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 ??
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.
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:
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
I'd use a heatsink at least this big for it: 25*36*16mm TO-220 Black Anodised Aluminium Transistor Regulator Heatsink Cooler | eBay
Last edited:
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.
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:
Been doing just that, with a 5 ohm resistor I get nearly 6v, when doing the final build I can reduce the 5 ohm with higher values in parallel to get the 6v desired. Not the best way of doing it but since I've already invested in the supply transformer it will have to do ! I will also invest in some genuine regulators as I still think there is something wrong there after all they are supposed to be able to regulate to 1.5A !! Thanks for the help everybody.
L200 Linear regulator.
https://www.tme.eu/nl/en/details/l200cv/regulated-voltage-regulators/stmicroelectronics/
Cheers,
V4LVE
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.