Control and protection Circuits

1
Control and protection Circuits
2
Need of protection circuit

• For this purpose we may first know
• What to protect ?
• Why to protect ?
• Possible way of implementation in current design.
• Complexities of the problem
• Easiest solution available with cost
  consideration with circuit description.
• Testing result, how it is tested
• Actual result with that of simulation
• Why not the Present protection effective?

3
FEE boards on Detector
4
What to protect?

• By past experience we found that due to any HV
  spike or any other reason there is over-current
  in the FEE board. And due to over-current
  FEE-boards are going bad.
• So we have to have a over current protection
  circuit to protect our FEE board.

5
Why to protect?

• As we all know that board going bad means all the
  channel associated with that board will be
  useless. Also we cant neglect the cost of
  replacement of boards.
• Also if one FEE board goes bad in a chain then
  due to current setting change at LVDB level other
  board in chain also goes bad (observation).
• Also if MARC goes bad in present scenario then
  whole chain will be gone bad.
• Due to these problem we can say that protection
  of over current should be done for the protection
  of the data as well as cost (In long term). Also
  we must have a control circuit to check MARC
  going bad

6
How it is to be implemented with current design
?

• Board Level Protection
• In this method we can have a protection circuit
  at board level. In this we have to modify the
  design of the Fee board.
• The basic concept of this circuit is
• We have a current sensor
• A precision resistance
• Electronic switches (in our case it is a MOSFET)

7
Basic Circuit
S
MOSFET
G
MAX 4373
D
MAX 4373
O/P
O/P
Differential Amplifier
Rs
Comparator
Latch
Rs
3.3V
Rs Precision Resistance MOSFET is IRLML 2502
8
Basic circuit description

• As soon as the current exceeds maximum
  permissible limit, the differential amplifier
  will amplify the voltage across the sense
  resistor.
• Then at the max limit the comparator will be
  triggered and the output state of the comparator
  will be changed
• As soon as the output of the comparator is
  latched the switch get tripped and supply is cut
  off.

9
Full proposed circuit with different modifications
Latch
Latch
Latch
10
Full proposed circuit with lower no of components
11
Circuit description

• There are three units of basic involved with the
  complete circuit.
• The point to be noted is that all the tree unit
  will be tripped at the same time for overflow in
  any of the circuit (i.e. full power supply is cut
  down).
• As the TKIN and TKOUT are from the same line so
  they are also shorted to make the chain working
  the condition of tripping of the board. So in a
  twelve board chain all 11 will continue their
  usual work.
• Also there is a additional facility to restart
  the power supply from the remote point.

12
Testing conditions

• For testing right now we have used IRF 150 MOS
  with voltage rating 400V with MAX4373.
• Base voltage as specified for the given MOS is 7V
  in datasheet so it is tested for 7V base voltage
  and on state resistance was .85 Ohm approx.
• When base voltage was 3-5V the on state
  resistance was 4-5 ohms.
• Margin for the current offset with set current
  200mA is /- (1-2)mA.
• Also circuit is tested with 2.5V source to drain
  voltage.

13
Test Results

• The Basic need of tripping the circuit at the
  over-current is tested and now we are almost sure
  about the functionality of the circuit.
• At low base voltage the circuit functionality is
  not up to mark. The resistance was high for 3-4V
  base voltage. Its resistance is following its
  characteristics as given in datasheet. At higher
  base voltage resistance was .85 Ohms .
• Restart of the circuit externally is done and the
  supply can be restarted with ease.

14
Expected Result

• With the IRLML2502 MOSFET, the on state
  resistance will be 140 milli ohms.
• With same MOSFET base voltage required will be 2V
  which was 7V earlier.
• Off state resistance will be in mega ohms.
• As there is no use of relay in the circuit so the
  circuit response will be much faster as in case
  of the older DB circuit with relays.

15
Complexities of the problem

• Although the circuit is not a big one but the
  basic complexities are
• Redesigning of Back Plane PCB
• Redesigning of Translator Board
• Redesigning of FEE board
• Redesigning of Software for analyzing the FEE
  board going bad and also to control it we may be
  needing additional lines, which has to be taken
  into account, which are to be handled by
  software.

