(Topic ID: 140331)

Adding resistors to the aux lamp driver to eliminate LED flicker

By barakandl

8 years ago

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Latest reply 8 years ago by HHaase
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Here is a (rough) example of adding 330 ohm resistors to the lamp aux board outputs to eliminate flickering when using LEDs. One side of each resistor goes to a lamp output pin. The other end of the resistors are all bussed together and then sent to a 2 pin molex header. The added female connector goes to the feature lamp bus. The 330 ohm resistors will keep the SCRs latched so the LEDs they driver will not flicker.

I totally winged it with 330ohm resistors, 2 pin .156" connector, length of wire, and a hand drill.

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Quoted from HHaase:
Noticeable difference? I've had most people tell me they didn't need for the aux board. But if there's a need.....

Interesting. LEDs flicker for me on the aux lamp driver board. I don't see how it would be any different. How much current it takes to latch a SCR is component specific, not really signal/board specific.

Quoted from Lindsey:
You need the resistor to put enough load on the SCR to meet it's minimum holding current. If you look at the data sheets for MCR106 and 2N5060 you'll find that the requirements are basically the same so the AUX lamp driver should need them the same way the main lamp driver would. I've noticed that it's not consistent from game to game and the results won't even be exactly the same from SCR to SCR so it might not be as noticeable in some cases. The AUX lamp driver boards also use only the larger SCR which will drive multiple lamps in some cases which might draw enough current to eliminate flicker when driving multiple LEDs.
Ohms law tells us that 470Ω resistors are the closest to the minimum holding current while going slightly over, drawing approx 13 mA. 330Ω will draw only approx. 7mA more so not really a big deal either way, even if someone should install a #44 lamp at some point, but we only need to draw 10mA thought the SCR, according to the data sheet, to keep it on and the LED is going to draw at least a few mA on it's own. I've also seen people using as high as 1.5KΩ with success.
It's also going to be really dependent on which LEDs you use. The current draw will vary quite a bit. The brighter LEDs which draw more current might not even need the resistors. Based on the specs in the data sheet I would expect this to be the case with a lot of pinball LEDs, but it doesn't always work out like that in practice.
Data Sheets:
http://www.onsemi.com/pub_link/Collateral/MCR106-D.PDF
http://www.onsemi.com/pub_link/Collateral/2N5060-D.PDF

330 ohm is the lowest value that i have found that keeps the SCRs latched across a variety of lamp drivers/ games. 470 ohm work 90% of the time, but some games that run the feature lamps at a lower (older transformers/rectifier assemblies) had trouble with single LED bulbs flickering when many lamps are lit.

Also to consider is the feature lamp voltage. Early games run lower around 5v. The later cabinet rectifier / transformer runs right around 6.3v. The number of lamps lit at one time will also effect the voltage. Some games will still flicker using 470 ohm during lamp test because all lamps are turned on at once reducing the voltage yet work fine in normal game play.

Quoted from KenH:
lets just use #47 lamps for the controlled lights...

You can take that attitude right back to RGP. this is pinside.... MORE LEDS ZOMGOSH AHHHH. =D

wrong forum i know, but is this any use to anyone? I dont need them anymore as i put a prototype aux lamp driver repro in each game. Kind of uggo but functional. $20 shipped. I have another 2nd aux lamp driver that is stock and works 100% for same deal $20 shipped.

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