What is a Switching Diode : Working & Its Applications

A diode is one kind of semiconductor device which includes two terminals like an anode and a cathode. The main function of the diode is to allow the current flow in one direction only because it has less resistance in one direction & high resistance in another direction. Semiconductor diodes were the first semiconductor electronic components. At present, most diodes are made of silicon and also other semiconducting materials like germanium (Ge) and gallium arsenide (GaAs). There are different types of diodes available in the market which is used based on the applications. So, this article discusses one of the types of diodes namely – a switching diode, working with applications.

What is a Switching Diode?

Switching Diode Definition is; a diode that has a switching function known as a switching diode. This diode is specially designed for ON & OFF on a circuit. So, once a voltage supply is given in the forward direction then it supplies current and it stops the current supply when a voltage supply is given in the reverse direction.

As compared to other types of diodes, this diode’s reverse recovery time is short which means the time taken from the ON state to the completely OFF state is very short. The common series of switching diodes are 2DK, and 2Ak which are used in switching circuits, electronic computers, etc. The switching diode symbol is shown below.

Switching Diode Working Principle

The working principle of switching diode is, that once a specified voltage is increased then the resistance of the diode will be increased. So the diode is reverse biased, so it acts as an open switch. Similarly, when the applied voltage is under the reference voltage then the resistance of the diode will be reduced so the diode is in forward biased, so it acts like a closed switch.

Specifications

The specifications of the 1N4148 switching diode include the following.

Forward Voltage ranges from 0.4 – 1.2V based on forward current.
The reverse breakdown voltage is 100V.
Diode capacitance is 4pF.
The peak forward surge current is 4A.
The repetitive peak forward current is 500mA.
The average forward current is 200mA.
Repetitive peak reverse voltage is 100V
The reverse voltage is 75V.
Power dissipation is 500mW.
Weight is 0.1g.
DC forward current is 300 mA.
The maximum reverse-recovery time (trr) is 4 ns.
The recurring peak forward current is 400 mA.
The maximum forward voltage is 1 V at 10 mA.
Breakdown voltage (Max) & reverse leakage current is 75 V @ 5 μA and 100 V @100 μA.
Non-repetitive peak forward surges current is 1Amp at 1-sec pulse width and 4 Amp at 1 μs pulse width.

Switching Diode Vs Zener Diode

The difference between switching diode and Zener diode includes the following.

Switching Diode	Zener Diode
The Switching diode allows the flow of current in only one direction.	Zener diode allows the flow of current in a forward and reverses direction once the reverse voltage is over a certain value.
The example of a switching diode is 1N4148.	The example of a Zener diode is 1N5225.
This diode is applicable in switching a small signal and also it works as a rectifier.	Zener diode is applicable in voltage regulation, surge suppressors, clipper circuits, and switching applications.
The current handled by switching diode is up to 100 mA.	The current handled by the Zener diode is approximately 5 – 10 mA.
These diodes handle voltage below tens of volts.	These diodes handle voltage between 0.3 & 0.7 V.

Switching Diode Circuit & Its Working

The switching diode circuit using the VD1 diode is shown below. In the following circuit, S1 is the switch, VD1 is the switching diode, and L1 & C1 can form a parallel LC resonant circuit. The main purpose of this switching diode circuit is to control the resonance frequency for the LC parallel resonance circuit. The following switching diode circuit works in two conditions when the switch is turned OFF (open) and turned ON (closed).

Once the S1 switch is open, the DC voltage cannot be supplied to the switching diode’s positive terminal. At the moment, the switching diode is cut off & the resistance between the two terminals of the diode is high. Thus ‘C2’ capacitor cannot be connected to the switching circuit because VD1 is an open circuit. Here, L1 & C1 are connected in parallel to form an LC circuit.

Similarly, once the ‘S1’ switch is closed, then the DC voltage is supplied to the positive terminal of the VD1 diode through R1 to switch on VD1. So, the resistance between the two electrodes is extremely small. So, the C2 capacitor is connected in parallel with the resonant circuit.

In the above two conditions, because of the dissimilar capacitances within the LC parallel resonant circuit, the LC parallel resonant circuit’s resonance frequency is different. So, the VD1 diode in the switching circuit controls the resonance frequency of the LC circuit.

