one-chip DC converter I 121 R =(Vour-1.2) Finally, the output current may, of course, be boosted by means of a medium power transistor in a suitable configuration at the V o output. HS This DC step-up circuit may prove useful for the incorporation in equip- ment that requires the presence of a supply voltage in excess of the nor- mal circuit supply rail of, for instance, +5 V. Ideal therefore for generating the necessary + 8 . . .12 V voltage to feed RS232 transmitter devices, or the + 25 V programming voltage for EPROMs, the Type L497 DC con- verter requires very few additional passive parts to produce any of the output voltages listed in the table below. As to the components in support of the converter chip, note Li, which is a small coil, readily made by winding about 85 turns of 34 SWG (4 0.2 mm) enamelled copper wire on a small (11 x 7 mm) pot core having an Al rating of 160, e.g. the Siemens Type 6531-L160-A48. The total inductance of Li should be of the order of 100 p...
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