Agilent Technologies 90B manual Overvoltage Crowbar Circuit Details

B.RFI Choke - Minimizes spikes at output of supply by slowing down turn-on of triac.

C.Rectifier Damping Network - RC network protects other elements in supply against short-duration input line transients.

D.Series Regulator Diode - Protects the series regulator against reverse voltages which could be delivered by an active load or parallel power supply.

E.Slow Start Circuit - A long time-constant network that reduces turn-on overshoot and helps limit inrush current. When supply is first turned on, this circuit holds off both the series regulator (to reduce output overshoot) and the preregulator triac (to limit inrush current).

F.Amplifier Input Clamp Diodes - Limit the maximum input to the amplifier to protect it against excessive voltage excursions.

G.Output Diode - Protects components in the power supply against reverse voltages that might be generated by an active load or series connected power supply.

H.Sensing Protection Resistors - Protect the load from receiving full rectifier voltage if remote sensing leads are accidentally open-circuited.

Figure 21. Protection Circuits, Linear Type Supply

Overcurrent and Overvoltage Protection - All Agilent supplies are short-circuit proof and can operate under any current overload condition indefinitely without risk of internal damage. Overvoltage protection is also available if required during constant current operation. The CV/CC and CV/CL automatic crossover circuitry discussed previously is ideal for these purposes since it allows the user to select the maximum safe current or voltage for the particular load device.

Overvoltage Crowbar - The crowbar circuit is connected across the output terminals, and provides protection against any output overvoltage condition which might occur because of operator error or failure within the power supply or load. Most Agilent power supplies of this type have either a built-in or optional crowbar circuit. Because of its importance in many applications, the crowbar circuit is discussed in more depth on the following pages.

Overvoltage Crowbar Circuit Details

An operator error or a component failure within the regulating feedback loop can drive a power supply's output voltage to many times its preset value. The function of the crowbar circuit is to protect the load against this

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