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I have a 12VDC @50mA_Max supply line. I need to inject a +2V 50us offset pulse to the +12VDC line, having an effective +14V for 50us.

I have access to an external power supply, where I can have higher voltages.

What would be the best way to achieve this?

I was thinking about just generating +14VDC and joining both lines with a P-Channel Mosfet for 50us. The +14VDC would be able to supply more current than the +12VDC line so it should be able to inject the extra +2V. However, I think there must be a more elegant way of doing it.

Thanks

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  • \$\begingroup\$ This is not quite clear, so maybe this answer can't apply to your case but have a look at electronics.stackexchange.com/questions/240911/…. \$\endgroup\$ – dim Jun 26 '16 at 19:11
  • \$\begingroup\$ What about using a decent low ESL capacitor to couple in the pulse? that way you only need to generate a 2V pulse which the capacitor will allow you to superimpose on the power supply's output. capacitive coupling allows you to couple AC stuff (fast pulses included) while isolating the DC components (i.e. keeping the 12Vdc out of whatever pulse generator you're using without affecting the pulse) \$\endgroup\$ – Sam Jun 27 '16 at 0:26
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How about using diodes?

The only downside would be a small voltage drop (0.3V if you use schottky)

schematic

simulate this circuit – Schematic created using CircuitLab

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Use an inductor. Connect one end to 12V and the other to a transistor and limiting resistor. Turn on the transistor to let current through and then when you turn it off, you will get a "kickback" of current in the opposite direction which will have no where to go and thus it will (depending on the load impedance) create a spike in voltage. This spike will be greater than 12V. With enough current it could be a LOT higher than this. Use an LED w/ 2V drop to clip the spike limiting it to 2V. Vary source and load resistances to control the spike. Use a capacitor to critically dampen the ringing so that the offset is nice and flat. I cannot tell you what the circuit would look like off-the-top-of-my-head but LTSpice could be used to devise a circuit.

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