High Power DAC for SM-10 (0-1000VDC)

[Jdo300]

Hello All,

I have this High voltage IC I purchased from Gamma high voltage here:

http://www.gammahighvoltage.com/html/series_sm.htm

The one I bought, the SM-10, takes a variable input from 0 to 12VDC and generates an output from 0 to 1000VDC.

I want to find the simplest way to digitally control the input voltage so that I can throttle this IC using a microcontroller. The simplest thing I can think of is a DAC, but I don't know if there are any out there that are capable of driving the chip. The datasheet says that the maximum input current is 85 mA but for my application, I measured the input current to be only about 30 mA. Does anyone know if there is a DAC out there that can supply this much output current at 12V?

If not, my other thought was to use a regular DAC with an Op-amp to scale the output voltage and current, but I just thought I would run the question past you all before going that route.

Thanks,
Jason O

 

[berkeman]

Just make your own R-2R ladder DAC and drive it with the uC IO pins. Then follow the DAC with an amplifier to get your 12V power output.

http://en.wikipedia.org/wiki/Resistor_Ladder

 

[Jdo300]

Hi Berkeman,

Hmm that's the first time I've heard of an R-2R ladder. Looks pretty useful. That would work quite well for my application but unfortunately, I only have three available IO pins to dedicate to this part of the circuit. I was going to use a SPI compatable DAC so that I can get 10 bits of resolution on the output voltage. I was thinking about using the AD7390 10-bit DAC but I'm still looking around for an op-amp that can source the amount of current I need. So far, I keep finding ones that are either too wimpy or to beefy for my application. The best one I found so far is the LT1206 but I'm not sure if it is okay for it to source a constant current (aparently, it's used as some kind of video amplifier). Would you happen to know of any good op-amps that can do at least 30mA @ 12V? Preferably something that isn't in a metal can would be nice since I don't have much room on the board I'm mounting it on.

Thanks,
Jason O

 

[berkeman]

Sounds like you have the DAC covered. You didn't mention the frequency range of this circuit -- if it's audio, you could just use an audio amp module for the post-DAC amplification. I used to use some audio amp modules (like big ICs with heat sinks) from National Semicondoctor, but I don't have any current part numbers. You could probably find them quickly with a search at National Semi's website.

Alternately, just use a regular opamp, and add some BJTs in as a linear amp at the opamp's output, and close the feedback around the whole shebang.