Zener Diode and Bridge Rectification

introducing sine voltages across it in range of 40 volts peak to peak to 70 volts peak to peak depending upon the magnitude of the magnetic field. I do not know how much flux is there or magnetic field.

diode gets really hot. So, hot that it unsolders itself after an hour . The inductor stays cool.

not get hot as when L1 = 100uH.

burned and if I lower than the inductance reactance than the inductor itself gets hot.

input voltage to DC to DC converter between 30 to 40 volts and keep the inductor and zener diode functionally working and not hot? If yes than how?

Use a little common sense..when the voltage from the bridge gets above the zener diode breakdown, the diode's current increases rapidly, and that high current may even get sufficiently large to create thermal problems to the bridge rectifiers. Naturally, the zener gets the hottest first in that situation (I*V drop). Use a decent design.

snipped-for-privacy@gmail.com was thinking very hard :

Electronics 99 might be good plce to start. Electronics 101 is too advanced yet.

--
John G

introducing sine voltages across it in range of 40 volts peak to peak to 70 volts peak to peak depending upon the magnitude of the magnetic field. I do not know how much flux is there or magnetic field.

diode gets really hot. So, hot that it unsolders itself after an hour . The inductor stays cool.

not get hot as when L1 = 100uH.

burned and if I lower than the inductance reactance than the inductor itself gets hot.

input voltage to DC to DC converter between 30 to 40 volts and keep the inductor and zener diode functionally working and not hot? If yes than how?

AFAIK conventional use of a zener in that manner would use a resistor between the bridge and the zener to maintain the voltage at that of the zener.

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Grin... be nice to have a cap after the bridge. Jess, do you own a copy of the "Art of Electronics" by H&H*? Go read the chapter on power supplies (chap 6 in 2nd ed.) There's a nice 'power zener circuit'. But it's still gonna get hot. (Energy conseravtion and all....)

George H.

*If not, go buy one.

introducing sine voltages across it in range of 40 volts peak to peak to 70 volts peak to peak depending upon the magnitude of the magnetic field. I do not know how much flux is there or magnetic field.

--
Why are you using the choke as part of a tank instead of just as the
secondary of a transformer?

introducing sine voltages across it in range of 40 volts peak to peak to 70 volts peak to peak depending upon the magnitude of the magnetic field. I do not know how much flux is there or magnetic field.

diode gets really hot. So, hot that it unsolders itself after an hour . The inductor stays cool.

not get hot as when L1 = 100uH.

burned and if I lower than the inductance reactance than the inductor itself gets hot.

voltage to DC to DC converter between 30 to 40 volts and keep the inductor and zener diode functionally working and not hot? If yes than how?

To get a better idea of the characteristics of the source, measure the voltage across the zener's position (zener and downstream components removed) as a resistive load is varied. There should probably be a capacitor across this position as well.

Calculate the power delivered - there should be a reduction at both ends of the resistance range. Zener's are shunt regulators, so the power delivered must be shared between series limiters (source internal and series introduced) and the shunting load itself. You'll want to work in the region of the load curve where the voltage is also conveniently reduced.

Heating of the pick-up inductor can probably be reduced by selecting a core material that is not intended for EM suppression, as these are intentionally lossy. adding a series current limiter may also be effective. Heating of the inductor is generally benign below the ratings of the materials employed. In some cases, self-heating might also be used as a power-limiting feature, if core materials that have a low curie temperature are intentionally used.

RL

1 and introducing sine voltages across it in range of 40 volts peak to peak= to 70 volts peak to peak depending upon the magnitude of the magnetic fiel= d. I do not know how much flux is there or magnetic field.

r diode gets really hot. So, hot that it unsolders itself after an hour . T= he inductor stays cool.

does not get hot as when L1 =3D 100uH.

=3D2103978

).pdf

gets burned and if I lower than the inductance reactance than the inductor= itself gets hot.

input voltage to DC to DC converter between 30 to 40 volts and keep the in= ductor and zener diode functionally working and not hot? If yes than how?

You're going to get far less heating all round if you a) add a reservoir cap across the zener b) use an active device in or after the BR to only allow current flow to the reservoir when needed, using L to limit current, or add more passive limiting.

NT

I could not make any sense of the circuit so I didn't bother replying. = This=20 is the sort of design that benefits greatly from an LTSpice simulation, = and=20 it makes it easier to read the schematic than a hand-drawn image.

Something is missing or there is a major misunderstanding about what = this=20 circuit is supposed to do. It seems like it is a DC-DC converter but the =

input part is missing, so the inductor could be interpreted as the = secondary=20 of a transformer. But there does not seem to be any reason why that = voltage=20 should be 40-70 VAC at 100kHz, since obviously it must be generated from = a=20 DC source if it is indeed a DC-DC converter.

