Power Protection for Staves/Supermodules Two Approaches Purpose of circuit: Provide an alternate current path for serial power current on the module level to prevent disabling an entire stave in case of an open in the module. It also gives a module level of control allowing a specific module to be turned on and off. Prototype Circuits for both approaches Measurement Results for both Future Effort February 24, 2009 CERN J. Matheson, Rutherford Lab D. Lynn, J Kierstead, BNL

Rutherford Laboratory AC-DC Protection Circuit

Rutherford Lab Protection Circuit Theory of Operation Serially addressable switches are used to select and turn on a local oscillator. Isolation is maintained by feeding the output from the oscillator to a capacitor The capacitively coupled AC oscillator output drives a ladder of diodes and capacitors giving a DC voltage gain of x 4 The DC voltage then turns on a MOSFET which in turn supplies current to the base of the shunt transistor dropping the voltage to the V CESat of the transistor To test this circuit the diode/capacitor ladder and MOSFET was constructed using discrete components. A signal generator was substituted for the addressable switch and oscillator. The output of the MOSFET attached to existing serial power boards. Two modules were switched on and off in loaded and unloaded states with the results in the next slides.

Rutherford Laboratory AC-DC Protection Circuit Shown are results of switching adjacent modules on and off with no load. Some perturbation is seen in the module that is not switched but it is not excessive

Rutherford Laboratory AC-DC Protection Circuit Shown is the same test as in the previous slide except that the modules are loaded As can be seen loading produces little difference in response.

Brookhaven Over-voltage and Slow Control Bypass Protection Circuit Shown below are the segments of the circuit. The green circle is the dummy module Strategy is that module should have both slow control and real time protection. Also, when bypass is used the voltage drop across the module should be as small as possible. The red circle is the low resistance slow control bypass. DCS enable/disable through a serial addressable latch. The zener shown protects the gate of the MOSFET from both under and over voltage. Less than 100 mV voltage drop is achievable The blue circle is the over-voltage protection latch. At a selected voltage (e.g. 2.5 V) the zener conducts and turns the both bipolar transistor pair latch and MOSFET on. This provides real time protection

Brookhaven Over-voltage and Slow Control Bypass Protection Circuit Shown are 3 simulated modules with the Brookhaven proposed protection on each module Again, the blue circle is the over-voltage protection which turns on when the voltage rises above a set point. The turn on time has been measured as being on the order of 100 ns. The circuit latches and requires a power recycle to reset. The overall low voltage achievable in this approach is about volts. The over-voltage protection circuit has been prototyped with discrete components as shown in the picture to the right of the circuit on a Euro. The red circle and adjacent components are the slow control protection circuit. This was tested a 3 module serial chain for characteristics. And achieves a low voltage across the module of about 100 mV

Slow Control Bypass Response When Switched Shown is the slow control “bypass on” response (top plot) and “bypass” off response (bottom plot) for the middle of 3 modules The orange curve is the voltage across a module and the green curve is voltage on the gate of the bypass MOSFET with respect to the ground of the serial chain. The module voltage is pulled down to about 100 mV when the bypass is enabled. The top and bottom modules show a similar response to this.

Slow Control Bypass Response in Adjacent Module This is similar to the previous slide except that the orange curve shows the voltage across the top module when the middle module is switched. As shown there is a small perturbation that occurs on adjacent modules when a module is switched on or off. The bottom module shows a similar perturbation to the top module.

Bypass MOSFET Vishay 1450 V THR Tuning The MOSFET has a gate threshold voltage that is too large for this application This was adjusted by exposing the MOSFET to gamma radiation to shift it to a lower value Shown is a curve showing the response with v g = v d at different gamma doses. At 500 krad the value is about right. This approach is used only to tune the circuit in the prototype and would not be used in the final design. With this the over-voltage circuit can lower the voltage across the module to 0.6 – 0.7 volts

Future Effort Can make prototype version of this circuit using discrete commercial components and optimizing for size. These could be used in stave prototypes (Stave 09?) Just beginning to investigate how much of circuit can be incorporated in a single chip. Need to determine which processes are available and what components and component characteristics are of available (e.g. FET breakdown and turn on thresholds).