Technical Guidance on Scaling ST AN2747 HID Ballast from 250W to 400W

[sonvu]

Hi,

We are developing a 380W/400W electronic ballast for a Mercury UV lamp (Dymax 36970), based on the circuit topology presented in ST AN2747 – 250W HID Metal Halide Electronic Ballast.

Lamp specifications:

• P/N: 36970 (Brand: DYMAX)

• Rated power: 380W

• Lamp voltage: 135V ±15V

• Lamp current: 3.2A

• AC input: 230V

We would appreciate technical guidance on the following questions:

1. Topology: Is the AN2747 circuit suitable for scaling from 250W to 380–400W for a Mercury UV lamp?

2. Power stage: Which components and design calculations need to be revised, particularly the PFC, MOSFETs/IGBTs, buck inductor, output capacitor, and gate drivers?

3. Control: What changes are required for ignition, warm-up current limiting, and constant-power regulation?

Regards.

[Peter BENSCH]

Welcome ​@sonvu, to the community!

Under no circumstances should you use a ballast designed for an HID metal halide lamp with a mercury UV lamp! Normally, a choke is perfectly adequate as a ballast for a mercury UV lamp.

Hope that helps?

Regards
/Peter

[sonvu]

Thank you for your advice. We understand that a ballast designed for a metal-halide lamp should not be used directly with a mercury UV lamp.

However, our objective is to develop a new electronic ballast specifically for the Dymax 36970 mercury UV lamp, replacing its conventional magnetic ballast.

Would a PFC + low-frequency full-bridge current-regulated topology, similar to AN2747, be technically suitable if the ignition, warm-up, and steady-state control parameters are redesigned specifically for this lamp?

Or would ST recommend a different electronic ballast topology for mercury UV lamps?

[Peter BENSCH]

I have looked into it again and am correcting my previous statement, because I am not familiar with the specification of the Dymax 36970 and had assumed a different lamp type. It may still be possible to redevelop the AN2747, which was developed decades ago, for the 400W Dymax 36970, but worldwide there is only very limited interest in such mercury lamps, so ST can no longer make any proposal or help with this. However, you are welcome to try whether the FAE of your local distributor can support you with this.

As I can see, though, you have essentially asked the same question at the same time via the personal online support OLS under number 00271792 and 00271793, but they cannot help you further for the reasons stated above. Making as much noise as possible about the same topic, perhaps even with several people, e.g. here, will not lead to a faster answer, which unfortunately does not exist in this case either.

I am very sorry that I cannot give a more positive answer,

Regards
/Peter