Can a diode be used to lower voltage

[TheOhmBreaker]

I've been pondering something pretty straightforward,but now I'm starting to think I might be overlooking something.Can you use a diode to reduce voltage?I get that diodes mainly manage the flow of current,but I'm curious if they can also decrease the voltage in a circuit.I'd love to hear any thoughts or insights on this

 

[Robert Hayward]

I'm sure that diodes introduce a voltage drop across them. That's part of what makes them useful in gnarly analogue filter circuitry..

 

[barfle]

I've been pondering something pretty straightforward,but now I'm starting to think I might be overlooking something.Can you use a diode to reduce voltage?I get that diodes mainly manage the flow of current,but I'm curious if they can also decrease the voltage in a circuit.I'd love to hear any thoughts or insights on this

Silicon diodes, when operated in their rated range and forward:biased, typocally drop 0.6 to 0.7V. They aren’t necessarily linear, so if you’re using one to couple analog circuits, you may have other issues.

 

[computerlen]

There are also diodes called zener which have set voltages where they conduct.

 

[paolor]

Yes, diodes drop a predictable 0.7 V. I have a Superphon preamp (Stan Warren for those of you that are familiar with PS Audio) that uses diodes for predictable voltage references. Cheap maybe not the best way to design but effective.

 

[alan-bc]

Yes, diodes drop a predictable 0.7 V. I have a Superphon preamp (Stan Warren for those of you that are familiar with PS Audio) that uses diodes for predictable voltage references. Cheap maybe not the best way to design but effective.

Diodes do NOT drop a predictable .7v .. the drop is dependent upon the temperature, the current going through it and mostly, the characteristics of the diode itself.

If you look at the datasheet for the ubiquitous 1n4001, you'll see a forward drop of .6v at very low current (10 ma), up to 1.8 volts at a peak maximum (short term) current, measured at 25 degrees C.

Looking at the datasheet for a 1n5817, you'll see a Vf ranging from .32v to .75 volts over a range of ma to 3 amps, again measured at 25 C.

So, a diode CAN be used to drop voltage, but it's an inelegant way to do it and the voltage dropped is non-linear. Moreover, it's important to calculate dissipation. Many small package diodes, run near their maximum current, dissipate more heat than their package can get rid of in still air.

Note that the temperature dependent Vf can be used to advantage. Many transistorized hifi amps have a diode in the bias circuit of the output stage, thermally coupled to the heatsink. Should the heatsink start getting hot, the changing Vf will be used to compensate.

Finally, a diode for a voltage reference is generally considered to be a spectacularly bad idea. Quite aside from the non-linear temperature dependent behavior mentioned above, they are also electrically "noisy" .. kinda exactly what you don't want in an audio product. When such a drop is desired, often the emitter/base junction of a small signal transistor is used instead; similar drop, less noise.

 

[francsxz39]

I've been pondering something pretty straightforward,but now I'm starting to think I might be overlooking something.Can you use a diode to reduce voltage?I get that diodes mainly manage the flow of current,but I'm curious if they can also decrease the voltage in a circuit.I'd love to hear any thoughts or insights on this

I think how @alan-bc explained it here is not only good but also important. The 0.7V is just a rule of thumb and not a precise, constant value. The dependence on current, temperature, and specific diode characteristics is crucial, and those datasheet examples really drive the point home. The discussion about dissipation and using the temperature-dependent Vf in amplifier bias circuits is particularly insightful. And yes, for any kind of precise voltage reference or in noise-sensitive applications, a diode drop is definitely not the way to go. The B-E junction tip is a great alternative

 

[ohmsweetohm761]

Agreed. That breakdown got the subtle stuff right, like how temp and flow mess with things

 

[lupo_audio]

A typical silicon P/N diode (or BE-tips of an BJT) exhibits a poor, but in some cases sufficient voltage reference which is used in several electronic circuits (also bipolar integrated circuits like OP-Amps). The intrinsic voltage drop in silicon is approximately 0.7V with an almost linear temperature coefficient of -2mV/Kelvin. It is important to maintain a temperature matching between diffentt pn diodes in order to get matching reference voltages! The voltage drop is a logarithmic function of the diode current over several decades of current density. Voltage drops of the contact resistances (and also the diffusion regions next to the pn junction) are involved if the voltage drop of an silicon diode is much larger than 0.7V - these voltage drops introduce different temperature coefficients. Better to use an LED as a reference voltage source - lower temp depency and steeper V/C characteristic. Best choice is of course a shunt bandgap reference circuit which behaves like a diode with constant drop.

 

[Shiminet]

Hey there! @TheOhmBreaker You can technically drop voltage with a diode, but as others mentioned, it's not precise and depends heavily on current and temperature. For anything critical, a transistor B-E junction or a proper voltage reference is way more reliable.

 

[voltagepathmaker]

Diodes do NOT drop a predictable .7v .. the drop is dependent upon the temperature, the current going through it and mostly, the characteristics of the diode itself.

This is really well explained, and I completely agree. Diodes just aren't dependable when it comes to voltage reference, and your examples make that very clear.

 

[Orph@n]

Diodes are fine when you just need a little voltage drop that doesn't change, but if you need to drop the voltage by a lot, they're not your best bet.

 

[Kim Isanan]

Unlike resistors, diodes don't drop voltage evenly with current. They're not great for cutting voltage in big drops or powerful circuits. Voltage regulators or buck converters do a much better job.

 

[capacitorkid]

Absolutely, diodes can lower voltage, but they aren't the best choice for applications that require precision or involve high currents. The voltage drop across a diode changes based on the current flowing through it and the temp, which means it's not consistent. Plus, relying on them to reduce significant voltages could lead to inefficiencies and excess heat generation.