HP HP-Bench-Briefs-1984-01-02 free download

File name HP-Bench-Briefs-1984-01-02.pdf

PBHEWLETT PACKARD SERVICE INFORMATION FROM HEWLETT-PAC..,. .- JANUARY/FEBRUARY 1984 Preregulation to Reduce Power Dissipation dc power supplies Don Fielder, Hewlett-Packard One of the major considerations given a linear supply is the internal power dissipated by the series reg- ulator. Figure 1 shows a simple diagram of a fixed input power sup- ply. If this were a 50-amp supply such as the HP 6269B DC Power Supply operated at full current and minimum voltage (RL shorted), the c power dissipated in the series reg- ulator would be about 2.5 KW Figure 1. Sample fixed input power supply. (Vin-Vout X 50A). Since the practical power limit for a TO3 transistor is about 50 watts, this would mean using 50 transistors for the regulator-a prohibitive solu- tion both from an initial cost and the reduced operating efficiency that would result. Figure 2 shows one approach to solve this problem. By monitoring the voltage across the series regulator and adjusting Vin to maintain the regulator voltage at about 3 volts, the power is reduced from 2 5 KW to . 150 watts. This 3-volt regulator voltage is held relatively constant regardless of input o r output conditions. Keep this i n mind when trou- Figure 2. Sample regulator solution. bleshooting a unit that has no con- trol (either locked up or down). In (- almost every case, if you have any output, the preregulator is probably the preregulator. ONLY when you operating properly. If you have no have BOTH no output AND no reg- output but do have regulator voltage ulator voltage (<1 volt) should you (3 to 6 volts), again no problem with suspect the preregulator. Pub. NO. 5952-01 16 @ Hewlett-Packard 1984 WWW.HPARCHIVE.COM _I - -.- _c-- Got a Scratch That Needs Repairing? Use HP Touch-up Paint our older and some newer instru- also identify System I cabinets by ments. It is very close in shading their handles. The handles are an Hewlett-packad stocks touch-up to Cocoa black, except the olive has integral extension of t h e paint in air-drying aerosol spray a little more aluminum side frame. cans. The available colors ma