# What do the following circuits do

#### beggi9

Joined Mar 3, 2016
42
Explain how these circuits work ( see photo), assume that the diodes have a voltage drop of 0.7V.

In b) I'm fairly certain that the diodes would limit the voltage across Rload to 1.4 volts with respect to ground.

In a) i'm more confused, my first thought was that it would work as a negative limiter if the voltage (Vin) is lower than -1.4V and would limit Vout (over Rload) to -1.4V. But as Vin is DC I'm not sure, maybe the diodes are never forward biased so then the circuit functions as a simple R1 - Rload voltage divider and the diodes never come into play.

Any tips well appreciated!

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#### #12

Joined Nov 30, 2010
18,224
I believe you are correct.

#### WBahn

Joined Mar 31, 2012
29,175
Explain how these circuits work ( see photo), assume that the diodes have a voltage drop of 0.7V.

In b) I'm fairly certain that the diodes would limit the voltage across Rload to 1.4 volts with respect to ground.

In a) i'm more confused, my first thought was that it would work as a negative limiter if the voltage (Vin) is lower than -1.4V and would limit Vout (over Rload) to -1.4V. But as Vin is DC I'm not sure, maybe the diodes are never forward biased so then the circuit functions as a simple R1 - Rload voltage divider and the diodes never come into play.

Any tips well appreciated!
Your thinking is good. Ask yourself what might happen if someone plugged in the DC source backwards.

Also, if Rload is inductive, the diodes will contain the back emf (the "kick") when the voltage source is turned off (or removed). That may be beyond where your studies have gotten you so far.