Hello friends! Recently I have been working on my own linear power supply design as part of my requirements for lab equipment and the need to improve/refresh my knowledge.
The goal of this supply is to provide voltage regulation, current limiting and short-circuit protection in the ranges 1.5-30V, 0-5A. The requirements are not strict however I intend to implement every best practice and the best affordable components to make this power supply as good as I can.
My design revolves the 2n3055 as a power transistor and the LM317 as the basis for the control circuitry.
This part of the circuit is fairly straightforward and common - transformer, Graetz/diode bridge and capacitors to smooth out the output.
In the primary circuit, shown above, I intend to use a KBPC5010 diode bridge rectifier and Nichicon BY-series capacitors with minimal ESR.
This is the series voltage/current regulation circuit containing the LM317 and 2n3055 components.
The above circuit contains two potentiometers through which we can set the voltage and current limits. This is based on textbook examples for current regulation using two transistors and a feedback loop (read more here).
The way I understand it - R4 is connected to the output of the LM317 (configured as a variable voltage regulator) and acts as a voltage divider, piping current into Q2. The collector of Q2 is connected to the ADJ pin of the LM317 and draws current away from the ADJ pin (effectively reducing the current provided to the base of Q1). Depending the current drawn by the load (shown in figure 1) and the position of R4, Q2 may draw more or less current from the ADJ pin, effectively regulating the output current by Q1.
The R4 potentiometer is basically acting as a Rsense / current sensing probe.
I realize Q2 may be a much smaller transistor, so lets leave that out of focus for the moment.
This circuit seems to work and operate smoothly and predictably when simulated in NI Multisim, however I would really appreciate any suggestions for improvements/criticism/mistakes pointed out. What can we do to improve load and line regulation? Should an NTC be included for better thermal handling?
At first sight I would say another 2n3055 power transistor parallel to Q1 with resistors should be added, in order to increase the maximum current capability or at least split the thermal stress. I also bumped into many circuits using operation amplifiers instead of a transistor (Q2) in the current feedback stage - what would the benefits of the additional complexity be? Would it be maybe better to instead preserve the existing current regulation and just replace the Zener diode (D7) with an integrated voltage reference? I am also uncertain if there is a need to implement output overvoltage protection, in case Q1 fails (this was pointed out on some forum somewhere)?
I am grateful for any feedback you may provide.
The goal of this supply is to provide voltage regulation, current limiting and short-circuit protection in the ranges 1.5-30V, 0-5A. The requirements are not strict however I intend to implement every best practice and the best affordable components to make this power supply as good as I can.
My design revolves the 2n3055 as a power transistor and the LM317 as the basis for the control circuitry.
This part of the circuit is fairly straightforward and common - transformer, Graetz/diode bridge and capacitors to smooth out the output.
In the primary circuit, shown above, I intend to use a KBPC5010 diode bridge rectifier and Nichicon BY-series capacitors with minimal ESR.
This is the series voltage/current regulation circuit containing the LM317 and 2n3055 components.
The above circuit contains two potentiometers through which we can set the voltage and current limits. This is based on textbook examples for current regulation using two transistors and a feedback loop (read more here).
The way I understand it - R4 is connected to the output of the LM317 (configured as a variable voltage regulator) and acts as a voltage divider, piping current into Q2. The collector of Q2 is connected to the ADJ pin of the LM317 and draws current away from the ADJ pin (effectively reducing the current provided to the base of Q1). Depending the current drawn by the load (shown in figure 1) and the position of R4, Q2 may draw more or less current from the ADJ pin, effectively regulating the output current by Q1.
The R4 potentiometer is basically acting as a Rsense / current sensing probe.
I realize Q2 may be a much smaller transistor, so lets leave that out of focus for the moment.
This circuit seems to work and operate smoothly and predictably when simulated in NI Multisim, however I would really appreciate any suggestions for improvements/criticism/mistakes pointed out. What can we do to improve load and line regulation? Should an NTC be included for better thermal handling?
At first sight I would say another 2n3055 power transistor parallel to Q1 with resistors should be added, in order to increase the maximum current capability or at least split the thermal stress. I also bumped into many circuits using operation amplifiers instead of a transistor (Q2) in the current feedback stage - what would the benefits of the additional complexity be? Would it be maybe better to instead preserve the existing current regulation and just replace the Zener diode (D7) with an integrated voltage reference? I am also uncertain if there is a need to implement output overvoltage protection, in case Q1 fails (this was pointed out on some forum somewhere)?
I am grateful for any feedback you may provide.