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LM2674: Buck regulate a positive and negative Vout

Part Number: LM2674
Other Parts Discussed in Thread: LM22674, LMR50410, LMR33610

Looking to make a pair of adjustable output voltage buck regulators (from a microcontroller)

Vin = +24v, Vout = +10 to +18v, Iout = 100mA (max.), AND separately

Vin = -24v, Vout = -10 to -18v, Iout = -100mA (max.)


a) For the positive, looks like LM2674 should work (although current limit is too high). Any other suggestions?

b) Is there a clever circuit to use the same buck regulator part number (but a second copy of that IC) for the negative regulation also? I plan to regulate Vout+ and Vout- independently of each other by the microcontroller.


  • Hello

    The LM2674 is OK for your application.

    Other devices you might consider are the LM22674, LMR33610, LMR50410

    I have attached some information about using a uC as a DAC to adjust your Vout. (you may need a filter if you are using PWM from the uC)

    If you have a -24V rail, then the simplest thing to do is to use a negative linear regulator for your negative Vout.

    You can use an ordinary buck as an inverting converter (IBB).  You would use your +24V rail and convert to your negative Vout.

    However, it is somewhat tricky to do the DAC with an IBB.  You will need level shifting.

    I have attached some information on the IBB that may be helpful.




  • Frank

    Excellent inputs on this. A few comments:

    a) I prefer not to use +24v to also generate the negative output rail. I prefer to use the -24v rail to generate the negative Vout. I have a lot of these regulators in the system, and I want to balance current loads on the +24v and -24v supplies (if possible).

    b) Regulating the negative voltage with a microprocessor should be easy since I plan to use PWM from the micro, and this can be AC coupled. I prefer to stay away from a DAC to control the output. Also, I will probably implement a feedback loop to the micro (which has a lot of 10-bit ADC inputs) to tightly control +Vout and -Vout (using perhaps an inverting op-amp).


  • Hello

    OK.  I will close this post for now.

    If you would like us to review your final design, don't hesitate to contact us.