Quick Question / Quick Answer? Regulators

[Space Varmint]

Hi, I am working on a prototype and I want to run a separate CE amp at 12 volts as a pre-driver. Well off hand I don't have a 12 volt regulator to work with my 13.6 volt power supply. Can I use a couple of 6 volt regulators and achieve the same results?

 

[k7elp60]

If your 6V regulator is a three terminal device, you can put a resistor from the output to the common lead and then a resistor from the common lead to ground. Be aware that the 1.6V input output differential may not be high enough for the 6V regulator, that is now a 12V regulator.

 

[Space Varmint]

If your 6V regulator is a three terminal device, you can put a resistor from the output to the common lead and then a resistor from the common lead to ground. Be aware that the 1.6V input output differential may not be high enough for the 6V regulator, that is now a 12V regulator.

OK, trying to follow this. Put a resistor from the output of the 1st regulator to the common of the second regulator? Then where would the 2nd regulator input pin be connected?

edit*

Oh, that would be from the power supply i think. Both input pins would be to the power supply. But I need a resistor huh? Let me try this.

 

[dougy83]

I think he was getting at using a single 6V regulator. Input and output are connected as usual. 2 series resistors then go from the output to ground, with the junction of the 2 resistors being connected to the regulator 'ground' pin. There is a few problems with this (due to the ~5mA quiescent current of many regulators) that can be overcome by using small resistors (so that the current through the resistors is >>5mA, or else the error will be quite large).

The other way, which should have better regulation is to connect the 2 regulators that you have as follows: both inputs to the 13.8V, ground of reg 'A' to the ground. 'ground' of the reg 'B' to the output of reg 'A'. You should also connect a resistor from the output of reg 'A' to ground to pass the quiescent current (plus a little extra) of reg 'B', so maybe a 560 ohm (note that general purpose regulators can't sink current).

Note that the regulator you're using may have an headroom requirement of more than 13.8-12=1.8V.

 

[Space Varmint]

OK cool! It works. I used 5 ohms. Actually I had a 6 volt regulator in the circuit that wasn't doing much work so I came off of that one with another 6 volt regulator and got my 12.

Thanks for help k7elp60

Say, are you a ham....WA4BJO here. I wor 40 meters a good bit but can work all bands.

 

[Space Varmint]

I think he was getting at using a single 6V regulator. Input and output are connected as usual. 2 series resistors then go from the output to ground, with the junction of the 2 resistors being connected to the regulator 'ground' pin. There is a few problems with this (due to the ~5mA quiescent current of many regulators) that can be overcome by using small resistors (so that the current through the resistors is >>5mA, or else the error will be quite large).

The other way, which should have better regulation is to connect the 2 regulators that you have as follows: both inputs to the 13.8V, ground of reg 'A' to the ground. 'ground' of the reg 'B' to the output of reg 'A'. You should also connect a resistor from the output of reg 'A' to ground to pass the quiescent current (plus a little extra) of reg 'B', so maybe a 560 ohm (note that general purpose regulators can't sink current).

Note that the regulator you're using may have an headroom requirement of more than 13.8-12=1.8V.

Oh, didn't see your post at first. I did it the second way but I only have 5 ohms. I figured it should be small and I need about a 1/2 watts of power. So I had some 10 ohm quarter watts and paralleled them. Seems OK. Still have to make the amp I want to run off of it. I might end up needing more power so I figure I could put another one or two 10 resistors in parallel. I got to feed two 11 watt push-pull transistors but don't think I will need the full 11 watts. Hope not but they will be driving two push-pull 100 watters. Their all matched pairs. Wish me luck...lol.

 

[Hero999]

I don't see the problem, if you design your circuit correctly it should work from 13.6V as well as 12V. If it's going to be run from a lead acid battery then you should design it so it works from 10V to 15V with optimum performance between 11V and 13V.