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 Voltage Controlled Voltage Source See our other Circuits. This circuit allows a smaller control voltage to linearly control a larger output voltage Vo. The Resistors R2 and R3 scale the feedback to an appropriate range for the opamp. R3/(R2+R3) = VCmax/VoNote: VS>Vomax+Vgs(th).      Voltage Controlled Voltage Source Schematic The disadvantage of the circuit above is that the supply of the op-amp is tied to the HV supply. Most op-amps are limited to around 30V on the supply, so the circuit wont work for higher output voltages.  The circuit below avoids this this problem by inserting a n-channel mosfet, which can be fully controlled within the range of the op-amps power supply.  Voltage Controlled Voltage Source with N-Chan MOSFET SchematicThe output voltage is directly proportional to the control voltage. R1 and R4 should be chosen such that Vgs(max) of Q2 is never exceeded.  Likewise Q2 should have an Idss greater than VHV.Vo= (R5+R6)/R6*VCVgs(max)is typically around 20V for many MOSFETs.   So the following should apply:VHV*R4/(R1+R4)< Vgs(max)The feedback resistors are set according to this equation:R6/(R5+R6) = VCmax/Vo Voltage Controlled Voltage Reference The circuit below is a voltage controlled voltage reference. The output voltage is directly proportional to the control voltage.  Note that the control voltage and feed back input of the op-amp is swapped. Vo= (R8+R9)/R9*VCThe feedback resistors are set according to this equation:R9/(R8+R9) = VCmax/VoThe capacitor stops oscillation, and should only be placed on the output. The circuit will tend to oscillate if a capacitor is placed across the feedback network, for example across R9.   Voltage Controlled Voltage Reference Schematic  Do you need help with an electronics design?  Daycounter provides contract electronics design services. Contact us to give you a quote on your electronics design project.   [Employment] [Downloads] [Articles] [Contact Us] Salt Lake City, UT, USA Disclaimer: Daycounter, Inc. doesn't guarantee the accuracy of any of it's content. Use at your own risk. © Copyright 2016 Daycounter, Inc. All rights Reserved.