Oscillation in CC mode of programmable power supply

Thread Starter

SHARANYADAS

Joined Apr 13, 2017
60
Hi experts
I was designing a programmable power supply 0-30v/0-4A.The control part is based totally on analog electronics.By far,my power supply is working as expected.But the main problem is the current control loop.Whenever the control loop is limiting current,I can hear humming sound from the Q1(In my schematic,it is TIP41 but in i am using MJE15032).I have captured the waveform of the Current control op-amp's output & the main output.Also the main output is fluctuating between 1V window.(For say,if i have set the output to 5v,then it is going to 6v).
The op-amp i am using is LT1013.The IC2(LM317) is powering the op-amps at 33v.The main power transistor(T1) is TIP35.Please take a look at the schematics.Is the oscillation normal?If not,then how to clear it??
 

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Thread Starter

SHARANYADAS

Joined Apr 13, 2017
60
Is there a resistor between 'current_set_dac' and C2?
Without some resistance there, C2 will be ineffective.
You just saved me!!!!!!!I just wired a 2k resistor after the dac and now the oscillation is gone!!!!!Please take a look at my circuit and tell me if i have to add/delete anything...................And also if the part's values are correct.
 

AlbertHall

Joined Jun 4, 2014
11,524
Because the base current for Q1 comes via R2 from the op-amp output, the voltage at the base of Q1, and therefore the output voltage, cannot be higher than the op-amp supply voltage. Your diagram doesn't say what that voltage is or what type the op-amp is, but there aren't many op-amps that will support 50V supply voltage so that will limit your output voltage.

If you get enough voltage for your needs then all is OK.

To avoid that problem connect a resistor or, better, a constant current circuit, between the base and collector of Q1. Then reverse the inputs to the voltage control op-amp and connect a resistor from its output to the base of T2, deleting R2. Note you will now need a resistor in series with the 'volt_set_dac' as per the current control.
 

Thread Starter

SHARANYADAS

Joined Apr 13, 2017
60
Because the base current for Q1 comes via R2 from the op-amp output, the voltage at the base of Q1, and therefore the output voltage, cannot be higher than the op-amp supply voltage. Your diagram doesn't say what that voltage is or what type the op-amp is, but there aren't many op-amps that will support 50V supply voltage so that will limit your output voltage.
The LM317HV(IC2) is powering the op-amp at 33v.So i am getting a max output of 30v(That is my target so no issue with that).I omitted the R4+C1 & R8+C3.Should i proceed with this circuit.Also should i add a resistor between the vout_dac & op amp input?
 
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