Fluke 960PS-210 Operation, 2.1 960PS-200Power Supply, Input Filter, DC to DC Converter, Section

Operation	2
960PS-200 Power Supply

Section 2

Operation

2.1 960PS-200 Power Supply

The 960PS-200 supplies three different DC voltage outputs to the 960 modules through the 960MB/961MB motherboard. 115 VAC is connected to terminal strip A3, part of the front panel. The AC line voltage is fed to a bridge rectifier circuit and rectified by diodes CR1, CR2, CR3, and CR4. A thermistor is connected in series with the incoming AC voltage to decrease the effect of "turn-on" in-rush current to the power supply. For all practical purposes this is a soft start device. On some models of the power supply a current limiting resistor is used rather than a thermistor. Refer to schematic drawing 960PS-200-53

2.2 Input Filter

The rectified voltage from the bridge goes to a filter network made up of inductor L1 and a capacitor C1. This filter removes the DC voltage line ripple resulting from the rectification process.

2.3 DC to DC Converter

The voltage is supplied to a DC to DC converter circuit. The converter has an oscillator circuit, with its transformer and transistors, converts the DC voltage to a high frequency AC voltage. Transformer T1 has the oscillator Q1 in the primary and as part of the secondary a feed back winding. The purpose of the feed back winding is maintaining oscillations independent of circuit loading. There are three outputs on T1's secondary that provide the source voltage for the power supply output voltage.

The output from T1 at pin 7 is rectified to DC by CR1 and CR2 and fed through another filter circuit. The output goes to two zener diodes VR1 and VR2. The zener diodes regulate the voltage down to 15 V. The 15 V is supplied to the circuits in the power supply.

2.4 Voltage Regulation

One of the zener diodes, VR2, regulates the voltage that is used in the 5 V and short circuit/overload protection circuit. Operational amplifier AR1 acts as a voltage regulator by comparing the voltage output to a reference 5 volts. The output 5 V is fed to terminal strip A3.

An output is also fed to the -15 V and +15 V circuits. These two circuits function much the same as the +5 V. The only difference is that the +5 V circuit is the primary output circuit and it controls all the other secondary circuits. In addition to this only the +5 V circuit has protection.

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