# Zener Diode Selection

Started by July 26, 2012
```Hi,

DC to DC Converter:=20
http://cds.linear.com/docs/Datasheet/3970fb.pdf

Zener Diode:=20
http://www.digikey.com/product-detail/en/1N5364B-TP/1N5364BTPMSCT-ND/111430=
6

The DC to DC converter can handle input voltage upto  40V. DC to DC convert=
er is configured to output 5V. I do not want the input voltage to exceed 33=
Volts. That is why I am using a 33V Zener. But I think that DC to DC conve=
rter will work fine if I use 6 to 7 volt  and 1A Zener. Since the goal is t=
o keep the output of the DC to DC converter stays at 5V. Am I right?=20

DC to DC converter is driving a Load of 15 ohms. As shown in the following =
=20
http://img51.imageshack.us/img51/4011/zener.jpg

Figure 1 showing a resistor in series with the voltage source of value 17.4=
V, Zener does not draw any current and output of the DC to DC converter is=
desirable. Though if I reduce the value of the resistor to 30 ohm than the=
voltage at the input of the DC to DC converter will raise to 13.2V.=20

Figure 3 shows that the Zener will burn and it did.=20

Questions:=20

1. Do I need a Zener that can activate at 33V and can handle 2A? OR should =
I get a 6 volt Zener that can handle 1 02 2 amps? I do want to keep the siz=
e of the Zener and resistor small.=20

2. I measured 62mA series current through 50ohm resistor but measured 300mA=
at the output of the DC to DC converter. Can someone explain how did this =
work?=20

Thanks
jess

```
```It is not necessary to limit the DC-DC converter to a voltage below 40V.  It
will maintain regulation at high efficiency.

Typically, a TVS (Transient Voltage Suppressor) is used to limit voltage to
safe values.  TVS are only intended for transient and fault conditions, not
for limiting voltages under continuous duty.  A series resistor is not
usually used with a TVS in power applications.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

<jsscshaw88@gmail.com> wrote in message
Hi,

DC to DC Converter:
http://cds.linear.com/docs/Datasheet/3970fb.pdf

Zener Diode:
http://www.digikey.com/product-detail/en/1N5364B-TP/1N5364BTPMSCT-ND/1114306

The DC to DC converter can handle input voltage upto  40V. DC to DC
converter is configured to output 5V. I do not want the input voltage to
exceed 33 Volts. That is why I am using a 33V Zener. But I think that DC to
DC converter will work fine if I use 6 to 7 volt  and 1A Zener. Since the
goal is to keep the output of the DC to DC converter stays at 5V. Am I
right?

DC to DC converter is driving a Load of 15 ohms. As shown in the following

http://img51.imageshack.us/img51/4011/zener.jpg

Figure 1 showing a resistor in series with the voltage source of value 17.4
V, Zener does not draw any current and output of the DC to DC converter is
desirable. Though if I reduce the value of the resistor to 30 ohm than the
voltage at the input of the DC to DC converter will raise to 13.2V.

Figure 3 shows that the Zener will burn and it did.

Questions:

1. Do I need a Zener that can activate at 33V and can handle 2A? OR should I
get a 6 volt Zener that can handle 1 02 2 amps? I do want to keep the size
of the Zener and resistor small.

2. I measured 62mA series current through 50ohm resistor but measured 300mA
at the output of the DC to DC converter. Can someone explain how did this
work?

Thanks
jess

```
```On 7/26/2012 3:27 PM, jsscshaw88@gmail.com wrote:
> Hi,
>
> DC to DC Converter:
> http://cds.linear.com/docs/Datasheet/3970fb.pdf
>
> Zener Diode:
> http://www.digikey.com/product-detail/en/1N5364B-TP/1N5364BTPMSCT-ND/1114306
>
>
> The DC to DC converter can handle input voltage upto  40V. DC to DC converter is configured to output 5V. I do not want the input voltage to exceed 33 Volts. That is why I am using a 33V Zener. But I think that DC to DC converter will work fine if I use 6 to 7 volt  and 1A Zener. Since the goal is to keep the output of the DC to DC converter stays at 5V. Am I right?
>
> DC to DC converter is driving a Load of 15 ohms. As shown in the following link
>
> http://img51.imageshack.us/img51/4011/zener.jpg
>
>
> Figure 1 showing a resistor in series with the voltage source of value 17.4 V, Zener does not draw any current and output of the DC to DC converter is desirable. Though if I reduce the value of the resistor to 30 ohm than the voltage at the input of the DC to DC converter will raise to 13.2V.
>
> Figure 3 shows that the Zener will burn and it did.
>
> Questions:
>
> 1. Do I need a Zener that can activate at 33V and can handle 2A? OR should I get a 6 volt Zener that can handle 1 02 2 amps? I do want to keep the size of the Zener and resistor small.
>
> 2. I measured 62mA series current through 50ohm resistor but measured 300mA at the output of the DC to DC converter. Can someone explain how did this work?
>
> Thanks
> jess

Don't do that. Get rid of the series resistor.

Use an emitter follower series pass transistor with the 33V zener
attached to the base and a resistor from base to collector to limit the
voltage inut to the converter to less than 40V.

