Hello from Germany,
I am looking for an ultra low noise voltage regulator with 24V (and -24V) output. Would it be possible to cascade two LT3042/3045 (and the same with LT3094) which are set to 12V output to get 24V? Like two batteries added serially.
You can achieve 24VOUT by combining positive and negative low noise LDOs, even if the abs. max. ratings of the LDOs are less than 24V.
To illustrate the idea, the simulation results in the image below show a positive LT3042 combined with a negative LT3090. I used the LT3090 LTspice model since the LT3094 model is not available at the moment. I inserted the corresponding LTspice file as well. The actual hardware will most likely work with a single input supply, but the simulation only worked with a split input supply - check startup carefully if you use a single input supply. Demonstration circuits DC2246B and DC2624A are available for the LT3042 and LT3094 respectively, so it should be easy to get this circuit running with hardware.
Many thanks, that helps a lot. Please allow two more questions:
1) LT3042 and LT3090 can output 200mA each. So this 24V circuit delivers 400mA @ 24V?
2) What must be changed/inverted to get an output of -24V? I need +/-24V
Thanks in advance
The LT3042 is a 200mA part and that limits the above circuit to a maximum of 200mA output current. You can use the 500mA LT3045 instead of the LT3042, and that will increase the output current capability of the circuit. There is no LT3045 LTspice model at the moment, but the concept is the same.
If V1 and V2 are floating supplies in the circuit above, you simply ground OUT- to achieve a positive +24V output and you ground OUT+ to achieve a -24V output.