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f ig. 4, Regulohon and efficiency of the self-regulating DC to DC converter shown in Fig, 3.

was used simply as a low-priced compromise to give: (1) Low saturation voltage, (2) fairly high frequency cutoff, (3) high current capability, and (4) high breakdown voltage. (I) is understandable since the 2NI74 is to act as a switch. (2) is to insure fast switching so that there is no large fraction of our duty cycle where there is appreciable voltage across the switch while current is being drawn through it (3) is necessary because the maximum current drawn through the switch may be as great as ii\e times the average input current. (4) because when tlie switch opens, iiiere is a rather large inductive spike at the switch collector, and attempts to suppress ibis by means of capacitors increase the rise time of switching.

Surely there are other transistors which will work as well, and some perhaps better, but the 2N1T4 is the best this author has found. Since the features of low saturation voltage and high frequency cut-off are mutually incompatible, one has to pick his switch transistor to be a compromise. Either a high satura-

bo oü 120 s40 OLTWT V41

Fig. 5, Output current and voltage regulation with 6, 12 and 24 volts input.

bo oü 120 s40 OLTWT V41

Fig. 5, Output current and voltage regulation with 6, 12 and 24 volts input.

tion or a low frequency cutoff will have the effects of lowering efficiency and raising the lower limit of regulated operation.

The converter is built on a circuit board which is etched to lit any oi several series switch transistors; so one can try others if one wants to do so. The board fits into an L.M.B, 108 box chassis, for packaging.

This particular unit is used to power an FM receiver made up of Gorier transistorized sections. The unit is used part time in a Yolks-wagon on 6Y with a positive grounded system and used part time in a Chevy II on 12v with a negative grounded system. The versatility of the converter makes this type of operation completely successful*

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