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Author Topic: Power supply circuit zener voltages?  (Read 5082 times)
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max
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« on: August 06, 2013, 09:58:48 21:58 »

please see the attached power supply circuit, need to know the Russian zener diodes voltages and power ratings and the resistors power ratings.

Regards
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sfiga69
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« Reply #1 on: August 06, 2013, 10:30:47 22:30 »

With google translator & google search:

http://chiplist.ru/stabilitrons/2S175ZH/

http://www.chipinfo.ru/dsheets/diodes/stablp.html


Bye
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« Reply #2 on: August 06, 2013, 10:34:44 22:34 »

max .. do you know and understand the danger of this circuit?
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metal
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« Reply #3 on: August 07, 2013, 03:26:04 03:26 »

Seems that the triac is used as a clamping device to prevent voltage at regulators inputs from reaching a specific voltage determined by the zener diodes, interesting indeed. This will protect it from killing the regulators and serves as a general protection preventing more than 220V rms from killing this circuit as well.

May be zeners are 150V?

max .. do you know and understand the danger of this circuit?

PICkit, it is a hot PSU, dangerous and will burn your huge old butt :- )
just kidding you Tongue
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« Reply #4 on: August 07, 2013, 04:56:36 04:56 »

This circuit made me think of the little AC powered LED, which utilize impedance of capacitor on AC line to limit overall current. This circuit seems use the same thought but added 2 zeners in different direction to provide two different voltage. So the zener should be 7.5v for supplying power for 5v regulator and another zener with 15v to supply power for -12v regulator.

Based on the input for 220v/50Hz, the impedance of 3.3uF capacitor should be around 1.3 kohms and lead to current source with 100mA in each direction. This the reason why the output being marked as 100mA.
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« Reply #5 on: August 07, 2013, 08:32:54 08:32 »

This circuit made me think of the little AC powered LED, which utilize impedance of capacitor on AC line to limit overall current. This circuit seems use the same thought but added 2 zeners in different direction to provide two different voltage. So the zener should be 7.5v for supplying power for 5v regulator and another zener with 15v to supply power for -12v regulator.

Based on the input for 220v/50Hz, the impedance of 3.3uF capacitor should be around 1.3 kohms and lead to current source with 100mA in each direction. This the reason why the output being marked as 100mA.
all replies seems to be correct as far as I understand other then the zener VD4 seems to be shown wrong way connected
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oxygen007m
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« Reply #6 on: August 07, 2013, 08:38:14 08:38 »

It is a conventional transformerless power supply which is used in many cheap but non line insulated  circuits . The suitable value for VD1 is 9V and for VD2  is between 15V - 18V which is connected back to back to provide ac clamping . VS1 is for boosting current capability of zeners and can be omitted if R3= 0 ohm and if you choose zeners power rating bigger than 1W .
------------------
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« Last Edit: August 07, 2013, 03:13:15 15:13 by oxygen007m » Logged
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« Reply #7 on: August 07, 2013, 08:52:13 08:52 »

all replies seems to be correct as far as I understand other then the zener VD4 seems to be shown wrong way connected
No, I don't think VD4 is zener. Both VD3 and VD4 should be only normal diode as half-wave rectifier. i.e. VD4 to limit current flow on +5v output, and VD3 to limit current flow for -12v output.
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metal
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« Reply #8 on: August 07, 2013, 02:00:17 14:00 »

May be zeners are 150V?

2С175Ж is 7.5V
2С215Ж is 15V

sorry about the mistake in my previous post.

all replies seems to be correct as far as I understand other then the zener VD4 seems to be shown wrong way connected

All diodes are connected correctly.

2С175Ж serves as a clamping diode for the +5V rail, while 2С215Ж serves as a clamping diode for the -12V rail. When mains is higher than +7.5V or -15V it is shorted out by the Triac, excellent protection for the components.

Based on the input for 220v/50Hz, the impedance of 3.3uF capacitor should be around 1.3 kohms and lead to current source with 100mA in each direction. This the reason why the output being marked as 100mA.

Don't forget that LM2931 is also rated at 100mA.

max, where did you find this circuit?
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« Reply #9 on: August 07, 2013, 02:16:12 14:16 »

is this circuit works correctly
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oxygen007m
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« Reply #10 on: August 07, 2013, 03:09:47 15:09 »

Complete information about Transformerless Power Supplies: Resistive and Capacitive by Microchip :
------------------------------------------------------------
http://ww1.microchip.com/downloads/en/appnotes/00954a.pdf
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« Reply #11 on: August 07, 2013, 03:48:17 15:48 »

Ever thought why  designers (except for the Chinese ones) tend to stay away from transformerless power suplies? I guess it is because there is always a chance for something going wrong. I would always use a transformer to provide isolation from the mains. As for this design, I am sorry but I must say: lengths some people go to avoid a hair-cut.
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metal
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« Reply #12 on: August 07, 2013, 11:10:49 23:10 »

This one has very good protection. As long as mains resistors and 3.3uF capacitor are rated 200V above the nominal mains voltage, then you are pretty safe.
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« Reply #13 on: August 08, 2013, 12:30:12 00:30 »

Much better and safer if a small transformer is used.
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« Reply #14 on: August 08, 2013, 01:04:30 01:04 »

Ever thought why  designers (except for the Chinese ones) tend to stay away from transformerless power suplies? I guess it is because there is always a chance for something going wrong. I would always use a transformer to provide isolation from the mains. As for this design, I am sorry but I must say: lengths some people go to avoid a hair-cut.

