Fluke 5720A service manual 2-75. FR1 Supply, 2-76. FR2 Supply

5700A/5720A Series II Calibrator

Service Manual

The -44S supply uses the unregulated -44SR supply from the Filter assembly. This supply uses three-terminal TO-39 regulator U13, Q1, VR1, VR2, VR6, R17, R18, R19, PTC Resistor R61, CR22, CR23, CR32, CR33, C22, C25, C26, and C66. The regulator IC, U13, provides the current and thermal limiting. Its regulated output voltage is set by R17 and R18, yielding a nominal output of -44.15V. Components Q1, R19, VR1, VR2 and CR32 act as an emitter follower and protect the regulator against a potentially excessive input-output voltage differential if a short circuit occurs. Capacitor C66 filters the voltage to the regulator. The regulator is shunted by R61 and VR6, which pass 28 mA. In an output short condition, the value of the PTC increases, limiting current through the device to less than 17 mA at 25ºC.

Diode CR32 removes VR2 from the circuit in a shorted condition to meet U13's input- output differential specifications. Diodes CR22 and CR33 protect the regulator against shorts at the output, while CR23 protects the regulated output from reverse voltage.

Capacitors C25 and C26 are for bypass. Capacitor C22 improves rejection of any input variations. The heat sink on regulator U13 guarantees thermal protection for both normal and short-circuit operating conditions.

The +17S supply uses the unregulated +17SR supply from the Filter assembly. This supply uses three-terminal TO-3 regulator U6 with heat sink, and R5 and R6. The output voltage is set by resistors R5 and R6 in the same manner as the +44S supply. Capacitors C8 and C9 are for bypass. Capacitor C11 improves ripple rejection. Diodes CR8 and CR26 protect the regulator against shorts at the input, while CR11 protects the regulated output from reverse voltage.

The -17S supply uses the unregulated -17SR supply from the Filter assembly. It uses three-terminal TO-3 regulator U7 and R10 and R11. The output voltage is set by resistors R10 and R11 in the same manner as the -44S supply. Capacitors C13 and C15 are for bypass. Capacitor C14 improves ripple rejection. Diodes CR15 and CR27 protect the regulator against shorts at the input, while CR13 protects the regulated output from reverse voltage.

The +15S supply uses the unregulated +17SR supply from the Filter assembly. It consists of +15V three-terminal TO-220 regulator U4. Capacitor C27 is required for the stability of U4. Diode CR28 protects the regulator against shorts at the input, while CR29 protects the regulated output from reverse voltage.

The -15S supply uses the unregulated -17SR supply from the Filter assembly. It consists of -15V three-terminal TO-220 regulator U9. Capacitor C29 stabilizes U9. Diode CR31 protects the regulator against shorts at the output, while CR30 protects the regulated output from reverse voltage.

2-75. FR1 Supply

FR1 COM is the return path for the +30FR1 supply. This supply uses the unregulated +30FR1R supply from the Filter assembly and consists of three-terminal TO-39 regulator U1 with heat sink, bypass capacitors C3 and C6 and protection diodes CR1, CR4, and CR6. Resistors R1 and R2 set the output voltage in the same manner as the +44S supply. Capacitor C7 improves ripple rejection. Diodes CR1 and CR4 protect U1 against input shorts, while CR6 protects against reverse voltage.

2-76. FR2 Supply

FR2 COM is the return path for the +30FR2 supply. This supply uses the unregulated +30FR2R supply from the filter assembly and consists of three-terminal TO-39 regulator U5 with heat sink, bypass capacitors C10 and C28, and protection diodes CR9, CR10, and CR12. Resistors R4 and R8 set the output voltage in the same manner as the +44S

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