Technical Introduction | What is Push-pull Output

In the field of electronic engineering, there are many specialized terms related to circuit design. Today, let's understand what "Push–pull output" is.

Concept Explanation

Push–pull output is a circuit that uses a pair of devices to selectively source current to or sink current from a connected load. It often uses a pair of power transistors or MOSFETs with matching parameters, working in a push-pull manner within the circuit. In operation, only one of the two symmetrical switches is turned on at any given time, allowing the output to either source current to or sink current from the load. The push-pull output stage can both improve the circuit's load capacity and enhance switching speed.

Simply put, push-pull output can output both high and low levels, and it has driving capability at both levels.

Example: Bucket and Valve

To illustrate this concept more clearly, let's look at a simple example of how push-pull output works and how it differs from PNP output.

PNP Normally Open Output

Imagine a large bucket filled with water with a control valve at the bottom. This setup can be used to analogize the working of PNP normally open output:

• Valve Closed State: By default, the bottom valve is closed, preventing water from flowing out of the bucket. This is similar to a PNP transistor remaining off when no activation signal is received, blocking current flow.


• Valve Open Operation: When you need to empty the bucket, you open the bottom valve. This is akin to a PNP transistor turning on when a low-level signal is received, allowing current to flow from the load back to the transistor, performing some operation.

This method of controlling water flow allows you to quickly and effectively drain the bucket when needed, similar to how PNP normally open output activates only when necessary. Such control mechanisms are suitable for systems that need to prevent operation in a safe or default state until a specific signal is received.

Push-pull Output

Now, imagine the same large bucket with both a top valve and a bottom valve. The top valve controls water intake, while the bottom valve controls water discharge. This setup is similar to the working of push-pull output:

• When you open the top valve, water flows into the bucket through a pipe, similar to the "push" operation where current is pushed to the load.


• When you open the bottom valve, water is discharged from the bucket, similar to the "pull" operation where current is pulled from the load.

This ability to control the direction of water flow allows you to manage water storage and usage quickly and effectively, just as push-pull output controls current in electronic devices quickly and efficiently.

Applications of Push-pull Output

Push-pull output is not only theoretically attractive but also widely used in practical applications. From simple circuit designs to complex industrial automation systems, push-pull output is adopted for its excellent performance:

1. Digital Devices: Many digital devices, such as computer interfaces and communication equipment, use push-pull output for fast data transmission.


2. Motor Control: In robotics and automation equipment, push-pull output helps precisely control motor movement.

Our newly launched smart sensors with integrated IO-Link functionality not only support normally open/closed, PNP/NPN but also support push-pull output mode settings, meeting the needs of complex industrial applications. The flexibility and efficiency of these sensors ensure accurate measurement and control even in harsh environments.

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[^1]: https://zh.wikipedia.org/wiki/推挽输出