ti functional block diagram 90 of ic 48 pin numbers i e in the small square tabs in diagram 90 plus a number 50 may correspond to pin numbers for ic 48 in fig2 e g pin number 4 ss tr of diagram 90 plus 50 equals pin number 54 ss tr of ic 48 some of the less common parts in diagram 80 may be noted varistor 28 may clamp a voltage in both directions such as an ac voltage whereas a zener diode may clamp a voltage in just one direction varistor 28 may have a part number v56mla1206nh and be available a from a littlefuse parts vendor full wave rectifier 24 may be a diode bridge hd04 t available from diodes inc or a schottky diode bridge mb16s from micro commercial components diode 33 may have a part number 1n4148w 13 and be available from a diodes incorporated parts vendor component 33 may have a reverse recovery time of four nanoseconds transistors 34 and 39 may have a part number mmbt3904lt1 and be available from a motorola parts vendor zener diode 38 may have a part number mmsz4703 and be available from a general semiconductor parts vendor diode 41 may have a part number lm431bim3 and be available from a national semiconductor parts vendor diode.