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User Connections 82
External Voltage Control
The setup shown in Figure 4-5g allows an external dc voltage to program the power supply output. A zero-to-full scale
voltage applied to the voltage programming input produces a proportional zero-to-full scale output voltage. The voltage
programming source is referenced to the programming
Common P (↓P) terminal. A zero-to-full scale voltage applied to
one of the current programming inputs produces a proportional zero-to-full scale output current. See Figure 4-1 for an
explanation of these programming input connections.
Wiring Considerations
The input impedance of the analog input is over 30 k
Ω. If the output impedance of your programming source is not negligible
with this, programming errors will result. Larger output impedances result in proportionally greater errors.
1 = Voltage programming source 0 to -5 V
2 = Current programming source 0 to +5 V
3 = Current programming source 0 to -5 V
4 = Current programming source floating 0 to 5 V
* Maximum potential between -IP and ↓
↓↓
↓P or between +IP and ↓
↓↓
↓P is ±15 V
Figure 4-5g. Series 668xA and 669xA Analog Programming Connections
Programming
Note from Figure 4-1 that you have three options for programming the current. You can use a voltage source that is positive,
negative, or floating with respect to
Common P. Do not exceed +15 V with respect to Common P.
Make certain that the common connection for your voltage programming source is isolated from the load.
Failure to do this may cause damage to the power supply.
The effect of the analog programming source is always summed with the values programmed over the GPIB or from the front
panel. The voltage source can act alone only if you set the other program sources to zero. Keep the total programmed setting of
the supply (the analog input summed with the GPIB or front panel settings) at or under the output ratings specified in Table 1-3a.
Exceeding the output ratings will not damage the supply, but it may not be able to regulate its output the higher levels. If this
happens, the
Unr annunciator will light to warn you that the output is unregulated.