Fluke 5720A Regulated LH Supplies, Regulated S Supplies, 2A 2A 2A 2A 2A 0.5A 0.5A 4A 6A 2A 1A 1A

Theory of Operation 2

Analog Section Detailed Circuit Description

Table 2-10. Regulated Outputs from the Regulator/Guard Crossing Assembly

Signal Name

+15 OSC -15 OSC

+5RLH

+5LH -5LH

+44S -44S

+17S -17S 15S

+30FR1

+30FR2

Nominal

Output

+15V -15V

+5.975V

+5.1V -5V

+44.15V -44.15V

+17.000V -17.000V -15V

+30.96V

+30.96V

Tolerance

+/-800 mV +/-800 mV

+/-425 mV +/-300 mV +/-300 mV

+/-2.03V +/-2.03V

+/-475 mV +/-835 mV +/-800 mV

+/-1.7V

+/-1.7V

Current

Limit

2A

2A

2A

2A

2A

0.5A

0.5A

4A

6A

2A

1A

1A

Rated Output

200mA

200mA

600mA

600mA

400mA

140mA

140mA

1.0A

1.0A

300mA

85mA

85mA

Test Point

TP3

TP5

TP14

TP11

TP15

TP13

TP16

TP8

TP12

TP19

TP2

TP7

2-73. Regulated LH Supplies

LH COM is the return path for the +5RLH, +5LH, -5LH and +8RLH supplies. The +5RLH, +8RLH, and +5LH supplies use the unregulated +5LHR supply from the Filter assembly. The +5RLH supply uses three-terminal TO-3 regulator U11 with heat sink, bypass capacitors C20 and C21, protection diodes CR17 and CR20, and the diode combination of CR34 and CR35. The +5LH supply uses three-terminal TO-3 regulator U8 with heat sink, bypass capacitor C16, protection diodes CR14 and CR16, and resistor R13. The -5LH supply uses the unregulated -5LHR from the Filter assembly and consists of three-terminal TO-220 regulator U12 with heat sink, bypass capacitors C23 and C24, and protection diodes CR21 and CR24. Capacitors C16, C21, and C24 improve the stability of U8, U11, and U12 respectively. Diodes CR14, CR17, and CR24 protect the regulators from input shorts. Diodes CR16, CR20, and CR21 protect the regulators from reverse voltage. Resistor R13 and diodes CR34 and CR35 increase the output of regulators U8 and U11. The unregulated +8RLH supply is generated by fusing the unregulated +5LHR supply from the Filter assembly with 3.15A slow-blow fuse F1.

2-74. Regulated S Supplies

Line S COM is the return path for the +44S, -44S, +17S, -17S, +15S and -15S supplies. Line S COM is also connected to LH COM. The +44S supply uses the unregulated +44SR from the Filter assembly. This supply uses three-terminal TO-39 regulator U10, Q2, VR3, VR4, VR5, R20, R14, R15, CR18, CR19, CR25, C17, C18, C19, C65, PTC resistor R60. The regulator IC (U10) provides the current and thermal limiting. Its regulated output voltage is set by R14 and R15, yielding a nominal output of +44.15V. Components Q2, R20, VR3 and VR4 act as an emitter follower to protect the regulator against a potentially excessive input-output voltage differential in the event of a short circuit. Capacitor C65 filters this voltage to the regulator. Diodes CR19 and CR25 protect the regulator against shorts at the input, while CR18 protects the regulated output from reverse voltage. Capacitors C17 and C18 are for bypass. Capacitor C19 improves rejection of input variations. Components U10 and Q2 have heat sinks to provide thermal protection for both normal and short-circuit conditions. The regulator is shunted by R60 and VR5, which normally pass 28 mA of current to remove the power from the regulator. In an output short condition, the value of the PTC increases, limiting current through the device to less than 17 mA at 25ºC.

2-39