Voltage Regulators for Line Level Audio. Part V : Graduation Day - diyAudio
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Voltage Regulators for Line Level Audio. Part V : Graduation Day

Posted 20th January 2014 at 03:32 AM by rjm
Updated 20th January 2014 at 10:21 PM by rjm

Part five of a series.

Last time, we'd got to a functional voltage regulator, with a pass transistor and op amp error amplifier but I cheated and used ideal voltages for the reference and op amp power supply.

This time I've sketched out a functional circuit using real parts found in the LTSpice library. I've chosen a rail-to-rail op amp to avoid problems with low voltage references. The LT1009 reference puts out 2.5 V, the op amp gain is 4, for an output of 10 V into 1 kohms.

Two versions of the circuit are included below. Voltageregulator5 has some additional RC filter stages to remove noise from the reference and op amp power supply Voltageregulator5b just takes everything straight from the input voltage. As you can see there's a fairly substantial advantage gained from judicial use of RC filtering.

So that's the end of Term 1. The basics have been covered, however briefly. I encourage you to download the LTSpice files and play around - changing the filter arrangements and component values. You should see that filtering only gets you so far before diminishing returns start to kick in.

I must reinforce my early point though: what looks good in simulation may not work out in practice. In particular, all bets are off regarding the stability of op amps when operating at high bandwidths (100k or more) into high capacitance loads.

Coming up in Term 2: some more discussion about voltage references, capacitance multipliers, revisiting the X-reg, and a collection of regulator circuits for around the web.
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