Analogue Metric Shunt Reg problem

[Almeg69]

I have built the Analog Metric SR50 variable shunt regulator.
I need 12v and 5v output which I can get when under no load, but if I connect a 5R dummy load to the output it drops down to 2.1v for the 12v one and 1.9v on the 5v version.

Where have I gone wrong or is there a problem with the circuit ?

Many thanks, Alex.

 

[merlin el mago]

Possible you need more current, or more in/out voltage difference or tx with more power, etc....

 

[merlin el mago]

What resistor set the current: R1?

 

[merlin el mago]

Do you know your load power consumption?

 

[merlin el mago]

If you use dummy load 5R for 12V your power consumption is 2.4A & for 5V is 1A, it seems to much current, surely you need more power in your transformers if your power target is OK.

 

[Almeg69]

I have a link instead of the resistor, I was going to limit it later after testing.
I have a 100VA 15v transformer which rectified goes up to 25v at the base of Q2. I will need 2A for the 12v one and 1.5A for the 5v one.

 

[merlin el mago]

Do you use only one tx?
Do you know if the shunt regulator can give your load power consumption?

 

[Almeg69]

I have noticed that there is no voltage drop at Q2 base when the dummy load is applied

 

[Almeg69]

Do you use only one tx?

Yes, one TX with 2 off 15v secondary.

 

[merlin el mago]

I will try to change the jumper wire for R1 and use 1R or 10R and measure there what's happen with the current, also you can play using a lighter dummy load, that's only to know if goes ok with other requirements.

Are you sure shunt regulator can support 2A or 1.5A?

 

[Almeg69]

I will try to change the jumper wire for R1 and use 1R or 10R and measure there what's happen with the current, also you can play using a lighter dummy load, that's only to know if goes ok with other requirements.

Are you sure shunt regulator can support 2A or 1.5A?

I did put a 3.3R on the 5v one and 10R on the 12v one to limit the current then took them out when I could not get any more than 2v out.
The transistors are rated at 6A so should be OK.

 

[merlin el mago]

3R3 & 10R for R1 with 5R dummy load, if voltage drops it seems your shunt regulator can't afford the current you want and drops the voltage.

 

[Almeg69]

3R3 & 10R for R1 with 5R dummy load, if voltage drops it seems your shunt regulator can't afford the current you want and drops the voltage.

It just seems strange that the 5v 5R load is only 1A and still restricted to 1.9v out which is why I wondered about the circuit ….

 

[merlin el mago]

Do you have 15R or 20R dummy load to try?

 

[Almeg69]

Do you have 15R or 20R dummy load to try?

Just tried a 20R dummy load and I now have 5v. Q2 is running at 65ºC and Q8 is cold.

 

[merlin el mago]

That's because the difference in/out is 20V. Use the same 20R dummy load for 12V.

 

[Almeg69]

That's because the difference in/out is 20V. Use the same 20R dummy load for 12V.

I will get some more dummy load resistors and have another play tomorrow, Thanks for your help, much appreciated,
Kind regards,
Alex.

 

[merlin el mago]

OK Alex, it seems the reg can't handle the current load needs.
Cheers
Felipe

 

[Almeg69]

Can some kind sole give me a bit of an explanation how the circuit works especially Q1.
It is supposed to be adjustable from 5-50v and a max current of 8A.

The adjustment is after Q1 and 2 so I am a bit lost as to where do I start trouble shooting.

I am not an electronic engineer but have a good grasp of basic electronics and know how to use a multimeter and scope.

The AC transformer is 2 off 15v 100VA and I want to have 12v 2A and 5v 1A.

Many thanks, Alex.

 

[merlin el mago]

Manual said "Two fast power PNP transistor MJE15031 is used to act as current source" are you sure are well connected and not burned or position reversed?

Could you post pic of your work? have you visually checked all components are well positioned, etc....?