Forums

Zener Diode Selection

Started by Unknown 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 =
link
=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 
news:71c52853-9c61-4c04-8045-cf332c9a04a6@googlegroups.com...
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





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 >> 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
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=
g link
>=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.