I can speak from the professional designer standpoint. I wouldn't consider this dangerous pile of junk no matter how cheap and easy. Even the fool that wrote the Microchip Appnote at least put in a warning about how these kinds of circuits can kill you. The safety of these kinds of circuits are not about looking at just the component ratings and theoretical calculations. The safety is more about the subtleties of how things can(read WILL) fail. Please stay away from it, it's not worth saving $5.
« Last Edit: August 08, 2013, 01:06:33 01:06 by optikon » Logged

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max
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« Reply #15 on: August 08, 2013, 05:26:31 05:26 »

Please see the attached updated sch's, there is another circuit for single supply output.
can someone explain the benefits of using -ve regulator in the single supply output circuit.
I have seen this type of implementation in many triac/scr phase control circuits using uC.

Hi metal I found the circuits from Russian magazine paano  www.radio.ru
« Last Edit: August 08, 2013, 05:52:43 05:52 by max » Logged

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« Reply #16 on: August 08, 2013, 06:32:23 06:32 »

When I out 100 ma, then 3.3 uFx400 Vac can used 1 uFx400 Vac.  Angry
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« Reply #17 on: August 08, 2013, 07:25:05 07:25 »

Please see the attached updated sch's, there is another circuit for single supply output....

If I remembered correctly, the -ve regulator is for "fail-safe" design. That means, if main ic (79L12) fails (short), the 220V input won't directly connect to output. Anyway, non-isolated design like this is still "dangerous".
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Vineyards
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« Reply #18 on: August 08, 2013, 06:40:01 18:40 »

Could someone explain to me what would happen if I touch the ground rail which is shared with the mains if that ground is connected to the live wire instead of Neutral?

P.S. In many countries (unlike the UK) the two wires are indistinguishable and are eaisily reversed when the plug is inserted in reversed position.


Posted on: August 08, 2013, 06:29:30 18:29 - Automerged

Having brought up transformers, maybe you've heard about that new breed of PSU's that incorporate a fully isolated switch mode power supply in a PCB transformer form factor providing excellent efficiency,ripple filtering and multiple voltages in a smaller housing. The name of the company is Myrra if I spell correctly.

Posted on: August 08, 2013, 06:36:51 18:36 - Automerged

Here I have found the link. you can check out their link at: http://www.myrra.com/en/productsmyrra
It is under electronic transformers.
« Last Edit: August 08, 2013, 06:45:18 18:45 by Vineyards » Logged
oxygen007m
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« Reply #19 on: August 08, 2013, 09:47:16 21:47 »

I can speak from the professional designer standpoint.
It is totally nonprofessional standpoint because here , we are talking about technical issues involved in circuit , not project cost or safety problems .
Quote
dangerous pile of junk
It is technology not junk and the circuit has it's own use in some special cases when
the size of components are critical .
Another info about this technology from Microchip Technology Inc. :
http://www.jimfranklin.info/microchipdatasheets/91008b.pdf
and from ST electronics :
http://www.st.com/st-web-ui/static/active/cn/resource/technical/document/application_note/CD00004287.pdf
and from ieee :
http://ieeexplore.ieee.org/iel7/6516132/6520164/06520779.pdf

-------------------------
and some useful images :
-------------------------
more current output :

-------------------------
conventional one :

-------------------------
other variation :

-------------------------
half wave :


-------------------------
for more safty :  Grin
« Last Edit: August 08, 2013, 11:31:34 23:31 by oxygen007m » Logged
Vineyards
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« Reply #20 on: August 10, 2013, 03:46:30 15:46 »

These might be good examples to what is called a hot chassis. If you touch the ground you may be electrocuted. If the entire assembly is mechanically isolated, this may not be a problem. However, we cannot employ these techniques in equipment which can be mistaken for a battery operated portable unit safe to handle and touch.
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« Reply #21 on: August 10, 2013, 05:26:42 17:26 »

These might be good examples to what is called a hot chassis. If you touch the ground you may be electrocuted. If the entire assembly is mechanically isolated, this may not be a problem. However, we cannot employ these techniques in equipment which can be mistaken for a battery operated portable unit safe to handle and touch.

http://www.bbc.co.uk/news/technology-23585898 report of  death by fake iphone phone charger.
Just to add any dc content via a diode, is more likely to kill you than pure ac current, which is more forgiven.

last place of work we bought in power supply units at a cost of 1.50 about $1.15 they passed all the us & eu safety tests.
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