Feedback loop, which contains an inductor in series with a saturable reactor, is added to a standard inverter circuit to permit the inverter power transistors to be switched in a controlled and efficient manner. This inverter is applicable where the power source has either high or low impedance properties

Pasciutti, E. R.

English

NASA Technical Reports Server

November 1970	 Brief 70-10425 
NASA TECH BRIEF 
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be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546.
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Efficient/ Reliable DC-to-DC Inverter Circuit 
T
Load	 1 Out 
Voltage 
Filter	 Regulator	 R L
(Overload 
Protected) 
.
I Low	 I 
-	
I Voltage I 
Source 
Frequency -
Determining 
Feedback	 _____	 LI SR	 L I	 Loop  
Certain types of primary electrical power sources 
have output voltages as low as one or two volts. A 
conventional practice is to step up the output voltage 
with a dc-to-dc inverter that employs large-area, 
high-current transistors. 
The long rise, decay, and storage times inherent 
in this type of transistor produce switching and circuit 
overlap losses which degrade inverter efficiency and 
reduce its operational lifetime. This problem has 
been eliminated by a novel frequency-determining 
feedback loop added to a standard inverter circuit 
shown in the schematic. The feedback loop contains 
an inductor (L) in series with a saturable reactor(SR);
the proper value of inductance in this loop permits 
the inverter power transistors QI and Q2 to be 
switched in a controlled and efficient manner. 
It is important to note that this inverter design is 
protected against T 1
 core saturation effects as well 
as storage time overlap. 
Advantages afforded by this improved dc-to-dc 
inverter include: (1) it can be used with a trans-
former current feedback inverter or with a voltage 
feedback driven inverter since the switchover is con-
trolled by the frequency-determining loop-function 
interval only; (2) total circuit switching-time per-
formance approaches the intrinsic transistor corn-
(continued overleaf) 
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	 information contained in this document, or warrants that such use 
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ponent rise and fall time; (3) overlap and switching 
inverter crossover ripple is minimized for a wide range 
of load demands and input voltages; (4) proper base-
drive current-shaping for optimum inverter per-
formance is provided during the entire cycle. 
The new crossover technique can be used with both 
high and low impedance sources. The base current 
control and shaping, used with push-pull oscillator 
inverters, improve total inverter crossover perform-
ance, and eliminate most of the transient voltage and 
current spiking conditions normally present at the 
source output. Output ripple conditions at the load are 
also reduced without the need of additional filters. 
Thus minimal input/output ripple can be obtained 
without incurring a size and weight penalty. 
Notes: 
1. This inverter can be used in dc-to-dc converter 
circuit applications where the power source may 
have either high or low impedance properties.
2. The following documentation may be obtained 
from: 
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.65) 
Reference: 
NASA-TM-X-63118 (N68-18065), Low Input 
Voltage Conversion-Regulation From Non-
conventional Primary and Secondary Sources 
Patent status: 
This invention has been patented by NASA (U.S. 
Patent No. 3,466,570), and royalty-free license rights 
will be granted for its commercial development. In-
quiries about obtaining a license should be addressed 
to NASA, Code GP, Washington, D.C. 20546. 
Source: E.R. Pasciutti 
Goddard Space Flight Center 
(XG S-06226) 
Brief 70-10425	 Category 01


Efficient/reliable dc-to-dc inverter circuit

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