Actually L1 appears to be a 100 uH RF choke and not part of a = transformer.=20 The 25 nF capacitor forms a resonant tank circuit at 100 kHz and the = voltage=20 will build up until it is limited by the characteristics of the driving=20 source and the load. Perhaps its purpose is to make a sine wave from a=20 square wave? But assuming the source is a low impedance its voltage will = be=20 rectified and the zener will be driven with a series of pulses up to 100 =

volts peak. But of course the zener will limit these to whatever the = zener=20 voltage is, which without further information could be 5.1 to 51 volts. = The=20 fact that it survives indicates that the source impedance is fairly = high,=20 but apparently it is seeing more than its rated 5 watts. And the 3.3 = volts=20 output will, at best, have a lot of ripple and at worst may oscillate,=20 without either input or output capacitance, and an undefined load.

It seems like this circuit has EVERYTHING wrong. Not easily done, except =

maybe for Always Wrong Missing Prong :)

Paul=20

Hi,

1. I did post the data sheet of the zener diode which gives Vz = 33 Volts.
2. Primary coil is not mentioned in the schematic. The generated magnetic field is cutting the coil L1 (mentioned in the schematic) . You can call L1 secondary coil if you want to.

jess

ts.

field is cutting the coil L1 (mentioned in the schematic) . You can call L=

1 secondary coil if you want to.

if L1 is really a voltage source then you have the Zener in effect across a voltage source... something's gotta give...

you need to add a series impedance someplace in the circuit.. Mark

The linked datasheet was for a family of 5 W zeners 5.1 to 51 V. The=20 schematic only said 5W.

Yes, and you will also need the other components as shown in the LT3970=20 datasheet. It's a switching regulator, which is normally used to provide =

higher efficiency, about 80% at the 100 mA 3.3V load shown. But a 5W = zener=20 that's getting hot means that efficiency must not be important. A series =

impedance will just transfer the losses elsewhere. The real problem is = that=20 the ratio of the primary of the transformer to the secondary is wrong. I =

assume the magnetic field is being generated by means of another coil=20 magnetically (or magically) coupled to the inductor shown. If the = coupling=20 is very poor, the secondary will act as a current source and you might = be=20 able to use the zener within its rating. But it's still wasteful, and = you=20 might as well just use a linear regulator that can handle the peak = voltage=20 at the output of the bridge. However, you still need energy storage so a =

capacitor will be needed.

The correct way to design this is to get the transformer ratio right so = that=20 the output voltage will be within the 40V limits of the switching = regulator=20 (or use one with a higher rating). Then you will not need the zener = (except=20 maybe for overvoltage transient protection), and the DC-DC converter = will=20 operate with reasonable efficiency.

I know you have posted before and I don't know if you are a student or=20 hobbyist, but these are very basic principles and not really appropriate = for=20 the sci.electronics.design newsgroup. But most of us are willing to = help,=20 although we don't want to do your homework for you, or do your job if = you=20 are tasked to design products.

BTW, I did not see your original post but only the follow-up by Robert.

Good luck.

Paul=20

On Mon, 2 Jul 2012 15:53:00 -0700 (PDT), snipped-for-privacy@gmail.com wrote:

is cutting the coil L1 (mentioned in the schematic) . You can call L1 secondary coil if you want to.

--- If the range of voltage out of L1 is 40 to 70VPP, after full-wave rectification the range will fall to 20 to 35V minus a couple of diode drops, so the voltage into the 3970 can never be more than 35V, eliminating the need for the Zener.

Also - unless I'm missing something - I don't understand why the choke needs to be parallel tuned to 100kHz.

Here's an LTspice simulation of your circuit, with the Zener and tuning cap eliminated and the 3970 circuit fleshed out per 3490 TA03a on page 17 of the data sheet at:

