Improving Diode Functionality: Forward and Reverse Bias Optimization

Diodes have many different uses and are essential components of electronic systems. Integrated circuits contain thousands of diodes that regulate signals and logic on a single chip. On the other hand, Zener Diode has its uses as PCB components.

Although diodes are rather simple, there are certain situations in which they can be quite useful in electrical systems, and this can only be achieved with a thorough knowledge of their electrical behaviour. Reviewing the two primary functions of diodes—forward bias and reverse bias diode—provides a foundational understanding of the device. You need to know how these operations differ to pick the right diode for the job.

Diode bias: what is it? Biasing Conditions

Diodes are non-linear devices with two nodes; the voltage applied across their anode and cathode causes the device’s electrical behaviour to change. Both forward bias and reverse bias emerge due to this non-linear behaviour.

A diode can function as a switch in electrical circuits when its anode is linked to a positive voltage source and its cathode to a negative voltage source; this configuration is known as forward bias.

On the other hand, in reverse bias diode, electronic circuits are protected against transient voltages because current cannot flow through the diode when the anode is linked to a negative voltage source and the cathode to a positive voltage source.

In electronic system design and implementation, familiarity with the many diode operating modes might be crucial. Except for catastrophic failure, the bias of diodes shouldn’t alter abruptly. The diode’s application should sync with the anticipated bias, which should be forward or reverse by design.

The Functions of Diodes

When operating in forward bias mode, a diode maintains a nearly off state and passes almost little current when the applied voltage falls below a certain threshold, called the device’s Vt. The datasheet for a diode will have the Vt characteristic, which is manufacturing and application-dependent. Typical range for Vt is 0.3V to 0.7V.

Diodes function as switches, enabling uniform current flow when the applied voltage exceeds Vt. A current-limiting resistor is often connected in series with the diode if the applied voltage exceeds Vt to avoid diode overheating in forward bias mode.

There is also a reverse bias mode as opposed to the forward bias mode. A reverse bias diode involves delivering a voltage higher than the anode to the cathode, the negative terminal.

When the applied voltage drops below a particular point, the diode cuts off all current flow at reverse voltage breakdown (Vbr). A reverse breakdown occurs when voltage exceeds Vbr, allowing current to flow in the opposite direction. Vbr is usually greater than Vt in forward bias mode, ranging from -15V to -20V.

Forward Bias vs. Reverse Bias

Diode functionality and forward bias

Diodes work best in forward bias mode in electronics. Many uses for diodes in this mode include: 

• Reducing the impact of transient signals
• Voltage clamping 
• AC/DC power correction 
• Current steering 
• Voltage source switching

LEDs are common electronic indicators made of forward bias diodes. Diodes limit signals, power domains, and grounds to 0.3V to 0.7V over their maximum voltage to prevent overvoltage.

Reverse bias and diode performance

The reverse bias diode inhibits current until Vbr is quite high. 10w zener diode purposefully has a reverse bias. This electrical device reduces power supply domain transients due to its 5V to 6V breakdown voltage.

Standard diodes can be operated in reverse bias mode, but their high breakdown voltage is too high for most power supply domains.

Tips for Creating an Effective PCBA

Consider the diode function when designing your system circuit. Forward bias inhibits transient voltage occurrences in signal, power domain, and ground protection. The diode’s non-linear behaviour and normal and excursion operation must be understood.

Due to the diode’s non-linear nature, knowing what system conditions cause the current to flow above Vt and not below Vt is crucial.

The forward bias voltage drop varies substantially per diode type. Some light-emitting diodes (LEDs) can drop up to 4 volts, but Schottky diodes usually lose about 0.2 volts. An extreme voltage drop can restrict the circuit, causing problems.

Model this possibility regardless of whether the current flow is normal or during an excursion because the diode can mistakenly turn on or off and perform outside its intended range. However, Vbr voltage and reverse bias necessitate the same considerations.

Conclusion

Discrete diode, often known as Zener Diode, has several real-world applications in electrical system design. Think about the application and the function the diode needs to do first. Second, find out if the diode needs a forward or reverse bias. Finally, make sure the use cases work as expected by testing for excursions that could alter the diode’s bias or cause a change in the current flow’s state. Collaborate with your contract manufacturer when choosing diodes for your board of measurement (BoM) and other use cases that could improve your design’s performance.