Agilent Technologies 6051A, 6050A manual Overvoltage, Overcurrent, Overpower

Overvoltage

The overvoltage protection circuit is set at a predetermined voltage, which cannot be changed. If the overvoltage circuit has tripped, the module will attempt to limit the voltage by drawing current from the DC source. The module limits the value of current drawn such that the resulting power is within the power rating. The overvoltage (OV) and voltage fault (VF) status register bits are set when the OV condition occurs, and will remain set until they are reset as previously described.

An overvoltage condition does not cause the module’s input to be turned off . However, a Fault signal output at the module’s rear-panel control connector will indicate when either an overvoltage condition or a reverse voltage condition has occurred. The Fault signal is latched true (high TTL level) when the VF bit in the status register goes true. The Fault output signal (see Chapter 3 - Installation) can be used to trip an external circuit breaker or control a relay (e.g., Agilent 59510A Relay Accessory) in order to disconnect the Electronic Load input from the source it is testing when an overvoltage or a reverse voltage condition occurs.

Overcurrent

The Electronic Load includes both hardware and software overcurrent protection features.

Hardware. When operating in the CR or CV mode, it is possible for a module to attempt to sink more current than it is rated for.

Under this condition, the load current will be limited by a current limit circuit, which is set at a value slightly above the current rating of the module. It protects both the Electronic Load and the device under test from operating too far beyond specified limits. The hardware current limit circuit does not turn the module’s input off. The overcurrent (OC) bit in the status register is set when an OC condition occurs, and is reset when the OC condition is removed.

Software. In addition to the hardware overcurrent protection circuit, the Electronic Load allows the user to define a current protection limit in software which will shut down a module’s input if the limit is exceeded. This feature can only be programmed via the GPIB. It is turned on/off using the CURR:PROT:STATE ONOFF command. The software current limit level (in amps) is set using the CURR:PROT command. A programmable delay (in seconds) before trip is also provided with the CURR:PROT:DEL command. If the software overcurrent limit is exceeded and persists beyond the specified delay time, the module is turned off. Also, for these conditions, the OC and PS (protection shutdown) status register bits are set and will remain set until the OC condition is removed and the bits are reset as previously described.

Overpower

A load module’s response to an overpower condition depends on whether the module was operating with the nominal power limit or the extended power limit when the overpower condition occurred.

Nominal Power Limit. The nominal power-limit boundary is set by software that monitors the input current and voltage. If the input power exceeds the nominal power limit, the load module sets the overpower status bit, which will reset if the overpower condition ceases. If the overpower condition persists for 3 seconds, the load module’s input circuit turns off, and the OP and PS status bits are both latched on. The input circuit remains off, and the OP and PS status bits remain set, until protection clear occurs. Of course, if the overpower condition is not corrected, the load will turn off again.

Extended Power Limit. The extended power-limit boundary is set by hardware circuits. This hardware power-limit circuit can be activated by any of three conditions:

1.If an overpower condition occurs while the module is operating in the extended power area.

2.During certain large programmed changes

3.If the nominal power limit is exceeded (the software limit sets the OP bit and starts the 3-second timer, but does limit the input power)

Operation Overview 29