Version 4 SHEET 1 880 852 WIRE -1056 0 -1200 0 WIRE -656 0 -816 0 WIRE -560 0 -656 0 WIRE -352 0 -560 0 WIRE -208 0 -224 0 WIRE -128 0 -144 0 WIRE -816 48 -816 0 WIRE -656 48 -656 0 WIRE -352 64 -352 0 WIRE -224 64 -224 0 WIRE -560 128 -560 0 WIRE -416 128 -560 128 WIRE -128 128 -128 0 WIRE -128 128 -160 128 WIRE -80 128 -128 128 WIRE 48 128 0 128 WIRE 144 128 48 128 WIRE -816 176 -816 112 WIRE -816 176 -912 176 WIRE -1056 224 -1056 0 WIRE -912 224 -912 176 WIRE 48 224 48 128 WIRE 48 224 -160 224 WIRE 144 272 144 128 WIRE -416 320 -480 320 WIRE 48 320 48 224 WIRE 48 320 -160 320 WIRE -912 352 -912 304 WIRE -656 352 -656 112 WIRE -656 352 -912 352 WIRE -1200 400 -1200 0 WIRE -480 400 -480 320 WIRE 48 400 48 320 WIRE -816 416 -816 176 WIRE -656 416 -656 352 WIRE -560 416 -560 128 WIRE -1200 528 -1200 480 WIRE -1056 528 -1056 304 WIRE -1056 528 -1200 528 WIRE -1024 528 -1056 528 WIRE -912 528 -944 528 WIRE -816 528 -816 480 WIRE -816 528 -912 528 WIRE -656 528 -656 480 WIRE -656 528 -816 528 WIRE -560 528 -560 480 WIRE -560 528 -656 528 WIRE -480 528 -480 480 WIRE -480 528 -560 528 WIRE -288 528 -288 384 WIRE -288 528 -480 528 WIRE 48 528 48 464 WIRE 48 528 -288 528 WIRE 144 528 144 352 WIRE 144 528 48 528 WIRE -912 592 -912 528 FLAG -912 592 0 SYMBOL ind2 -1072 208 R0 WINDOW 0 -43 40 Left 2 WINDOW 3 -54 72 Left 2 SYMATTR InstName L1 SYMATTR Value 100µ SYMATTR Type ind SYMATTR SpiceLine Rser=,1 SYMBOL voltage -1200 384 R0 WINDOW 3 24 104 Invisible 2 WINDOW 39 0 0 Left 2 SYMATTR Value SINE(0 20 10k) SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMBOL ind2 -896 208 M0 WINDOW 0 -46 46 Left 2 WINDOW 3 -53 76 Left 2 SYMATTR InstName L2 SYMATTR Value 100µ SYMATTR Type ind SYMBOL res -928 512 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 1G SYMBOL cap -208 16 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName C1 SYMATTR Value 220n SYMBOL ind -96 144 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName L3 SYMATTR Value 22µ SYMBOL cap 32 400 R0 SYMATTR InstName C2 SYMATTR Value 22µ SYMBOL res -496 384 R0 SYMATTR InstName R1 SYMATTR Value 226k SYMBOL cap -576 416 R0 SYMATTR InstName C3 SYMATTR Value 2.2µ SYMBOL res 128 256 R0 SYMATTR InstName R4 SYMATTR Value 33 SYMBOL PowerProducts\\LT3970-3.3 -288 224 R0 SYMATTR InstName U2 SYMBOL diode -640 112 R180 WINDOW 0 42 33 Left 2 WINDOW 3 26 -7 Left 2 SYMATTR InstName D3 SYMATTR Value MURS120 SYMBOL diode -800 112 R180 WINDOW 0 42 33 Left 2 WINDOW 3 26 -7 Left 2 SYMATTR InstName D1 SYMATTR Value MURS120 SYMBOL diode -800 480 R180 WINDOW 0 42 33 Left 2 WINDOW 3 26 -7 Left 2 SYMATTR InstName D2 SYMATTR Value MURS120 SYMBOL diode -640 480 R180 WINDOW 0 42 33 Left 2 WINDOW 3 26 -7 Left 2 SYMATTR InstName D4 SYMATTR Value MURS120 TEXT -880 552 Left 2 !.tran 1ms TEXT -1040 200 Left 2 !K1 L1 L2 1

-- JF

If you look at the thread on "Parallel LC Circuit", you will see that = the=20 primary in this case is a Helmholtz coil and the inductor is in effect = an=20 antenna which acts on the magnetic field. The tuned circuit will = resonate=20 and AFAIK the voltage and current will increase until it is limited by = the Q=20 of the circuit, the power available in the field, and the losses caused = by=20 other parts of the circuit, such as the 5W zener. I'm no expert on = magnetic=20 fields, but it seems like eliminating the tuned circuit would make the=20 induced voltage in the coil proportional to field strength, and maybe = then a=20 series resistor and the zener could protect against overvoltage due to = very=20 high field strength. If the voltage across the coil is 40 to 70 V P-P=20 without the capacitor, the circuit should work well.

An air core inductor may be even better. It would then be a Rogowski = coil=20 which basically provides a voltage proportional to the rate of change of = the=20 magnetic field. If you then integrate this with an RC network, you will = get=20 a voltage proportional to field strength, which in turn is proportional = to=20 the current in the coil. At least this is how we measure high AC = currents in=20 our breaker test sets.

Reading

I see that the = magnetic=20 field within this device is essentially constant and proportional to=20 current, so it is only a matter of choosing the correct inductor to = produce=20 the voltage required for the DC-DC converter.

I looked at some of Jess's posts over the past year and all of them seem = to=20 relate to similar concepts. But I don't know if her project is for a = physics=20 class or a commercial design, or as an attempt to obtain "free energy". = The=20 OP has not been very forthcoming about the overview of her project and = some=20 of the posts are difficult to understand without reading through all of=20 them. Even then, not so much...

Paul=20