Regulated power supply that switches between two values

[kukurio]

I'd like to make a power supply that takes in two DC inputs and either adds them together or just puts out one of them, depending on the logical value of an additional gate input. (Essentially, one of the inputs represents a DC offset and the other represents a gated AC.) The output voltage range should be 0-20 V and 0-2 A. I thought I'd be able to do this with a MOSFET, but I'm not really a circuits guy and hit a dead end when I realized that power FETs aren't really bidirectional, so a strong source-to-drain voltage will also conduct when the gate is off.

I saw on Digikey that there are diode laser drivers that can do something like this, but the currents are too low, probably because the frequency at which they switch is ridiculously high for my application (> 10 Gbps, when I need ~100 kHz). Does anyone have any ideas for a circuit that can do this? Alternatively, is there an IC type that already does this whose name I am just unaware of? I'm very overwhelmed by Digikey's selection. Thanks.

 

[karesz]

Gated power supply

Hi,
In my opinion your need is basically a regulated power supply with two extreme values_am I right?
Is your switching rate really at 100KHze, & what kind of regulation(stabilization) grad is to have?
K.

 

[kukurio]

Re: Gated power supply

Yeah, a regulated power supply that switches between two values sounds about right. 100 kHz is the fastest I'll be switching it, but the voltage values don't need to be that stable or accurate. (I'll be controlling the values from external DC supplies manually.)

Added after 7 minutes:

I was thinking about using this op-amp in a simple non-inverting adder configuration with one of the inputs tied to a FET, but I'm not sure it will work. It can certainly supply the current I need at the frequency I need, but I don't know if it can supply the voltage. When they say that the output is 4.1 V at I0=3 A, are they referring to the maximum voltage it will supply?

 

[karesz]

Gated power supply

Yea, it must work!
the SR is (at 1.5Vp=10V/us), hopfely by 20V is similar high speed & so is enough speedy for your application.
Otherwise are by Micrel very speedy regulators in program; I think their are more cheap as a special power OpAmp...
By Op solution too; you have only to switch the feed back voltage, also take different resistance values in the feedback: it is a really good usage for a FET.
It can switch on/off the second resistor parallel to the first or even make short one resistor from two serial resistors...
K.

 

[karesz]

Gated power supply

Hi,
Maybe you can use these (or similar)modern component, ADG819/820, has typ. ca. 0.5 Ohm! & is logic level controlled,SOT23-6 packaged :
https://www.analog.com/en/switchesmultiplexers/analog-switches/adg819/products/product.html
K.