16
Second Prototypes
17
Cost Estimation

• Cost is behind any building block so it is to be
  estimated first.
• We have to increase some 25 components per board
  so some assembly cost is to be taken in account.
• Component cost is approx 2.5 per board. If
  reduced scheme is used then it may be reduced
  upto 2 per board.
• Few counters and other control circuit is to be
  placed on the translator board which is around 1
  per translator board.
• Two layer of the back plane PCB has to be
  increased so its cost is to be taken in account.

18
Present Scenario

• Right now we are using LVDB circuit, but it has
  to set a margin of current must be atleast few
  board current.
• So if one board is going bad then we dont have
  any control or protection for that overcurrent on
  single board.

19
Proposal to take out relays from present DBS

• Looking at the data sheets we can now say that a
  MOSFET having 12amp current rating and on state
  resistance of 200 milli ohms and less will
  definitely replace our relays. Also negligible
  voltage drop at on state and also we will have
  full flexibility of use in magnetic field. And we
  can easily control supply from remote terminal.

20
Proposal for the control circuit for STAR with
current design

• Looking to the concept developed we can even
  introduce protection circuit for the present STAR
  boards without change in present design.
• We can have a board which can be put in between
  the supply connectors.
• Although we will be using a extra board but we
  can save boards going bad.

21
Control circuits

• One more important problem is if board didnt
  goes bad and it is to be restarted then what to
  do?
• For that we will be using some control circuit on
  the Translator board level. This circuit helps
  you to restart and control your board from remote
  places.
• There are various ways of designing this control
  circuit. Few of them are shown in next few slides

22
How it is to be implemented with current design
?

• There are several ways to implement the Control
  circuit as
• We can go for FPGA or CPLD for this purpose as a
  control circuit (i.e. TKIN and TKOUT monitoring)
• This need little modification in the FEE board
  design and space problem can be solved.
• This will also give us freedom to make a smart
  circuit which can do additional task we want to
  do as bridge board control etc.
• We will discuss in next slides

23
Below shown is the possible implementations
24
This is other way of doing same thing with
additional advantages
25
Replacement of FPGA with discrete components

• As our requirements are low and by reducing some
  of the flexibility we can go for a discrete
  component solution. This is cost effective and we
  can manage to make it on translator board since
  it is spacious till now. By this we can have a
  board level control and protection.
• Scheme is to use two counters and some other
  control circuits. This circuit is yet to be
  tested but we can rely on the discrete digital
  circuit for both output in general environment
  and in radiation environment.

26
Circuit Description

• In this circuit we enable the counter1 to count
  as soon as the TKIN is 0 and TKOUT is 1. Then if
  we didnt get TKOUT in limited time then cut
  supply signal is sent back to the board. Also
  TKIN and TKOUT is shorted as told earlier. So we
  are able to cut the faulty board out of the
  circuit.

27
Proposed control circuit at Translator board level
28

• Counter-2 is used to take care of the
  communication with the control circuit at the
  remote terminal. Counter every time counts the
  pulses of the TKIN and TKOUT. So when the
  counter-2 has a certain count and counter1
  exceeds certain count decided by us then
  particular channel will set and thus we came to
  know that which channel is gone bad.
• There is one provision from outside to restart
  the board again.

29
Need of bridge-board

• When there is no data in some exterior region
  then our DSP will be idle for a long time. So for
  making full utilization without hindering the
  speed of operation we can increase the no of
  boards in a chain.
• So if we somehow land up with one less DSP then
  we may separate the front panel with rear panel.

30
Tested bridge board control circuit
31
Circuit description

• In this circuit we are just taking care of the
  token in and token out which are control signal
  controlling data transfer.
• If we get token in then we transfer it to first
  chain and then after receiving token back from
  the first chain then circuit will switch token to
  second chain.

32
Other circuit required

• Now after switching we will be needing the buffer
  circuit. Need is due to the signal going bad
  after 12 boards. If we will make the chains
  parallel then also the signal will go bad and
  this time the no reduce to 6 only.
• So we have to have a buffer circuit in atleast
  one chain.

33
Conclusion

• So finally the problem of the boards going bad
  are to be taken into account and some protection
  measure has to be taken.
• The access to the board is always not possible so
  there must be some software control so some
  control circuit is to be taken in account.
• For faithful data bad boards are to be taken out
  of the system.
• Finally we must also consider that what we are
  getting and at what cost so bridge board must
  also taken care.