WTB 9.1 V Temp Comp Reference Zener

[tautech]

I have a Khrone Hite 5300A FG with a crook linear +17, -17V PSU

Schematic factory mod shows a change to a 1N4770A reference zener.

Hopefully not the unobtainium type.
Anybody got a couple in a bottom drawer?

Datasheet link: http://www3.microsemi.com/datasheets/sa6-23.pdf

Anybody got a work around solution?

[Jay_Diddy_B]

Hi Tautech and the group,

This is the schematic of the power supply in the Khrone Hite 5300A FG:



CR111 is the reference for the power supply. Using 1N4770 will improve the performance of the power supply over temperature. There are two work around solutions:



1) Use a regulator 9.1V Zener and see if the circuit is functional.

2) Replace with CR111 with a 6.2V Zener from the 1N821 -1N827 family. Change the value of R118 to 820 Ohms and then adjust R128 for 17V. It should be around mid scale.

Regards,

Jay_Diddy_B

[macboy]

Another viable option is to replace the entire regulator with a LM7818 or LM317. It doesn't seem to be very high current, so a basic TO-220 regulator should handle it. The performance might be even better.

I like the symmetric design of this power supply, with the negative supply set up to null out the positive supply's voltage, instead of having its own reference and adjustment.

[PedroDaGr8]

I've been down this path (looking for the 1N4579A) and you can usually find someone to help you out. First thing I did was to contact MicroSemi, they gave me a list of distributors that should have the item. I basically emailed everyone on the list explaining I need a particular diode. I asked what the cost would be for two explaing that I am just a hobbyist looking to repair a multimeter not an industrial user. Some couldn't help or wanted ridiculous prices ($90/diode) but a couple offered them for a good price ($10/diode) but Arrow took the cake. They generously sampled several of them to me. I was able to successfully repair the device with them.

[sync]

Maybe a TL431 adjusted to 9.1V?

[SeanB]

6V2 zener and 5 forward biased 1N4148 diodes will do a passable equivalent. Will not have the same tempco, but will be close enough at around room temp to get in adjustment range.

[tautech]

Thanks all for your wise assistance. 
I will progress with a trimmed  zener for now, just to go forward.
We all hate to have unfinished projects on the bench. 

[Simon]

I'm in need of a precision zener as i need reasonable accuracy from -46 through to +50 C the onsemi zeners are not too easy to find, can anyone tell me if any of the onsemi range is easy to obtain or are there any similar parts ? I don't need outstanding accuracy but just some reasonable accuracy over temperature range so that nothing starves or fries

[SeanB]

Try a TL431 and trim it with a pot to set the voltage, as described in the application sheet. Works as a good zener and is a lot better TC wise. You can also add a transistor to give a higher current range.

[Simon]

the TL431 has a minimum temperature of -40V i need 6 or lower

[PedroDaGr8]

I'm in need of a precision zener as i need reasonable accuracy from -46 through to +50 C the onsemi zeners are not too easy to find, can anyone tell me if any of the onsemi range is easy to obtain or are there any similar parts ? I don't need outstanding accuracy but just some reasonable accuracy over temperature range so that nothing starves or fries

I'm not sure about the degree of drift precision that you need but what about the series that includes the 1N4769A the A models are rated from  - 55 to 100oC. The temp coefficients range from 0.01%/oC to 0.0005%/oC.