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General Information - 2
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Caution To protect the electronic load from possible damage, the input voltage must not exceed the
maximum input voltage rating specified in the module-specific pages supplied with each
module. Never apply the ac line voltage to a module's input connectors.
Overvoltage
The overvoltage protection circuit is set at a predetermined voltage level, which cannot be changed. If the
overvoltage circuit has tripped, the module will attempt to limit the voltage level 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 (pin A6)
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 can be used to trip an external circuit breaker or control a relay
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 ON|OFF
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
The power-limit boundary is set by software that monitors the input current and voltage. If the input power
exceeds the 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.
Overtemperature
Each module has an overtemperature (OT) protection circuit, which will turn off the input if the internal
temperature exceeds safe limits. If the OT circuit activates, the OT and PS status register bits are set and will