (% )

-200-180 -160-140 -120-100 -80 -60 -40 -20 0 20 40

Tem p erature (°C )

0

1

2

3

4

O utput V oltage (V )

36Vin/0.5Aout

18Vin/0.5Aout

36Vin/2.5Aout

18Vin/2.5Aout
NASA/TM—2001-211130 5 

Figure 4. Voltage regulation and efficiency of module 4 versus temperature 

Figure 5. Voltage regulation and efficiency of module 5 versus temperature 

-200-180-160 -140 -120-100 -80 -60 -40 -20 0 20 40

Tem p erature (°C )

2 0

3 0

4 0

5 0

6 0

7 0

8 0

9 0

Efficiency (% )

-200-180 -160 -140-120-100 -80 -60 -40 -20 0 20 40

Tem p erature (°C )

0

1

2

3

4

Output Voltage (V)

36Vin/0.5Aout

18Vin/0.5Aout

36Vin/4.0Aout

18Vin/4.0Aout

-200-180-160-140-120-100 -80 -60 -40 -20 0 20 40

Tem p erature (°C )

2 0

3 0

4 0

5 0

6 0

7 0

8 0

9 0

Efficiency (% )

-200-180-160-140-120-100 -80 -60 -40 -20 0 20 40

Tem perature (°C )

0

1

2

3

4

Output Voltage (V)

36Vin/0.5A out

18Vin/0.5A out

36Vin/2.5A out

18Vin/2.5A out
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11

Performance of Power Converters at Cryogenic Temperatures

Malik E. Elbuluk, Scott Gerber, Ahmad Hammoud, and Richard L. Patterson

Power converters; Electronics; Low temperature; Cryogenics

Unclassified -Unlimited

Subject Category: 33 Distribution: Nonstandard

Prepared for the Eighth International Conference on Electronics, Circuits, and Systems (ICECS 2001) sponsored by the Institute

of Electrical and Electronics Engineers, Malta, September 2–5, 2001. Malik E. Elbuluk, University of Akron, 302 Buchtel Mall,

Akron, Ohio 44325–0001; Scott Gerber, ZIN Technologies, Inc., 3000 Aerospace Parkway, Brook Park, Ohio 44142;

Ahmad Hammoud, QSS Group, Inc., 2000 Aerospace Parkway, Brook Park, Ohio 44142; and Richard L. Patterson, NASA

Glenn Research Center. Responsible person, Richard L. Patterson, organization code 5480, 216–433–8166.

Power converters capable of operation at cryogenic temperatures are anticipated to play an important role in the power

system architecture of future NASA deep space missions. Design of such converters to survive cryogenic temperatures

will improve the power system performance and reduce development and launch costs. Aerospace power systems are

mainly a DC distribution network. Therefore, DC/DC and DC/AC converters provide the outputs needed to different

loads at various power levels. Recently, research efforts have been performed at the NASA Glenn Research Center

(GRC) to design and evaluate DC/DC converters that are capable of operating at cryogenic temperatures. This paper

presents a summary of the research performed to evaluate the low temperature performance of five DC/DC converters.

Various parameters were investigated as a function of temperature in the range of 20 to –196 °C. Data pertaining to the

output voltage regulation and efficiency of the converters is presented and discussed.