HP (Hewlett-Packard) HP 85660B ユーザーズマニュアル

The 

 V supply has as its reference a 6.2 V zener diode VR2 biased from the output of

the j-20 V supply,   on the schematic. The 

 V output is divided down by 

 R50, 

 to 6.2 V. This voltage is compared with the 

 V reference voltage by amplifier 

This amplifier sinks current from the current source 

 so that the voltage at the base of the

series-pass transistor 

 ( on A23 Motherboard) is such that the output of the supply is

at 

 V.

A simple form of 

 current limiting is provided by the current sensing resistor R3, R4,

R5, CR4, and Q3. 0 vervoltage protection is provided by the 

 V crowbar   consisting of

VR3 and 

 DS2 is an LED which indicates the presence of an output voltage. Fuse F2

provides further protection for the supply.

The 

 V switched supply provides power to the oscillator circuits of the A22 10 MHz

Frequency Standard. If the Reference Disable line HSTD is low, 

 is off, and 

 is off, so

no power is supplied to the internal 10 MHz oscillator. When HSTD goes high, both 

 and

 turn on, and 

 V is supplied to the internal 10 MHz oscillator.

The 

 V supply is a 12 V floating regulator with its reference terminal biased at 11 V by

R24 and VR8. This supply is enabled by the presence of the -5.2 V supply, which causes 
to turn off, allowing the zener diode VR8 to be biased by the current flowing from the output

of the supply through R24. LED DS4 provides a visible indication of an output voltage.

Overvoltage protection is provided by the 

 V crowbar 

 The regulator itself is internally

protected, but further protection is provided by CR3 and 

The operation of this supply is similar to that of the 

 V supply. Its reference is from the

voltage divider R36 and R49 from the 

 V supply. This voltage is compared with the

divided down output voltage by U2, which drives the Darlington-connected transistors Q6
and Q4 and the series-pass transistor 

 on the A23 Motherboard. 

 current

limit is provided by 

 R31, R32, and Q5. The output crowbar   provides overvoltage

protection. Further protection is provided by F3.

A power-up indication HPUP is provided to allow the instrument to turn on and off in an
orderly manner. The HPUP line goes high when all of the following conditions are met:

1. The rectified dc voltage of the 

 V Unreg supply is above 8.6 V (provides an indication

that the Line Voltage is present).

2. The 

 V output is higher than 

 V.

3. The front-panel shutdown and thermal shutdown circuits allow the instrument to be turned

on.

If both the front-panel shutdown and thermal shutdown transistors 

 and Q12 are

off, CR11 is reverse biased. If the output of the i-5.2 V supply is greater than i-4.9 V,

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