The signal within the LC parallel resonant circuit is included in the diode’s positive terminal throughout C2. But due to the signal’s amplitude within the circuit being fairly small, the amplitude of the positive half-cycle signal given to the positive terminal of the switching diode is extremely small & will not make the diode conductive. From the above switching circuit analysis, we can observe that the switching diode ‘VD1’ works as a switch.

Switching Diode Characteristics

The characteristics of switching diodes mainly include the following.

Turn-on time

The time taken to turn on the switching diode from the cut-off is known as turn-on time. When this time is shorter then it is better.

Reverse Recovery Time

Once the switching diode is activated then the forward voltage can be detached. The required time for the switching diode to off from ON is known as the reverse recovery time. In general, this time is greater as compared to the turn-on time.

Switching Time

The switching time is the sum of both the turn-on time & reverse recovery time.

The switching diode’s switching speed is quite fast. The reverse recovery time of the Ge switching diode is a few hundred nanoseconds whereas the Si switching diode has a few nanoseconds.

Once the forward voltage is provided to the two terminals of the switch, then the switching diode is said to be it is in the on-state, so that is equal to the ON state of the switch. Similarly, when a reverse voltage is provided to this diode, then the diode is said to be it is in the off state, which is equal to the OFF state of the switch.

The switching diode uses this main feature for faster and better switching speed characteristics, smaller internal resistance throughout conduction, higher resistance once-off & the small junction capacitance of the PN-junction.

Types of Switching Diode

Switching diodes are available in different types such as; ordinary switching diodes, ultra-high-speed switching diodes, high-speed switching diodes, high back-pressure switching diodes, low-power switching diodes, and silicon voltage switching diodes. The package form of these diodes is plastic and switching.

Ordinary Switching Diode

The ordinary switching diodes are commonly used diodes which are 2AK series germanium switching diodes like 2AK1 to 2AK6, 2AK7 to 2AK10, and 2AK11 to 2AK14. The main parameters of these series diodes are discussed below.

For 2AK1 to 2AK6 Series Switching Diodes

The forward voltage is 1V.
Forward current is 100 to 200 mA.
The maximum reverse working voltage is 10 to 50V.
Reverse breakdown voltage is 30 to 75V.
Reverse recovery time is 300 to 150 ns.
Junction capacitance ≤ 1.

For 2AK7 to 2AK610 Series Switching Diodes

The forward voltage is 0.45V.
Forward current is 10 mA.
The maximum reverse working voltage is 30 to 50V.
Reverse breakdown voltage is 50 to 70V
Reverse recovery time is 150 ns
Junction capacitance ≤ 1.

For 2AK11 to 2AK14 Series Switching Diodes

The forward voltage is 0.8V.
Forward current is 250 mA.
The maximum reverse working voltage is 30 to 50V.
Reverse breakdown voltage is 50 to 70V.
The reverse recovery time is 150 ns.
Junction capacitance ≤ 1.

High-speed Switching Diodes

As compared to general switching diodes, these diodes have a shorter reverse recovery time and also have faster ON & OFF frequencies. The most commonly used high-speed switching diodes are the 1N series, 2CK series, 1S series, RLS series & 1SS series. The 1SS series diodes are available in a leaded plastic package and the RLS series are surface mount. Some of the 1N series switching diodes’ main parameters are discussed below.

Series	Max reverse working voltage in Volts.	Reverse current uA.	Reverse breakdown voltage in Volts.	Forward current in mA	Forward voltage drop in Volts	Package	Reverse recovery time in ns	Zero bias capacitance pF
1N4148/1N914	75	0.025	100	150	1	DO-35	4	4
1N4149/1N916	75	0.025	100	150	1	DO-35	4	2
1N4150/1N3600	50	0.01	60	200	1	DO-35	6	2.5
1N4151/1N3604	50	0.05	75	150	1	DO-35	2	2
1N4152/1N3605	30	0.05	40	150	0.88	DO-35	2	2
1N4153/1N3606	50	0.05	75	150	0.88	DO-35	2	2
1N4154	25	0.1	35	150	1	DO-35	2	4
1N4446/1N914A	75	0.025	100	150	1	DO-35	4	4
1N4447/1N916A	75	0.025	100	150	1	DO-35	4	2
1N4448/1N914B	75	0.025	100	150	1	DO-35	4	4
1N4449/1N916B	75	0.025	100	150	1	DO-35	4	2

Ultra-high-Speed Switching Diode

The most frequently used ultra-high-speed switching diodes are the RLS series which are available in surface packages and the 1SS series available in a leaded plastic package.

