Moderators: Dave Moll, Andrew Davie, Steve Anderson
Steve Anderson wrote:That's a new device to me, but browsing through the datasheet it seems quite tame, shouldn't be any issues with it. Just remember to keep the input and output caps close by.
The only other issue is ripple. For this 12V regulator you're inputting a certain voltage as measured by your DC multimeter. What is next is to calculate the size of the capacitor in the raw supply. Any idea how much current you'll be drawing at 12V? The bottom of the ripple (as shown on an oscilloscope) should never go less than the regulator output voltage plus its drop-out, in this case around 12.8V.
In other words, if your multimeter shows 14V DC (on load) and the scope shows 2v p-p of ripple the rule of thumb is that the input varies at 100Hz from 13V to 15V - which for this device is OK. Just.
It could well do with a small heatsink as it will be dissipating around 2W.
Steve A.
Andrew Davie wrote:I could just junk this idea and use the two LM2596 adjustable output DC-DC converters I have in my parts drawer.
Steve Anderson wrote:I don't recommend switching regulators as 1) they are more complex and 2) they put out quite a lot of garbage on the supply. Usually OK for logic, but you could well have problems with analogue linear circuits, especially at low signal levels.
With all the televisors built thus far the vast majority have used linear regulators where required with no real issues regarding heat dissipation in the power supplies.
If you're planning to use one supply unregulated (+22V) for the LEDs there's no issue with regulator dissipation. The other supplying +12V regulated to all the other electronics I would be surprised if you got anywhere near 100mA, one tenth of an Amp. The drive motor may be a different issue though.
Steve A.
Klaas Robers wrote:Andrew, integrated voltage regulators have an automatic high temperature switch off. When the circuit runs too hot, it switches off. Then it cools down and switches on again. Be aware of this behaviour.! If you see that your monitor switches off now and then a regulator may become too hot. So it needs a larger heat sink, or even better, split up the circuitry and power them by separate regulator ICs.
Steve Anderson wrote:Somehow, somewhere, I suspect you created a short, or a least a low resistance path which stressed the transformer as you say. If all is OK now best leave it as is.
The old adage, "If it ain't broke don't fix it."
Transformers are usually very tolerant to overloads - of a reasonable duration. If you get excessive heat and/or that characteristic burning/melting smell you've probably gone past that stage.
Steve A.
Klaas Robers wrote:Andrew, scope your rectified voltages. If one of the diodes in the bridge rectifier is "blown up" due to previous experiments, you are working on half wave rectifying. That works, but your transformer is loaded with a DC current, which it doesn't like at all. It runs hot and more.
If the double wave rectifying is working properly you see a ripple in the rectified, not yet stabilized voltage of 100 Hz (10 msec). When not it is 50 Hz (20 msec) and you should replace the rectifier bridge.
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