```
```On 7/27/2012 12:52 PM, John S wrote:
> On 7/26/2012 3:27 PM, jsscshaw88@gmail.com wrote:
>> Hi,
>>
>> DC to DC Converter:
>> http://cds.linear.com/docs/Datasheet/3970fb.pdf
>>
>> Zener Diode:
>> http://www.digikey.com/product-detail/en/1N5364B-TP/1N5364BTPMSCT-ND/1114306
>>
>>
>>
>> The DC to DC converter can handle input voltage upto  40V. DC to DC
>> converter is configured to output 5V. I do not want the input voltage
>> to exceed 33 Volts. That is why I am using a 33V Zener. But I think
>> that DC to DC converter will work fine if I use 6 to 7 volt  and 1A
>> Zener. Since the goal is to keep the output of the DC to DC converter
>> stays at 5V. Am I right?
>>
>> DC to DC converter is driving a Load of 15 ohms. As shown in the
>>
>> http://img51.imageshack.us/img51/4011/zener.jpg
>>
>>
>> Figure 1 showing a resistor in series with the voltage source of value
>> 17.4 V, Zener does not draw any current and output of the DC to DC
>> converter is desirable. Though if I reduce the value of the resistor
>> to 30 ohm than the voltage at the input of the DC to DC converter will
>> raise to 13.2V.
>>
>> Figure 3 shows that the Zener will burn and it did.
>>
>> Questions:
>>
>> 1. Do I need a Zener that can activate at 33V and can handle 2A? OR
>> should I get a 6 volt Zener that can handle 1 02 2 amps? I do want to
>> keep the size of the Zener and resistor small.
>>
>> 2. I measured 62mA series current through 50ohm resistor but measured
>> 300mA at the output of the DC to DC converter. Can someone explain how
>> did this work?
>>
>> Thanks
>> jess
>
> Don't do that. Get rid of the series resistor.
>
> Use an emitter follower series pass transistor with the 33V zener

Or a source follower NMOS. There are better ways to do this at the
expense of a couple of components.

```
```On Thursday, July 26, 2012 4:27:03 PM UTC-4, (unknown) wrote:
> Hi,
>=20
>=20
>=20
> DC to DC Converter:=20
>=20
> http://cds.linear.com/docs/Datasheet/3970fb.pdf
>=20
>=20
>=20
> Zener Diode:=20
>=20
> http://www.digikey.com/product-detail/en/1N5364B-TP/1N5364BTPMSCT-ND/1114=
306
>=20
>=20
>=20
>=20
>=20
> The DC to DC converter can handle input voltage upto  40V. DC to DC conve=
rter is configured to output 5V. I do not want the input voltage to exceed =
33 Volts. That is why I am using a 33V Zener. But I think that DC to DC con=
verter will work fine if I use 6 to 7 volt  and 1A Zener. Since the goal is=
to keep the output of the DC to DC converter stays at 5V. Am I right?=20
>=20
>=20
>=20
> DC to DC converter is driving a Load of 15 ohms. As shown in the followin=
>=20
> =20
>=20
> http://img51.imageshack.us/img51/4011/zener.jpg
>=20
>=20
>=20
>=20
>=20
> Figure 1 showing a resistor in series with the voltage source of value 17=
.4 V, Zener does not draw any current and output of the DC to DC converter =
is desirable. Though if I reduce the value of the resistor to 30 ohm than t=
he voltage at the input of the DC to DC converter will raise to 13.2V.=20
>=20
>=20
>=20
> Figure 3 shows that the Zener will burn and it did.=20
>=20
>=20
>=20
> Questions:=20
>=20
>=20
>=20
> 1. Do I need a Zener that can activate at 33V and can handle 2A? OR shoul=
d I get a 6 volt Zener that can handle 1 02 2 amps? I do want to keep the s=
ize of the Zener and resistor small.=20
>=20
>=20
>=20
> 2. I measured 62mA series current through 50ohm resistor but measured 300=
mA at the output of the DC to DC converter. Can someone explain how did thi=
s work?=20
>=20
>=20
>=20
> Thanks
>=20
> jess

Haven't you been posting this same question for the past 6 months? If you h=
aven't caught on by now, you never will. Time to move on, this project is b=
eyond you.
```