Series	Package	Reverse recovery time in ns	Forward voltage drop in V	Reverse breakdown voltage in V	Max reverse working voltage in V	Forward current in mA	Reverse current in uA	Zero bias capacitance in pF
1SS92	DO-35	2	1	75	65	200	0.5	3
1SS93	DO-35	2	1	55	50	200	0.5	3
1SS136	DO-34	2	1	75	65	200	0.5	3
1SS137	DO-34	2	1	55	50	200	0.5	3
RLS92	LL-34	2	1	75	65	200	0.5	3
RLS93	LL-34	2	1	55	50	200	0.5	3

Low Power Switching Diode

These types of diodes have less power consumption, however, their reverse recovery time & zero-bias capacitance values are low as compared to high-speed Switching Diodes. The most frequently used low-power switching diodes are the 1SS series available in the leaded plastic packages & RLS series available in a surface package.

Series	Package	Reverse recovery time in ns	Forward voltage drop in V	Reverse breakdown voltage in V	Max reverse working voltage in V	Forward current in mA	Reverse current in uA	Zero bias capacitance in pF
RLS139	LL-34	50	1.2	90	80	130	0.02	5
RLS140	LL-34	50	1.2	55	50	120	0.01	5
1SS139	DO-35	50	1.2	90	80	130	0.02	5
1SS140	DO-35	50	1.2	55	50	120	0.01	5
ISS290	DO-34	50	1.2	90	80	130	0.02	5
ISS291	DO-34	50	1.2	55	50	120	0.01	5

High Backpressure Switching Diode

The reverse breakdown voltage of these diodes is above 220Volts; however, its reverse recovery time value & zero bias capacitance are fairly large. The most frequently used high backpressure switching diodes are the 1SS series available in the leaded plastic packages & RLS series available in the surface packages.

Series	Package	Reverse recovery time in ns	Forward voltage drop in V	Reverse breakdown voltage in V	Max reverse working voltage in V	Forward current in mA	Reverse current in uA	Zero bias capacitance in pF
RLS245	LL-34	75	1.5	250	220	200	10	3
1SS142	DO-35	400	1	300	300	200	0.5	10
1SS143	DO-35	400	1	250	200	200	10	10
1SS145	DO-34	400	1	300	250	200	10	10
1SS146	DO-34	400	1	250	200	200	10	10
1SS244	DO-35	75	1.5	200	220	200	3	3
1SS245	DO-35	75	1.5	250	220	200	3	3

Silicon Voltage Switching Diodes

These are a new kind of semiconductor devices, which are divided into unidirectional voltage & bidirectional voltage switching diodes. These types of diodes are applicable in different circuits like overvoltage protection, flip-flops, high-voltage output, pulse generators, electronic switches, delay, etc.

Unidirectional voltage switching diodes are also known as turning diodes which include silicon semiconductor materials and a four-layer PnPN structure. The positive and negative direction switching characteristics are not the same. The bidirectional voltage switching diode includes a five-layer NPnPN silicon semiconductor material where its negative resistance switching characteristics for both forward & reverse directions are similar.

Series	Inrush Current in A	Hold current in mA	Cornering voltage in V	Turn ON Current in mA	On stage voltage in V	On stage current in A
K130 (Unidirectional)	10	100	120 to 140	0.2	1.5	1
2CTK (Bidirectional)	20	100	80-300	0.2	1.5	1

Switching Diode Advantages

The advantages of switching diodes mainly include the following.

Fast switching speed.
Small size.
Long life.
High reliability.
Better performance.
Less noise.
Fast recovery time.
Operates in harsh environments.
It is appropriate for small signal switching up to 100 mA.

Applications

The applications of switching diodes mainly include the following.

Switching diodes are used in different circuits like Switching, Detection, High-frequency, Pulse rectification, and Automatic control circuits of electronic equipment.
These diodes are used in voltage clamping, high-speed rectifying & switching circuits.
Used as a rectifier in switched-mode power supplies.
Reverse current & discharge protection.

Thus, this is all about an overview of switching diodes and it’s working. This diode is used in discrete systems and it operates within switching configurations. Based on the application, this diode can also work as a simple rectifier diode, detection diode, or transient-voltage-suppressor. Here is a question for you, what are the drawbacks of switching diode?

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What is a Switching Diode : Working & Its Applications