Relative performance of three basic configurations of electronic conversion units (saturating, pseudo-saturating, nonsaturating) requiring low power levels is compared. Pseudo-saturating mode exhibits best overall performance, nonsaturating a close second, saturating a poor third

Agnew, C. V.

Radys, R. G.

English

NASA Technical Reports Server

1972	 B72-10042 
NASA TECH BRIEF
•1JAAI 
NASA Pasadena Office 
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Pseudo-Saturating Power Converter 
A study has been made of the relative performance 
of three basic configurations of electronic conversion 
units for space applications requiring low power 
levels (0-3 W). The conversion units are DC-to-DC 
power devices in which the critical component is the 
transformer and the parameter under study was the 
degree of saturation of its core. 
Depending on the extent to which the B-H loop 
of the transformer is utilized, an electronic converter 
unit is classified as saturating, pseudo-saturating, or 
nonsaturating. The saturating mode of operation sig-
nifies that the entire B-H loop is involved and, 
moreover, the transformer is driven so far into satura-
tion that Hsat is several orders of magnitude greater 
than Hmag. When operated in pseudo-saturation, 
almost the entire B-H loop is used; the electronic. 
conversion unit cuts off power supplied to the trans-
former as soon as saturation is imminent. In a non-
saturating mode of operation, only a small portion 
of the B-H loop is utilized. 
A typical circuit for the pseudo-saturating con-
version unit is shown in the diagram. Inductor Li 
and Zener diode CR1 prevent the transformer from 
going deeply into saturation. When the transformer 
core (a high-permeability material) begins to sat-
urate, current flow increases rapidly in inductor Li; 
this increases the voltage level at the emitters of Qi 
and Q2. Because of base-emitter capacitances, the 
bases of Q2 and Qi will follow the emitter until the 
base voltages are clamped by the Zener diode C111; 
the transistors then turn off and limit the current 
flow into the primary of transformer Ti. 
The base current that is fed back to the transistors 
by the feedback winding can be decreased to the 
point where the unit will stop functioning. In making
comparisons of the various configurations (with the 
same transformer and no secondary loads), the lower 
the cutoff current level, the better the regeneration; 
the pseudo-saturating configuration was found to 
9 
have an excellent regeneration figure and superior 
to the saturating configuration; the nonsaturating 
configuration was rated poor. 
The power conversion efficiency of the pseudo-
and nonsaturating units were comparable over a 
power output range of 0 to 3.5 watts; in contrast, 
the saturating converter showed poor efficiencies 
because of large losses from current spiking. 
The least amount of current spiking was observed 
in the unit operating in the nonsaturating mode at 
(continued overleaf) 
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low power levels; however, at higher power levels 
current spikes were formed. In contrast, current 
spikes were high at all power levels in units operat-
ing at saturation. The spiking level in the pseudo-
saturation mode of operation were found much lower 
than at saturation; the reduced spikes are attrib-
utable to the effect of Li and CRi on current flows. 
Another parameter of performance that was in-
vestigated relates to the amount of output filtering 
that is required and the amount of current modula-
tion reflected on the input power line. The parameter 
is called the crossover period, and it is defined as 
the period during which the converter unit does not 
deliver energy to the transformer secondary; no 
power is delivered when the unit switches. The sat-
urating mode of operation has the worst crossover 
characteristics because transistor switching speeds 
are deliberately made slow in order to prevent ex-
cessively large current spikes in the primary. The 
nonsaturating mode of operation provides the best 
crossover characteristics. The crossover gap in the 
pseudo-saturating mode of operation increases con-
siderably with load because of the decrease of in-
ductance caused by DC current flow in M. However, 
the crossover gap is quite acceptable. 
The pseudo-saturating mode exhibits the best 
overall performance, the nonsaturating a close second, 
the saturating a poor third. 
Note: 
Requests for further information may be di-
rected to: 
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: B72-10042 
Patent status: 
No patent action is contemplated by NASA. 
Source: R. G. Radys and C. V. Agnew of

Hughes Aircraft Company 
under contract to

NASA Pasadena Office

(NPO-11368)
. 
. 
S 
Category 01


Pseudo-saturating power converter

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