Agilent Technologies 6811B, 6813B, 6812B Peak Current/Dynamic Power Capability, Peak Current Limit

1 - General Information

Peak Current/Dynamic Power Capability

The ac source can generate peak currents that exceed the rms current capability of the unit. This not only applies when operating in ac mode, but also when programming output pulses in dc mode. Although the unit will generate peak output currents up to 40A (Agilent 6811B/6812B) or 80A (Agilent 6813B), the unit can only maintain this output for a limited time. If the output of the unit exceeds the limit of the safe operating area (SOA), the unit will activate its internal protection mode and turn its output off. This SOA limit is based on output voltage, output current, output duration, and heatsink temperature.

NOTE: Refer to Chapter 4 on how to clear the unit when the internal protection mode has been activated.

Peak Current Limit

By programming the peak current limit, you can prevent the unit from exceeding the safe operating area, activating its internal protection mode, and turning the output off. The peak current limit circuit limits the instantaneous output current. It functions by reducing the instantaneous output voltage to keep the output peak current within the programmed limit. Because the circuit acts instantly, the effect is that it will clip the peaks of the output voltage waveform. Additionally, with fast and/or large voltage transitions, the unit may momentarily go into CC operating mode due to current in the output capacitor. This serves to limit the rate of change of output voltage.

The following table gives approximate indications of how long the unit will tolerate peak output currents before the SOA limits are exceeded. Because these values are voltage dependent, the table includes various equivalent dc voltages along with the peak current values. The voltages shown in the table are NOT the programmed voltages, but the average voltage values that will appear at the output when the indicated high current condition exists. The SOA circuit becomes active at higher voltage and current values as well as at longer duration times.

Agilent

6813B

Table 1-3. Typical Peak Current Output Capacities
Agilent 6811B		equivalent dc voltage when current is flowing 1
Agilent 6812B	25		75	125	190	250	360

20A

30A

40A

50A

60A

70A

80A

10A

15A

20A

25A

30A

35A

40A

>100 ms >100 ms

12ms

5.6 ms

3.7 ms

2.6 ms

2 ms

>100 ms

100ms

9.2 ms

5.1 ms

3.4 ms

2.4 ms

1.8 ms

>100 ms

30ms

8.4 ms

4.7 ms

3.1 ms

2.2 ms

1.7 ms

>100 ms

24ms

7.6 ms

4.4 ms

2.9 ms

2.1 ms

1.6 ms

>100 ms

19ms

6.8 ms

4 ms

2.6 ms

1.9 ms

1.4 ms

>100 ms

15ms

5.9 ms

3.5 ms

2.3 ms

1.7 ms

1.3 ms

1Based on 25C ambient temperature, with heatsink temperature less than 50C.

Peak Inrush Example

The following table gives the recommended initial Ipeak settings when the ac source output is a 127 Vac or 254 Vac 60 Hz sine wave, as a function of load capacitance. The load on the output is a full-wave bridge along with the indicated capacitor. The load resistance across the capacitor is infinite. The recommended Ipeak will change as a function of changes in input as follows:

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