How does one extend the power handling capability of a zener regulator. Can they be paralleled or is a pass transistor the way to go. I need about .08 mA through the 90V zener.
- posted
18 years ago
90 volt DC power
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- posted
18 years ago
-- That doesn\'t make any sense. What are you trying to do?
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- posted
18 years ago
0.08mA through the zener makes for Pd=7.2mW, so how fragile is that thing?
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- posted
18 years ago
Use lower voltage zeners in series
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- posted
18 years ago
"James F. Mayer" Wrote news:3xNAf.3710$ snipped-for-privacy@newsread2.news.atl.earthlink.net...
Can
.08
Why dont you use a linear regulator, such as a LM78xx where you put a zener in series with the gnd pin? The quiescent current of the regulator doesn't generate too much dissipation in the zener. I've used this to stabilize 85V in an amplifier.
The_Al
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- posted
18 years ago
Drive myself crazy.
I checked my max load current and it is supposed to be 80 mA and the current through the zener should be 8 mA as opposed to my previous hurriedly posted material. It came to me as I was driving back from church that I made a mistake and my math for what I was trying to say was off by a factor of 10. I've recalculated and it looks MUCH better now. My power rating for the zener comes in now less than a Watt and the resistors a little over 5 Watts.
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- posted
18 years ago
Do this: Get an NPN transistor, and connect the Zener between base and collector; positive end of Zener to collector.
Connect the emitter of the transistor to ground; connect the base of the transistor to ground through a 1K resistor.
Connect the series dropping resistor from collector to source voltage; connect the load to the collector.
The output voltage will be about V(Z) + 0.65. If you want more load current, add an NPN emitter follower, and the output voltage will be ~V(Z). The collector of the emitter follower would go directly to the source voltage.
Tam
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- posted
18 years ago
--
Other than the greedy resistors, it sounds decent.
I\'ve let church go, but I get solutions in the shower.
Maybe this\'ll help:
Q1
Vin>--+------C E---->>--+--Vout
| B |
| | |
+--[R1]--+--Vz [RL]
|K |
[ZENER] |
| |
GROUND>--------+----->>---+
Vout ~ Vz - 0.7V as long as the pass transitor\'s alpha doesn\'t crap
out with changes in RL
Size R1 so that the zener can absorb the changes in Vbe as the load
resistance changes and you should be OK.
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- posted
18 years ago
John, you took the words right out of my keyboard. ;-)
Cheers! Rich