Series and Parallel Operations of Diodes: -
When working with electronic circuits, diodes are among the
most widely used semiconductor devices. They allow current to flow in only one
direction and block it in the other. Because of this property, diodes are
applied in rectifiers, clamping circuits, voltage regulation, and even signal
processing. In real-world applications, however, a single diode may not always
be sufficient to handle the required current or voltage. That’s when series and
parallel operations of diodes become important.
In this blog, we’ll explore how diodes behave when connected
in series and parallel, why such configurations are used, and what precautions
engineers must take in practical circuits.
1. Series Operation of Diodes
When diodes are connected end-to-end, i.e., the anode of one
diode is connected to the cathode of the next, they are said to be in series.
Why use a series connection?
The main reason for connecting diodes in series is to share
the reverse voltage. In high-voltage applications, a single diode may not
withstand the entire voltage stress. For example, if a diode has a maximum
reverse voltage rating (Peak Inverse Voltage, PIV) of 100 V, and the circuit
requires blocking 400 V, then at least four diodes in series are needed.
Voltage sharing issue
In an ideal world, the applied reverse voltage would be divided equally among all the diodes. But practically, each diode may have slightly
different reverse resistance and leakage current, leading to unequal voltage
sharing. If one diode takes more stress than the others, it may fail and cause a
chain reaction, damaging all diodes.
Solution – Balancing resistors
To solve this, engineers often connect resistors in parallel
with each diode (called voltage-sharing resistors). These resistors help
equalize the reverse voltage across each diode. Sometimes, small capacitors are
also added to handle fast-changing voltages in high-frequency applications.
2. Parallel Operation of Diodes
When diodes are connected side-by-side, i.e., all anodes
tied together and all cathodes tied together, they are in parallel.
Why use a parallel connection?
The main purpose of a parallel connection is to share current.
For instance, if one diode can carry a maximum of 1 A, and the load requires 3
A, then three diodes are connected in parallel.
Current sharing issue
In practice, the parallel connection of diodes faces the problem
of unequal current distribution. This happens because of slight variations in
diode forward voltage drops. Even a small difference of 0.1 V can cause one
diode to carry much more current than the others, leading to overheating and
possible failure.
Solution – Balancing resistors
To achieve proper current sharing, small resistors (called
current-sharing resistors) are connected in series with each diode. These
resistors introduce a small voltage drop that helps balance the current
distribution among all the parallel diodes.
3. Practical Considerations
Whether diodes are used in series or parallel, some
precautions must be taken:
- Matching diodes—Always use diodes of the same type and rating to minimize variations.
- Temperature effect—The forward voltage drop of diodes decreases with temperature. This can worsen the current imbalance in parallel connections.
- Derating—Engineers often use more diodes than theoretically required, operating them below their maximum ratings for safety.
- Protection circuits—Resistors, capacitors, and sometimes active balancing circuits are used for reliable operation in industrial power electronics.
4. Applications
- Series diodes: Commonly used in high-voltage rectifiers like X-ray machines, power transmission equipment, and industrial inverters.
- Parallel diodes: Found in power supplies, battery charging circuits, and devices requiring higher current output than a single diode can handle.
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| Multiple Diodes |
5. Summary
- Series operation is mainly for voltage sharing.
- Parallel operation is mainly for current sharing.
- Both require additional balancing resistors (and sometimes capacitors) for safe operation.
- Diode mismatches, temperature variations, and unequal load distribution are practical issues engineers must carefully address.
Final Thoughts
The series and parallel operations of diodes show us a key
principle of electronics: real components are not perfect. While the textbook
diode may look simple, practical usage demands careful design to ensure
reliability. Whether you’re working on a simple rectifier circuit or a
high-power industrial system, understanding how diodes behave in these
configurations helps in building robust and safe electronics.
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