Break the circuit in half. Get the current regulator working first. You can test it simply by taking a current meter off the collector of Q1 to ground. It will vary from near zero to 20ma when it is working. If you need to take voltage measurements throughout the circuit and only have one meter then short the collector of Q1 and use the meter to take the measurements.

 

Break the circuit in half. Get the current regulator working first. You can test it simply by taking a current meter off the collector of Q1 to ground. It will vary from near zero to 20ma when it is working. If you need to take voltage measurements throughout the circuit and only have one meter then short the collector of Q1 and use the meter to take the measurements.

Hmm well ok here are my measurement. I believe i have made a wrong measurement somewhere, all readings can be ignored but not the schematic components connection.

Well placing the current meter from the Q1 collector to ground, a current reading of 90mA is read. The current is constant and cannot be changed with either potentiometer which i believe is the role of the circuitry of the current regulator.

Now it makes more sense as i believe the high current is present due to the newly replaced 7815.

However it could be a reason why i placed a 105M at R6, this was to reduce the current to the desire value which i want at the output.

 

If you're not getting a variable current then there is a fault there, don't worry about the voltage regulator. The Base of Q1 should vary in voltage, as should the + input to the op amp, they should be the same voltage. This voltage is variable.

 

If you're not getting a variable current then there is a fault there, don't worry about the voltage regulator. The Base of Q1 should vary in voltage, as should the + input to the op amp, they should be the same voltage. This voltage is variable.

12V can be seen across the positive pin of the op-amp but however what is strange is that the voltages at any point that is related to R3 cannot be adjusted. It just fixed to 12V. Does it mean i can have the circuitry to perfrom in a way but just removing this potentiometer and making use of R5 for just one adjustment on both the current and the voltage.

 

OK, what is the opamp that you are using?

If it isn't a rail-to-rail opamp, the opamp's +V supply needs to be about 2v higher than your regulator's output, and within the limits of the opamp's supply specifications.

If you're supplying the opamps V+ from the output of the 7815, and the opamp is not a rail-to-rail type, it will not be able to output a voltage higher than about +V-1.5v. You might be seeing a higher voltage than that due to the emitter-base current, which will be somewhat confusing.

 

OK, what is the opamp that you are using?

If it isn't a rail-to-rail opamp, the opamp's V+ supply must be about 2v higher than your regulator's output, and within the limits of the opamp's supply specifications.

i am using the LM358P. which has 2 op-amp inside.

 

i am using the LM358P. which has 2 op-amp inside.

OK. The LM358's output swing over the full temp range is +VS-2V. So, if your +VS is 15v, the highest voltage your opamp can output is 13v. That would turn on Q1 hard, since Vbe would be about -2v. However, you say that your +VS is measuring 12v, so the highest the opamp can output is 10v. Due to this, Q1 is turned on hard (Vbe is about -5v), and you have no way to turn Q1 off.

So, you should have your +VS about two volts higher than the output of the regulator.

Since Q1 will begin to conduct when Vbe > about -0.6v, you might get by with having +VS just 1.4v higher than the output of the 7815. But to keep things simple, just go with the 2v above your 7815 regulator's output, or 17v.

 

BTW, you can use your original 7809 regulator to provide the higher +VS to the opamp.

Just add a 1.6k resistor between the 7809's ground lead and GND, and 3.4k resistor between the output and GND. Yes, you will need a 1uF capacitor on the output, and a 100nF cap across the opamp's supply leads.

 

Boy this tread has legs. I apologize for coming in so late, there are a few thinks I would like to comment on the circuit at reply #109
Although it is unothodox for a constant current constant voltage supply it should still work, it would all depend on how well regulated the output needs to be.
Wookie is absolutely right you will need a minimum of 2 volts between the OPamp supply and the line side of R1. keep the 7815 to feed the LM358 and add a 7812 (wish less that 10 volts out) to feed line side of R1 junction point then you will find that the current adjust pot will work.
The inverting input of U1 should be attached to the load side of R1. the way it is now the emmeter base junction is included in the feedback loop therefore the current output will be be temperature sensitive (~2.2mv per c).
Again on the voltage output the non inverting pin needs to be tied to the voltage output as close to the output voltage terminal as possible. A small capacitor 1uf shoould be paralelled with output.
The problem with having the voltage regulator in series with the current regulatoer is that the voltage regulator will add current to the circuit and the current will very somewhat under different loads.
Just remember when you are testing the circuit. If the current is below the set value of the current source then the voltage can be varied. once the current regulator is in control the voltage will not change until it is lowered below the amount need to drive the load at that current.

 

Boy this thread has legs. I apologize for coming in so late, there are a few thinks I would like to comment on the circuit at reply #109
Although it is unothodox for a constant current constant voltage supply it should still work, it would all depend on how well regulated the output needs to be.

Unfortunately, the more input at the later part of a thread, the more confusing it becomes for the original poster.

Wookie is absolutely right you will need a minimum of 2 volts between the OPamp supply and the line side of R1. keep the 7815 to feed the LM358 and add a 7812 (wish less that 10 volts out) to feed line side of R1 junction point then you will find that the current adjust pot will work.

This was more or less covered in my last post about using what our OP had along with some resistors. A 78xx series regulator requires a 5mA load to ensure regulation.

The inverting input of U1 should be attached to the load side of R1. the way it is now the emmeter base junction is included in the feedback loop therefore the current output will be be temperature sensitive (~2.2mv per c).
Again on the voltage output the non inverting pin needs to be tied to the voltage output as close to the output voltage terminal as possible. A small capacitor 1uf shoould be paralelled with output.
The problem with having the voltage regulator in series with the current regulatoer is that the voltage regulator will add current to the circuit and the current will very somewhat under different loads.
Just remember when you are testing the circuit. If the current is below the set value of the current source then the voltage can be varied. once the current regulator is in control the voltage will not change until it is lowered below the amount need to drive the load at that current.

I'm not feeling like sorting all of that out at the moment. Globbing a bunch of text together makes it very tiring for the reader.

Keep it to two or three sentences per paragraph.