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TO-220 6V Regulator
TO-220 6V Regulator
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Old 6th March 2021, 06:30 PM   #1
Jabiru is offline Jabiru  United Kingdom
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Default TO-220 6V Regulator

I am trying to use 6v 1.5A regulators to heat ECC88 valves. I have approx 12.2DC going in and with one valve connected I get a little over 5v out with a very slow voltage build up. If I put 28DC in I get nothing out like it's shut down. The heater current is 600mA so what is going on ? Have I been sold some bad regulators, they did come from Spain ! It is mounted on a heatsink and never gets too hot to touch. Any idea's anybody ??
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Old 6th March 2021, 07:05 PM   #2
martin clark is offline martin clark  Europe
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At the moment you switched-on, the heater is cold - so it is much lower resistance than when hot; the inrush current might be at least 2-3x nominal 600ma rating, perhaps a tad more - and that is causing the 3-pin regulator to go into over-current/foldback limiting - esp with such massive momentary dissipation internally at 28V! 28v in for a 6.x V /600mA output supply is daft with such a tiny chip reg.

Read the datasheet of the 3-pin reg you are using - the graphs will show you the safe operating area vs input voltage vs current draw. You need a lower voltage raw dc supply that can fully support the instant and prospective load current. Do note that you are going to run into such an issue at such a high supply voltage - regardless of what 3-pin reg you are using: say, with an LM338 nominally capable of 5A output - no it will behave exactly like an LM317 with nom 1.5A output under these circs; it will shut-down. To take advantage of the higher potential current limit, you have to keep the voltage drop across the reg IC low (around 5v max differential for the lm338's full performance). There's no magic here.

And yes - there are a lot cheap/fake parts out there; that might be a cause. Buy branded parts from reputable suppliers; yes, you have to pay more for them.

Good luck - let us know how you get on.

Last edited by martin clark; 6th March 2021 at 07:14 PM.
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Old 6th March 2021, 07:19 PM   #3
Jabiru is offline Jabiru  United Kingdom
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So do you think 12.2VDC in is too high ? Even when it's been on for half an hour and the valve is hot I still only get 5.2VDC ! At 600ma ( when hot ) that would indicate a bad regulator ? Would a TO-3 device be any better ? Thanks in advance
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Old 6th March 2021, 07:23 PM   #4
duncan2 is offline duncan2  United Kingdom
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Mullard ECC88 valve -


Heater =6.3 volts /365ma



A genuine 7806 / 1.5 amp regulator needs just 9 volts DC going into it .


Have you made a circuit for it including stability capacitors as well as a smoothing capacitor at the input ?
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Old 6th March 2021, 07:30 PM   #5
Jabiru is offline Jabiru  United Kingdom
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Yes, 4700uF on input and 1000uF on output, your right about heater current which makes it even worse !
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Old 6th March 2021, 07:32 PM   #6
kodabmx is offline kodabmx  Canada
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TO-220 6V Regulator
7806 has protections built in... How big is the heat sink you're using? It's probably just getting too hot. I use 22uF on the output of a 78xx regulator.

I'd use a heatsink at least this big for it: 25*36*16mm TO-220 Black Anodised Aluminium Transistor Regulator Heatsink Cooler | eBay
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Last edited by kodabmx; 6th March 2021 at 07:38 PM.
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Old 6th March 2021, 07:42 PM   #7
Jabiru is offline Jabiru  United Kingdom
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Heat sink is never hotter than warm to the touch, I'm building the LITE LS9D circuit board which has an HT section and provision for two TO-220 devices which I assumed was to mount regulators for valve heaters but probably not given what I'm finding out now ! Should I reduce the value of the output capacitor ? I can't see that making much difference.
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Old 6th March 2021, 08:06 PM   #8
Boydk is offline Boydk  Denmark
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As said, lower the cap on output to 10-22uF.
Also do decoupling of both input- and output pin with a 100nF on each to ground.
Else, you might have a bad regulator.
I used one 7806 for years driving heaters on two 6N16B/V without any problems ever
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Old 6th March 2021, 08:09 PM   #9
v4lve lover is offline v4lve lover  Netherlands
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TO-220 6V Regulator TO-220 6V Regulator
Try L200 and set it for 150% of expected current, a normal three terminal reg will dump a lot of current into a cold heater.



Given that you have 12V to play with, this shouldnt be a problem,


Cheers,
V4LVE
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Old 6th March 2021, 08:21 PM   #10
tommost is offline tommost
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Quote:
Originally Posted by kodabmx View Post
7806 has protections built in... How big is the heat sink you're using? It's probably just getting too hot. I use 22uF on the output of a 78xx regulator.

I'd use a heatsink at least this big for it: 25*36*16mm TO-220 Black Anodised Aluminium Transistor Regulator Heatsink Cooler | eBay

The protection might be what's causing the problem, with 12 V in and a very large load it might not start at all. The way to find out is to use an external supply and slowly bring up the input voltage, if that works it's the protection. Or a 6.8 ohm 10 W resistor in series might allow it to start.

Once it starts then heat might be a problem....

Last edited by tommost; 6th March 2021 at 08:24 PM.
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