HP HP-Bench-Briefs-1975-01-02 free download

File name HP-Bench-Briefs-1975-01-02.pdf

SERVICE INFORMATION FROM HEWLETT-PACKARD JANUARY-FEBRUARY 1975 ALL ABOUT POWER SUPPLIES (1 \ by Dick Gasperini, Editor I ' .f . Virttrally every-piece of electronic . Clear has a power supply so the probability of having to repair a failure is rath- high. Therefore, knowledge of p o w t supply opera- tion is essential for repair personnel. A power supply that may look familiar is in Figure 1. It will con- This change of output voltage with helps to stabilize the output voltage. vert the AC line voltage to a DC a change in load ("load regula- tion") would not be a problem if This technique does have its limita-r voltage, say 175 volts, for our load, tions. Assume that CR3 is rated at 0 lumped hefe as a single resistor RL. we atways had a fixed load that dmanded a constant amount of cbrrent. Most times, though, a load 20 mA. We would select the value of R2 so that 10 mA of current is not constant. Therefore, the flowed thru CR3. If the load were power supply voltage will change reduced by 10 mA, the voltage and this may be undesirable. would tend to rise and CR3 would conduct more current, keeping the Also, what happens if the line volt- voltage at 175V. Similarly, if the age variets by 2 % In this supply 0? load were to draw more current, the output voltage will again vary. less current would be drawn by This supply lacks "line regulation". CR3, again stabilizing the voltage. To obtain a more stable voltape But we are very limited in the load we will want an improved supply. variation that can be compen-