Shunt Regulator

Discussion in 'General Electronics Chat' started by DexterMccoy, Apr 15, 2014.

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  1. DexterMccoy

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    Feb 19, 2014
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    I have seen power supplies that have a Linear Regulator and after the linear regulator it goes to a Shunt Regulator and then it gets paralleled or fanned out to multiple Op amps that are called precision reference voltage circuits that supply reference voltages , like + 5 volts, + 10volts, + 15 volts , each supply output has a precision reference voltage circuit


    Why is there a shunt regulator after a linear regulator? what does the shunt regulator do?

    What does these precision reference voltage circuits do? source more output current then a linear regulator can?
     
  2. Veracohr

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    Jan 3, 2011
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    I don't know for sure, but this is my guess:

    As 'precision' references, they probably need to be very very stable. The regulator would provide the stable, constant voltage, which is then amplified to the various desired levels with the opamps. However, the linear regulator probably requires a certain amount of current going through it to achieve the optimum regulation, so maybe that's what the shunt regulator is for, since the opamps wouldn't draw much current at their inputs.

    Sine they're reference voltages, they probably aren't required to source much current. A reference doesn't really 'do' anything, it's just a reference that some other circuit uses for its own action.
     
  3. DexterMccoy

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    What really is the difference between a linear regulator vs a SHUNT regulator, what do they do that is different or an advantage of?

    Does a SHunt regulator not have a drop off voltage or sources more current? VS a linear regulator?

    Does a SHUNT regulator handle SHORT circuits on it's output pin VS a linear regulator would get damaged faster when there is a shorted circuit on it's output pin?
     
  4. Veracohr

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    The shunt probably is linear, and thus does have a dropout voltage. 'Shunt' and 'linear' aren't comparable adjectives. 'Shunt' just means it is in parallel with the load; the complement to 'shunt' is 'series'. A shunt is something that redirects a flow from its original path (in this case current).

    The complement to a 'linear' regulator is a switching one.
     
  5. DexterMccoy

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    So having a Shunt Regulation buts the regulator in parallel with the Circuit/load

    Having a Regulator that is in parallel with a circuit/load , does what? what advantage?

    when would you want to have a regulator in parallel with a load?

    When do you use Shunt Regulators mostly in circuits?
     
  6. Veracohr

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  7. Wendy

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    Mar 24, 2008
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    Dexter, have you ever studied zener diodes? They are the ultimate shunt regulator. They are very simple, cheap, and mostly reliable.

    Zener diodes
     
  8. DexterMccoy

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    Feb 19, 2014
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    True

    But My question is when you have a parallel regulator connected to the circuit which is a LOAD , how is it different then having a series regulator

    I'm trying to look at it in how it's connected to the LOAD and how the function is different

    A Parallel regulator does something different VS a series regulator from a LOADING effect
     
  9. BillB3857

    Senior Member

    Feb 28, 2009
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    A SERIES regulator goes between the power supply and the load (in series) and will allow a variable amount of current to PASS THROUGH to the LOAD thus allowing the needed current to maintain voltage at the load as the load's effective resistance chages. (OHMS Law for two series resistors)

    A SHUNT regulator will tend to keep the voltage to the load constant by making the load on the power supply constant. As the effective load resistance increases, the effective resistance of the SHUNT regulator will decrease to keep the effective load constant. A shunt regulator requires a fixed resistor between it and the power supply in order to work properly. That resistor may even be part of the filter circuit.

    Each regulator will monitor the voltage output and adjust their internal effective resistance as needed to keep the output voltage constant.
     
  10. Wendy

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    You really need to google some of these subjects, they are very basic. I would refer you to the section in the AAC ebook about power supplies and regulators, but I haven't finished writing it yet.
     
  11. ian field

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    Oct 27, 2012
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    Are you actually sure its a shunt regulator and not crowbar protection?

    A zener diode is one example of a shunt regulator, if you stick one across the output of a regulated supply, one of two things will happen - either the regulated voltage is lower than the zener voltage and nothing will happen. Or the regulated voltage is higher than Vz, in which case the zener will be destroyed - if its a big fat power zener that's pretty much guaranteed to fail short circuit, it could be a sacrificial crowbar protector that blows the fuse if the series pass transistor goes short.

    A self resetting crowbar is a thyristor across the supply output with a zener from gate to +ve, at Vz + Vtrig the thyristor shorts the supply and blows the fuse.

    For very low current additional supplies, shunt regulators are sometimes fed from the main rail by current limiting resistors - its cheaper than additional series regulators in the design.
     
  12. DexterMccoy

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    Well these current limiting resistors change the Impedance of the power supply to the circuit/load

    The current limiting resistor change the Impedance of the powers supply from a HIGH impedance power supply to a low impedance power supply
     
  13. DexterMccoy

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    Feb 19, 2014
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    Yes I understand this

    But what I don't understand is why would some designs or circuits want to have a Series regulator and other circuits want a SHUNT regulator

    When you use you a SHUNT regulator? for what kinds of circuits?

    Yes I'm sure

    I'm guessing you're saying a crowbar protection is a SHUNT regulator? and using a Thysistor is a SHUNT regulator?
     
  14. bertus

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  15. ian field

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    Apparently you're not so sure - I asked whether it was definitely a shunt regulator or a thyristor crowbar.
     
  16. BillB3857

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    Think about a thyristor. It is even on or off and once on, needs to have current reduced below the holding level in order to stop conducting. Tell us how you see that as a voltage regulator.
     
  17. ian field

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    The first buck regulator I ever had to repair was based on a thyristor - it was commutated by the kick from the dirty-great choke it was driving.

    That took about 320V (peak of rectified 230VRMS) and dropped it down to whatever the TV HT rail was - probably somewhere between 90 - 110V.
     
  18. BillB3857

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    WOW! Never too old to learn something. I knew about commutating a thyristor by shunting current around it with a cap, but never thought about using an inductive kick.
     
  19. ian field

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    There was a particularly nasty CTV from Skandinavia with a funny name (Something like SABA or Nordemende) that had thyristor horizontal sweep. The Bush/Rank/Murphy company did one too.

    I remember studying the service manual and noticing a commutatiing coil to switch the thyristor off at the end of the sweep - never had much luck repairing those, and eventually got pretty good at not picking any up by mistake.
     
  20. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Early Sony colour TVs (mid 1970s?) had thyristor driven h-out stages. I still have stocks of the large metal can HV thryristors.

    And I remember fixing a few of those thyristor driven PSU European sets, they were a small TV and the PSU inductor was a big blocky laminated thing near the middle of the PCB.
    :)
     
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