Variable dual power supply

EE April 1986 Technical characteristics Output voltage Output current Output ripple Current limit Internal resistance Internal dissipation Ambient temperature 2x0...20 V 2x0...1.25 A 5 mV peak-to-peak 7.3 A 0.002 ohms 2x8 W 25 °C Internal protection circuits prevent the output current exceeding safe limits under overload conditions. Since the whole of the supply is housed in a standard ABS verobox, great attention has been paid to the problem of internal heat generation, which could be as high as 60 joules. A novel pre-regulation system, which reduces the input to the series regulators in a controlled manner, is used to overcome this problem. Figure 1 illustrates the basic oper- ation of one section of the supply. The smoothing capacitor is charged via the bridge rectifier only if the (electronic) switch in the pre- regulator is closed. For a given load current, this effectively lowers the direct voltage across the capacitor and, therefore, the dissipation in the series regulator...