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10 Tech How-To

USB-C HDMI Alt Mode: How to Connect a Display

Guide 10-9663 · Updated · Step by step

USB-C HDMI Alt Mode lets a single USB-C port carry an HDMI video signal, so you can connect a laptop, phone, or tablet directly to a monitor or TV without a dedicated HDMI port. This guide explains how the mode works, how to check if your device supports it, and how to connect a display successfully.

What You’ll Need

  • A USB-C device (laptop, tablet, or phone) that supports DisplayPort Alt Mode or HDMI Alt Mode.
  • A USB-C to HDMI cable or adapter (passive or active, depending on your device).
  • A display with an HDMI input (monitor, TV, or projector).
  • Optional: a USB-C cable that supports data and video if you’re using a direct connection.

Step-by-Step

  1. Check your device’s USB-C port for the DisplayPort or HDMI logo. Look for a small icon next to the port: a “D” with an “P” inside (DisplayPort) or an “HDMI” text. If you see it, the port supports Alt Mode. If not, check your device’s manual or manufacturer’s spec sheet online.
  2. Verify the cable or adapter is rated for video. Not all USB-C cables carry video. Look for a cable that explicitly states “4K@60Hz” or “Video” support. A passive USB-C to HDMI cable works if your device outputs HDMI Alt Mode natively; otherwise, you may need an active adapter that converts DisplayPort to HDMI.
  3. Connect the USB-C end to your device and the HDMI end to the display. Make sure both connections are secure.
  4. Turn on the display and select the correct HDMI input. Use the display’s remote or on-screen menu to choose the HDMI port you plugged into.
  5. If nothing appears, adjust your device’s display settings. On Windows, press Win + P and choose “Duplicate” or “Extend.” On macOS, go to System Settings > Displays and click “Detect Displays.” On Android, pull down the notification shade and look for a “Display” or “Screen mirroring” option.
  6. If the display still shows nothing, try a different cable or adapter. Faulty cables are a common cause. Also try a different USB-C port if your device has more than one.

Common Mistakes

  • Using a USB-C cable that only supports charging. Many cables are power-only and lack the data/video lines needed for Alt Mode.
  • Assuming every USB-C port supports video. Some ports are data-only or power-only, especially on budget laptops or older phones.
  • Forgetting to select the correct HDMI input on the display. The display may be set to a different port.
  • Using a passive adapter with a device that doesn’t output HDMI Alt Mode. Some devices only output DisplayPort Alt Mode, so you need an active adapter that converts the signal.
  • Not checking if the cable is plugged in fully. A loose connection can cause intermittent or no signal.

Tips

  • Check your device’s specifications before buying a cable. Look for “DisplayPort Alt Mode” or “HDMI Alt Mode” in the specs.
  • For 4K at 60Hz, use a cable rated for HDMI 2.0 or higher. Older cables may only support 30Hz.
  • If you’re using a phone, make sure it supports video out over USB-C. Not all phones do, even if they have USB-C.
  • Keep your device’s firmware and graphics drivers updated. Updates can improve Alt Mode compatibility.
  • Use a high-quality, certified cable (e.g., USB-IF certified) to avoid signal issues.

Troubleshooting

If the display doesn’t show anything after following the steps:

  • Try a different USB-C port. Some laptops have multiple ports, but only one or two may support video.
  • Restart your device. Sometimes a simple reboot reinitializes the video output.
  • Check if the display is set to the correct input. Cycle through the inputs on the display to find the one you’re using.
  • Test the cable with another device. If the cable works elsewhere, the issue is likely your device’s port or settings.
  • Update your graphics driver. On Windows, go to Device Manager and update the display adapter driver. On macOS, update the OS.
  • If using a dock or hub, try connecting directly instead. Some hubs don’t pass through video properly.
  • Check if your device needs a specific adapter. Some phones, like certain Samsung models, require a proprietary adapter for video out.

Frequently Asked Questions

Can I use any USB-C cable for HDMI Alt Mode?

No. The cable must support video data. Look for a cable that explicitly states it carries video or is rated for DisplayPort/HDMI Alt Mode.

Does HDMI Alt Mode work on all USB-C ports?

No. Only ports that are designed with Alt Mode support will output video. Check the port’s logo or your device’s specs.

What’s the difference between HDMI Alt Mode and DisplayPort Alt Mode?

HDMI Alt Mode sends the HDMI signal directly over USB-C. DisplayPort Alt Mode sends a DisplayPort signal, which can be converted to HDMI with an adapter. Many devices support DisplayPort Alt Mode but not HDMI Alt Mode.

Can I charge my device while using HDMI Alt Mode?

Yes, if your device supports Power Delivery (PD) simultaneously. Many laptops and phones can charge and output video at the same time, but this depends on the device’s design.

Why does my phone not show video even though it has USB-C?

Most phones do not support video output over USB-C, even if they have the port. Only certain flagship models (e.g., Samsung Galaxy, Huawei, or some gaming phones) support it.

Do I need an active or passive adapter?

If your device outputs HDMI Alt Mode natively, a passive cable works. If it outputs DisplayPort Alt Mode, you need an active adapter that converts DisplayPort to HDMI. Check your device’s specs to know which one you need.

Related

General steps for current mainstream versions; menus can differ by device and version. See the disclaimer or report an error.

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